Sclerosing encapsulating peritonitis (SEP) is a rare condition characterized by partial or complete encasement of small bowel loops by a peritoneal fibrotic membrane, also known as 'cocoon abdomen' or 'abdominal cocoon.' Most commonly seen in peritoneal dialysis patients; other causes include beta-blocker (practolol) use, post-surgical, VP shunt, and idiopathic form. The pathognomonic finding on CT is the 'cocoon sign' — small bowel loops encased by a dense fibrotic membrane forming a conglomerate mass. Clinically presents with recurrent intestinal obstruction episodes. Treatment includes conservative approach, discontinuation of peritoneal dialysis, and surgical membrane excision (capsulectomy).
Age Range
30-70
Peak Age
50
Gender
Equal
Prevalence
Rare
The pathogenesis of SEP is chronic inflammatory response and progressive fibrosis development following peritoneal mesothelium damage. In peritoneal dialysis, high glucose concentration, low pH, and glucose degradation products of dialysate fluid cause mesothelial cell damage, peritoneal membrane thickening, and neo-angiogenesis. Growth factors such as TGF-beta and VEGF stimulate fibrosis and new vessel formation. Progressive fibrosis forms a dense collagen membrane around small bowel loops, and this membrane restricts bowel motility leading to functional obstruction. The 'cocoon sign' on CT reflects this fibrotic membrane encasing small bowel loops like a cocoon — membrane enhancement reflects neo-angiogenesis-derived vascular structures. Membrane thickness can vary from millimeters to centimeters and may contain calcification. In advanced stages, bowel wall thickening, dilatation, and adhesions develop.
Small bowel loops encased by dense fibrotic membrane forming a central conglomerate mass on CT — resembling a silkworm cocoon. This finding is pathognomonic for SEP and combined with peritoneal dialysis history confirms the diagnosis.
Small bowel loops partially or completely encased by a dense fibrotic membrane on CT — 'cocoon sign.' The membrane is thin (1-5 mm), with smooth or nodular contour showing post-contrast enhancement. Contained bowel loops appear dilated and conglomerate. Membrane calcification may be seen in advanced stages.
Report Sentence
A dense fibrotic membrane encasing small bowel loops is seen (cocoon sign); consistent with sclerosing encapsulating peritonitis.
Linear or plaque-like calcifications along the peritoneal membrane on non-contrast CT. This finding is seen in advanced-stage SEP and reflects the chronicity of peritoneal membrane damage. Calcification distribution may be diffuse or focal.
Report Sentence
Linear calcifications along the peritoneal membrane are seen; consistent with advanced-stage sclerosing encapsulating peritonitis.
Bowel wall thickening and increased enhancement in small bowel loops contained within the fibrotic membrane. Bowel lumen may be dilated with air-fluid levels (obstruction signs). Mesenteric vessels appear clustered near the conglomerate bowel mass.
Report Sentence
Bowel wall thickening and luminal dilatation are seen in conglomerate small bowel loops; mechanical obstruction signs are present.
The fibrotic membrane shows hypointense signal on T2-weighted images — reflecting mature collagen tissue. Contained bowel loops may be filled with T2 hyperintense fluid. Membrane-bowel wall interface is better visualized on MRI than CT.
Report Sentence
The fibrotic membrane encasing small bowel loops shows hypointense signal on T2-weighted sequence; consistent with sclerosing peritonitis.
Clustering of small bowel loops into a central conglomerate mass on US — encased by an echogenic fibrotic membrane. Peristaltic movement is reduced or absent. Ascites may accompany. US may not directly show the fibrotic membrane but abnormal clustering of bowel loops provides a clue.
Report Sentence
Central clustering of small bowel loops and reduced peristaltic movement are seen; sclerosing encapsulating peritonitis should be considered.
Post-contrast fibrotic membrane shows thin, smooth enhancement — reflecting neo-angiogenesis-derived vascular structures. Membrane enhancement indicates active inflammatory process. In inactive/chronic stage, enhancement decreases or disappears and calcification becomes prominent.
Report Sentence
The fibrotic membrane shows thin post-contrast enhancement; consistent with active inflammatory process.
Criteria
Most common form (50-80%). Usually after >4 years dialysis. Peritoneal membrane damage from continuous PD fluid exposure. Discontinuation of dialysis is part of treatment.
Distinct Features
Peritoneal calcification more frequent; bilateral involvement; ascites frequently accompanies.
Criteria
No known cause. More common in young women (tropical countries). May have more localized involvement.
Distinct Features
Peritoneal calcification rare; more focal membrane; no dialysis history.
Criteria
Practolol (beta-blocker) classic cause; other drugs rarely associated. May regress with drug discontinuation.
Distinct Features
Relation with drug history; regression of membrane thickening possible after drug discontinuation.
Distinguishing Feature
In carcinomatosis peritoneal implants are nodular and irregular, omental cake is thick; in SEP fibrotic membrane is smooth-contoured and thin, cocoon pattern is not seen in carcinomatosis.
Distinguishing Feature
TB peritonitis shows smooth or nodular peritoneal thickening and rim-enhancing necrotic lymph nodes; SEP has specific cocoon sign and peritoneal dialysis history as distinguishing features.
Distinguishing Feature
Sclerosing mesenteritis shows misty mesentery and fat ring sign in mesenteric fat; SEP shows fibrotic membrane encasing bowel loops (cocoon sign) — two different patterns.
Distinguishing Feature
Mesothelioma shows thick, irregular peritoneal thickening and large ascites; SEP shows thin, smooth membrane and cocoon pattern.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
3-monthSEP requires urgent evaluation due to risk of recurrent intestinal obstruction. Discontinuation of peritoneal dialysis is the first step in PD patients. Conservative treatment with tamoxifen (antifibrotic effect) and corticosteroids may be tried. Surgical treatment with membrane excision (capsulectomy/peeling) resolves obstruction but carries serious complication risk (bowel perforation, fistula). Early diagnosis and timely discontinuation of dialysis improves prognosis. In advanced stages, mortality may reach 25-55%.
Sclerosing encapsulating peritonitis can cause recurrent bowel obstruction. Early diagnosis is important in peritoneal dialysis patients — change of dialysis modality may be needed. Surgical treatment involves careful excision of the membrane. Tamoxifen and steroids may be used as adjunctive therapy.