eMedicine Specialties > Radiology > Gastrointestinal

Spleen, Trauma: Imaging

Author: Steven R Klepac, MD, Associate Professor of Radiology, University of Illinois School of Medicine; Consulting Staff, Department of Radiology, University of Illinois Medical Center
Coauthor(s): Evan J Samett, MD, Consulting Staff, Department of Radiology, MacNeal Hospital
Contributor Information and Disclosures

Updated: Jan 16, 2009

Radiography

Findings

In most circumstances, chest and abdominal radiography is the initial step in the evaluation of patients with blunt torso trauma. However, the effects of blunt trauma are frequently masked by more obvious associated injuries. In most patients, the symptoms of blunt splenic trauma are absent or subtle; this characteristic probably explains the higher mortality associated with blunt abdominal trauma than with penetrating injury.

Missed splenic rupture or delayed diagnosis is associated with a 10-fold increase in mortality over the rate associated with prompt recognition of injury. Therefore, the radiologist must have a high index of suspicion and a low threshold for suggesting further evaluation with cross-sectional imaging.

Plain radiographic findings are numerous but occasionally subtle, and awareness of the imaging possibilities is important in effectively evaluating the information. Plain radiographs demonstrate a wide variety of abnormal findings. The constitution of findings reflects whether the spleen has sustained capsular rupture. Normal findings on chest and abdominal radiographs do not exclude splenic injury.

