In this descriptive study, we performed microanatomical evaluations and intraoperative imaging analysis in a cadaver and patients with rectal cancer. Specimens with India ink injection were collected from a cadaver and six patients who underwent abdominoperineal resection. Intraoperative indocyanine green fluorescence imaging was performed on four patients who underwent surgery for lower rectal cancer. India ink was injected into the submucosa at the dentate line of specimens. Tissue sections were examined by immunohistochemistry for D2‐40 and CD31. Intraoperative indocyanine green was injected into the submucosa at the dentate line. Lymph flow was traced using a near‐infrared camera system.
Fascia branching from the rectal longitudinal muscle layer extended to the posterior hiatal ligament and lateral endopelvic fascia connective tissue lamina on the surface of the levator ani muscle. The fascia contained veins labeled with ink in their lumina and initial lymphatics. Intraoperative indocyanine green fluorescence imaging revealed extensive lymph flow from the muscle layer of the anal canal to the hiatal ligament and endopelvic fascia along the longitudinal muscle layer fibers.
The anorectal region contained widespread venous and lymphatic networks in proportion to its specific connective tissue framework around the longitudinal muscle layer‐extending muscle bundles, which provides extensive networks for tissue fluid and cells.