eMedicine Specialties > Radiology > Pediatrics

Asplenia/Polysplenia

Marta Hernanz-Schulman, MD, FAAP, Professor, Radiology, Radiological Sciences, and Pediatrics, Director, Department of Pediatric Radiology, Radiologist-in-Chief, Director, Department of Diagnostic Imaging, Vanderbilt University Medical Center, Vanderbilt Children's Hospital

Updated: Jun 17, 2009

Introduction

Background

Although symmetry is a characteristic of the external mammalian phenotype and of some internal organs, notably the genitourinary system, much of our internal anatomy, notably the cardiovascular, pulmonary, and gastrointestinal systems, is asymmetrical.^1,2,3,4 The asymmetry is specific and originates in the genetic and molecular identity of the embryonic midline developmental field complex.^5,6,7 This normal asymmetrical arrangement is called situs solitus, a descriptive term derived from the Latin situs, which means position, and solitus, which means customary. Thus, situs solitus signifies the customary, or normal, asymmetrical arrangement of the viscerovascular anatomy.^8,9

Computed tomography scan obtained in the excretory phase during the intravenous administration of contrast material in a patient with polysplenia. This image demonstrates multiple splenules in the right upper quadrant, along the greater curvature of the right-sided stomach. Note that the liver extends over the splenic mass.

Interruption of the inferior vena cava. Coronal T1-weighted magnetic resonance image of the abdomen in a patient with polysplenia. This image demonstrates the enlarged azygous vein, which is parallel to the aorta and to its right. A partial volume-averaging artifact is present in the azygous vein and arch.

The concept of situs or laterality of the viscerovascular anatomy is important to the understanding, imaging, and interpretation of congenital visceral and vascular malformations. Assignment of laterality can be inherently difficult and affected by specific clinical biases. For example, to the cardiologist applying the concept of segmental classification of cardiac anomalies, situs refers to atrial morphology.¹⁰ The pulmonologist is likely to assess lung lobation and bronchovascular anatomy. The gastroenterologist may focus on the presence or absence of the spleen.¹¹

Patients with situs ambiguus tend to be grouped with those in whom right- or left-sided structures predominate. Generalizations may be made in these groups. Patients with right-sided symmetry typically lack a spleen, whereas patients with left-sided symmetry typically have a segmented spleen or multiple splenules.¹²

These common characteristics have led to the somewhat arbitrary classification of asplenia and polysplenia. However, heterotaxia, or situs ambiguus, occurs in a continuum; this is acknowledged in the classification of polyasplenia syndrome. This term recognizes the fact that left- and right- sided tendencies are on a continuum of heterotaxy or midline derangement. Radiologists and other clinicians must be cognizant of the viscerovascular arrangements that are possible in infants with these conditions, and they must describe the specific viscerovascular anomalies in the patient. Many infants with situs ambiguus present with severe congenital cardiac anomalies. In these patients, knowing the presence of an associated interruption of the inferior vena cava is helpful before performing cardiac catheterization.¹³

Situs ambiguus, or heterotaxia, is associated with other conditions of major clinical relevance, such as intestinal malrotation, biliary atresia, splenic abnormalities and consequent immunologic derangements, faulty gastric suspension mechanisms, displacement of abdominal viscera, and aberrant vascular structures and vascular connections. Each of these abnormalities is derived from an embryologic inability to determine laterality and establish the complex solitus asymmetry, whereas symmetrical structures remain unaffected.¹⁴

In a retrospective review (1994-2008) of heterotaxy patients by Anagnostopoulos et al, the authors sought to determine whether current management has improved patient outcomes. They found that surgical outcomes have improved with current procedures. They also determined that patients with left atrial isomerism (LIA) had a higher incidence of sinus node dysfunction than patients with right atrial isomerism (RIA). Risk of operative mortality and attrition was found to be highest during first- and second-stage palliation. In RAI, significant atrioventricular valve regurgitation and obstructed total anomalous pulmonary venous return (TAPVR) were found to be risk factors.¹⁵  

Pathophysiology

The control of normal human somatic asymmetry is not yet known.

A mouse animal model exists in which a spontaneous mutation called the iv locus is localized to the 12th chromosome.^16,17 Homozygous animals have a random phenotype: approximately 30% have situs solitus; 30%, situs inversus; and 40%, situs ambiguus. A second murine genetic mutation has been identified in the inv gene.^18,19 Homozygous individuals have shown reversed embryonic turning, the earliest manifestation of laterality in mouse embryos. Asymmetrical expressions of genes have been identified in other animal models, notably Xenopus species and chick embryos.²⁰

In humans, familial situs ambiguus has been related to both autosomal and X-linked inheritance patterns, although most cases arise sporadically.^{2,21,22,23,24} Situs inversus and situs ambiguus have been described within the same family trees; this finding indicates a phenotypic arrangement similar to that in the iv/iv mice. ZIC 3 is an X-linked gene identified in both sporadic and familial cases; affected males typically have the situs ambiguus phenotype, and females have either situs solitus or situs inversus. This particular genetic code is also associated with midline anomalies, particularly neural tube defects.

A submicroscopic deletion in Xq26 and a deletion at 18p have been associated with familial situs ambiguus.^25,26 Further, balanced and unbalanced autosomal translocations have also been described in sporadic cases of situs ambiguus.²⁷ Finally, environmental factors, including exposure to retinoic acid and maternal diabetes, have been implicated in laterality defects among the offspring of affected parents.^28,29

Asymmetrical or unilateral organs are derived from embryologic midline structures. Disruption of embryonic laterality leads to faulty development of asymmetrical organs. Importantly, in the absence of solitus control, the viscerovascular arrangement becomes largely random, within broad generalizations regarding right- or left-sided tendencies. However, the affected organs or systems are predictable and characterized by complex asymmetry.

The heart is most often affected, and it is the organ that most frequently leads to clinically detectable abnormalities. The liver and spleen have a variety of patterns, ranging from malformation to malpositioning, to an absence of the spleen or biliary structures. The gastrointestinal tract has a variety of malrotation anomalies. As a result of selective resorption of embryonic paired structures, vascular structures typically demonstrate a variety of abnormalities related to malpositioning or segmental absence.^30,31

Frequency

United States

The true incidence of situs abnormalities is not known. Some estimates suggest that situs inversus totalis occurs in approximately 1 per 8,000-25,000 live births, and approximately 20-25% of these are associated with immotile cilia, or Kartagener syndrome.

In situs ambiguus, there are estimates that 1.44 infants per 10,000 are affected. This number is based on patients with congenital heart disease and is likely to be an underestimation, although it may include most of these patients. Others estimate the incidence as 1 case per 5000 births, with the affected cases evenly divided between situs inversus and situs ambiguus.

Mortality/Morbidity

The major causes of mortality and morbidity in the heterotaxy syndromes are undoubtedly the cardiac malformations that typically occur in these conditions. These are based on the inability of the complex asymmetrical connections to develop correctly, and they predictably consist of an ambiguus and single atrium, a single ventricle, and conotruncal anomalies such as truncus arteriosus and transposition of the great vessels.^32,33,15

Vascular malconnections that are associated with high mortality and morbidity rates include total anomalous pulmonary venous connections (TAPVCs).³⁴ Visceral abnormalities with clinically notable adverse consequences include biliary atresia and the absence of the spleen. Malrotation may become clinically evident if obstruction develops secondary to the presence of Ladd bands or if a midgut volvulus supervenes.³⁵ Intrinsic duodenal obstruction, such as that secondary to duodenal diaphragm, may also occur.

