Local Excision of Rectal Neoplasms

An alternative to radical resection for selected rectal lesions — removes the lesion without a formal oncologic (TME) resection. Content below is from a textbook reference chapter (Sabiston Ch52 - Rectal Cancer Surgery), not primary literature. See Total Mesorectal Excision (TME) & Sphincter-Sparing Resection for the radical alternative.

Endoscopic techniques

Routine polypectomy, endoscopic mucosal resection (EMR), and endoscopic submucosal dissection (ESD). Surgical excision can also be performed via standard transanal excision, transanal MIS (TAMIS), and transanal endoscopic microsurgery (TEM).

Endoscopy for transanal removal of large rectal lesions has expanded with improved staging techniques (ERUS, MRI — see Rectal Cancer). Careful digital exam is also accurate at staging lesions within reach of the examining finger — a lesion that is soft to the touch typically is benign. This is particularly true for villous adenomas of the lower rectum, which are commonly amenable to transanal excision or endoscopic excision. Key principle regardless of technique: excision of a lesion with a free margin, to reduce local recurrence risk.

Both partial- and full-thickness (for cancers) excision can be performed. For partial-thickness excision (as done for benign lesions), submucosal injection of a solution elevates the lesion off the underlying muscularis mucosa — some injection solutions are colored, making visualization easier. Endoscopic submucosal dissection is used for superficial lesions: a hollow cap is placed over the tip of the endoscope, submucosal injection lifts the lesion away from the underlying muscularis, suction draws the lesion into the cap, and the snare tightened around the cap cuts off the area of mucosa (much like a routine polypectomy but capable of removing fairly large areas). When lesions go somewhat deeper through the muscle wall, endoscopic submucosal resection is performed, with submucosal injection facilitating dissection off the underlying colon wall after the margin has been scored.

Surgical (transanal) local excision

Traditional criteria for a local excision candidate: small lesions (<2 cm diameter), well-differentiated cancers, and lesions mobile (not fixed) within reach of the index finger. T1 lesions are ideal; patients with T2 or T3 lesions are generally not suitable, as the recurrence rate following local excision in this group has been unacceptable.

Technique: cautery scores a 1-cm margin around the lesion; traction is used, and a full-thickness incision is carried down to perirectal fat. Local excision is safe for lesions located lateral to or posterior to the rectum, given the presence of the mesorectum there. If lesions are located in the anterior rectum: in women, there is risk of iatrogenic rectovaginal fistula; in men, risk of injury to the prostate. Above 6–7 cm, there is also concern that the peritoneal cavity may be entered. These procedures are most safely performed in the lower rectum.

Transanal endoscopic microsurgery (TEM), developed in the early 1990s, made possible the excision of larger lesions, and lesions higher up, than could be safely reached with conventional transanal surgery — but required a specialized rigid-instrument set with a high learning curve. TEM has now largely been supplanted by TAMIS, which uses standard laparoscopic instruments and an access port similar to that used for single-port laparoscopy, inserted in the anal canal. This allows safe excision of lesions above the level of the very distal rectum, but — because the laparoscopic access device itself anchors in place — is not suitable for lesions in the very lower rectum (where standard transanal excision is used instead).

Open items / gaps

• No primary trial data yet comparing TEM/TAMIS oncologic outcomes to formal TME resection for T1 lesions specifically.
• No detail on how local excision interacts with the watch-and-wait strategy described on Rectal Cancer (e.g. as a way to remove residual disease after a near-complete response) — worth checking if this appears elsewhere in the chapter or needs its own source.