Widespread anorectal lymphovascular networks and tissue drainage: analyses from submucosal India ink injection and indocyanine green fluorescence imaging

AIM: Abdominoperineal resection is associated with poor prognosis in patients with advanced lower rectal cancer. This study aimed to analyse the functional lymphovascular network and tissue drainage in the anorectal region. METHODS: In this descriptive study, we performed microanatomical evaluations and intra‐operative imaging analysis in a cadaver and patients with rectal cancer. Specimens with India ink injection were collected from a cadaver and from six patients who underwent abdominoperineal resection. Intra‐operative 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. Intra‐operative indocyanine green was injected into the submucosa at the dentate line. Lymph flow was traced using a near‐infrared camera system. RESULTS: 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 labelled with ink in their lumina and initial lymphatics. Intra‐operative 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 fibres. CONCLUSIONS: 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.