Anorectal Surgery

Chapter 75 Anorectal Surgery

Ronald M. Bright

Surgery of the rectum and anus is associated with a high rate of complications. The high bacterial population of the rectum increases the risk of wound infection and dehiscence. Bowel preparation with multiple enemas can mechanically remove large numbers of bacteria; however, enemas should not be done within 8 hours of anorectal surgery to avoid leakage of rectal contents during surgery. Prophylactic antibiotics are indicated with surgery of this area due to high numbers of bacteria. Synthetic absorbable sutures or monofilament non-absorbable sutures are recommended for surgery of the rectum and anus.

ANATOMY

The rectum begins at the brim of the pelvis and joins the anal canal just inside the anal opening. The anal canal is approximately 1 to 2 cm in length. The circumanal glands, anal glands, and anal sacs are associated with the anus.

The rectum receives its blood supply from the caudal mesenteric artery and its branch coursing caudally, the cranial rectal artery. This artery forms anastomoses with the middle and caudal rectal arteries, which arise, in the male, from the prostatic artery, and in the female, from the internal pudendal arteries. At the caudal demarcation of the rectum are two anal sphincters (internal and external). Fecal continence is maintained by these sphincters, and surgery in this area always threatens their integrity.

RECTAL PROLAPSE

Rectal prolapse is almost exclusively limited to young dogs and cats. The most common cause is straining to defecate, associated with severe colitis or proctitis due to endoparasites. Other causes include foreign bodies, rectal neoplasia, dystocia, and, in the cat, persistent straining related to urethral obstruction or cystic calculi.

Differentiate this condition from prolapsed intussusception. In the latter condition, a probe can be inserted and advanced cranially into a space between the cylindrical mass and the edge of the anus. This cannot be done with rectal prolapse.

Preoperative Considerations

• Treat underlying diseases (e.g., parasitism) while attempting conservative management of rectal prolapse.
• Initial management consists of cleaning and lubricating the prolapse, determining viability of the tissue, and then manually reducing the prolapsed tissue followed by a loose pursestring suture. The pursestring suture should be loose enough to allow passage of loose feces, but tight enough to keep the prolapsed tissue reduced.
• Feed a digestible low-fiber diet for 7 to 8 days while the pursestring suture is in place.
• Failure of conservative management may necessitate a surgical procedure.
• The preferred surgical procedure is colopexy (see Chapter 70), unless there is non-viable tissue within the prolapsed segment of rectum that requires resection and anastomosis.

Surgical Procedure: Resection and Anastomosis

Objectives

• Remove devitalized tissue involved in the rectal prolapse.
• Remove excessive rectal tissue that continues to prolapse in spite of manual reduction or use of the pursestring suture technique alone or in conjunction with a colopexy.

Equipment

• General surgery pack
• A 3-cc syringe case

Technique

1. Place the animal in sternal recumbency in a perineal stand.
2. Insert a well-lubricated 3-cc syringe case into the rectum.
3. Place three or four stay sutures around the circumference of the prolapsed tissue through all the layers of tissue. The needle should be against the syringe case at its deepest penetration (Fig. 75-1A).
4. Resect the prolapse around 180 degrees of the circumference, caudal to the stay sutures (Fig. 75-1B).
5. Place synthetic absorbable sutures (3-0 or 4-0) through the full thickness of the incised bowel, being sure to incorporate the serosal layers. A simple interrupted appositional pattern is preferred (Fig. 75-1C).
6. Incise the remaining 180 degrees and suture as described in Step 5. Push the rectum cranially into the pelvic canal.
image

Figure 75-1 Resection and anastomosis of rectal prolapse.

Postoperative Care and Complications

Short Term

• Give a stool softener (see Chapter 74) with food, which is offered the day after surgery. Continue giving the stool softener for 2 weeks.
• Closely monitor for leakage from the anastomotic site for at least 48 hours by observing the animal’s temperature, level of activity, eating habits, and signs of excessive pain around the anorectal region. Be careful when placing a rectal thermometer.
• Recurrence of rectal prolapse may occur. A pursestring suture may have to be used again or a colopexy performed if it has not been done previously.

