Midgut Volvulus Imaging 

Midgut volvulus is a condition in which the intestine has become twisted as a result of malrotation of the intestine during fetal development. Malrotation of the intestine occurs when the normal embryologic sequence of bowel development and fixation is interrupted. The malrotated bowel is prone to torsion (as demonstrated in the first image below), which can lead to midgut volvulus. The second image, from a GI series, shows a lateral view of midgut volvulus.

In neonates, malrotation with midgut volvulus classically presents with bilious vomiting and, as the radiograph below demonstrates, high intestinal obstruction. While most neonates with bilious vomiting do not have midgut volvulus, this diagnosis must be ruled out.

Older children with malrotation may manifest a failure to thrive, chronic recurrent abdominal pain, malabsorption, or other vague presentations. The older the child is, the less readily identifiable is the clinical presentation. Nonrotation of the intestine may be asymptomatic and is an incidental finding on upper GI series performed for other reasons.

Associated anomalies are seen in approximately 60% of patients and include congenital heart disease with heterotaxy (abnormal positioning and arrangement of the abdominal organs, such as the spleen, liver, and major blood vessels; right-sided or left-sided isomerism). Malrotation is almost always present in patients with congenital diaphragmatic hernia and abdominal wall defects, such as omphalocele and gastroschisis. Also, malrotation is more common with imperforate anus, duodenal atresia, duodenal web, stenosis, preduodenal portal vein, annular pancreas, and biliary atresia.

Malrotation in a patient with congenital heart disease and heterotaxy is shown below.

Preferred examination

The diagnostic test of choice in a child with possible malrotation, with or without midgut volvulus, is an upper GI series.^{[1, 2]}

In a study by Sizemore et al, an upper GI series in the detection of intestinal malrotation and midgut volvulus in infants and youths had a sensitivity of 96%, providing positive results in 156 of the 163 patients with surgically verified malrotation. In addition, the series showed midgut volvulus in 30 out of 38 patients in whom volvulus was surgically verified. Data from the study indicated that jejunal position can result in inaccurate interpretation of UGI series.^[1]

According to Gilbertson-Dahdal et al, when surgical treatment of patients with the double-bubble sign (the first bubble corresponds to the stomach, and the second bubble to the dilated duodenal loop) is delayed, an upper GI radiographic or ultrasound study is needed to identify possible malrotation with midgut volvulus.^[3]

In most patients with malrotation, an upper GI series is easy to perform and, in experienced hands, is easy to interpret, with the following exceptions:

• With complete duodenal obstruction, an upper GI series does not differentiate between the causes of proximal intestinal obstruction. In such cases, surgical exploration is indicated.
• A redundant duodenum, seen in some normal individuals, can be confused with malrotation. A careful following of the barium shows a normal duodenojejunal junction (DJJ); if uncertainty exists, barium can confirm normal rotation if the cecum is seen in the right lower quadrant.

A false-negative diagnosis of malrotation with midgut volvulus can lead to delays in the diagnosis and, possibly, death or severe morbidity. A false-positive diagnosis can lead to an unnecessary laparotomy and a delay in obtaining the correct diagnosis.

The highest sensitivities and specificities with upper GI series are in pediatric centers where operators with experience and pediatric expertise perform the examinations. If the upper GI results are in question, the examination should be repeated through a nasogastric feeding tube or the study should be continued to determine the position of the cecum.

An upper GI series is the preferred diagnostic test for malrotation with midgut volvulus and must be performed, unless a delay in surgical treatment will compromise outcome (as in the case of a moribund child).^{[1, 2, 4]} Upper GI series sensitivity is 85-95%, with a higher specificity (false positives are rare).

In midgut volvulus, the classic radiographic finding is a partial duodenal obstruction (dilation of both the stomach and proximal duodenum, with a small amount of distal bowel gas). Complete obstruction of the duodenum may also be found. Less frequent, but more ominous, signs are a gasless abdomen, ileus, or a distal small bowel obstruction with multiple dilated loops and air-fluid levels. A normal abdominal film does not exclude malrotation.