• The most common finding associated with splenic injury is left lower rib fracture. Rib fractures signify that adequate force has been transmitted to the LUQ to cause splenic pathology. Left lower rib fracture is present in 44% of patients with splenic rupture and necessitates further workup by abdominal CT.
• The classic triad indicative of acute splenic rupture (ie, left hemidiaphragm elevation, left lower lobe atelectasis, and pleural effusion) is not commonly present and should not be regarded as a reliable sign. However, any patient with apparent left hemidiaphragm elevation following blunt abdominal trauma should be considered to have splenic injury until proven otherwise.
• More reliable signs of LUQ injury are medial displacement of the gastric bubble and inferior displacement of the splenic flexure gas pattern. These findings are indicative of a LUQ mass and result from either subcapsular or perisplenic hematoma.
  • LUQ hematoma, if sufficiently large, can displace the shadow of the inferior splenic margin caudally, simulating splenomegaly.
  • Subcapsular hematoma can produce a similar appearance, and the appreciated mass has distinct borders.
  • Associated displacement of the left renal shadow also may be evident.
• The constitution of findings present when retroperitoneal hemorrhage or free intra-abdominal blood exists contrasts with those mentioned above.
  • Little, if any, mass effect on LUQ organs is apparent.
  • Splenic margins are obscured, but this finding is not specific.
  • Retroperitoneal blood can obliterate the left renal outline and psoas muscle margin.
  • Free blood pools exist dependently in the left paracolic gutter, displacing the descending colon gas pattern medially.
  • Larger amounts of abdominal hemorrhage can obliterate the flank stripe.
  • The small bowel gas pattern can be displaced out of the pelvis by collecting hemorrhage.
  • A midpelvic opacity with sharp convex lateral borders may result.
  • The bladder margin is enhanced and demarcated by a thin lucency outlining the dome and representing extraperitoneal fat.
• Chronic splenic hematoma appears different and is more problematic because it is accompanied by a long list of differential diagnoses. The usual course of a subcapsular or parenchymal hematoma is to contract; liquefy; and, usually, resorb.
• Occasionally, cystic degeneration of an intrasplenic hematoma results in formation of a false cyst.
  • Approximately 80% of splenic cysts are estimated to be posttraumatic in origin. Approximately 80% of these are termed hemorrhagic cysts, and the other 20% are termed serous cysts and probably represent hemorrhagic cysts in which the blood has been resorbed totally.
  • Thin, regular, annular calcification develops in the fibrous lining of approximately 30% of cysts.¹⁰
  • Cysts are symmetric and unilocular, and their calcified lining has a smooth inner and outer margin.
  • A single, large, annular, splenic calcification most likely represents a residual traumatic cyst in areas not endemic for Echinococcus organisms.
  • The imaging characteristics of traumatic cysts are not distinctive.
  • The most common cause of calcified splenic cysts worldwide is infection by Echinococcus granulosus, but the organism is rare outside its normal geographic distribution.
    • E granulosus affects the liver more commonly than other organs, with a minority of patients having concurrent splenic disease.
    • Isolated splenic involvement is uncommon. When it occurs, multiple lesions are present; however, calcification almost always is restricted to a single cyst.¹¹
    • Cysts tend to have a smooth outer wall, but calcification can be irregular.
    • Often, part of the wall appears flattened or indented, and intracystic opacities are common.
    • Collapse of the hydatid cyst can occur with infolding of the walls. Splitting of the wall calcification represents separation of the endocyst and pericyst linings.
    • A single cyst in an enlarged left lobe of the liver may simulate splenic pathology. Careful observation reveals mass effect directed laterally, in contrast to the medial displacement appreciated with a splenic mass.
• SA aneurysm is the number one visceral aneurysm. The etiology can be atherosclerotic disease, pancreatitis, or previous trauma.
  • The incidence in females is higher than that in males, and it is highest in women of childbearing age who have had 2 or more pregnancies.
  • Although usually asymptomatic, LUQ pain or fullness is a complaint in 50% of patients.
  • As many as 66% of aneurysms develop calcification, which is annular but characteristically thicker and more irregular than that seen in splenic cysts.
  • Associated SA calcification may be present if atherosclerotic disease is the cause.
  • Plain radiographs can show a diagnostic interruption in the calcification where the aneurysm originates in the SA.
  • Complex multiloculated configurations also are possible and are distinct from traumatic splenic cysts.
• An epidermoid cyst of the spleen is a congenital abnormality that results from infolding or entrapment of peritoneal mesothelium within the spleen.
  • Cysts are slow growing and usually appear in those aged 10-30 years.
  • Cysts are unilocular and solitary 80% of the time, with an average size of 10 cm.
  • Curvilinear wall calcification occurs in 9-25% of cysts, and appearance is identical to a traumatic splenic cyst.
• Calcified cysts of surrounding organs in the LUQ can simulate chronic splenic injury.
  • Simple renal cysts have a peak incidence in patients older than 30 years. Renal cysts are present in 3-5% of all individuals at autopsy and account for 62% of all renal masses. Although only 1% of renal cysts show marginal calcification, a calcified renal cyst is not an uncommon finding, considering the large number that exist.
  • Adrenal cysts usually are solitary, and 50% are larger than 5 cm. They most commonly appear in those aged 20-60 years, with a slight female predominance. Rimlike nodular calcification is present in 51-69% of adrenal cysts.
  • Pancreatic pseudocysts and mesenteric cysts are possible but rarely calcify.
• Subcapsular hematoma is a common result of splenic trauma and demonstrates imaging characteristics different from those of parenchymal pathology. As the hematoma resolves, fine marginal calcification of the cavity can develop. Depending on the projection, the calcified cavity can appear linear or discoid. The degree of mass effect depends on the size of the regressing hematoma.
• Many pathologic entities can have similar findings, most notably sickle cell disease. A chronic splenic infarct may develop calcification similar to that of subcapsular hematoma. A large hematoma viewed en face can be misinterpreted as a contracted hyperopaque spleen of sickle cell disease. In sickle cell disease or thalassemia, the spleen remains enlarged despite calcification or increased density, confusing the differential. In fact, any process leading to splenic infarction or fibrosis can cause calcification and simulate chronic subcapsular hematoma.

Causes of splenic infarction include the following:

• Embolic - Endocarditis, atherosclerotic plaque, cardiac thrombus, and metastasis (gastric and/or pancreatic)
• Local thrombosis - Sickle cell disease, myelofibrosis, myelolymphoproliferative disorders (chronic myelogenous leukemia type 1), polycythemia vera, and Gaucher disease
• Vasculitis - Polyarteritis nodosa, systemic lupus erythematosus, and drug abuse
• Pancreatitis
• SA aneurysm
• Splenic torsion

Degree of Confidence

See Findings above.

False Positives/Negatives

See Findings above.

Computed Tomography

Findings

At most institutions, CT is the modality of choice for evaluation of blunt abdominal trauma. Overall, sensitivity and specificity are high for detection of splenic trauma. Intravenous contrast material is necessary for complete evaluation because areas of hematoma are frequently isoattenuating relative to the parenchyma on nonenhanced images.

