Comparison of ventral and dorsal lymph node metastases of obturator nerve in radical prostatectomy]

In this study, we assessed the significance of complete dissection of the dorsal lymph node of the obturator nerve during radical prostatectomy.Fifty-six patients undergoing open radical prostatectomy and pelvic lymph node dissection for treatment of prostate cancer were included in this study. Neoadjuvant hormonal therapy and radiation therapy were not performed in any of the patients. First, pelvic lymph node dissection was performed between the external iliac vein and obturator nerve and classified as "ventral lymph node of the obturator nerve". Then, the tissue located in the area between the obturator nerve and the surface of the obturator internus muscle was removed and classified as "dorsal lymph node of the obturator nerve". Both lymph nodes were meticulously examined by identical pathologist. Lymph node yields, lymph node positive rate, and the factors associated with lymph node metastasis were studied.Eight of the 56 patients had pelvic lymph node metastases (6 were high risk and 2 were intermediate risk according to the D'Amico's criteria). In the 8 node-positive patients, only 1 patient had positive lymph node in "ventral lymph node of the obturator nerve" exclusively. Four patients had positive lymph node exclusively in "dorsal lymph node of the obturator nerve" and 3 patients had in both "ventral and dorsal lymph nodes of the obturator nerve". The total lymph node yields from "ventral lymph node of the obturator nerve" and "dorsal lymph node of the obturator nerve" were 459 (8.2 per patient) and 117 (2.1 per patient), respectively. The total numbers of positive lymph nodes from "ventral lymph node of the obturator nerve" and "dorsal lymph node of the obturator nerve" were 6 and 12, respectively. Lymph node positive rate was significantly higher in "dorsal lymph node of the obturator nerve" (10%) than "ventral lymph node of the obturator nerve" (1.3%) (P < 0.0001). The level of prostate-specific antigen (> or = 20 ng ml), Gleason score sum at prostate biopsy (> or = 9), and lymph node yield (> or = 16) were associated with lymph node status on univariate analysis. In multivariate analysis, only lymph node yield was associated with lymph node status.Dorsal lymph nodes of the obturator nerve should be dissected completely during radical prostatectomy.