Ultrasound in the diagnosis of small bowel obstruction secondary to an incarcerated jejunal loop in Morison’s pouch

Internal hernias are rare, accounting for <1% of all instances of intestinal obstruction and leading to only 0.5–4.1% of cases of acute intestinal obstruction caused by hernias [1]. They typically involve the small bowel herniating through a peritoneal or mesenteric aperture within the peritoneal cavity [1]. The hernial orifice is commonly an anatomic structure or pathological defect of congenital or acquired origin related to defective approximation of peritoneal flaps during embryogenesis or surgically created spaces [1, 2].

Internal hernias are generally classified into six main groups: paraduodenal, tranmesenteric, pericecal, supravesical, intersigmoid, foramen of Winslow, and omental hernias [1]. To our knowledge, there are no other reports in the literature of a hernia arising from a retroperitoneal defect resulting in the incarceration of small bowel in Morison’s pouch. Other unusual sites include the inferior ileocecal recess [3], falciform ligament [4] and descriptions of a potential space for herniation between the fourth portion of the duodenum and abdominal aorta [5]. The origin of this patient’s hernia remains unclear; however, the possibility of a preexisting congenital anomaly of the retroperitoneal space just above the superior pole of the right kidney would have to be considered.

The diagnosis of an internal hernia can be challenging because the symptoms are often intermittent and nonspecific [6]. Small and easily reducible hernias may not produce clinical symptoms while other patients may experience intermittent periods of pain [1]. Radiological studies are most likely to diagnose an internal hernia if they are performed while the patient has symptoms [1]. Contrast studies and CT examinations may identify an abnormal location or disturbed arrangement of the small intestine, the presence of several bowel loops within a hernial sac, or bowel dilatation and stasis within the herniated loops [1]. Studies performed once the hernia has spontaneously reduced are often negative and may result in the patient being mislabeled as psychoneurotic [1]. More commonly, internal hernias are diagnosed during a laparotomy performed for acute intestinal obstruction [1].

In patients with SBO plain abdominal radiography is diagnostic in about 50–70% of cases but may be normal in patients who have complete, closed-loop, or strangulated obstructions [7]. Further work up for a clinically suspected SBO may include a small bowel follow through, enteroclysis, CT, ultrasound, or MRI. Ultrasound is as sensitive and is more specific than plain abdominal radiograph, but it is infrequently used for suspected SBO because other tests such as CT can be done rapidly and are more accurate [7]. Signs of small bowel obstruction on ultrasound may include exaggerated peristaltic activity producing a to-and-fro motion (which may decrease or cease with strangulation), dilation of the proximal intestinal segment, and accumulation of fluid and gas [8]. The patient in this case exhibited all of the aforementioned sonographic signs of obstruction. In addition, the presence of bowel in an atypical retroperitoneal location led to the diagnosis of an internal hernia within Morison’s pouch, which was later confirmed intraoperatively.

In cases of obstruction, secondary to an incarcerated loop of bowel, an immediate diagnosis is essential because ischemia and necrosis can result from delay in proper treatment [1]. The presence of an early or partial SBO had been suggested by plain radiograph. The gas seen on the technically limited ultrasound study of the right upper quadrant was a clue to the presence of a developing obstruction in an atypical location. This case illustrates how physician performed ultrasound examination can be used in concert with the patient’s clinical presentation to yield an unlikely diagnosis, even when earlier attempts at radiological assessment have failed.