Ultrasound anatomy of the prostate: the normal gland and anatomical variations.

Knowledge of the normal prostatic anatomy is paramount to understanding the pathological conditions of the gland observed on ultrasound imaging. Through transverse and sagittal histological sections of normal prostates, model ultrasound images of the prostate and periprostatic tissues were constructed. Various shades of gray were assigned to these structures depending upon the histological composition. We found that ultrasonic characteristics of the normal prostate and its surrounding tissues could be predicted accurately by knowledge of the histology of these structures. Histological sections of 100 prostates from patients who underwent transrectal ultrasound and subsequent radical prostatectomy for prostate cancer were examined. The congenital anatomical variations observed in this group are described histologically and sonographically. Caudal formation of the ejaculatory ducts within the central zone occurred in 18% of the cases, abnormal posterior penetration of the ejaculatory ducts at the rectal surface in 12% and abnormally large muscle bundles with the ejaculatory duct sheath in 6%. Concomitant ejaculatory duct and seminal vesicle dilatation was observed in 5% of the patients, whereas dilated ejaculatory ducts alone, dilated seminal vesicles alone and cystic utricles each were seen in 2%.