This may be the operation of choice in selected individuals with malignant lesions in the rectosigmoid or low sigmoid area in order to reestablish the continuity of the bowel. The operation is based on the premises (1) that the viability of the lower rectum can be sustained from the middle or inferior hemorrhoidal vessels and (2) that carcinoma in this region as a rule metastasizes cephalad, only rarely metastasizing 3–4 cm below the primary growth. While most patients prefer restored continuity over a permanent colostomy, low colorectal anastomoses carry a significant risk of postoperative bowel dysfunction (post-low-anterior syndrome) that is highest in patients with anastomoses within 3 cm of the anal verge and those with preoperative dysfunction such as incontinence. The absolute indications for abdominoperineal resection are discussed in Chapter 64, but there are many times when the growth can be mobilized much more than anticipated, especially when the bowel is released down to the levator muscles. The exposure is another factor that may influence the surgeon for or against a low anastomosis. A low anastomosis is much easier and safer in females than in males, especially if the pelvic organs of the former have been removed previously. A loop ileostomy (see Chapter 55) is sometimes done at the time to divert the fecal stream temporarily from the end-to-end anastomosis.
While the principles of resection remain constant, several approaches to restoration of bowel continuity have been described. A stapled end-to-end anastomosis is by far the most popular technique, and hand-sewn anastomoses are performed less frequently. The success of a properly performed anastomosis depends on an adequate blood supply to the residual bowel segments, which can be brought together easily without tension.
Lesion location (anterior versus posterior, distance from anal verge) is confirmed and polyps or secondary lesions ruled out by a complete colonoscopy. Small, flat lesions often can evade palpation during surgery, and endoscopic tattoo placement may be prudent for tumor localization in these cases. Patient are referred for appropriate computed tomography scans and endorectal ultrasound or pelvic magnetic resonance imaging for locoregional staging of the tumor. If indicated, patients are referred for neoadjuvant chemoradiation therapy. The usual mechanical and oral antibiotic bowel preparation is given the day prior to surgery, while intravenous antibiotics are administered just prior to the start of the procedure. A povidone-iodine enema is optional. A gastric decompression tube is typically inserted before the incision, and an indwelling bladder catheter is inserted.
General endotracheal anesthesia is indicated for this operation.
The patient is placed in a relaxed lithotomy position using Allen stirrups. A modest Trendelenburg position is then assumed to enhance exposure of the deep pelvis and permit introduction of the stapler via the anus.