• The spleen demonstrates a multitude of normal variations in shape. Lobulations are common, and clefts between lobulations can be as deep as 2-3 cm. Clefts can mimic lacerations but should appear more smoothly contoured and sharply marginated than lacerations.
• Accessory splenic tissue occurs in 10-30% of individuals and develops in multiple sites in approximately 10%. The most common location is in the hilar region, followed by the suspensory ligaments, particularly the gastrosplenic ligament. Accessory tissue can mimic fragmentation, but margins are smooth and better defined than they are in lacerations.
• Blunt splenic trauma can result in subcapsular hematoma, intraparenchymal hematoma, laceration, or fragmentation with autosplenectomy.
  • Laceration appears as an irregular hypodense area of nonenhancement, with somewhat indistinct borders compared to the margin in an unlacerated spleen.
  • Subcapsular hematomas are regularly shaped, crescentic, hypoattenuating collections closely applied to the perceived splenic margin. The margins are usually sharp in distinction to a perisplenic clot. Underlying deformity or indentation of the parenchyma is appreciated.
  • Intraparenchymal hematoma is a broader, more irregular, hypoattenuating area with mass effect and enlargement of the spleen. A parenchymal hematoma, which is contained within the spleen, should have a discernible rim of surrounding splenic tissue on contrast-enhanced images. On nonenhanced images, the hematoma can appear hypoattenuating, isoattenuating, or hyperattenuating compared with the parenchyma.
• Many grading systems for splenic injury have been formulated, with the earliest by Buntain et al.¹² The Organ Injury Scaling Committee of the American Association for the Surgery of Trauma was organized to devise universal grading systems for individual organs in 1987 and revised the splenic system in 1994.¹³ The spleen injury grading scale is as follows:
  • Grade I
    • Subcapsular hematoma of less than 10% of surface area
    • Capsular tear of less than 1 cm in depth
  • Grade II
    • Subcapsular hematoma of 10-50% of surface area
    • Intraparenchymal hematoma of less than 5 cm in diameter
    • Laceration of 1-3 cm in depth and not involving trabecular vessels
  • Grade III
    • Subcapsular hematoma of greater than 50% of surface area or expanding and ruptured subcapsular or parenchymal hematoma
    • Intraparenchymal hematoma of greater than 5 cm or expanding
    • Laceration of greater than 3 cm in depth or involving trabecular vessels
  • Grade IV - Laceration involving segmental or hilar vessels with devascularization of more than 25% of the spleen
  • Grade V - Shattered spleen or hilar vascular injury
• Hemoperitoneum almost always accompanies splenic injury. Uncommonly, a perisplenic clot is present without evidence for capsular disruption, which has been reported in approximately 9% of patients and is termed the sentinel clot.¹⁴ The sentinel clot is a sensitive sign of visceral injury and should prompt careful inspection of the images for an etiology; however, a small laceration can be compressed by perisplenic clot, rendering it invisible.
• The CT appearance of intraperitoneal blood depends on the age and physical state of the clot.
  • Immediately after hemorrhage, intraperitoneal blood has the same attenuation as circulating blood of 20-30 HU. However, attenuation values less than 20 HU are a frequent finding in the acute setting.¹⁵ The proposed reason for this is that blood, being a strong peritoneal irritant, causes a local inflammatory response with transudation of fluid across the peritoneum.
  • Transudate fluid mixes with and dilutes the blood before coagulation begins, decreasing the attenuation. Within hours, a clot forms.
  • Attenuation increases as hemoglobin concentrates, and values in the range of 50-75 HU are seen.
  • Densely clotted blood may have attenuation values upwards of 100 HU.
  • Clot lysis begins within 48-72 hours, and attenuation decreases to fluid values. Lysis proceeds more rapidly for intraperitoneal hematomas than visceral hematomas secondary to abdominal and respiratory motion and bowel peristalsis.¹⁶
