[A case of malignant lymphoma in the pelvis suspected to be a neurogenic tumor].

A 70-year-old man visited a urological clinic with a chief complaint of pollakiuria, which was refractory to various medications. Pelvic magnetic resonance imaging (MRI) revealed a mass 6 cm in diameter immediately next to the left side of the bladder. The patient was referred to our hospital for further examination. Since he had a past history of neurofibroma of cauda equina, we suspected neurofibromatosis type 1. (18)Fluorodeoxyglucose (FDG)-positron emission tomography (PET) demonstrated a high accumulation of FDG in the pelvic mass. Under a diagnosis of neurogenic tumor, surgery was performed. As an examination of frozen section during the surgery led us to suspect a sarcoma, the tumor was excised radically. The pathological examination demonstrated diffuse large B cell lymphoma.