Sex

Although most cases of heterotaxia are sporadic, many cases are familial, and some are X linked. Thus, the abnormality is more common in males than in females.

Age

Situs is congenital; therefore, situs abnormalities are always present in affected neonates. However, clinical manifestations depend on the individual's specific anatomic derangements. Severe and complex cardiac abnormalities are likely to be apparent at birth or soon afterward. Individuals without congenital heart disease may present later with conditions such as biliary atresia or volvulus. In persons without clinically morbid abnormalities, these conditions may be discovered during an evaluation for an unrelated problem or complaint when they are adults.^36,37

Anatomy

Anatomic pathologic findings in patients with heterotaxy syndrome are described in this section within the broad categories of right- and left-sided tendencies. Some of the more notable exceptions to these general groupings are also discussed.^38,39,40

Splenic anomalies

Patients with asplenia lack a spleen, and they typically have a right-sided tendency. In these patients, Howell-Jolly bodies may be present, and diminished immunologic defenses may result in overwhelming sepsis.

Polysplenia. Ultrasonogram of the left upper quadrant reveals multiple, widely spaced splenules above the left kidney (same patient in Images 1 and 3 in Multimedia). Reproduced with permission.

Polysplenia. Ultrasonogram of the left upper quadrant reveals few, closely spaced splenules above the left kidney. The adrenal gland lies medial and immediately adjacent to the splenules. Reproduced with permission.

T1-weighted magnetic resonance image obtained in a patient with polysplenia (same patient in Images 1 and 3 in Multimedia). Multiple widely spaced splenules are obvious along the greater curvature of the left-sided stomach. Reproduced with permission from Hernanz-Schulman M et al. AJR Am J Roentgenol. 1990;154(4):797-802.

Computed tomography scan obtained in the excretory phase during the intravenous administration of contrast material in a patient with polysplenia. This image demonstrates multiple splenules in the right upper quadrant, along the greater curvature of the right-sided stomach. Note that the liver extends over the splenic mass.

Gastrointestinal and hepatic anomalies

Patients in both the asplenia and polysplenia subgroups have a variety of gastrointestinal abnormalities. The stomach may be located on the right, on the left, or in the midline. Faulty mesenteric attachments of the stomach may result in gastric volvulus. Malrotation anomalies encompass a wide spectrum that ranges from nonrotation to reversed rotation and faulty peritoneal attachments. Duodenal atresia or stenosis may also be present (see Images 3-6).

Abnormalities of rotation. Upper gastrointestinal image demonstrates inverted nonrotation and a right-sided stomach in a patient with polysplenia (same patient in Images 5-6 in Multimedia).

Abnormalities of rotation. Image obtained during a barium enema examination in a patient with polysplenia (same patient in Images 5-6 in Multimedia). This radiograph demonstrates inverted nonrotation.

Some patients with heterotaxy, notably those with polysplenia, may also have a congenitally short pancreas, which is the result of maldevelopment or agenesis of the dorsal pancreas (which develops in the dorsal mesogastrium).¹² A midline adrenal gland or a horseshoe adrenal gland may be seen in other patients, notably those with asplenia. Approximately 1% of patients may also have renal anomalies, such as a multicystic dysplastic kidney.

Central nervous system anomalies

A small subset of individuals with situs ambiguus also has a variety of midline defects, including central nervous system (CNS) anomalies (eg, holoprosencephaly, neural tube defects) and caudal regression syndrome. This association underscores the derangement of the midline developmental complex, which is implicated in the early genesis of situs derangements.

Vascular anomalies

Interruption of the inferior vena cava is most common in patients with polysplenia. This occurs in approximately 50-60% of patients with this condition. In patients with an interrupted inferior vena cava, venous return occurs via the right- or left-sided azygous systems (see Images 7-9). This condition is rare in patients with asplenia, but it has been reported in several patients. This finding underscores both the heterogeneity and underlying similarities among all patients with situs ambiguus. As a generalization, in a patient with heterotaxy, interruption of the inferior vena cava suggests polysplenia, with very few exceptions, as discussed.

Interruption of the inferior vena cava. Transverse ultrasonogram of the abdomen in a patient with polysplenia (same patient in Images 7-8 in Multimedia). This image demonstrates a large retrocrural vessel, which is similar in size and adjacent to the right side of the aorta, a finding that indicates azygous continuation and caval interruption.

Interruption of the inferior vena cava. Axial T1-weighted magnetic resonance image of the abdomen (same patient in Images 7-8 in Multimedia). This image demonstrates a large retrocrural vessel, which is similar in size and adjacent to the right side of the aorta, a finding that indicates azygous continuation and caval interruption.

Interruption of the inferior vena cava. Coronal T1-weighted magnetic resonance image of the abdomen in a patient with polysplenia. This image demonstrates the enlarged azygous vein, which is parallel to the aorta and to its right. A partial volume-averaging artifact is present in the azygous vein and arch.

Intact inferior vena cava. Transverse ultrasonogram of the abdomen in patient with polysplenia (same patient in Images 10-11 in Multimedia). This image demonstrates an antecrural vessel, a finding that indicates an intact inferior vena cava, which is in the process of crossing over anterior to the aorta to enter the atrium.

Intact inferior cava. Sagittal ultrasonogram of the abdomen in a patient with polysplenia (same patient in Images 10-11 in Multimedia). This image demonstrates an antecrural vessel, a finding that indicates an intact inferior cava, which is in the process of crossing over anterior to the aorta to enter the atrium. Compare this ultrasonogram with the transverse ultrasonogram in Image 10.

Intact inferior cava. Sagittal ultrasonogram of the abdomen in a patient with polysplenia. This image demonstrates an intact intrahepatic cava with a normal appearance. Because the abdominal caval laterality was congruent with that of the atria in this patient, crossing over did not occur. Reproduced with permission.

Intact inferior vena cava. Transverse ultrasonogram in a patient with asplenia. This image demonstrates the aorta and vena cava on either side of the midline, an appearance that simulates solitus anatomy. Reproduced with permission.

Total anomalous pulmonary venous connection (TAPVC). Sagittal abdominal ultrasonogram in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-16 and 22-23 in Multimedia). This image shows that the anomalous vessel bypasses the portal vein and connects to a hepatic vein. Note the abrupt caliber change in the draining pulmonary vein in this patient with severe pulmonary venous outflow obstruction. Reproduced with permission.

Total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-16 and 22-23 in Multimedia). This image shows the anomalous vessel anterior to the gastroesophageal junction (high-intensity focus). The hepatic draining vein is the smaller-caliber vessel immediately anterior to the anomalous vessel. The caliber difference indicates the presence of an obstruction. The intrahepatic vena cava is seen to the right, and the aorta is anterior to the spine to the left of the midline.

