A 62-year-old man undergoes anterior resection for a rectal cancer at 8 cm from the anal verge. Total mesorectal excision (TME) is performed. Which anatomical landmark defines the distal boundary of the mesorectum and guides the distal extent of sharp dissection during TME?

• A Waldeyer's fascia posteriorly at the level of S4
• B The peritoneal reflection anteriorly
• C The rectosacral fascia (Waldeyer's fascia) at the anorectal junction
• D The pelvic floor (levator ani) where mesorectal fat tapers away ✓

Explanation

The mesorectal fat tapers and terminates at the pelvic floor (levator ani level), which constitutes the distal anatomical boundary of TME dissection. Waldeyer's fascia (rectosacral fascia) is a condensation posteriorly between S4 and the posterior rectal wall that must be divided to enter the correct plane between the visceral and parietal pelvic fascia. The peritoneal reflection is an anterior landmark but is not the distal mesorectal limit. Proper TME requires sharp dissection within the mesorectal fascial envelope down to the levators.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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