Long Term

Long-term complications can include the following:

• Recurrence of rectal prolapse
• Fecal incontinence
• Anorectal stricture

ANORECTAL STRICTURE

Causes of anorectal stricture can be benign (e.g., inflammation) or malignant (e.g., adenocarcinoma):

• Inflammatory causes include perianal fistulas, prior anorectal surgery (including cryosurgery), and accidental trauma.
• Adenocarcinoma of the rectum and anus is the most common cause of stricture, resulting in a scirrhous, annular ring-type lesion.

Preoperative Considerations

Simple, annular non-neoplastic lesions that are not too cranial in location may respond to a series of bougienage or balloon dilations. During this therapy, give prednisolone for 10 to 14 days (1 mg/kg q12h).

• For other lesions (e.g., adenocarcinoma), resection/anastomosis (described below) is the treatment of choice.

Surgical Procedure: Resection/Anastomosis with Rectal Pull-Through

Objective

• Restore bowel lumen size that will accommodate the passage of feces with minimal resistance while preserving competence of the anorectal sphincter.

Equipment

• General surgery pack
• Senn retractors

Technique

1. Clip and aseptically prepare the perineal region.
2. Place a pursestring suture in the anus.
3. When the lesion is cranial to the anorectal junction, make an incision circumferentially around the anal ring.
4. Continue the perirectal dissection to normal tissue just cranial to the stricture ring. Avoid trauma to the sphincter muscles.
5. Place four stay sutures circumferentially through the normal rectal wall just ahead of the stricture.
6. Resect the diseased rectal tissue.
7. Pull the healthy tissue being held by the stay sutures caudally and appose to the anus. Avoid suturing under tension; mobilize more rectal tissue if necessary.
8. Close the tissues in two layers: subcutaneous tissue apposed to seromuscular layer of rectum (monofilament absorbable suture), and skin to rectal mucosa (monofilament non-absorbable suture).

Postoperative Care and Complications

Short Term

• Feed the animal the following day.
• Give stool softeners (see Chapter 74) for 2 weeks following surgery.
• Monitor for leakage from the anastomotic site, especially during the first 48 hours.
• Fecal incontinence may occur.

Long Term

• A pelvic abscess due to earlier leakage from the anastomosis can occur.
• Postoperative stricture can occur, especially if tension was present at the suture line.

Prognosis

The prognosis is poor if the stricture is due to an adenocarcinoma. It is poor to guarded if the stricture is related to an inflammatory process.

ANAL STRICTURE LIMITED

TO THE ANAL RING

Causes, preoperative considerations, and objectives are similar to those for anorectal strictures, as described in the previous section.

Surgical Procedure

Technique

1. Cut the stricture in four places around the anal ring at 3, 6, 9, and 12 o’clock.
2. Make the incisions perpendicular to the ring. Extend one-half of each incision outward into the skin and the other half inward through the fibrotic mucosa.
3. Suture the incisions in the opposite direction to the edge of the anal ring with monofilament non-absorbable sutures.
4. Alternatively, excise the stricture and suture rectal mucosa to skin with monofilament non-absorbable sutures.

ATRESIA ANI

This condition exists in several forms, the most common being type I (imperforate anus) and type II, in which the rectal pouch is located cranial to the membrane overlying the anus. Regardless of the type, the main problem is loss of continuity between the rectum and anus during embryonal development of the cloacal membrane.

Preoperative Considerations

• Plain film radiography of the abdomen and pelvis with the animal standing helps to differentiate between type I and type II.
• Because the patient usually is only days or weeks old, there is a relatively high anesthetic risk.

Surgical Procedure

Objective

• Relieve the obstruction of feces in the rectum by opening the anus and reconstructing the anorectal junction.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Anorectal Surgery

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