Carcinoma of the prostate: value of transrectal sonography in detecting extension into the neurovascular bundle

Detection of involvement of the neurovascular bundles (NVB) by tumor is important in deciding whether sexual function can be preserved in patients undergoing radical prostatectomy for prostatic cancer. The nerve branches innervating the corpora cavernosa have a rather constant association with the capsular arteries and veins of the prostate, forming the periprostatic neurovascular bundle, which can be identified intraoperatively and spared during radical surgery, thus preserving potency. We examined 160 patients with biopsy-proved clinical stage A or B adenocarcinoma with transrectal sonography before radical prostatectomy to determine how useful the procedure is for predicting tumor extension into the NVB. Correlation with pathologic serial sections was obtained in each patient. The sonograms depicted the NVB on both sides in 77 patients (50%), on the right side only in 13 (8%), and on the left side only in 36 patients (23%). In 29 patients (19%) neither neurovascular bundle could be identified on the sonograms. Ninety-one tumors in this series showed evidence of extraglandular spread pathologically, which was posterolateral or into the NVB in 70 tumors involving 82 hemispheres. Using transrectal sonography, we correctly identified invasion of the NVB in 54 cases and missed it in 28 cases. NVB invasion was predicted incorrectly with transrectal sonography in 51 cases; absence of involvement of the NVB was correctly predicted in 177 hemispheres. The sensitivity of sonography for predicting invasion of the NVB was 66%, with a specificity of 78% and an accuracy of 75%. Positive predictive values and negative predictive values were 51% and 86%, respectively. We conclude that transrectal sonography currently suffers from lack of sufficient spatial resolution to detect accurately invasion of the NVB.