An Intra-Abdominal Desmoid Tumor Mimicking Malignant Recurrence after Distal Pancreatectomy for Pancreatic Neuroendocrine Tumor: A Case Report

Summary

Introduction: Intra-abdominal desmoid tumors (DTs) are rare non-metastatic fibroblastic neoplasms that commonly develop at sites of prior surgical trauma or inflammation. Here, we report a diagnostically challenging case of a DT mimicking tumor recurrence or primary malignancy following laparoscopic distal pancreatectomy. Case presentation: A 69-year-old woman with a history of laparoscopic ileocecal resection for Stage I cecal cancer underwent laparoscopic distal pancreatectomy with splenectomy for suspected pancreatic cancer. Histopathology of the resected pancreas revealed low-grade pancreatic intraepithelial neoplasia (PanIN-1/2), which was considered responsible for the main pancreatic duct obstruction, with a minute neuroendocrine tumor (NET) (Grade 1, 1.9 mm) identified in the vicinity. The patient developed a Grade B postoperative pancreatic fistula (POPF) requiring prolonged drainage. Ten months later, follow-up CT revealed an 18-mm nodule in the transverse mesocolon. 18F-fluorodeoxyglucose PET/CT (FDG-PET/CT) demonstrated intense focal FDG accumulation (maximum standardized uptake value = 4.6), whereas somatostatin receptor scintigraphy was negative. The tumor grew rapidly to 31 mm over 4 months. Differential diagnoses included recurrence of the primary NET, peritoneal dissemination from occult pancreatic adenocarcinoma (given the PanIN background), or a primary mesenteric gastrointestinal stromal tumor. Due to a high suspicion of malignancy, laparoscopic diagnostic resection was performed. Intraoperatively, the tumor was found to have infiltrated the mesentery of the transverse colon and jejunum, requiring delicate dissection to preserve the middle colic artery and first jejunal vessels. Histopathological examination revealed a spindle cell neoplasm with nuclear accumulation of β-catenin, ruling out malignant recurrence and confirming a DT. Chronic chemical irritation resulting from the preceding POPF is considered a likely trigger. Conclusions: Intra-abdominal DTs can mimic malignant recurrence on FDG-PET/CT after pancreatic surgery. This case highlights that clinicians should include DTs in the differential diagnosis of mesenteric masses arising at the site of prior postoperative complications, such as a pancreatic fistula.