Small bowel necrosis in the context of acute small-bowel obstruction, with normal CT findings

Clinical History

The patient presented with nausea and right lower quadrant abdominal pain. On clinical examination, diffuse abdominal guarding was found together with a palpable mass in the iliac fossa.

Imaging Findings

The patient presented late at night with nausea and right lower quadrant abdominal pain. The pain had migrated to this site from the epigastrium, where it had been located earlier in the day. The patient had undergone an appendectomy 2 years previously. She also had an incident of incomplete ileus 6 months previously, treated with enterectomy.

On clinical examination, diffuse abdominal guarding was found together with a palpable mass in the iliac fossa, which was thought to be a distended bowel loop. Laboratory tests revealed leucocytosis (WBC: 18200). A plain abdominal upright imaging study showed no air-fluid levels or other signs of obstruction.

Abdominal spiral computed tomography (CT) performed the next day, after iv contrast material administration, depicted distended small bowel loops (both of the jejunum and ileum). The loop with the largest diameter was located at the right iliac fossa, had mild wall thickening and a fluid collection around it. Fluid was also present in the peritoneal cavity. There was no abnormal pattern of bowel wall enhancement or other signs of intestinal ischaemia or necrosis.

The diagnosis on laparotomy and adhesionlysis was strangulation and bowel necrosis; a 15cm portion of ileum was removed.

Discussion

Although small bowel obstruction is a common occurrence, proper diagnosis and treatment requires a variety of diagnostic radiological procedures together with a detailed history, examination and laboratory tests to determine the site, level and cause of the obstruction.

There are many different mechanisms and causes of obstruction. These include:

• Extrinsic causes: adhesions, closed loop, strangulation, hernia;
• Extrinsic masses: carcinoid tumours, lymphoma, peritoneal carcinomatosis, appendicitis, diverticulitis;
• Intrinsic causes: adenocarcinoma, Crohn's disease, tuberculosis, radiation enteropathy, intramural haemorrhage, intussusception; and
• Intraluminal causes: bezoars, intestinal malrotation.

Because of the high incidence of surgical operations, the commonest cause of small bowel obstruction in the developed world is adhesions, comprising 75-80% of all cases. The diagnosis of adhesions causing bowel obstruction is made when all other causes of obstruction have been excluded at CT.

Typically, plain abdominal imaging is the first imaging procedure used in patients with bowel obstruction. However its sensitivity in determining the presence of obstruction is only 69%, whereas the specificity is 57%.

Enteroclysis, although it is particularly helpful in depicting the severity of partial obstruction and the sites of multifocal incomplete obstruction, is contradicted in patients with acute and complete or high-grade bowel obstruction, strangulation, suspected perforation and paralytic ileus.

Ultrasonography is now frequently used for the initial evaluation of patients with abdominal pain. Small bowel thickening can be identified sonographically. A small bowel wall more than 3mm thick should be considered abnormal. Sonography can also detect gas within the portal or mesenteric vein and, with Doppler technique, is used for the assessment of visceral vasculature.

Recent studies have shown the superiority of CT in demonstrating the site, level and cause of obstruction; signs of bowel inviability; and pathological processes involving the bowel, mesentery, mesenteric vessels, and peritoneal cavity. Oral and iv administration of contrast medium is essential to produce accurate diagnostic results. In addition, bowel wall enhancement patterns are useful in diagnosing intestinal ischaemia and necrosis associated with obstruction and in the recognition of thrombi within a vessel. In general, a small bowel with a calibre greater than 2.5cm is considered dilated. The presence of a transitional zone and the "small bowel faeces sign" are reliable indicators of intestinal obstruction. The reported sensitivity of CT ranges from 78% to 100% for complete obstruction. For incomplete obstruction the diagnostic accuracy of CT may not be sufficient. In such cases, enteroclysis is the best method for evaluating the presence and degree of bowel obstruction.

Because the adhesive band itself cannot be identified on CT scanning, CT diagnosis of adhesions must be based on an abrupt change in bowel calibre without evidence of another cause of obstruction. Findings described on CT examination in ischaemic bowel are divided into two categories. Non-specific findings include focal or diffuse bowel wall thickening, focally dilated fluid-filled loops of bowel, the target or double halo sign, mesenteric oedema, engorgement of mesenteric veins, and ascites. Specific signs are intramural gas, mesenteric and portal venous gas, and occlusion of mesenteric vessels. However, none of these findings is pathognomonic. Bowel wall thickening and high attenuation of the bowel wall are the most important signs of ischaemia on unenhanced CT scans, whereas abnormal bowel wall enhancement and mesenteric fluid are important signs on enhanced CT examinations.

In conclusion: a normal CT scan or one with non-specific findings does not exclude ischaemic bowel or necrosis.

Differential Diagnosis List

Final Diagnosis

Small bowel necrosis due to obstruction caused of post-operative adhesions

URL:	https://eurorad.org/case/1454
DOI:	10.1594/EURORAD/CASE.1454
ISSN:	1563-4086