Visualization of Anorectal Lymphatic Flow Using Indocyanine Green Fluorescence Imaging: An Observational Study

Currently, only a small part of functional lymphatic flow around the anorectal region has been anatomically analyzed. Despite the fact that local recurrence is often experienced in the pelvic floor, the functional lymphatic network in this region has rarely been studied due to difficulties in observation. This prospective observational study aimed to observe anorectal lymphatic flow around the pelvic floor using intraoperative indocyanine green fluorescence imaging during laparoscopic or robot-assisted rectal surgery.

Fourteen patients who underwent laparoscopic (n=7) or robot-assisted (n=7) surgery without any preoperative therapy between April and December 2022 were enrolled. Indocyanine green solution (0.25 mg) was injected into the submucosa at the dentate line of the anterior, posterior, and bilateral walls prior to surgery. During and after total mesorectal excision, lymphatic flow was observed using a near-infrared camera system.

Lymphatic flow visualized by indocyanine green was detected not only in the already-known route from the low rectum to the lateral pelvic lymph nodes via the lateral ligament, but also in the novel route from the low rectum to the surface of the levator ani muscle and hiatal ligament. Fluorescence was widely spread in the pelvic floor between the longitudinal muscle of the low rectum and the surface of the levator ani muscle.

Even though the results are preliminary since histological analyses were not performed, a novel widespread lymphatic network on the surface of the levator ani muscle originating from the longitudinal muscle fibers of the low rectum was revealed.