March's Paper of the Month looks at a study aimed to analyse the functional lymphovascular network and tissue drainage in the anorectal region.
Widespread anorectal lymphovascular networks and tissue drainage: analyses from submucosal India ink injection and indocyanine green fluorescence imaging.
Kentaro Sato, Hiroshi Shimoda, Takuya Miura, Yoshiyuki Sakamoto, Hajime Morohashi, Seiji Watanabe, Hirokazu Narita, Yuto Mitsuhashi, Kotaro Umemura, Kenichi Hakamada
Colorectal Dis. 2021; 00:1–12.
What is known about the subject?
Optimal surgical treatment of low rectal cancer is a controversial issue. For T3 tumors in the lower third of the rectum, for example, many options are currently in practice: sphincter saving procedures or abdominoiperineal resection; with or without neoadjuvant therapy; with or without lateral pelvic lymph nodes dissection; what operative technique – ultralow anterior resection, TaTME, intersphincteric resection, extralevator abdominoperineal resection etc. Local tumor growth as well as rectal wall and lymphatic involvement are among the factors that contribute most to development of postoperative local recurrence. Local excision is an option for early staged cancer. Despite the vast interest in the subject by surgeons, pathologists, oncologists and radiologists, there are no recent precise anatomical and functional studies of the anorectal lymphatic drainage. Most studies simply describe identify draining lymph nodes of the lower rectum and anal canal, or pathological features of local tumor regrowth. Also, the lymphatic drainage from the levator ani muscle and its surrounding fascia has not been investigated yet.
What the study adds?
This study provides a detailed description of microanatomical and functional lymphovascular networks in the anorectal region, which has not been previously reported. The authors evaluated the microanatomical organization of lymphovascular communications from data obtained by immunohistochemistry with antibodies against podoplanin and CD31 after submucosal India ink injection into fresh cadavers and resected specimens, and from intra-operative indocyanine green fluorescence imaging. Microanatomical examinations demonstrated an extensive musculostromal framework connecting the anorectal muscle coat to fascia spreading dorsolaterally on levator ani and to external anal sphincter. The framework generally developed blood and lymphatic vascular networks indicating that the anorectal canal cooperates with pelvic parietal organs to build a functional complex structure with proper vasculature. The article presented the histological composition of the perivascular space, which shows reticular tissue such as that in lymphoid organs. The authors concluded that the perivascular stromal tissue and lymphatic invasion were the actual tumour-spreading pathway in patients with low rectal cancer. The results of the experiments show that there is a peculiar circulation route between anal submucosal veins and veins in the levator ani fascia and the external anal sphincter epimysium/perimysium. Authors’ illustrations of the anorectal functional lymphovascular network are precise and informative.
Implications for colorectal practice
The focus of the study is to direct appropriate therapeutic strategies for early and advanced low rectal cancer, based on information of the fascial organization of lymphovascular drainage of anorectal region. The data in the article support and provide a biological explanation of better results of extralevator abdominoperineal resection – the suggested widespread functional lymphovascular flow pathways and tissue drainage around the anorectal region along the fascia on the surfaces of the levator ani and endopelvic fascia. On the other hand, local excision in early cancer is associated with high recurrence. This can be explained by the microanatomical data which indicates that tumor cells invading the submucosal space in anorectal regions can spread widely through the endopelvic fascia. Adjuvant and neoadjuvant radiotherapy and chemoradiotherapy could be considered to improve the recurrence rates.
As this was an early-stage investigation of an uncharted area, further studies are welcomed. Nevertheless, the paper may provide information to discuss therapeutic strategies for low rectal cancer.
