eP171 - A Symptomatic Mucinous Cystic Neoplasm of the Mesentery: Case Report

Purpose/Background: Mucinous Cystic Neoplasms (MCN) are rare tumors clasically arising in the pancreas. Less frequently, they have been identified in the retroperitoneum, ovary, liver and spleen. MCNs are classified histologically into those having low-grade dysplasia, high-grade dysplaia, or those associated with invasive carcinoma. These lesions are rarely seen by colorectal surgeons and due to their unusual nature, case reports provide an opportunity for advancement of knowledge. We present a 68-year-old female with an enlarging presumed ovarian mass found to have a MCN of the sigmoid mesentery.Methods/Interventions: A 68-year-old female presented to the gynecology service with an enlarging apparent 8.6 x 8.7cm ovarian cyst which had been present for over 10 years on imaging. The patient developed urinary frequency and pelvic pressure and was taken to the operating room for salpingoophorectomy. Intra-operatively, the procedure was aborted given the cyst was found to be adherent to the sigmoid and remote to the adnexa. The patient was referred to colorectal surgery. Her exam was unremarkable. Her CA-125 and CEA levels were normal. She underwent a colonoscopy which was negative for luminal disease. She was taken to the operating room and underwent a laparotomy. A large cystic mass was identified at the mesenteric aspect of the very mobile sigmoid colon and resected intact without difficulty with the adjacent sigmoid colon. The patient made an uneventful recovery.Results/Outcomes: The patient’s surgical pathology revealed a 12cm cyst lined by mucinous epithelium with intestinal and foveolar subtypes with a complex papillary architecture and extensive cytologic atypia. Immunohistochemical stains with adequate controls were performed. The lesional cells were positive for CK7, SATB2 (focally), CDX2 (focally) and negative for CK20 and PAX-8. Immunohistochemical staining for ER highlighted ovarian type stroma. There was no involvement of the adherent colon. Final diagnosis was a mucinous cystic neoplasm of the mesentery.Conclusion/

Discussion: MCNs are rare lesions, occurring almost exclusively in the pancreas or liver of women, often presenting as large uni- or multilocular cysts. They have been rarely described in the mesentery and are histologically similar to ovarian mucinous neoplasms, including pathognomonic ovarian stroma which is thought to be either recapitulation or persistence of fetal mesenchyme. Mesenteric MCN’s are a diagnostic challenge secondary to the anatomic location, often subtle histologic findings, and uncommonness. Aspiration cytology is associated with a high false positive value and is thus not recommended. Given the malignant potential of MCNs in other anatomic locations, as well as their high recurrence rate and risk of hemorrhage or infection, complete excision of mesenteric MCN’s is the recommended surgical treatment.Gross and Histopathology MCN