  • After a few weeks, most hematomas have attenuation values approaching those of water, namely, 0-20 HU.
  • The scenario just described is a simplified version based on a single episode of hemorrhage. In reality, hemoperitoneum can have a complex appearance as a result of recurrent hemorrhage and irregular resorption. Blood may exist in many different stages at the time of imaging if hemorrhage has been intermittent. Fresh blood that is confined to a localized space or that has been relatively undisturbed may separate, with plasma layered on top of precipitated red blood cells causing the hematocrit effect.
  • Hemoperitoneum does not indicate whether active hemorrhage is present. Repeat imaging, as clinically warranted, can aid in detecting ongoing hemorrhage. Increasing hematoma size or changes in character contrary to the expected sequence are indications of continued hemorrhage. In most instances, hemoperitoneum significantly resolves within 1 week. In one study, intra-abdominal hematoma with a stable appearance 3-7 days after injury was suggestive of continued hemorrhage. Depending on the physical state of the existing hematoma, fresh blood appears either relatively hypoattenuating or hyperattenuating.
• On contrast-enhanced CT, extrasplenic extravasation of contrast material rarely is seen. When extravasation occurs, patients most likely have hemodynamic instability and proceed to laparotomy. However, an intraparenchymal vascular blush may appear as single or multiple well-defined areas of contrast material collection when a bolus injection is performed.
  • Hyperattenuating areas represent localized areas of contrast material extravasation from pseudoaneurysms or arteriovenous fistulas.^17,18
  • Pseudoaneurysm formation is reportedly a delayed finding in 10% of patients with splenic injury.¹⁹ The presence of a pseudoaneurysm is a strong predictor of nonoperative failure. Davis et al found that of patients in whom conservative treatment failed, CT scans in 67% demonstrated a contrast blush. Note that 74% of pseudoaneurysms were not documented on the initial CT scan; this observation provides strong support for repeat examination in patients who receive conservative treatment.¹⁹
• Many authors have attempted to develop grading systems and delineate specific findings to predict the need for laparotomy and assess the success of conservative treatment. Resciniti et al proposed a CT scoring system to address the need.²⁰ The region CT scoring system is as follows:
  • Splenic parenchyma
    • Intact - 0
    • Laceration (thin, linear defect) - 1
    • Fracture (thick, irregular defect) - 2
    • Shattered - 3
  • Splenic capsule
    • Intact - 0
    • Perisplenic fluid present - 1
  • Abdominal fluid
    • No fluid - 0
    • Any fluid except perisplenic - 1
  • Pelvic fluid
    • No fluid - 0
    • Any pelvic fluid - 1
• In adult patients with a total CT score of less than 2.5, nonsurgical treatment was successful in all patients.
  • A score of 2.5 or more is correlated with a 46% likelihood of successful nonsurgical treatment. In one study, all pediatric patients younger than 17 years had successful conservative treatment without delayed complications irrespective of the score.
  • A subsequent study elucidated potential errors of the scoring system, particularly in discriminating subcapsular from perisplenic fluid and accounting for interobserver variability.²¹ However, 13 of 15 patients treated nonsurgically who had a score of less than 2.5 had favorable outcomes.
  • Despite the criticisms, overall conservative treatment failed in only 2 (10%) of 21 patients. This result represents a significant improvement over the 22-75% failure rates reported in the literature.
  • Conversely, 8 unnecessary laparotomies would have been performed if the grading system had been used. This would have been an 89% increase. Obviously, the scoring system created by Resciniti is imperfect, and further evaluation is needed²⁰ .
  • Initial reports describing conservative treatment for blunt splenic trauma found that patient age greater than 55 years is an indicator of poor outcome. Perhaps the addition of patient age to the CT scoring system would improve results.^{22,23,24,25,26}

