A case of groove pancreatic carcinoma presenting with rapidly progressive ascending colon stenosis: a rare case report.

INTRODUCTION: Groove pancreatic carcinoma is a rare pancreatic cancer arising in the space between the pancreatic head, the duodenum, and the common bile duct. Owing to its unusual growth pattern and its resemblance to inflammatory conditions such as groove pancreatitis, preoperative diagnosis remains challenging. PRESENTATION OF THE CASE: An 80-year-old man presented with abdominal pain and progressive stenosis of the ascending colon. Endoscopy demonstrated edematous narrowing of the duodenum and ascending colon without mucosal abnormalities. Cross-sectional imaging showed inflammatory changes around the pancreatic groove, but no definite mass lesion. Two months later, bowel obstruction developed due to the rapid progression of colonic stenosis, and a right hemicolectomy was performed. Histopathology demonstrated metastatic poorly differentiated adenocarcinoma involving the colonic wall. Postoperative positron emission tomography-computed tomography (PET-CT) revealed a retroperitoneal mass; however, the primary site remained unclear. Three months later, the disease progressed rapidly with multiple hepatic metastases. A pathological autopsy revealed a tumor in the pancreatic groove region with extensive retroperitoneal invasion, leading to the final diagnosis of groove pancreatic carcinoma. DISCUSSION: Groove pancreatic carcinoma commonly presents with duodenal stenosis and is frequently difficult to distinguish from inflammatory conditions. Direct invasion of the colon is extremely rare. In this case, retroperitoneal tumor spread from the pancreatic groove resulted in rapidly progressive ascending colon stenosis, which preceded the diagnosis of the primary tumor. CONCLUSION: This case highlights the diagnostic difficulty and unusual clinical presentation of groove pancreatic carcinoma. Rapidly progressive colonic stenosis adjacent to the pancreatic groove should raise suspicion for this rare malignancy, even in the absence of typical pancreatic findings.