The anatomy of transanal minimally invasive surgery: Perineal distances and transanal angles.

The recent interest in transanal, minimally invasive surgery has highlighted the importance of an in depth understanding of this complex region. We applied data from an anatomical study of the perineum to the concept of transanal minimally invasive surgery with the aim to describe more accurately anatomy relevant to this surgical technique. A consecutive series of adult patients undergoing colonoscopy were approached for consent to measure dimensions and angles of the perineum before the examination. Distances from the posterior margin of the anus to the coccyx, and the anterior margin of the anus to the posterior edge of the scrotum or introitus were measured. Then, using a pediatric proctoscope and a protractor, the anoperineal angle and the recto perineal angles were measured. The anorectal angle was derived from these measurements. Data is described using means and standard deviations. Measurements were obtained from 106 patients undergoing elective colonoscopy for average risk screening with no history of defecatory disorder. Posterior perineal length was similar in both sexes (4.5 cm ± 0.9 in women and 4.6 cm ±0.7 in men) but the anterior perineum was significantly shorter in women (2.5 ± 0.8). The mean anoperineal angle was 93° (±9), and mean rectoperineal angle was 73° (±9). These angles varied significantly between the sexes. The mean anorectal angle (derived) was 160° (±9), and did not differ significantly between the sexes. There was no correlation between the posterior perineal length and ano perineal, recto perineal, or anorectal angles. Limitations: small sample size. Anoperineal and recto perineal differ significantly between the sexes. Surgeons using transanal minimally invasive surgical techniques should expect to alter the alignment of their dissection accordingly. This study shows the magnitude of the differences that can exist. Clin. Anat. 32:68-72, 2019. © 2018 Wiley Periodicals, Inc.