Congenital peritoneal encapsulation

Case contributed by Dr Abdallah Mohamed


The patient presented with acute diffuse and colicky abdominal pain associated with nausea and vomiting.

Patient Data

Age: 45 years
Gender: Male

CT shows mildly dilated and clustered small bowel loops giving the appearance of a cocoon. The bowel loops are encapsulated with a thin layer of peritoneum starting from the duodenojejunal junction to the terminal ileum, forming a tight sac, a small amount of fluid density is also seen in the sac. The ascending and descending colons were posterolateral to the sac with no evidence of malrotation. There is displacement and splaying of the mesenteric vessels posterior to the sac.

Lumber spinolamentomy with metal prosthesis is noted.

The urinary bladder is opacified by excreted contrast from prior faulty contrast injection.

Annotated image

1. Axial image shows tight sac encapsulating a cluster of small bowel loops.

2. Coronal reformatted image demonstrating thin peritoneal layer encapsulating the dilated small bowel loops (green arrows)

3. MIP sagittal reformatted image, showing the peritoneal sac splaying the mesenteric vessels and the cocooned, dilated small bowel loops within the sac.

4.MIP axial image, showing the relation of the peritoneal sac to the inferior mesenteric artery (blue arrow), ascending left colic artery (red arrow), and ileocolic arterial branches (yellow arrow). The right ureter is opacified from prior contrast administration (black arrow)

Case Discussion

The differential diagnosis for the CT appearance was peritoneal encapsulation (either congenital or acquired) and internal hernias.

The patient underwent laparotomy, where an accessory retroperitoneal sac encapsulating the entire small bowel was found distending the upper and central abdomen. The sac was opened, and the small bowel loops were found to be cocooned and greatly dilated with a lot of adhesions. Mechanical obstruction confirmed with transition zone at the distal ileum. The membrane was resected and adhesiolysis achieved

Acquired peritoneal encapsulation is secondary to the formation of a thick fibrotic membrane encasing the bowel. It can be idiopathic, known as the abdominal cocoon, or secondary to an underlying disease process, known as encapsulating peritoneal sclerosis, and ambulatory peritoneal dialysis is the most underlying etiology. In both conditions, the formed membrane is a thick fibrotic membrane and tends to have adhesions with the peritoneal membrane with or without calcifications in the case of encapsulating peritoneal sclerosis.

Congenital peritoneal encapsulation (CPE), on the other hand, will show a thin mesothelial membrane encasing the bowel and identical histologically to the peritoneum. 

Internally hernias such as paraduodenal hernias were excluded as the appearance was not typical and by the relationship of the sac anterior to the stretched mesenteric vessels, descending colon, as well as the presence of the ascending left colic artery posterior to the sac (annotated images 3 and 4).

Histopathology of the excised membrane had identical mesothelial lining to peritoneum confirming the diagnosis of congenital peritoneal encapsulation.

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Case information

rID: 82086
Published: 12th Oct 2020
Last edited: 12th Oct 2020
Inclusion in quiz mode: Included