An anatomical study on intersphincteric space related to intersphincteric resection for ultra-low rectal cancer

Intersphincteric resection (ISR) has been proposed to offer sphincter-sparing solution for patients with ultra-low rectal cancer. However, complete and accurate concepts about the intersphincteric space (ISS) related anatomy are not demonstrated clearly. This study aimed to provide a comprehensive description about the anatomic structure of ISS related to ISR.

This was a descriptive morphological study. 28 pelvic specimens were obtained from body donors. Macroscopic and microscopic observation of ISS was performed via gross anatomy, plastinated sections and histologic staining. The anatomical parameters of the anal canal were measured. Images of laparoscopic ISS dissection procedures were real-timely captured during ISR.

The hiatal ligament, microvessels on supra fascia of LAM and rectal longitudinal muscle at the level of anorectal ring, especially at 1, 5, 7, and 11o'clock, could be the preferred entrance of ISS. The conjoint longitudinal muscle (CLM), the major component of ISS, was the continuum of the rectal longitudinal muscle and got reinforcement from the elastic fibers from LAM and EAS. Microvessels and neuro tissues were also found in ISS. The ISS was split into two spaces by the CLM in the middle and might subjectively be divided into three segments according to its different compositions. The length and width of ISS varied from different segments and directions.

We provided a systemic description of boundaries, contents and topographic structure of ISS, which may help proper determination of surgical approaches and dissection planes during ISR.