Mesenteric Fat Necrosis Mimicking a Malignant Mesenteric Tumor: A Case Report

Mesenteric fat necrosis, an uncommon benign condition, can present as a mass-forming lesion and can closely mimic malignant mesenteric disease on imaging. Because its radiologic findings may overlap with those of malignant mesenteric tumors, preoperative diagnosis can be challenging, particularly when tissue sampling is difficult. This report describes a rare case of mesenteric fat necrosis, presenting as an enlarging mesenteric mass suspicious for malignancy.

An 85-year-old man who had undergone laparoscopic low anterior resection for rectal cancer 13 years prior was found on follow-up imaging to have an enlarged mass at the jejunal mesenteric root. The lesion showed contrast enhancement on CT, diffusion restriction on MRI, and increased ¹⁸F-fluorodeoxyglucose uptake on PET, strongly implying a malignant mesenteric tumor, including primary or metastatic mesenteric neoplasms. The biopsy was not feasible because of its deep mesenteric location. Therefore, laparoscopic partial resection of the jejunum containing the mass was performed for definitive diagnosis and treatment. Intraoperatively, a well-circumscribed mass was identified at the mesenteric root of the jejunum. Approximately 30 cm of jejunum was resected. Histopathological examination revealed fibrosis and fat necrosis without malignant features. He recovered uneventfully. No recurrence was observed during 1 year of follow-up.

Mesenteric fat necrosis can closely mimic malignant mesenteric tumors on multimodality imaging and should be considered in the differential diagnosis of an enlarging mesenteric mass. When biopsy is not feasible, but imaging findings raise concern about malignancy, surgical resection can be a definitive diagnostic and therapeutic option.