Seminal vesicles: biopsy-related hemorrhage simulating tumor invasion at endorectal MR imaging.

The diagnosis of seminal vesicle invasion by prostatic carcinoma is based on observation of foci of relatively decreased signal intensity on T2-weighted magnetic resonance (MR) images. Similar findings were observed in the absence of tumor invasion in nine patients who had recently undergone prostatic needle biopsy. Noncorresponding foci of abnormally increased signal intensity were also present on T1-weighted images in eight patients. These signal intensity abnormalities were of variable location and extent, and usually did not follow the expected pattern of spread from the primary prostatic tumor site. Radical prostatectomy in all patients showed the seminal vesicles to be normal. Signal intensity patterns observed on MR images appear to represent hemorrhagic breakdown products related to prostatic needle biopsy, which may result in direct trauma to the seminal vesicles. Another potential mechanism is retrograde transport of blood products from the site of prostatic biopsy to the seminal vesicles via the ejaculatory ducts. Awareness of this phenomenon will assist in accurate interpretation of MR images for staging of prostate cancer.