Rears of Joy: Anorectal Surgery Made Easy Christopher Adin, DVM, DACVS North Carolina State University Raleigh, NC

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1 Rears of Joy: Anorectal Surgery Made Easy Christopher Adin, DVM, DACVS North Carolina State University Raleigh, NC Objectives 1. Know surgical anatomy of the rectum, anus and perineum 2. Describe perioperative care for surgery of the rectum, anus or perineum 3. Make a diagnostic and surgical plan for a dog with a rectal mass 4. Describe two techniques for anal sacculectomy and their advantages/disadvantages 5. Review differential diagnoses for masses in the perineum and relate these to signalment of dog Surgical anatomy The cranial aspect of the rectum is marked by the entry of the cranial rectal artery (a branch of the caudal mesenteric artery) at the cranial aspect of the pelvic inlet. Although the rectum also receives blood supply from the middle and caudal rectal arteries (branches from the internal pudendal), the cranial rectal artery serves as the primary blood supply and this vessel must be carefully preserved during surgery of the rectum. The anus is continuous with the caudal aspect of the rectum and represents a transition between the rectal mucosa and the cutaneous tissue of the perineum. To achieve this transition, the anus has 3 regions: the columnar region which is composed of longitudinal folds (or columns) of mucosa, the anocutaneous line or intermediate region, and the cutaneous region. The paired anal sac ducts enter into the cutaneous region a few millimeters caudal to the anocutaneous line and can be cannulated by slightly everting this tissue to visualize the duct openings at the 7 and 5 o clock positions on the anus. An internal anal sphincter (smooth muscle) and external anal sphincter (striated muscle) are located around the terminal rectum and anus, but the external sphincter is the primary contributor to maintaining fecal continence. Innervation to the external anal sphincter is provided by the left and right caudal rectal nerves, branches of the Figure 1. Caudal rectal nerve to external anal sphincter, from pudendal nerve (Fig 1.). These nerves enter from the ventrolateral Slatter, Textbook of SA Surgery, 3 rd ed., Saunders, p.696. aspect of the external anal sphincter and should be carefully preserved in surgical approaches to the perianal region. However, it should be noted that unilateral severance of the caudal rectal nerve would not cause fecal incontinence. Lymphatic drainage of the anus and rectum is to the medial iliac lymph nodes and it is important to palpate for enlargement of these lymph nodes via rectal exam when assessing animals with suspected neoplasia. Perioperative care Fecal contents in the colon and rectum have an extremely high bacterial load (sorry, couldn t resist), comprising nearly 70% of the dry matter. Anaerobes outnumber aerobes by 1000:1, with the aerobes being composed mostly of gram negative enterics. Antibiotics directed against colonic anaerobes (e.g. neomycin) can be administered prior to surgery to decrease anaerobic bacterial flora prior to elective surgery, but this practice has not been documented to affect outcome in colorectal surgery of animals. Historically, patients were also given multiple enemas to clear the rectum and colon of feces prior to surgery. Unfortunately, this treatment has the side effect of producing liquid feces that are very difficult to contain during resection/anastomosis, leading to a possibility of massive abdominal contamination during surgery. In addition, large studies performed in human beings undergoing colorectal surgery have shown no benefit to mechanical removal of feces prior to surgery. Currently, surgeons avoid the administration of enemas or stool softeners prior to elective rectal or colonic surgery. On the other hand, broad spectrum antibiotics with good efficacy against anaerobes and gram negative enterics have been shown to significantly reduce surgical site infections and are administered perioperatively (e.g. Unasyn [amoxicillin sulbactam] at induction and every 2-3 hours during surgery). 1

2 Rectum Clinical signs of rectal disease include straining to defecate and hematochezia (fresh blood in the stool as opposed to digested blood or melena, which indicates a more proximal problem). Differentials include endoparasitism, rectal polyp, rectal adenocarcinoma, or rectal strictures. Masses can be polypoid in shape, or they can more malignant in biological behavior, with a wide based or circumferential configuration that makes resection much more challenging. Rectal adenocarcinomas that assume a circumferential apple core lesion phenotype can be very difficult to distinguish from benign strictures, but should be suspected in an older dog with no history of trauma or previous surgery to explain the development of a benign stricture. It is simple to digitally examine the rectum for these lesions, but is extremely difficult to access for other diagnostic or surgical procedures due to the location within the pelvic canal. Due to the potential for malignant neoplasia in this area, a diagnostic evaluation for dogs with a rectal mass should include: rectal examination palpation/ultrasound of sublumbar lymph nodes CBC/chem. thoracic radiographs (3 view) consider proctoscopy and biopsy: though this is not always practical due to multiple anesthetic procedures and increased cost, it would be ideal to complete staging before surgery Surgical approaches to the rectum: After staging is complete, surgical resection of rectal masses is almost always indicated as part of a treatment plan. The surgical approach to the rectum is determined by the location and size/extent of the rectal lesion to be addressed (see Figures 2-4). The following table can be used as a guideline: Approach Location of mass Size of mass Comments Caudal Abdominal Colorectal junction Any Can extend access by incising pubic symphysis Ventral transpelvic Cranial 1/3 to mid rectum Any Requires pubic symphysiotomy or ischial pubic flap ostectomy Dorsal Middle to caudal 1/3 of rectum Small to medium (<4cm) Good for extramural lesions such as leiomyomas Rectal pull-through Caudal 1/3 of rectum Small to medium (<4cm) Can prolapse rectum to allow conservative (submucosal resection) Procedural tips Figure 2. Ventral approach with pubic and ischial ostectomy, from Fossum, Small Animal Surgery, 3 rd ed., Mosby, p Figure 3. Dorsal approach to the rectum, from Fossum, Small Animal Surgery, 3 rd ed., Mosby, p Figure 4. Pull-through approach with submucosal resection, from Fossum, Small Animal Surgery, 3 rd ed., Mosby, p