Total anomalous pulmonary venous connection (TAPVC). Coronal T1-weighted magnetic resonance image obtained in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-15, 22-23 in Multimedia). The anomalous vessel receives the pulmonary veins in the chest and courses below the diaphragm. Reproduced with permission.

Conotruncal anomalies and total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 14-16 and 22-23 in Multimedia). This image demonstrates truncus arteriosus type II, with pulmonary arteries arising from the arterial trunk. A single right-sided superior vena cava is noted to the right of the truncus (see also Image 23 in Multimedia).

Conotruncal anomalies and total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 14-16 and 22-23 in Multimedia). This image demonstrates the common pulmonary vein is dorsal to the ambiguus atrium and receives pulmonary venous return. The signal intensity of the lung fields is relatively high; this finding indicates increased water content in the edematous lung, which is due to obstruction of pulmonary venous return. Note the single-atrium, single-ventricle anatomy. The descending aorta lies to the left of the spine. The cardiac apex is to the right.

Chest and abdominal radiograph in a neonate with asplenia. This image demonstrates a midline liver, mesocardia, and a right-sided stomach. Severe pulmonary edema is present, with a normal heart size; this finding is strongly suggestive of total anomalous pulmonary venous connection (TAPVC) with obstruction, which most likely drains subdiaphragmatically. Note the extension of the liver into both upper quadrants.

Bilateral superior vena cavae are common in both asplenia and polysplenia (see Image 17).

Bilateral superior cavae. Coronal T1-weighted magnetic resonance image in a patient with polysplenia. This image demonstrates bilateral superior cavae, a large atrial septal defect, and a single-ventricle anatomy. Portions of a transverse aortic arch and pulmonary outflow tract are also visible.

Preduodenal portal vein. Transverse ultrasonogram obtained just caudal to the pancreas in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates the superior mesenteric vein just ventral to and to the left of the superior mesenteric artery (denoted by the characteristic hyperechoic halo) (see Image 19 in Multimedia). The relationship of the artery and vein is abnormal; the vein is to the left and anterior to the artery, rather than to the right and in the same plane as the artery in the normal relationship. Reproduced with permission.

Preduodenal portal vein. Transverse ultrasonogram obtained at the level of the pancreas in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates that the superior mesenteric vein lies ventral to the pancreas and is separated from the superior mesenteric artery (denoted by the characteristic hyperechoic halo) by the pancreas. Reproduced with permission.

Preduodenal portal vein. Sagittal ultrasonogram obtained in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates the superior mesenteric vein, which courses ventral to the pancreas, in a staircase configuration. Reproduced with permission.

Preduodenal portal vein. Sagittal ultrasonogram in an infant with asplenia. This image demonstrates the characteristic staircase configuration of the ventral course of the superior mesenteric–portal junction anterior to the pancreas and duodenum. The hyperechoic triangular structure indicates gas within the duodenal cap.

Cardiac anomalies

Patients with asplenia and those with polysplenia often have biventricular hearts, in which large atrioventricular defects result in a single-atrium, single-ventricle configuration. However, in general, patients with asplenia tend to have complex cardiac lesions more frequently than those with polysplenia. Patients with polysplenia may have only a ventricular septal defect or no cardiac anomalies at all. (Interestingly, this is the subset of patients who most often have biliary atresia.)

When the patients with cardiac abnormalities are examined, a description of the lesions based on the cardiac segmental anatomy is helpful. Atrial morphology is described in terms of the situs condition, as follows: solitus (S), inversus (I), or ambiguus (A). Ventricular morphology is described in terms of cardiac looping, either to the right or dextroposed (D), which results in the normal position of the left ventricle on the left side and the right ventricle on the right side, or to the left or levoposed (L), which results in an inverted ventricular configuration. The great arteries are described in terms of the position of the aorta relative to the pulmonary artery, either normal (ie, to the right [D]) or abnormal (ie, to the left [L]).

In normal hearts, solitus atria is present, with a morphologic right atrium. This contains nodal tissue, a coronary sinus, and a wide-based atrial appendage; it receives the systemic veins; and it is located on the right.⁴⁵ Also present is a morphologic left atrium, which has a narrow-based atrial appendage, receives the pulmonary veins, and is located on the left. Patients with situs ambiguus typically have atrial isomerism. In patients with asplenia, a single atrium that morphologically resembles a right atrium tends to be present, whereas in patients with polysplenia, the atrium morphologically resembles a left atrium.

Abnormal ventricular looping is also present in patients with an ambiguus situs. The incidence of L-loop ventricles occurs in approximately 38% of patients with asplenia and in 30% of those with polysplenia. A normal heart, with solitus atria, a D loop, and a right-sided aortic valve with respect to the pulmonary valve, is designated SDD. Patients with congenital heart disease and situs ambiguus tend to have discordant cardiac segmental anatomic features.

In patients with asplenia, conotruncal abnormalities are common. They include truncus arteriosus, conal hypoplasia with pulmonary outflow obstruction or pulmonary atresia, and anomalous pulmonary venous connections (see Images 14-16, Images 21-23). These patients tend to have diminished pulmonary blood flow and cyanosis. In patients with polysplenia, atrioventricular septal defects are common (see Image 17). Pulmonary stenosis is not common, and these patients tend to have increased pulmonary blood flow.

Presentation

See the Anatomy section, above.

Preferred Examination

No single examination is best for the evaluation of heterotaxy. What may be best, however, is an ambiguous and subjective term that can be defined as the fastest and easiest study (eg, plain radiography), the least invasive study (in terms of radiation exposure or the need for sedation), the least expensive study, or the most sensitive or specific study. Knowledge of the various anatomic derangements that occur in these patients enables the informed radiologist to make the appropriate observations on most cross-sectional images.

Often, the initial examination performed in these patients is plain chest radiography, which is often performed in patients with suspected congenital heart disease, for which the patients may seek clinical attention in the first place.^46,47,48 Patients with an abdominal catastrophe, such as midgut or gastric volvulus, also undergo plain radiography as part of their initial diagnostic imaging examination.⁴⁹ On the other hand, patients with biliary atresia do not undergo plain radiography as part of their initial workup.

Historically, the diagnosis often depends on the angiographic findings in the cardiac and abdominal structures or on the results of abdominal examination via an iatrogenic pneumoperitoneum. However, ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are all useful in assessing the various viscerovascular abnormalities in patients with heterotaxy.^{37,48,50,51,52,53,54,55} MRI is particularly useful because it can also delineate cardiac defects.

Limitations of Techniques

Plain radiographs can be helpful in delineating an abnormal visceroatrial situs. A midline heart and liver, with a midline or right-sided stomach, and symmetrical bronchial branching are diagnostic findings. However, many patients with situs ambiguus do not have any of these findings, and plain radiographic findings may erroneously suggest situs solitus or situs inversus totalis.

Ultrasonography is extremely useful, but it is operator dependent, and findings may be unrevealing in cases in which the operator fails to understand the complex anatomic relationships that result from derangement of the normal laterality.

CT scanning may be limited in young infants because they have little body fat, especially if the contrast agent bolus is suboptimal.

MRI is limited by patient motion and its relatively long imaging times, which require optimal sedation.

