[What may be expected from endorectal echography and magnetic resonance imaging in the evaluation of local extension of cancer of the prostate?].

Thirty patients presenting with a clinical stage A or B cancer underwent TRUS and MRI with a body coil prior to radical prostatectomy. Imaging and pathology were correlated to assess the limits of TRUS and MRI in pre-operative staging of prostatic carcinoma. Results showed that TRUS and MRI had a sensitivity of 42 and 66% and a specificity of 89 and 94% respectively, for the diagnosis of macroscopic capsular effraction. Seminal vesicle invasion was diagnosed by TRUS with a sensitivity of 16% and a specificity of 81%. With MRI, the sensitivity and the specificity were 85 and 94% if only gross infiltration was considered. Sensitivity dropped to 45% if microscopic invasion was included. We conclude that: 1) postero-lateral venous plexus are more easily delineated by MRI, permitting a more accurate diagnosis of capsular penetration. 2) Seminal vesicle invasion cannot be diagnosed by TRUS as the echo-structure of the cancer and the caudal junction of the seminal vesicles and vas deferent are similar. 3) A normal caudal junction on TRUS or a normal bilateral hypersignal of the seminal vesicles on MRI are associated with seminal vesicle invasion in less than 5% of cases. 4) A normal caudal junction on TRUS eliminates false positive cases of MRI related to non tumoral hyposignals of the seminal vesicles.