Pathologic basis of the sonographic appearance of the normal and malignant prostate.
The hypoechoic nature of prostatic cancer is now well recognized. In fact, not all cancers are purely hypoechoic; many are isoechoic, and some have a mixed echogenicity. Rarely, we have seen a cancer that was predominantly hyperechoic. Other signs of disturbance of the normal internal anatomy of the prostate may suggest the diagnosis of prostate cancer and are particularly valuable in assessing patients with more advanced disease. Approximately one third of early-stage cancers detected by palpation or transurethral resection are isoechoic. These tumors are anteriorly located, small, and well differentiated and infiltrate among normal glands or are composed of malignant glands similar in size to normal acini. Not all hypoechoic areas within the prostate are cancer; both normal anatomic structures and various benign conditions may appear less echogenic than the normal prostatic parenchyma. A comprehensive understanding of normal prostatic anatomy and the morphology of prostate cancer is essential to the accurate interpretation of the sonogram. Precise interpretation of prostatic sonograms requires detailed correlations of high-quality images with pathologic examinations of the whole prostate. The development of accurate criteria for the sonographic diagnosis of both malignant and benign prostatic diseases can be achieved only by such studies. As the possibilities and limitations of transrectal ultrasonography become apparent from pathologic correlation, the role of ultrasound in the diagnosis of prostate cancer will be placed on a more rational basis.