Complicated intra-abdominal fibromatosis masked by a perforated jejunal diverticulitis

Desmoid-type fibromatosis is a rare group of locally aggressive fibroblastic proliferations of connective tissue. The incidence of synchronous intra-abdominal fibromatosis and jejunal diverticulitis is unreported. Both conditions typically present with non-specific symptoms and can be challenging to diagnose. We present the case of a female patient in her 70s with a diagnosis of intra-abdominal fibromatosis and perforated jejunal diverticulitis. This patient was found to have a large distal jejunal mesenteric mass and an adjoining perforated diverticulum intraoperatively. The diagnostic laparoscopy was converted to a limited laparotomy to allow for en bloc resection of the mesenteric mass. Subsequent immunohistochemistry confirmed fibromatosis with positive β-catenin and further molecular analysis confirmed a CTNNB1 gene mutation. The patient remained clinically well at follow-up, with no evidence of recurrence.