[Amputation neuroma with a difficult differential diagnosis from perihilar cholangiocarcinoma:a case report].

Biliary amputation neuroma is a rare benign tumor that develops due to the peribiliary dissection of nerve fibers during cholecystectomy, a common bile duct surgery, or lymph node dissection performed in gastric cancer surgery. We report a case of amputation neuroma that presented a challenging differential diagnosis from perihilar cholangiocarcinoma. A 64-year-old man, who had undergone open cholecystectomy 30 years ago, was incidentally found to have a bile duct tumor during computed tomography (CT) following surgery for renal cell carcinoma. He had no specific symptoms, and blood test results showed only a slight elevation in alkaline phosphatase levels. Contrast-enhanced CT revealed a 10-mm solid tumor with contrast effect in the common bile duct. On cholangiography, the tumor appeared as a protruding lesion with a smooth surface unilaterally. Given the atypical findings suggestive of cholangiocarcinoma, three bile duct biopsies were performed. Pathological examination did not rule out adenocarcinoma. The patient opted for surgery;however, an intraoperative rapid histological examination confirmed a benign disease, thereby avoiding extensive surgery. Consequently, a minimally invasive bile duct resection was performed. Postoperative histopathological examination revealed the tumor to be an amputation neuroma. Biliary amputation neuromas are characterized as unilateral protruding lesions with contrast effect or benign strictures. If such findings are observed in a patient with a history of surgery around the bile duct, the possibility of an amputation neuroma should be considered. However, completely ruling out malignancy preoperatively, even when suspecting amputation neuroma, can be challenging;therefore, considering surgery to achieve a definitive diagnosis is reasonable. During surgery, a rapid intraoperative histological examination is useful to avoid extensive procedures. In conclusion, diagnosing an amputation neuroma before surgery can be difficult, as it can mimic malignant tumors such as bile duct cancers. In this case, although a preoperative diagnosis of amputation neuroma was not feasible, performing a rapid intraoperative pathological examination helped avoid extensive surgery.