The upper GI series is performed with barium administered either orally or through a nasogastric tube. The normal duodenojejunal junction (DJJ) lies to the left of the left-sided spinal pedicle at the level of the duodenal bulb on a true frontal view. The duodenal C-sweep courses posteriorly, inferiorly, anteriorly, and then superiorly.

The findings of a malrotation on upper GI series include the following:

• The DJJ is displaced downward and to the right on frontal view.
• The duodenum has an abnormal course on lateral view.
• Abnormal positioning of the jejunum (lying on right side of abdomen) should alert the physician to the possibility of a malrotation, but this finding should not be relied upon to either make or exclude the diagnosis.

In malrotation with midgut volvulus, the findings also include the following:

• A dilated, fluid-filled duodenum
• A proximal small bowel obstruction
• A "corkscrew" pattern (proximal jejunum spiraling downward in the right- or mid-upper abdomen in midgut volvulus, which is rare), as seen in the images below.
• Mural edema and thick foldsUpper GI series shows malrotation with midgut volvulus. An incomplete duodenal obstruction and dilation of the first and second portions are seen, as is the "corkscrew sign." Upper GI series shows the "corkscrew sign" in a frontal view.

False-negatives and false-positives

Normal radiographs are common with malrotation. In malrotation without midgut volvulus, the degree of confidence on plain radiographs is low. Radiographs are rarely normal in malrotation with midgut volvulus, increasing the degree of confidence in this clinical scenario.

Findings in midgut volvulus are nonspecific and can be seen in other conditions that may cause ileus or ischemia, such as acute pyelonephritis, appendicitis, and necrotizing enterocolitis.

Duodenal obstruction, seen in midgut volvulus and malrotation, is also seen with duodenal stenosis, duodenal web, annular pancreas, preduodenal portal vein, and duodenal atresia.

Although a DJJ low and to the right of normal is a sensitive indicator of malrotation, this finding can also occur secondary to distended bowel, masses, and splenomegaly, especially in children younger than 4 years, whose mesenteric attachments are not as well fixed as they are in later years. Scoliosis makes it difficult to rule out malrotation because the normal bony landmarks are lost.

Diagnosis of malrotation with midgut volvulus on fetal magnetic resonance imaging (MRI) has been reported.^[5] In practice, this is a difficult diagnosis to make, and MRI is not recommended in infants suspected of having malrotation with midgut volvulus.

Ultrasonography and CT may suggest the diagnosis of malrotation; however, their sensitivities and specificities are low compared with those of an upper GI series. An upper GI examination is mandatory to confirm the diagnosis, if it is suspected on CT or ultrasonography. If the superior mesenteric vein (SMV) lies to the left of or posterior to the SMA (as demonstrated in the CT scan below), malrotation is suggested; however, normal vascular positioning (the SMV being slightly ventral and to the right of SMA) can be seen in approximately 30% of patients with malrotation.

The "whirlpool sign" on color Doppler ultrasonography (as seen in the image below) shows mesentery and flow within the SMV wrapping around the SMA (in a clockwise direction), suggesting, but not entirely specific for, malrotation with midgut volvulus.^{[6, 7]} A dilated, fluid-filled duodenum is frequently seen in patients who have obstruction without volvulus.

The moderate-to-low degree of confidence associated with ultrasonography and CT necessitates an upper GI series to confirm the diagnosis. Ultrasonography and CT have false-negative rates of approximately 30% and false-positive rates as high as 20%.

Angiographic abnormalities with chronic volvulus have been well described, and they include proximal occlusion of the SMA, a "barber-pole sign" (whirling SMA and its branches),^[8] extensive collateral vessels, and thickening of the small bowel folds. Angiography is not used to diagnose acute midgut volvulus. The degree of confidence is high, but this examination is rarely indicated.