A 58-year-old patient with a T2N0 rectal cancer at 4 cm from the anal verge is evaluated for sphincter preservation. Which anatomical landmark defines the distal margin required for adequate total mesorectal excision (TME)?

• A The dentate line
• B The levator ani muscle insertion
• C The Waldeyer's fascia (rectosacral fascia)
• D The puborectalis muscle at the anorectal junction ✓

Explanation

The anorectal junction (ARJ), defined by the level of the puborectalis sling, is the landmark for complete total mesorectal excision. TME requires sharp dissection in the avascular embryological plane between the visceral and parietal pelvic fascia, extending to the levator ani floor. Waldeyer's (rectosacral) fascia is the posterior presacral condensation that must be divided to enter the retrorectal space. The dentate line marks the squamo-columnar junction of the anal canal, which is further distal. For distal rectal cancers requiring a 1 cm distal margin, awareness of the ARJ is critical for deciding between sphincter-preserving and abdominoperineal resection.

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

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Written and medically reviewed by the StethoPrep medical team.