転移性腫瘍を模倣した卵管子宮内膜症：症例報告と文献レビュー

This case discusses a 76-year-old female patient with a large mass at the major papilla of Vater, initially suspected to be an ampullary adenoma. The lesion, identified during an upper endoscopy for anemia and fatigue, showed chronic inflammation but no malignancy. The patient's medical history included breast cancer and a partial distal pancreatectomy for an intraductal papillary mucinous neoplasm. Further imaging and biopsies did not confirm malignancy or adenoma but suggested actinomycosis. Actinomycosis, caused by Actinomyces species, presents challenges due to its rarity, slow progression, and difficulty in diagnosis. It can mimic malignancies, especially occurs following surgery, and requires long-term antibiotic therapy. We present the first documented case of actinomycosis involving the ampulla of Vater and emphasize the importance of considering actinomycosis in the differential diagnosis of ampullary masses, particularly in postsurgical patients with granulomatous tissue.