[A case of primary malignant lymphoma of the prostate with characteristic MRI findings].

Here, we report a case of malignant lymphoma (ML) of the prostate. A 77-year-old man was referred to our hospital with the chief complaint of left lumbago. Computed tomography imaging showed a large mass below the bladder, as well as left hydronephrosis resulting from infiltration of the mass. Magnetic resonance imaging (MRI) revealed enlargement and high-intensity of the whole prostate with diffusionweighted image. An enlarged, stony, hard prostate was palpable on digital rectal examination, but the prostate-specific antigen (PSA) level was 4.65 ng/ml. Since the patient developed urinary retention and macrohematuria, transurethral hemostasis and biopsy were performed. Histological findings and immunohistochemical studies revealed diffuse large B-cell non-Hodgkin's lymphoma (DLBCL). MRI is thought to play a critical role in localization diagnosis of Non-Hodgkin's lymphoma (NHL) since NHL demonstrates characteristic signs. Although the frequency of primary ML of the prostate is low, by paying careful attention to the characteristic signs on MRI and examination findings, we should consider a differential diagnosis of ML of the prostate, which is not a typical manifestation of prostatic cancer.