Abstract
INTRODUCTION: Urachus carcinoma is a rare malignancy with an aggressive potential and a poor prognosis, and evidence is limited for its diagnosis and treatment. CASE PRESENTATION: A 75-year-old man underwent fluorodeoxyglucose positron emission tomography/computed tomography for staging prostate cancer, and a mass (standardized uptake value max 9.5) was observed on the outside of the urinary bladder dome. T2-weighted magnetic resonance imaging showed the urachus and a low-intensity tumor, which suggested a malignant tumor. We suspected urachal carcinoma and performed total resection of the urachus and partial cystectomy. Pathological examination revealed mucosa-associated lymphoid tissue lymphoma with cells positive for CD20 and negative for CD3, CD5, and cyclin D1. After the surgery, no recurrence has been observed for more than 2 years. CONCLUSION: We encountered an extremely rare case of mucosa-associated lymphoid tissue lymphoma of the urachus. Surgical resection of the tumor provided an accurate diagnosis and good disease control.