Abdominal cocoon: preoperative diagnosis on CT

Abstract

A 23-year-old man presented to the emergency department with a history of recurrent episodes of subacute intestinal obstruction. Palpation revealed a firm, non-tender, mobile, non-pulsatile mass of size 8–10 cm with indistinct margins and smooth surface in the hypogastrium. Contrast-enhanced CT scan of the abdomen showed clumping of the small bowel loops within a well-defined membrane-like structure without dilatation or thickening of bowel loops. The patient underwent a laparotomy with incision of the membrane and separation of all the small bowel loops inside the cocoon. Abdominal cocoon is the idiopathic variety of sclerosing encapsulating peritonitis and is an unusual cause of acute or subacute intestinal obstruction. Clinical diagnosis is difficult because of non-specific symptoms. CT has facilitated accurate preoperative diagnosis, long before the patient presents with full-fledged symptoms of acute intestinal obstruction. CT scan plays a significant role in excluding the secondary causes and helps in patient management.

Background

Abdominal cocoon is a rare entity of unknown aetiology in which small intestinal loops are encapsulated by a fibrocollagenous membrane. The prevalence of abdominal cocoon is unknown.¹ It is one of that 6% of rare cases which cause intestinal obstruction.² Lack of specific symptoms causes delayed diagnosis which has a poor prognosis. Contrast-enhanced CT scan (CECT) is diagnostic and helps in early management.³

Case presentation

A 23-year-old male patient presented to the emergency department with the history of recurrent episodes of colicky abdominal pain, associated with abdominal distension, nausea and occasional non-bilious vomiting for 5 months. No history of constipation was there. The patient complained of 4 kg weight loss over a period of the last 5 months. There was no history of fever, cough, haemoptysis, haematemesis or melena. There was no history of tuberculosis, diabetes, hypertension, previous abdominal surgery or trauma. No history of antihypertensive medication was found. No family history of any chronic disease was found. On examination, there was no pallor, icterus or lymphadenopathy. Abdominal palpation revealed a firm, non-tender, non-pulsatile mass of size approximately 8–10 cm with indistinct margins and smooth surface in the hypogastrium with mobility at right angles to the axis of the mesentery.

Investigations

Laboratory investigations showed normal haemogram, liver function tests and renal function tests. The chest X-ray was normal. Ultrasonography of abdomen showed grossly normal solid organs without evidence of ascites or retroperitoneal lymphadenopathy. In a clinical background of recurrent subacute intestinal obstruction, CECT was performed. It revealed clumping of the small bowel loops within a well-defined membrane-like structure occupying the left upper quadrant (figure 1) and reaching up to right lower quadrant of the abdomen (figure 2). All the small bowel loops were lying along the posterior abdominal wall. However, there was no dilatation or thickening of bowel loops. The membrane was smooth and uniformly enhancing without nodularity or calcification.

Figure 1.

Contrast-enhanced CT scan of the abdomen at the level of aortic bifurcation, showing clumped bowel loops enclosed in a membrane-like structure (arrows).

Figure 2.

Contrast-enhanced CT scan of the abdomen, inferior section reveals the extension of the membrane (arrow) downwards into the right iliac fossa with encasement of ileal loops.

Differential diagnosis

The differential diagnoses are an internal hernia and idiopathic intestinal pseudo-obstruction. The membrane is absent in these conditions, and both large and small bowels are dilated in the later condition.

The other common differential diagnoses are peritoneal tuberculosis, cirrhosis and neoplasms with peritoneal seedings leading to cocoon formation. These are excluded by proper clinical history, laboratory investigations and imaging findings. The absence of the various imaging findings like shrunken liver size, hypertrophied left lobe, irregular hepatic outlines and features of portal hypertension rules out cirrhosis as an underlying cause. In conditions like tuberculosis and tumours, there will be associated lymphadenopathy and ascites. The tubercular nodes may be conglomerated and show peripheral enhancement with central non-enhancing hypodense areas corresponding to necrosis. In malignant conditions, there may be direct visualisation of neoplasms, local invasion of adjacent structures or secondaries to distant organs like liver, lungs or bones.

Treatment

The patient was taken up for surgery. Laparotomy revealed a thick membrane enveloping the entire small bowel from duodenojejunal flexure to ileocecal junction adherent to the posterior abdominal wall. The cocoon membrane was incised; all the small bowel loops inside the cocoon were separated by adhesiolysis. The bowel loops were adherent to the capsule and separated from it. The membrane was completely excised. There was no bowel stricture or dilatation. The serosa was normal, and the gut was viable requiring no bowel resection. There was no intraoperative complication.

