Transrectal ultrasonography for the early detection and staging of prostate cancer

Abstract

Relatively recent changes and improvements in equipment have vastly increased image resolution for transrectal ultrasonography of the prostate. The expanded use of transrectal ultrasonography has greatly furthered knowledge of prostate zonal anatomy and permitted clinical evaluation of internal prostate architecture. The technique is operator dependent, as the quality of the results is related directly to that person's knowledge and experience. The significant majority of prostate cancers originate from the peripheral zone. Palpable stage B nodules characteristically have a hypoechoic appearance. There is disagreement about the tumor characteristics that cause hypoechogenicity, but large tumors may obscure the normal prostate anatomy and appear isoechoic because of the lack of contrast with surrounding prostate tissue. The transition zone of the prostate is the origin of benign prostatic hyperplasia and almost 20 per cent of prostate cancers. These tumors probably correspond to most stage A lesions. Transrectal ultrasonography is less accurate in identifying transition zone tumors because of the mixed echogenicity of the transition zone, interference from prostatic calculi or calcified corpora amylacea, and poorer image resolution in this area. Studies evaluating the use of transrectal ultrasonography for early detection of prostate cancer generally have shown a twofold increase in the detection rate compared with digital rectal examination. However, the decreased morbidity and expense of transrectal prostate biopsy using an automatic gun device have increased the frequency of biopsy in ultrasound-examined patients compared with those historically evaluated by digital rectal examination. The increased detection rate may in part be a function of the increased use of biopsies, independent of other factors. Transrectal ultrasonography rarely detects cancer in patient with normal digital rectal examination and a normal serum prostate-specific antigen level. Transrectal ultrasonography may be capable of identifying early capsular penetration or seminal vesicle invasion in some patients with known prostate cancer. However, its superiority to digital rectal examination for this purpose has not been demonstrated unequivocally. Ultrasonography does allow directed biopsies of the seminal vesicles or other suspect areas, and this may be helpful in staging the disease. The use of transrectal ultrasonography in prostate cancer has evolved rapidly, and changes in technology antiquate reports within a few years.(ABSTRACT TRUNCATED AT 400 WORDS)