Degree of Confidence

In the authors' experience, the overall sensitivity and specificity of CT in the detection of splenic injury is close to 100%.

False Positives/Negatives

One pitfall of the use of contrast material is that bolus injection with early imaging can produce heterogeneous splenic enhancement, because red and white pulps demonstrate differing blood flow rates. The characteristic tiger-stripe pattern results. The pattern should not be confused with traumatic change and can be remedied by delayed imaging or slower injection rates.

An overall decrease in splenic enhancement compared to that of the liver can occur in patients with hypotension and can be misinterpreted as vascular pedicle injury. This phenomenon is believed to result from adrenergic effects on blood flow.²⁷

Ultrasonography

Findings

The primary goal of splenic ultrasonography in the setting of blunt abdominal trauma is to detect the presence of blood in the LUQ.

• Acute blood is hypoechoic and can be almost anechoic.
• Differentiating subcapsular from perisplenic blood is difficult, but a few clues are available.
  • A smooth crescentic collection conforming to the splenic margin probably should be considered subcapsular.
  • In comparison, extracapsular blood is usually shaped more irregularly.
  • Although mass effect is produced in both cases, subcapsular blood is more likely to distort splenic shape.
  • The membrane overlying subcapsular collections is thin and uncommonly depicted; therefore, the absence of this finding does not suggest either diagnosis.
• Within hours, coagulation of hemorrhage occurs. Echogenicity increases as the thrombus condenses. Mature hematomas demonstrate echogenicity equal to or slightly greater than parenchyma and retain this appearance for approximately 48 hours until lysis begins. The echogenic phase usually corresponds to the time when imaging is performed in most acute circumstances. As lysis proceeds, the hematoma returns to fluid echogenicity, and the pathology is again more apparent.
• Parenchymal abnormalities commonly are subtle.
  • Lacerations appear as hypoechoic regions, which can be irregular or linear in configuration.
  • Splenic infarct has a similar appearance, but it is usually better defined. Infarcts are wedge shaped, with the apex toward the hilum, compared to traumatic injury in which a more complex distribution is seen.
  • Subtlety of parenchymal injury probably relates to associated local hemorrhage. Any trapped blood soon coagulates, becoming isoechoic with the surrounding tissue.

Degree of Confidence

In the past decade, increasing support has emerged for using ultrasonography in the initial assessment of blunt abdominal trauma. The focused assessment for the sonographic examination of the trauma patient test has been developed.²⁸ The evaluation surveys for fluid in the pericardium and peritoneum. Dependent areas of the abdomen are imaged (ie, the hepatorenal space [right upper quadrant, or RUQ]; splenorenal space, LUQ; and pelvis, rectovesical or rectouterine space). Cadaver studies have shown that as little as 100 mL of fluid can be discerned.²⁹

A study aimed at correlating the presence of abdominal fluid with visceral injury seen on sonograms revealed fluid in the RUQ in 71% of the 69 patients confirmed to have isolated blunt splenic injury; fluid in the LUQ in 33%; and fluid in the pelvis in 30%.³⁰ Although individual patient data were not supplied, a significant number of patients had fluid in the RUQ without any appreciated in the LUQ. Obviously, blood must have been present in the LUQ at some point after the initial injury. Although the authors concluded that ultrasonography was sensitive for detection of blunt visceral injury overall, the study revealed its insensitivity in recognizing splenic injury. Surely, something is amiss if the LUQ was interpreted as being fluid-free in 69 patients with documented blunt splenic trauma.

A number of possible reasons may explain the discrepancy. First, blood in the LUQ is, on average, older than blood elsewhere in the abdomen. Hemorrhage initially pools in the perisplenic area and spills over into the remainder of the abdomen as a larger amount accumulates. With lower grades of injury or slower bleeding rates, the blood coagulates and fills the potential space. On subsequent episodes of hemorrhage, fresh blood may be displaced from the LUQ secondary to mass effect from the thrombus. Ultrasonography of the LUQ does not show any free fluid. Conversely, the hemorrhage may be subdiaphragmatic and difficult to image. The spleen is displaced inferiorly, and no fluid is appreciated in the splenorenal space.

Second, the echogenicity of an acute clot is equal to or greater than that of the splenic parenchyma. A clot may be inseparable from the adjacent spleen. The injury is misdiagnosed as splenomegaly or not appreciated at all. The clot also may be mistaken for overlying bowel or artifact from a poor acoustic window.

False Positives/Negatives

Yoshii et al found 90% specificity for detecting splenic injury irrespective of the presence of fluid. Of the 9 false-negative results, 3 were classified as major injuries requiring celiotomy. Compared with the 96% or better sensitivity of CT and the superiority of CT in determining injury extent, the authors concluded that CT should be the preferred test in hemodynamically stable patients able to cooperate for the examination. The sensitivity, accuracy, and negative predictive value of ultrasonography were comparable to those of diagnostic peritoneal lavage. Perhaps ultrasonography can play a role in evaluation of the unstable patient or in situations in which diagnostic peritoneal lavage is chosen.³¹

Nuclear Imaging

Findings

The use of nuclear radiology to assess trauma has decreased significantly over the past several decades. The advent of dedicated trauma centers and new treatment protocols, as well as improved imaging technology, are the reasons for this waning use in the acute setting. The use of nuclear imaging is relegated to evaluation of chronic injury or injuries with delayed presentation. The role of nuclear imaging with respect to splenic trauma is limited to distinguishing findings in the differential diagnosis when the presentation or clinical history does not equivocally indicate trauma.

The importance of obtaining multiple views cannot be stressed enough. Imaging must include both anterior and posterior projections, with multiple oblique images because small defects may be discernible on only 1 image or a few images.