3 Gentle tissue handling and avoidance of electrocautery will decrease stricture formation Use monofilament absorbable sutures and close rectal incisions in appositional patterns Take extreme caution to prevent contamination of the abdomen with fecal material o Pack off with laparotomy sponges o Use Doyen forceps on either side of the incision o Use stay sutures to elevate the cut ends of the rectum during closure Complications Rectal surgery is associated with a relatively high complication rate and most dogs suffer from significant postoperative tenesmus (straining to defecate) and hematochezia. Unfortunately, from the client s perspective, this represents a WORSENING of the original complaint and it is extremely important to convey your expectations that things will get worse before they get better. Other complications can include fecal incontinence, peritonitis, and stricture formation at the operative site. Not surprisingly, resolution of clinical signs after surgery is an even more important prognostic indicator than clean margins, because clients will euthanize dogs that continue to strain and show severe discomfort following surgery. Anal sacs Anal sacculitis Anal sac disease is a common complaint in the dog and includes a wide variety of clinical signs. Anal sacculitis is commonly manifested by scooting or dragging of the hind end on the floor. Dogs may also express signs of discomfort during defecation. When anal sacculitis progresses to abscessation, rupture of the abscess can create a fistulous tract ventrolateral to the anus. Although dietary and allergic causes have been proposed, there is no effective method of preventing anal sacculitis in affected dogs aside from frequent expression (emptying) of the glands by a groomer or veterinarian. Diagnosis of anal sacculitis is achieved during rectal examination during which the anal sac is symmetrically enlarged, thickened, and painful. Expression of the contents of the sac distinguishes this condition from other differentials such as anal sac neoplasia (next section). In dogs with recurrent anal sacculitis or in dogs with abscessation and rupture of the anal sac, anal sacculectomy should be considered. Anal sac disease is rare in cats, a fact that is attributed to the higher lipid content of the secretions which facilitates emptying of the glands during defecation. Anal sac neoplasia Apocrine gland adenocarcinoma (AGAC) is the most common neoplasm of the canine anal sac. This neoplasm has a strong sex predilection and 90% of affected dogs are spayed females. The mass is diagnosed either by observation of a mass in the area of the anal sac (lateral perineum) or by clinical signs associated with hypercalcemia, a common paraneoplastic syndrome associated with AGAC. Occasionally, animals are diagnosed with hypercalcemia incidentally on screening bloodwork- careful palpation of the anal sac region should be part of the diagnostic evaluation for this condition. Unfortunately, the biological behavior of AGAC is extremely aggressive and metastasis to local (submlumbar) lymph nodes is rapid, being present in 50% of dogs and the time of diagnosis. In animals with an identified anal sac mass, diagnostic evaluations should include: CBC/chem. (check calcium) Fine needle aspirate and cytology of mass Abdominal ultrasound to check for metastasis to sublumbar lymph nodes Thoracic radiographs (3 view) Anal sacculectomy Anal sacculectomy for dogs with anal sacculitis may be performed using either an open or closed technique. Prior to surgery, dogs with active infections should be treated with antibiotics to get the infection controlled, rather than operating on infected tissues. Typically, oral clavamox (amoxicillin clauvulanic acid) is effective against the anaerobes and gram negative enterics involved in anal sac abscesses or infections. Culture and sensitivity is not indicated, as mixed populations are expected and resistance is unlikely in a naïve infection. Preparation for surgery involves placing the dog in a perineal surgery position, with the legs off the back of the table and the tail elevated. The rectum is packed with a gauze square to prevent leakage of feces during surgery, but no purse string is placed so that the anal sac apertures are able to be identified. Closed technique (preferred) To aid in identification and dissection of the anal sac, melted paraffin can be injected into the sac prior to aseptic preparation of the perineum. A kit is available from JorVet. The anal sac is expressed, flushed with dilute betadine and injected with warmed paraffin which hardens inside the sac, leaving an easily palpable grape sized anal sac. A 3 cm perianal incision is made over the palpable sac and the anal sac is 3 Figure 5. Closed technique for anal sacculectomy, from Fossum, Small Animal Surgery, 3 rd ed., Mosby, p. 515.