Differential Diagnoses

Situs Inversus

Other Problems to Be Considered

Isolated dextrocardia
Isolated interruption of the inferior vena cava
Isolated preduodenal portal vein

Radiography

Abnormalities of rotation. Upper gastrointestinal image demonstrates inverted nonrotation and a right-sided stomach in a patient with polysplenia (same patient in Images 5-6 in Multimedia).

Abnormalities of rotation. Image obtained during a barium enema examination in a patient with polysplenia (same patient in Images 5-6 in Multimedia). This radiograph demonstrates inverted nonrotation.

Chest and abdominal radiograph in a neonate with asplenia. This image demonstrates a midline liver, mesocardia, and a right-sided stomach. Severe pulmonary edema is present, with a normal heart size; this finding is strongly suggestive of total anomalous pulmonary venous connection (TAPVC) with obstruction, which most likely drains subdiaphragmatically. Note the extension of the liver into both upper quadrants.

Chest radiograph in a female adolescent with polysplenia. This image demonstrates characteristic findings such as an enlarged, left-sided azygous arch (black arrows) that indicates inverted caval interruption anatomy. Bilateral hyparterial bronchi also strongly suggest heterotaxy with a left-sided tendency. The aortic arch (A) is on the right, and the cardiac apex and stomach are on the left. The white arrowheads point to symmetrical epibronchial pulmonary arteries. Reproduced with permission.

Radiograph in an infant with polysplenia. This image seems to demonstrate solitus anatomy. The cardiac apex and stomach lie on the left side. A large thymic shadow overlies and obscures the hilar anatomy. A surgical clip is noted on the left. Reproduced with permission.

Findings

As discussed previously, plain radiography is the first study conducted in patients with suspected heterotaxy. In many patients with situs ambiguus, radiographs provide the initial clues to the diagnosis, which should be made in patients with a midline liver, in those with a right-sided or midline stomach, and in those with mesocardia or dextrocardia. Special attention should be directed to the pulmonary hila for the detection of inverted or symmetrical anatomy. This evaluation is often not possible in infants, in whom the overlying thymus effectively obscures the pulmonary hila anatomy.

When identified, bilateral eparterial bronchi (bronchus above the artery, as in a typical right hilum) are suggestive but not diagnostic of asplenia, whereas bilateral hyparterial bronchi (bronchus underneath the artery, as in a typical left hilum) are suggestive but not diagnostic of polysplenia. The presence of a large azygous arch with the absence of the caval shadow on the lateral view further confirms heterotaxy, and these findings are highly suggestive of the polysplenia complex because of the interruption of the inferior vena cava with a right- or left-sided azygous continuation (see Images 24-26).

The laterality of the aortic arch is relatively unhelpful because a right-sided aortic arch occurs frequently in situs solitus, and the arch may be either right- or left-sided in situs ambiguus.

Contrast-enhanced studies of the gastrointestinal tract invariably demonstrate a rotational anomaly, which encompasses a wide spectrum. Malrotation, nonrotation, mirror-image nonrotation, and reversed rotation can all be seen in individual patients (see Images 5-6). Duodenal atresia and/or stenosis, sometimes due to an annular pancreas, may also be present. The external indentation of a preduodenal portal vein may also be identified.

Degree of Confidence

Findings with plain radiography are accurate for the diagnosis of situs ambiguus, when present. However, in some series, radiographic results in as many as 50% of patients with situs ambiguus falsely suggest either situs solitus or situs inversus totalis.

Gastrointestinal anomalies detected with contrast-enhanced examinations are present in all patients with situs ambiguus. However, these anomalies may also be present in situs solitus. Therefore, outside the clinical context, these findings are not specific for situs ambiguus.

False Positives/Negatives

Interruption of the inferior vena cava with azygous continuation should suggest situs ambiguus, particularly polysplenia. However, this finding is not specific, and it can be seen as an isolated anomaly in those in whom a solitus condition is otherwise present.

A right-sided aortic arch is most frequently encountered in patients with situs solitus. Typically, it indicates congenital heart disease, particularly tetralogy and truncus arteriosus, if mirror-image branching is present. The presence of a vascular ring is strongly suggested in cases of non–mirror-image branching. In situs ambiguus, the aortic arch could be either right- or left-sided. Thus, a right-sided aortic arch should not be initially construed as an indicator of a derangement in the laterality. Rotational anomalies of the midgut are most often encountered in individuals with a solitus condition.

Computed Tomography

Computed tomography scan obtained in the excretory phase during the intravenous administration of contrast material in a patient with polysplenia. This image demonstrates multiple splenules in the right upper quadrant, along the greater curvature of the right-sided stomach. Note that the liver extends over the splenic mass.

Findings

CT scanning may be helpful in delineating viscerovascular abnormalities in patients with heterotaxy and in determining whether they should be grouped with patients who have asplenia and a right-sided tendency or with those who have polysplenia and a left-sided tendency.⁵⁶

The collimation should be set to encompass the smallest structures of interest; therefore, the scanner setting varies with the age of the patient. In infants, 3-mm collimation is necessary to illustrate the bronchovascular anatomy. Intravenously administered contrast material is essential for delineation of the cardiovascular anatomy, as well as for adequate evaluation of the abdominal visceral anatomy.

An abnormal bronchial situs is highly likely in patients with these conditions; bilateral eparterial bronchi suggest asplenia, whereas bilateral hyparterial bronchi suggest polysplenia. Bilateral superior vena cavae are often present, or a single vena cava may be present on the right or left side. Malseptation of the cardiac chambers may be seen with contrast enhancement. Conotruncal anomalies, such as transposition with anterior placement of the aorta or truncus arteriosus may be identified. Abnormal drainage of the pulmonary veins can also be defined. The common pulmonary vein is a contrast-enhancing chamber dorsal to the atrium that resembles cor triatriatum.

In the abdomen, the presence of abnormal splenic tissue may be identified along the greater curvature of the stomach with contrast enhancement (see Image 4). Splenules are highly variable and may consist of multiple small structures, a few small structures, or a large or lobulated spleen. Lack of any splenic tissue and the absence of a splenic artery and vein indicate asplenia.

Anomalies of the pancreas may be somewhat more difficult to assess in the absence of the spleen because of the lack of splenic vascular landmarks, particularly in young patients in whom pancreatic attenuation may be similar to that of the surrounding tissue and in whom abdominal fat is scarce or absent. Lateralization of the liver, anomalous hepatic venous anatomy, and malpositioning or absence of the gallbladder are evident.

A preduodenal portal vein is characterized by an anterior course of the superior mesenteric venous–portal junction ventral to the pancreas. Interruption of the intrahepatic inferior vena cava occurs when this vessel is absent; instead, a large right- or left-sided azygous vein is seen adjacent to the aorta in the retrocrural area. This finding is far more characteristic of polysplenia than of asplenia. When the inferior vena cava is present, it typically lies to either side of the midline in both conditions.

Infradiaphragmatic drainage of TAPVC can be identified by following the vertical vessel that arises in the common pulmonary vein through the esophageal hiatus into its abdominal insertion. Malrotation is also evidenced by the lack of the normal retroperitoneal course of the duodenum and the abnormal position of the cecum.

