Sclerosing encapsulating peritonitis

Dr Tim Luijkx and Radswiki et al.

Sclerosing encapsulating peritonitis (SEP) is a rare benign cause of acute or subacute small bowel obstruction. It is characterised by total or partial encasement of the small bowel within a thick fibrocollagenous membrane.


SEP was originally termed abdominal cocoon. It has also been known as sclerosing peritonitis, encapsulating peritonitis, and peritonitis chronica fibrosa incapsulata.


SEP can be idiopathic or secondary due to:

  • chronic ambulatory peritoneal dialysis
  • peritoneovenous or ventriculoperitoneal shunts
  • treatment with practolol

Various abdominal disorders such as tuberculosis, sarcoidosis, familial Mediterranean fever, gastrointestinal malignancy, protein S deficiency, liver transplantation, fibrogenic foreign material, and luteinised ovarian thecomas are the other rare causes.

Radiographic features

Abdominal radiograph

Radiographic appearances are nonspecific. Radiographs of the abdomen may show:

  • air-fluid levels similar to those in patients with any other cause of small-bowel obstruction
  • the wall of the "cocoon" may calcify

In the appropriate clinical setting, recognition of the entire dilated small bowel at the centre of the abdomen and encased within a thick fibrocollagenous membrane, as though it were in a cocoon, on a CT image is diagnostic of SEP. The other imaging findings may include signs of obstruction, fixation of intestinal loops, ascites or localised fluid collections, bowel wall thickening, peritoneal or mural calcification, and reactive adenopathy.

Differential diagnosis

SEP may be confused with congenital peritoneal encapsulation, which is characterised by a thin accessory peritoneal sac surrounding the small bowel. 

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