Ballooning of the rectum

The anatomy of transanal minimally invasive surgery: Perineal distances and transanal angles

“…Dissection of the distal rectum in the infra peritoneal plane can be particularly challenging. In this region, the mesocolon is virtually absent distally (for the last 1 cm of the rectum), and the rectum tends to "balloon" into the concavity of the sacrum, creating a sharp angle, as first described by Hamilton (1892). Low cancers are at risk of invasion into adjacent surrounding structures, especially the pelvic floor, external anal sphincter, vagina, and prostate, because of the paucity of mesorectum at this level.…”