Degree of Confidence

For the constellation of findings described above, the degree of confidence for CT scanning is 100%. By definition, the absence of the spleen or the presence of multiple splenules are likewise diagnostic findings. However, for any one of the associated abnormalities, the degree of confidence can be substantially lower, depending on the particular abnormality.

Discordant positioning of the heart and abdominal viscera is characteristic and diagnostic of heterotaxy. Ambiguity of the atrial morphology and symmetrical bronchial branching are also characteristic. However, individual lesions, including conotruncal anomalies, anomalous pulmonary venous connections, intrahepatic interruption of the inferior vena cava, malrotation, and biliary atresia, may be seen in patients with normal solitus anatomy. Bilobed spleens and accessory spleens can be seen in 10% of the healthy population.

False Positives/Negatives

Please see the discussion about false-positive and false-negative findings in Radiograph, False Positives/Negatives.

Magnetic Resonance Imaging

T1-weighted magnetic resonance image obtained in a patient with polysplenia (same patient in Images 1 and 3 in Multimedia). Multiple widely spaced splenules are obvious along the greater curvature of the left-sided stomach. Reproduced with permission from Hernanz-Schulman M et al. AJR Am J Roentgenol. 1990;154(4):797-802.

Interruption of the inferior vena cava. Axial T1-weighted magnetic resonance image of the abdomen (same patient in Images 7-8 in Multimedia). This image demonstrates a large retrocrural vessel, which is similar in size and adjacent to the right side of the aorta, a finding that indicates azygous continuation and caval interruption.

Interruption of the inferior vena cava. Coronal T1-weighted magnetic resonance image of the abdomen in a patient with polysplenia. This image demonstrates the enlarged azygous vein, which is parallel to the aorta and to its right. A partial volume-averaging artifact is present in the azygous vein and arch.

Total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-16 and 22-23 in Multimedia). This image shows the anomalous vessel anterior to the gastroesophageal junction (high-intensity focus). The hepatic draining vein is the smaller-caliber vessel immediately anterior to the anomalous vessel. The caliber difference indicates the presence of an obstruction. The intrahepatic vena cava is seen to the right, and the aorta is anterior to the spine to the left of the midline.

Total anomalous pulmonary venous connection (TAPVC). Coronal T1-weighted magnetic resonance image obtained in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-15, 22-23 in Multimedia). The anomalous vessel receives the pulmonary veins in the chest and courses below the diaphragm. Reproduced with permission.

Bilateral superior cavae. Coronal T1-weighted magnetic resonance image in a patient with polysplenia. This image demonstrates bilateral superior cavae, a large atrial septal defect, and a single-ventricle anatomy. Portions of a transverse aortic arch and pulmonary outflow tract are also visible.

Conotruncal anomalies and total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 14-16 and 22-23 in Multimedia). This image demonstrates truncus arteriosus type II, with pulmonary arteries arising from the arterial trunk. A single right-sided superior vena cava is noted to the right of the truncus (see also Image 23 in Multimedia).

Conotruncal anomalies and total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 14-16 and 22-23 in Multimedia). This image demonstrates the common pulmonary vein is dorsal to the ambiguus atrium and receives pulmonary venous return. The signal intensity of the lung fields is relatively high; this finding indicates increased water content in the edematous lung, which is due to obstruction of pulmonary venous return. Note the single-atrium, single-ventricle anatomy. The descending aorta lies to the left of the spine. The cardiac apex is to the right.

Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 27-29 in Multimedia). This image demonstrates hepatic extension over the greater curvature of the stomach. Mesogastria and microgastria are also present. Reproduced with permission.

Findings

In many ways, MRI is an ideal modality for the examination of patients with heterotaxic conditions. As with CT scanning, the section thickness should be set to the diameter that encompasses the structures of interest. Cardiac gating is needed in the evaluation of the cardiovascular system.^52,55,57

Abnormal bronchial and pulmonary arterial branching anatomy are evident in both the coronal and axial MRI planes. The anatomy of the superior cavae, anomalous pulmonary venous connections, conotruncal anomalies, ventricular inversion, and atrial and ventricular divisions can be identified (see Images 16-17, Images 22-23).

Abdominal findings, including hepatic laterality, hepatic vascular anatomy, interruption or malpositioning of the inferior vena cava, positioning and size of the stomach, and presence or absence of splenic tissue, are clearly delineated with MRI. Intra-abdominal connections of the common pulmonary vein in cases of TAPVC can also be identified (see Images 3, 8-9, 15-16, 22-23, 27).

Degree of Confidence

The degree of confidence for MRI is the same as that of CT scanning.

Ultrasonography

Polysplenia. Ultrasonogram of the left upper quadrant reveals multiple, widely spaced splenules above the left kidney (same patient in Images 1 and 3 in Multimedia). Reproduced with permission.

Polysplenia. Ultrasonogram of the left upper quadrant reveals few, closely spaced splenules above the left kidney. The adrenal gland lies medial and immediately adjacent to the splenules. Reproduced with permission.

Interruption of the inferior vena cava. Transverse ultrasonogram of the abdomen in a patient with polysplenia (same patient in Images 7-8 in Multimedia). This image demonstrates a large retrocrural vessel, which is similar in size and adjacent to the right side of the aorta, a finding that indicates azygous continuation and caval interruption.

Intact inferior vena cava. Transverse ultrasonogram of the abdomen in patient with polysplenia (same patient in Images 10-11 in Multimedia). This image demonstrates an antecrural vessel, a finding that indicates an intact inferior vena cava, which is in the process of crossing over anterior to the aorta to enter the atrium.

Intact inferior cava. Sagittal ultrasonogram of the abdomen in a patient with polysplenia (same patient in Images 10-11 in Multimedia). This image demonstrates an antecrural vessel, a finding that indicates an intact inferior cava, which is in the process of crossing over anterior to the aorta to enter the atrium. Compare this ultrasonogram with the transverse ultrasonogram in Image 10.

Intact inferior cava. Sagittal ultrasonogram of the abdomen in a patient with polysplenia. This image demonstrates an intact intrahepatic cava with a normal appearance. Because the abdominal caval laterality was congruent with that of the atria in this patient, crossing over did not occur. Reproduced with permission.

Intact inferior vena cava. Transverse ultrasonogram in a patient with asplenia. This image demonstrates the aorta and vena cava on either side of the midline, an appearance that simulates solitus anatomy. Reproduced with permission.

Total anomalous pulmonary venous connection (TAPVC). Sagittal abdominal ultrasonogram in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-16 and 22-23 in Multimedia). This image shows that the anomalous vessel bypasses the portal vein and connects to a hepatic vein. Note the abrupt caliber change in the draining pulmonary vein in this patient with severe pulmonary venous outflow obstruction. Reproduced with permission.

Preduodenal portal vein. Transverse ultrasonogram obtained just caudal to the pancreas in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates the superior mesenteric vein just ventral to and to the left of the superior mesenteric artery (denoted by the characteristic hyperechoic halo) (see Image 19 in Multimedia). The relationship of the artery and vein is abnormal; the vein is to the left and anterior to the artery, rather than to the right and in the same plane as the artery in the normal relationship. Reproduced with permission.