4 dissected away from the fibers of the external anal sphincter, which it is encased in. The external anal sphincter and the caudal rectal nerve are identified and preserved. After isolation of the anal sac, the sac is dissected down to the duct and the duct is ligated with absorbable suture where it enters the cutaneous zone of the anus. The wound is flushed and the SQ and skin are closed routinely. Open technique In this technique, a groove director is inserted into the anal sac opening and threaded into the sac. A radial incision is made over the groove director, extending from the anal sac opening through the skin and external anal sphincter until the anal sac is opened. Once the silver/green lining of the anal sac is visible, the tissue is dissected away from the external anal sphincter and removed in entirety. After apposing the transected edge of the external anal sphincter, the incision is closed in 2 layers: SQ and skin. Although this technique appears to cause more trauma to the external anal sphincter anatomy and may increase contamination by opening the gland during dissection, there is no evidence to suggest that the risk of incontinence or infection is increased. However, the open technique is obviously contraindicated if neoplasia of the anal sac is suspected. Rectal prolapse Rectal prolapse occurs most commonly in young animals secondary to endoparasitism, although any cause of repeated abdominal straining can cause this condition (e.g. rectal masses, constipation, recent anorectal surgery, etc). Diagnostic evaluation includes complete physical examination with thorough rectal exam to investigate for rectal masses or strictures. Fecal float is performed to investigate for intestinal parasites. Abdominal imaging with ultrasound or radiographs should be considered to rule out intra-abdominal neoplasia that was not detected on physical exam. If no specific cause is identified, acute rectal prolapse is initially treated in a conservative manner, with digital reduction of the prolapsed segment and placement of an anal purse-string suture (Figure 6). The suture is performed using monofilament non-absorbable material and can be tied around a small (3mL) syringe case to prevent over-tightening of the purse-string. Highly digestible bland food is fed and the suture is maintained for 3-5 days. If prolapse recurs, surgical intervention is recommended. Surgical procedures: the type of surgery recommended for rectal prolapse depends upon the cause of the prolapse and the condition of the prolapsed segment. Resection/anastomosis When prolapsed tissue has become necrotic due to prolonged exposure and poor perfusion, or if a rectal mass is noted in the prolapsed segment, then the prolapsed tissues is resected and submitted for biopsy. Prior to resection, stay sutures are placed through the entire thickness (both layers) of the prolapsed segment to prevent the orad section from retracting into the pelvic canal. The prolapsed segment is then partially transected near the anus; the distal and proximal rectum are then apposed with interrupted appositional sutures (3-0 to 4-0 monofilament absorbable), continuing this alternating incision and suturing technique until a circumferential anastomosis is performed. Colopexy If the prolapsed segment is not necrotic and no masses have been detected, abdominal colopexy can be considered. A caudal abdominal approach is made and the colon is pulled cranially until the rectal prolapse is reduced. A longitudinal 3cm incision is made in the seromuscular layer of the colon, being careful not to penetrate the lumen. A matching 3cm incision is made in the left abdominal wall muscle and peritoneum. The two incisions are then apposed using two simple continuous patterns with monofilament absorbable or non-absorbable suture. The abdomen is closed routinely. Complications after rectal prolapse repair include recurrence (most common), continued hematochezia and tenesmus, and anastomotic leakage. If the primary cause can be identified and resolved, long term prognosis is good. Perianal adenomas Perianal adenoma is a common benign tumor seen in older intact male dogs. Perianal adenomas can occur in any region that the sebaceous perianal glands are located, including the perineal region and tail base. They may be ulcerated or non-ulcerated and can become quite extensive, despite their benign biological behavior. Perianal adenomas are often termed hepatoid due to their characteristic appearance on cytologic examination and fine needle aspiration is sufficient to diagnose these masses in most dogs. Treatment involves castration to remove androgen stimulus. If the masses are small, they may be removed at the time of castration. Larger, more extensive masses should not be aggressively resected as they will regress spontaneously after castration (though this may 4 Figure 6. Manual reduction of rectal prolapse and purse-strong suture, from Fossum, Small Animal Surgery, 3 rd ed., Mosby, p. 526.

5 require several months). Occasionally, male dogs will be diagnosed with perianal adenocarcinoma, the rare malignant form of this disease. In this case, aggressive surgical resection and ancillary therapy with radiation or chemotherapy should be considered. Postoperative care Following anorectal surgery, a highly digestible bland diet is prescribed (prescription I/d or E/N or boiled chicken and rice) for 2 weeks to decrease fecal volume and straining. Stool softeners can be considered, but should be used cautiously as diarrhea will often complicate healing. Elizabethan collars are essential in preventing self-maceration after surgery of the anus or perineum and should be maintained for days. Postoperative antibiotics are not specifically indicated unless ongoing infection is present. Epidural analgesia is extremely helpful in the immediate postoperative period, followed by oral NSAIDS and opioids for 3-5 days postop. Recommended reading/reference text Fossum, Small Animal Surgery, 3 rd Ed. Mosby, pp and