A Chylous Mesenteric Cyst Masquerading as a Pancreatic Mass

Abstract

A 51 year-old male was referred for further evaluation of an incidental finding of a large cystic mass inferior to the uncinate process of the pancreas and anterior to the 3rd portion of the duodenum. The cystic mass was initially noted on a CT pyelogram ordered to evaluate microscopic hematuria. His past medical history was remarkable only for morbid obesity; he had no history of abdominal surgery or alcohol abuse. He reported feeling well and specifically denied fevers, chills, night sweats, weight loss, nausea, vomiting, abdominal pain, and diarrhea. A comprehensive metabolic panel and complete blood count were unremarkable. Further imaging with MRCP/MRI of the pancreas showed a T2 hyperintense, microlobulated, multiseptated, and multi-cystic mass measuring 6.0 x 5.1 x 3.6 cm overall with the largest cystic component measuring about 3 cm in size. The mass was centered at the third portion of the duodenum but also in close proximity to the tip of the uncinate process with lack of a fat plane between the uncinate process and the mass. It appeared to partially surround and cause mild narrowing of the third portion of the duodenum. There was no demonstrated communication between the mass and the pancreatic duct. The patient subsequently underwent endoscopic ultrasound (EUS) with fine-needle aspiration, during which 18 mL of milky-white fluid was aspirated from the largest cyst. Analysis revealed fluid CEA 27.3 ng/mL, amylase 47 U/L, and triglycerides 6162 mg/dL. Cytology showed scant lymphocytes and macrophages in a background of acellular debris with no malignant cells identified. This case exemplifies the rare but fascinating diagnosis of a chylous mesenteric cyst. A recent review found only 19 cases reported in the literature since 1980. This review noted an average age of 46, a slight male predominance (1.4:1), and many cases were discovered incidentally in asymptomatic patients. Surgical resection has been the mainstay of treatment, but there is no clear evidence of malignant potential and overall prognosis appears to be good. This case also demonstrates the utility of EUS as a minimally invasive diagnostic tool in the initial evaluation of intra-abdominal cystic lesions. Our patient remained asymptomatic following his diagnosis and we plan periodic surveillance with MRI given the limited information regarding the natural history of these lesions.