Preduodenal portal vein. Transverse ultrasonogram obtained at the level of the pancreas in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates that the superior mesenteric vein lies ventral to the pancreas and is separated from the superior mesenteric artery (denoted by the characteristic hyperechoic halo) by the pancreas. Reproduced with permission.

Preduodenal portal vein. Sagittal ultrasonogram obtained in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates the superior mesenteric vein, which courses ventral to the pancreas, in a staircase configuration. Reproduced with permission.

Preduodenal portal vein. Sagittal ultrasonogram in an infant with asplenia. This image demonstrates the characteristic staircase configuration of the ventral course of the superior mesenteric–portal junction anterior to the pancreas and duodenum. The hyperechoic triangular structure indicates gas within the duodenal cap.

Left coronal ultrasonogram obtained along the greater curvature of the stomach in a patient with asplenia (same patient in Images 27-29 in Multimedia). Although identification of a solid viscus in the expected location of the spleen may be misleading, note the absence of a splenic hilum and the characteristic portal echoes that parallel the long axis of the organ. These findings reveal that the solid viscus represents extension of the liver rather than splenic tissue. Reproduced with permission.

Findings

In addition to MRI, ultrasonography may also be an ideal imaging modality in the examination of patients with situs ambiguus. Its advantages are the same as those of other modalities: ultrasonography is noninvasive, does not require radiation, and can be used to image pathology in its own plane. The disadvantages of ultrasonography are also the same: it is operator dependent, and sound waves cannot penetrate bone or air. Therefore, bronchial branching anatomy cannot be accurately evaluated, and the abdominal examination may be relatively impeded in patients with large amounts of bowel gas.

An appropriate transducer, usually one of 6-MHz or higher, should be used for neonates or young infants. The infant is best examined after feeding, to prevent him or her from swallowing large amounts of air during crying and to help the infant remain quiet or asleep, conditions that enable detailed imaging.

In infants, chest ultrasonography can be used to evaluate the mediastinal anatomy via the poorly calcified chest wall with the use of large cartilaginous windows and the thymic window. Laterality or bilaterality of the superior vena cavae, great vessel anatomy, ventricular position and relationships, and intracardiac anatomy can be readily assessed. The common pulmonary vein is identified dorsal to the left atrium. These findings are routinely made with echocardiography.

Abdominal ultrasonography is best begun by determining the position of the stomach. This can be found by identifying the esophagus at the midline hiatus and by following it either to the right or left. Splenic tissue, when present, is found along the greater curvature of the stomach. Usually, finding the adrenal gland ipsilateral to the stomach is best. Scanning along this plane reveals the splenic tissue, if present. The appearance of the spleen, again, is highly variable; it may range from a large, septate spleen to one with multiple, small splenules that may lie close together (see Images 1-2).

In some patients with asplenia, the liver extends across the midline and overlies the stomach; it may resemble splenic tissue. However, close attention to the internal architecture of the organ reveals the important differences. Splenic tissue has large hilar vascular structures, whereas hepatic extension has only small peripheral branches, which can be followed to larger trunks within the main hepatic mass (see Image 28).

The position of the liver in the abdomen, the location of the gallbladder, and the hepatic venous anatomy can be easily evaluated. The course of the portal vein, whether preduodenal or retroduodenal, can also be evaluated in both the longitudinal and transverse planes. In the longitudinal plane, the superior mesenteric vein extends anterior to the pancreas and duodenum and courses ventrally into the liver; on transverse images, its cross-section is seen anterior to the pancreas (see Images 18-21).

Azygous continuation of an interrupted intrahepatic inferior vena cava is best evaluated on the transverse view. The intrahepatic cava is absent. Instead, a vessel is present adjacent to the aorta in the retrocrural region; it represents the right- or left-sided azygous continuation. Doppler ultrasonographic imaging can reveal the arterial signal of the aorta and the venous signal of the azygous vein. On coronal images, the 2 parallel vessels are seen along the retroperitoneum, entering the chest cavity. An intact inferior vena cava tends to line up with the aorta to either side of the midline and to cross over in piggyback fashion, when necessary, to enter the ambiguus atrium (see Image 7, Images 10-13).

In cases of total anomalous venous connections below the diaphragm, the anomalous connecting vein is easily identified; it enters the abdomen anterior to the esophagus through the esophageal hiatus. Its course to the exact point of abdominal drainage can then be determined (see Image 14).

Other anomalies, such as a dilated duodenum in cases of duodenal stenosis and/or atresia, midline horseshoe adrenal gland, and renal anomalies, can also be identified.

Degree of Confidence

The degree of confidence for ultrasonography is similar to that of MRI.

False Positives/Negatives

Although ultrasonography is extremely useful in heterotaxic conditions, this modality is also highly operator dependent. The operator's failure to understand the anomalies that occur could lead to a significant number of both false-positive and false-negative results. For example, a failure to understand the location of splenules along the greater curvature of the stomach could prevent a diagnosis. Conversely, imaging of the hepatic extension in asplenia could lead to a false diagnosis of polysplenia or situs inversus totalis.

Nuclear Imaging

Preduodenal portal vein. Transverse ultrasonogram obtained at the level of the pancreas in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates that the superior mesenteric vein lies ventral to the pancreas and is separated from the superior mesenteric artery (denoted by the characteristic hyperechoic halo) by the pancreas. Reproduced with permission.

Findings

In the diagnosis of asplenia versus polysplenia, resorting to the liver-spleen scan is tempting. Indeed, in healthy patients with solitus anatomy, the liver and spleen are clearly identified with the use of technetium-99m sulfur-colloid (^99m Tc-SC) scintigraphy. However, differentiation of hepatic versus splenic activity is considerably more difficult (1) in patients who may have no spleen and in whom the liver may extend into both upper quadrants and (2) in those who may have splenic tissue in either quadrant (see Image 19). Unlike ultrasonography and MRI, scintigraphy requires radiation exposure and venipuncture.

In some patients, splenic activity may be clearly distinct from that of the liver if the splenules are clearly distinguished from the liver and from each other.

Scintigraphy with a bolus of contrast material that is administered during angiography may demonstrate caval interruption with azygous continuation, if the agent is injected into a foot vein. The images may demonstrate the absence of a direct connection to the inferior atrium. However, other viscerovascular abnormalities are not typically depicted. Given the availability of ultrasonography, CT scanning, and MRI, scintigraphic evaluation is needed infrequently.

Degree of Confidence

When splenules are close together, the splenic mass appears as a single spleen, which is difficult to differentiate from situs solitus or situs inversus totalis. If the hepatic mass extends to both upper quadrants, identification of the splenic tissue may necessitate selective splenic scintigraphy with radiolabeled, heat-damaged red blood cells and/or hepatobiliary scintigraphy.

False Positives/Negatives

See the discussions about false-positive and false-negative findings in Radiograph, False Positives/Negatives and Ultrasound, False Positives/Negatives.

Angiography

Findings

Before the advent of cross-sectional imaging techniques, angiography was used to diagnose heterotaxy, define cardiac anatomy, and define abdominal viscerovascular heterotaxy.

