[A case of malignant lymphoma mimicking a seminal vesicle tumor].

A 76-year-old man was admitted to our hospital with severe diarrhea and syncope. Abdominal computed tomography (CT) showed a mass 7 cm in diameter mimicking a seminal vesicle tumor and magnetic resonance imaging showed a heterogeneously enhanced mass with an unclear borderline to the rectum. The differential diagnosis of the lesion included a tumor arising from a seminal vesicle, a local recurrence of rectal cancer, a rectal GIST, and a mesenchymal tumor. Transrectal needle biopsy revealed non-Hodgkin's malignant lymphoma (diffuse large B cell lymphoma). Chest and abdominal CT showed no specific findings except the lesion for the seminal vesicle lesion, but positron emission tomography showed accumulations in the gastrointestinal tract, pleura, and lymph nodes. The patient was thus determined to have stage IV malignant lymphoma and was given two courses of combination chemotherapy including RCHOP. The tumor responded to one course, but the patient died of neutropenic sepsis during the second course.