A rare sporadic pancreatic desmoid fibromatosis diagnosed by endoscopic ultrasound-guided fine-needle aspiration: Case report and literature review.

Abstract

Intra-abdominal desmoid fibromatosis (also known as desmoid tumor) is a rare benign but often locally aggressive infiltrative fibrous proliferation. Pancreatic desmoid fibromatosis is even rarer, with only 31 cases previously reported in the English-language literature. These tumors present a distinct diagnostic challenge due to their rarity and non-specific image findings and presentation, with most cases diagnosed as desmoid fibromatosis only after surgical resection. This report presents a rare case of pancreatic desmoid fibromatosis in a 72 year old man, who on a follow-up CT for a previously diagnosed angiomyolipoma of the kidney was found to have a 4.0 cm pancreatic tail mass. This was sampled pre-operatively by endoscopic ultrasound (EUS)-guided fine-needle aspiration (FNA). Examination of the cytology material showed a low-grade spindle cell lesion. Immunohistochemistry (IHC) performed on FNA cell block showed the lesional cells to be positive for beta-catenin, consistent with fibromatosis. Additional mutational analysis on cell block material revealed the characteristic CTNNB1 gene mutation (T41A), confirming the diagnosis. The mass was then surgically resected and again confirmed to be desmoid fibromatosis on histopathologic examination. On review of previously published cases of pancreatic desmoid fibromatosis, most were initially suspected to be some type of pancreatic neoplasm and were not biopsied prior to surgical resection. This case suggests a potential key role for fine-needle aspiration cytology in the preoperative diagnosis of pancreatic and other intra-abdominal desmoid tumors, particularly as evidence emerges that non-surgical treatment may be a viable first option for some cases.