Abdominal angiograms in patients with polysplenia demonstrate a variable arterial supply to the splenules. Typically, these are supplied by 2 or more arteries, which may arise as branches of a common celiacomesenteric trunk, from terminal branches of the gastroepiploic artery, or directly from the ipsilateral side of the abdominal aorta. The splenules are identified with a blush that moves more rapidly through the splenic tissue than through the overlying liver.

Although MRI and echocardiography are extensively used for the evaluation of cardiac malformations in these patients, cineangiography retains an eminent place in the preoperative cardiac evaluation in these complex cases. Abdominal angiography is no longer used for the evaluation of these conditions.

Degree of Confidence

The degree of confidence in a reported series of angiographic evaluation of the polysplenia syndrome is high. Although venous anomalies such as azygous continuation of an interrupted intrahepatic inferior cava may occur as an isolated anomaly in situs solitus, the lobulated splenules and abnormal celiacomesenteric anatomic branching is highly suggestive of the syndrome.

Multimedia

Media file 1: Polysplenia. Ultrasonogram of the left upper quadrant reveals multiple, widely spaced splenules above the left kidney (same patient in Images 1 and 3 in Multimedia). Reproduced with permission.

Media file 2: Polysplenia. Ultrasonogram of the left upper quadrant reveals few, closely spaced splenules above the left kidney. The adrenal gland lies medial and immediately adjacent to the splenules. Reproduced with permission.

Media file 3: T1-weighted magnetic resonance image obtained in a patient with polysplenia (same patient in Images 1 and 3 in Multimedia). Multiple widely spaced splenules are obvious along the greater curvature of the left-sided stomach. Reproduced with permission from Hernanz-Schulman M et al. AJR Am J Roentgenol. 1990;154(4):797-802.

Media file 4: Computed tomography scan obtained in the excretory phase during the intravenous administration of contrast material in a patient with polysplenia. This image demonstrates multiple splenules in the right upper quadrant, along the greater curvature of the right-sided stomach. Note that the liver extends over the splenic mass.

Media file 5: Abnormalities of rotation. Upper gastrointestinal image demonstrates inverted nonrotation and a right-sided stomach in a patient with polysplenia (same patient in Images 5-6 in Multimedia).

Media file 6: Abnormalities of rotation. Image obtained during a barium enema examination in a patient with polysplenia (same patient in Images 5-6 in Multimedia). This radiograph demonstrates inverted nonrotation.

Media file 7: Interruption of the inferior vena cava. Transverse ultrasonogram of the abdomen in a patient with polysplenia (same patient in Images 7-8 in Multimedia). This image demonstrates a large retrocrural vessel, which is similar in size and adjacent to the right side of the aorta, a finding that indicates azygous continuation and caval interruption.

Media file 8: Interruption of the inferior vena cava. Axial T1-weighted magnetic resonance image of the abdomen (same patient in Images 7-8 in Multimedia). This image demonstrates a large retrocrural vessel, which is similar in size and adjacent to the right side of the aorta, a finding that indicates azygous continuation and caval interruption.

Media file 9: Interruption of the inferior vena cava. Coronal T1-weighted magnetic resonance image of the abdomen in a patient with polysplenia. This image demonstrates the enlarged azygous vein, which is parallel to the aorta and to its right. A partial volume-averaging artifact is present in the azygous vein and arch.

Media file 10: Intact inferior vena cava. Transverse ultrasonogram of the abdomen in patient with polysplenia (same patient in Images 10-11 in Multimedia). This image demonstrates an antecrural vessel, a finding that indicates an intact inferior vena cava, which is in the process of crossing over anterior to the aorta to enter the atrium.

Media file 11: Intact inferior cava. Sagittal ultrasonogram of the abdomen in a patient with polysplenia (same patient in Images 10-11 in Multimedia). This image demonstrates an antecrural vessel, a finding that indicates an intact inferior cava, which is in the process of crossing over anterior to the aorta to enter the atrium. Compare this ultrasonogram with the transverse ultrasonogram in Image 10.

Media file 12: Intact inferior cava. Sagittal ultrasonogram of the abdomen in a patient with polysplenia. This image demonstrates an intact intrahepatic cava with a normal appearance. Because the abdominal caval laterality was congruent with that of the atria in this patient, crossing over did not occur. Reproduced with permission.

Media file 13: Intact inferior vena cava. Transverse ultrasonogram in a patient with asplenia. This image demonstrates the aorta and vena cava on either side of the midline, an appearance that simulates solitus anatomy. Reproduced with permission.

Media file 14: Total anomalous pulmonary venous connection (TAPVC). Sagittal abdominal ultrasonogram in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-16 and 22-23 in Multimedia). This image shows that the anomalous vessel bypasses the portal vein and connects to a hepatic vein. Note the abrupt caliber change in the draining pulmonary vein in this patient with severe pulmonary venous outflow obstruction. Reproduced with permission.

Media file 15: Total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-16 and 22-23 in Multimedia). This image shows the anomalous vessel anterior to the gastroesophageal junction (high-intensity focus). The hepatic draining vein is the smaller-caliber vessel immediately anterior to the anomalous vessel. The caliber difference indicates the presence of an obstruction. The intrahepatic vena cava is seen to the right, and the aorta is anterior to the spine to the left of the midline.

Media file 16: Total anomalous pulmonary venous connection (TAPVC). Coronal T1-weighted magnetic resonance image obtained in a patient with asplenia and TAPVC below the diaphragm (same patient in Images 14-15, 22-23 in Multimedia). The anomalous vessel receives the pulmonary veins in the chest and courses below the diaphragm. Reproduced with permission.

Media file 17: Bilateral superior cavae. Coronal T1-weighted magnetic resonance image in a patient with polysplenia. This image demonstrates bilateral superior cavae, a large atrial septal defect, and a single-ventricle anatomy. Portions of a transverse aortic arch and pulmonary outflow tract are also visible.

Media file 18: Preduodenal portal vein. Transverse ultrasonogram obtained just caudal to the pancreas in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates the superior mesenteric vein just ventral to and to the left of the superior mesenteric artery (denoted by the characteristic hyperechoic halo) (see Image 19 in Multimedia). The relationship of the artery and vein is abnormal; the vein is to the left and anterior to the artery, rather than to the right and in the same plane as the artery in the normal relationship. Reproduced with permission.

Media file 19: Preduodenal portal vein. Transverse ultrasonogram obtained at the level of the pancreas in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates that the superior mesenteric vein lies ventral to the pancreas and is separated from the superior mesenteric artery (denoted by the characteristic hyperechoic halo) by the pancreas. Reproduced with permission.

Media file 20: Preduodenal portal vein. Sagittal ultrasonogram obtained in an infant with polysplenia (same patient in Images 18-20 in Multimedia). This image demonstrates the superior mesenteric vein, which courses ventral to the pancreas, in a staircase configuration. Reproduced with permission.

Media file 21: Preduodenal portal vein. Sagittal ultrasonogram in an infant with asplenia. This image demonstrates the characteristic staircase configuration of the ventral course of the superior mesenteric–portal junction anterior to the pancreas and duodenum. The hyperechoic triangular structure indicates gas within the duodenal cap.

Media file 22: Conotruncal anomalies and total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 14-16 and 22-23 in Multimedia). This image demonstrates truncus arteriosus type II, with pulmonary arteries arising from the arterial trunk. A single right-sided superior vena cava is noted to the right of the truncus (see also Image 23 in Multimedia).