Splenic trauma may appear as simple displacement, reduced size, focal defects, a band of decreased activity, or loss of splenic contours.

Currently, the trend is toward splenic salvage, as opposed to splenectomy, whenever possible. In a patient who has undergone splenorrhaphy or has received conservative treatment, physical activity is limited significantly for 8-12 weeks. Some institutions image the spleen prior to releasing the restrictions to document adequate fracture healing.

The liver-spleen scan is a viable alternative to CT for follow-up studies of splenic injury. Intravenous contrast material is not required and the whole-body radiation dose of 0.0002 Gy/mCi (range, 3-5 mCi) is less than that of conventional CT. Scans demonstrate resolution of the defect in uptake, although a small area of decreased activity may persist secondary to scar formation.

Degree of Confidence

In splenic imaging, technetium-99m sulfur colloid scanning remains the test of choice. Acute splenic injury can be diagnosed with a high degree of sensitivity, but the specificity is less than desirable.

Small subcapsular hematomas or contusions may be missed. Splenic abscesses, infarcts, cysts, and benign or malignant masses present with the same findings and are indistinguishable from trauma.

False Positives/Negatives

False-positive findings may result from variations in the normal shape of the spleen.

Angiography

Findings

A discussion of splenic angiography must begin with a review of splenic arterial anatomy (see Anatomy). A thorough knowledge of the SA is needed to analyze traumatic damage correctly and offer therapeutic options.

Splenic trauma can produce a wide variety of angiographic findings, either directly or indirectly.

• Indirect signs include displacement of the spleen from the abdominal wall and avascular parenchymal areas from hematoma.
• Peripheral parenchymal defects may represent subcapsular hematomas, but care must be taken not to confuse traumatic change with developmental notching or lobulation.
• Mass effect can be identified with traumatic injury.
• Compression of the vascular pattern along the defect margin is characteristic of subcapsular hematoma.
• Defects from chronic change, such as infarct, should have clear margins that are more regular in contour without mass effect.
• Parenchymal hematoma usually demonstrates hazy borders with splaying of the surrounding vessels. Hematoma age affects the degree to which these characteristics are visualized.
• Parenchymal irregularity or mottling may result from localized edema of a contusion without apparent vessel abnormalities.
• The most reliable angiographic sign of splenic trauma is contrast-material extravasation, either parenchymal or extrasplenic. At times, extravasation may be observed only after the administration of vasopressin or epinephrine. These medications enhance detection of vascular injury by increasing precapillary arteriolar resistance.
• Abrupt cutoff of vessels, vessel wall irregularity, pseudoaneurysms, and early filling of splenic veins are findings of traumatic injury.

The liberalization of treatment for blunt splenic trauma over the last decade has increased the role of angiography. Interest in splenic angiography has also been sparked by the inadequacy of CT grading systems to predict successful nonoperative treatment in certain patients. As a result, angiography has been used to elucidate risk factors for delayed complications of splenic injury. The literature reports an approximate 5% incidence of delayed hemorrhage more than 4 days after injury.³²

Classically, rupture of a subcapsular hematoma had been implicated as the cause of delayed bleeding; however, it has been found that subcapsular hematoma may not be a predictor of delayed splenic rupture and that lysis of hematoma at the injury site may be the most likely cause. Angiographic criteria have been proposed in an attempt to determine which injuries pose the greatest risk of delayed hemorrhage. Many authors have proposed grading systems of splenic injury, but these systems are somewhat confusing and complicated.

Splenic fragmentation or major arterial injury signifies impending life-threatening complications in most patients, and they require immediate surgical intervention. The absence of contrast-material extravasation from the parenchymal vessels was correlated with successful conservative treatment in one study.³³ Active extravasation, even intraparenchymal extravasation, can cause tamponade and cease spontaneously, but it is correlated with delayed capsular rupture. Large avascular areas, defined as those involving more than 25% of the spleen, is correlated with a poor outcome. An avascular area of less than 25% is associated with a good outcome.

These differences are probably related to more than one factor. A large avascular area requires injury to either a more central, larger vessel or multiple regional peripheral vessels, as opposed to a smaller avascular area. A central vessel has greater blood flow and higher systolic pressure, both of which increase the likelihood of rupture as the hematoma matures and undergoes lysis. When small vessel disruption is suspected, an increased risk of delayed hemorrhage between the large and small avascular areas may be related to statistical chance when a large number of vascular branches are injured.

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