Outcome and follow-up

Histopathological analysis of cocoon showed fibrocollagenous tissue infiltrated by minimal inflammatory cell infiltrates and few congested blood vessels. There was no evidence of granulomatous pathology or malignancy. The postoperative period was uneventful. He was discharged from the hospital after 1 week of laparotomy. The patient recovered and was doing well until the last follow-up.

Discussion

Sclerosing encapsulating peritonitis (SEP) is characterised by the formation of a fibrous membrane encasing a variable length of small bowel loops. The small bowel loops tend to adhere with each other leading to mechanical compression, kinking or fibrotic constriction and may present with non-strangulating small bowel obstruction.^{3 4} Such a membrane can be formed secondary to numerous causes leading to chronic peritonitis and peritoneal fibrogenesis.³ The secondary causes are various abdominal procedures like repeated peritoneal dialysis, surgery, ventriculoperitoneal shunting, treatment with practolol-a beta-blocker, intraperitoneal drug administration (like chemotherapy), infections (peritoneal tuberculosis), endometriosis, cirrhosis and neoplasms with peritoneal seedings.^{2 5 6} The rarer idiopathic variety where no cause can be attributed to membrane formation is known as an abdominal cocoon and was first described in 1978 by Foo et al.² Although it was first reported in young female, there is no gender predilection, and it can present at any age.^{6 7} The clinical symptoms are variable ranging from asymptomatic to recurrent colicky abdominal pain, nausea, vomiting, abdominal distension and weight loss. More than 50% of patients present with a palpable non-tender abdominal mass. Majority of the patients present with an intestinal obstruction which may be acute, subacute to chronic in nature.³

The various diagnostic imaging modalities available are the X-ray abdomen, ultrasonography, barium meal follow-through study and CECT. Erect abdominal X-ray shows non-specific findings related to intestinal obstruction for example, multiple air–fluid levels and dilated small intestinal loops. Transabdominal ultrasound may show dilated bowel loops enclosed within a membrane, peritoneal thickening and ascites. Barium meal follow-through study provides a clue to bowel encapsulation by showing clumped small bowel loops at the centre of the abdomen referred to as the cauliflower sign. The intestinal transit time may be prolonged.^{2 8 9}

CECT is the imaging modality of choice for the diagnosis of an abdominal cocoon.^{2 9 10}

Preoperative CECT can diagnose this condition accurately by demonstrating the characteristic membrane enclosing a cluster of dilated or non-dilated small bowel loops.^{3 11} Other associated findings may be ascites, loculated fluid, bowel wall thickening, peritoneal calcification and reactive lymphadenopathy.² The secondary causes can also be excluded from CT. Delayed diagnosis can lead to complications of bleeding, intra-abdominal collections, recurrent obstruction, fistula and sepsis increasing morbidity and leading to a difficult surgery. The patient may develop complete intestinal obstruction requiring an emergency surgery which has a very high mortality rate.⁵ The typical CT findings along with histopathology finding of fibrocollagenous tissue with a mixed inflammatory infiltrate provide the complete diagnosis of idiopathic sclerosing encapsulating peritonitis when all other possible underlying predisposing conditions are excluded.⁴

Surgery is curative and comprises membrane dissection and adhesiolysis with separation of the entrapped bowel.^{3 4}

Laparotomy not laparoscopy is the preferred method of surgical management of abdominal cocoon. However, laparoscopy may be used for both the diagnosis and treatment of abdominal cocoon when operated by an expert hand to avoid bowel injury.¹²

Bowel resection may be required in complicated cases. The secondary SEPs like tubercular are generally managed conservatively by antitubercular treatment.¹³ Medical management can be done with corticosteroids, tamoxifen due to its anti-transforming growth factor beta properties and immunosuppressants, such as azathioprine or cyclosporin, especially in secondary SEPs.⁵ In our case, the patient presented with recurrent subacute intestinal obstruction and a palpable abdominal mass. CECT scan showed the characteristic membrane encasing the small bowel loops. We did not find any of the secondary causes as described above, thus accounting for the rare idiopathic SEP. Early preoperative diagnosis on CECT helped in the timely management of the condition reducing the morbidity.

Learning points.

• Idiopathic sclerosing encapsulitis or abdominal cocoon is a diagnosis of exclusion.

• CT is a very reliable, accurate and non-invasive diagnostic modality and helpful in excluding various other secondary causes which can be managed medically, thus, avoiding unnecessary diagnostic laparotomies in all the cases.

• The characteristic contrast-enhanced CT (CECT) finding of abdominal cocoon is a cluster of dilated or non-dilated small bowel loops encapsulated by a membranous sac.

• Early surgical treatment of abdominal cocoon can be offered if diagnosed before the development of complete intestinal obstruction or other complications.

• Preoperative diagnosis of abdominal cocoon on CECT helps in early management and reduces morbidity and mortality.