Media file 23: Conotruncal anomalies and total anomalous pulmonary venous connection (TAPVC). Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 14-16 and 22-23 in Multimedia). This image demonstrates the common pulmonary vein is dorsal to the ambiguus atrium and receives pulmonary venous return. The signal intensity of the lung fields is relatively high; this finding indicates increased water content in the edematous lung, which is due to obstruction of pulmonary venous return. Note the single-atrium, single-ventricle anatomy. The descending aorta lies to the left of the spine. The cardiac apex is to the right.

Media file 24: Chest and abdominal radiograph in a neonate with asplenia. This image demonstrates a midline liver, mesocardia, and a right-sided stomach. Severe pulmonary edema is present, with a normal heart size; this finding is strongly suggestive of total anomalous pulmonary venous connection (TAPVC) with obstruction, which most likely drains subdiaphragmatically. Note the extension of the liver into both upper quadrants.

Media file 25: Chest radiograph in a female adolescent with polysplenia. This image demonstrates characteristic findings such as an enlarged, left-sided azygous arch (black arrows) that indicates inverted caval interruption anatomy. Bilateral hyparterial bronchi also strongly suggest heterotaxy with a left-sided tendency. The aortic arch (A) is on the right, and the cardiac apex and stomach are on the left. The white arrowheads point to symmetrical epibronchial pulmonary arteries. Reproduced with permission.

Media file 26: Radiograph in an infant with polysplenia. This image seems to demonstrate solitus anatomy. The cardiac apex and stomach lie on the left side. A large thymic shadow overlies and obscures the hilar anatomy. A surgical clip is noted on the left. Reproduced with permission.

Media file 27: Axial T1-weighted magnetic resonance image in a patient with asplenia (same patient in Images 27-29 in Multimedia). This image demonstrates hepatic extension over the greater curvature of the stomach. Mesogastria and microgastria are also present. Reproduced with permission.

Media file 28: Left coronal ultrasonogram obtained along the greater curvature of the stomach in a patient with asplenia (same patient in Images 27-29 in Multimedia). Although identification of a solid viscus in the expected location of the spleen may be misleading, note the absence of a splenic hilum and the characteristic portal echoes that parallel the long axis of the organ. These findings reveal that the solid viscus represents extension of the liver rather than splenic tissue. Reproduced with permission.

Media file 29: Anterior scintigraphic examination obtained in a patient with asplenia (same patient in Images 27-29 in Multimedia). Hepatic extension into the left upper quadrant may simulate nonexistent splenic tissue. Reproduced with permission.

Media file 30: Total anomalous pulmonary venous connection (TAPVC). Radiograph from a newborn following insertion of an umbilical catheter. This image shows dextrocardia, a midline liver, an abnormal course of the umbilical catheters, and a venous line that courses to the left of the arterial line. Findings of heterotaxy or situs ambiguus are present. This radiograph also reveals severe pulmonary edema. In this setting, the findings strongly suggest the presence of TAPVC with obstruction to the venous outflow.

Media file 31: Polysplenia. Upper gastrointestinal (UGI) radiograph in a patient who presented with vomiting. Although many patients with heterotaxy present with severe congenital cardiac malformations, (eg, truncus arteriosus, anomalous pulmonary venous connections, atrioventricular septal defects), not all do. Some patients have milder forms of congenital heart disease, such as ventricular septal defect (VSD), or no cardiac disease. Patients with these conditions may have other anomalies, such as vomiting due to malrotation, duodenal stenosis, or jaundice due to biliary atresia. UGI studies in the patient who presented with vomiting revealed a right-sided stomach, malrotation, and a duodenal diaphragm. Findings from further evaluation were diagnostic of polysplenia. Rarely, asymptomatic manifestations, such as interruption of the inferior vena cava and polysplenia, may be discovered during medical imaging performed for unrelated complaints.

Media file 32: Sagittal ultrasonogram in a patient with asplenia and total anomalous pulmonary venous connections (TAPVCs) below the diaphragm. This image demonstrates an anomalous vessel that enters the abdomen and courses into the liver. Although pulmonary angiograms could delineate the anomalous pulmonary venous connection, the anomalous vessel can be easily identified with less-invasive imaging. Ultrasonography, magnetic resonance imaging, or computed tomography scanning can demonstrate the anomalous vessel as it enters the abdomen anterior to the esophagus.

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Keywords

asplenia, polysplenia, heterotaxy, heterotaxia, laterality, isomerism, right-sided isomerism, left-sided isomerism, right isomerism, left isomerism, Ivemark syndrome, situs ambiguus, situs ambiguous, partial situs inversus, polyasplenia, polyasplenia syndrome, situs solitus, visceral symmetry, visceral asymmetry, situs inversus, laterality, situs inversus totalis, Kartagener syndrome, total anomalous pulmonary venous connection, TAPVC, viscerovascular anomalies, Xq26, 18p, interrupted inferior vena cava

Contributor Information and Disclosures

Author

Marta Hernanz-Schulman, MD, FAAP, Professor, Radiology, Radiological Sciences, and Pediatrics, Director, Department of Pediatric Radiology, Radiologist-in-Chief, Director, Department of Diagnostic Imaging, Vanderbilt University Medical Center, Vanderbilt Children's Hospital
Marta Hernanz-Schulman, MD, FAAP is a member of the following medical societies: American Institute of Ultrasound in Medicine and American Roentgen Ray Society
Disclosure: Nothing to disclose.

Medical Editor

Henrique M Lederman, MD, PhD, Consulting Staff, Department of Radiology, LeBonheur Children's Medical Center and St Jude Children's Research Hospital; Professor of Radiology and Pediatric Radiology, Chief, Division of Diagnostic Imaging in Pediatrics, Federal University of Sao Paulo, Brazil
Henrique M Lederman, MD, PhD is a member of the following medical societies: Society for Pediatric Radiology
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

Managing Editor

David A Stringer, BSc, MBBS, FRCR, FRCPC, Professor, National University of Singapore; Head, Diagnostic Imaging, KK Women's and Children's Hospital, Singapore
David A Stringer, BSc, MBBS, FRCR, FRCPC is a member of the following medical societies: British Columbia Medical Association, Canadian Association of Radiologists, European Society of Paediatric Radiology, Ontario Medical Association, Radiological Society of North America, Royal College of Physicians and Surgeons of Canada, Royal College of Radiologists, and Society for Pediatric Radiology
Disclosure: Sirius d'innovation None Board membership

CME Editor

Robert M Krasny, MD, Consulting Staff, Department of Radiology, Resolution Imaging Medical Corporation
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

John Karani, MBBS, FRCR, Clinical Director of Radiology and Consultant Radiologist, Department of Radiology, King's College Hospital, London
John Karani, MBBS, FRCR is a member of the following medical societies: British Institute of Radiology, British Society of Interventional Radiology, Cardiovascular and Interventional Radiological Society of Europe, European Society of Gastrointestinal and Abdominal Radiology, European Society of Radiology, Radiological Society of North America, and Royal College of Radiologists
Disclosure: Nothing to disclose.

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