Author

Stephen J. Birchard DVM, MS, Diplomate ACVS

Friday, November 1, 2013

Idiopathic Megacolon in Cats: Let's Get This Pooping Started!

Fig. 1: Excised colon from a cat with megacolon
Idiopathic megacolon in cats is a chronic functional disorder of the large intestine that causes obstipation.1,2 The etiology is poorly understood but it is thought to be due to a neuromuscular problem in the colon that impairs motility. Histopathology of excised colons from affected cats usually does not show significant lesions.1 Fecal retention in the colon can be severe causing extreme enlargement of the large intestine and rectum and clinical deterioration of the affected cat. (Fig. 1)

Clinical Signs and Diagnosis

Clinical signs of megacolon are constipation, anorexia, chronic malaise and weight loss. Physical examination findings may include: poor body condition, dehydration, and a variably enlarged colon filled with hard feces.  The diagnosis is confirmed with abdominal radiographs. (Fig. 2-3)
Fig. 2: Lateral radiograph of a cat with megacolon

Fig. 3: Ventrodorsal radiograph of same cat as  in Fig. 2

Treatment

Initial medical therapy of megacolon is with pro-motility drugs such as Cisapride combined with stool softeners (e.g. lactulose). Repeated enemas and manual de-obstipation is usually necessary to evacuate the colon and rectum. Although medical therapy can be effective at first, surgical intervention is frequently necessary for long-term relief of clinical signs and return of normal defecation.

Subtotal colectomy is the recommended surgical procedure for megacolon. The majority of the colon is removed, from the ileum or proximal colon to the distal colon. (Fig. 4)
Fig. 4: Intraoperative appearance of megacolon in a cat. Ileum is to the left, rectum to the right.
Preservation of the ileal-colic junction results is less postoperative diarrhea in cats.3 Since the ileum is tethered to the abdominal cavity by its mesentery it has limited mobility and the surgeon must avoid suturing the anastomosis under tension. Leaving 2-4 cm of distal colon may be necessary to achieve a tension-free closure.  However, leaving too much distal colon can result in recurrence of obstipation.

Subtotal colectomy in a cat is a more challenging surgical procedure than small intestinal resection and anastomosis. The blood supply is oriented differently and the colon contains a higher concentration of bacteria making contamination and anastomotic leakage even more devastating. Surgeons with proper training and experience are best suited to perform this operation.

Preoperative Considerations

Most surgeons prefer not to give enemas to megacolon cats before colectomy even if the colon is severely impacted with feces. Retained enema fluid in the colon will increase the chance of leakage and contamination during surgery. Administer prophylactic antibiotics preoperatively, such as a third generation cephalosporin or unasyn.

Surgical Technique

Perform a ventral midline abdominal approach and do a thorough exploratory of all structures. Isolate the large intestine from the rest of the abdominal cavity with moistened abdominal sponges. Ligate the colonic blood vessels. Although not recommended by all surgeons, I prefer to preserve the cranial rectal artery and vein to ensure good blood supply to the distal aspect of the anastomosis. To do this, it is necessary to individually ligate the multiple small vessels entering the bowel from perpendicular to its long axis.

It may be necessary to manually move the hard fecal material from the rectum to the descending colon or vice verse to provide space to make the distal incision. Pick up the ileum and move it caudally to determine how much distal colon should be retained to assure a tension free anastomosis. Place clamps on the bowel to be removed and assistant’s fingers adjacent to them to prevent leakage. I also place 2 or more stay sutures on the rectum to prevent retraction into the pelvic canal after resection of the colon. Perform anastomosis as described in the previous blog, i.e., simple continuous using 2 suture lines, 4-0 PDS with the RB 1 taper needle. (Fig. 5) Wrap the anastomosis with omentum and close the abdominal incision routinely.
Fig. 5: Completed ileal-colic anastomosis after subtotal colectomy

Postoperative Care

Maintain intravenous fluids until the cat is eating and drinking on its own. Antibiotics are not continued postoperatively since there is no benefit to prolonged administration when using them as a prophylactic measure. Keep the cats on their usual diet assuming it is a good quality maintenance food. Ample fresh water should be available at all times.

After subtotal colectomy, many cats will have a variable period of soft stool or diarrhea but eventually the majority of operated cats will return to formed stool. As previously mentioned, if the ileo-colic junction is preserved diarrhea is less common as a postoperative problem.

Recurrence of obstipation is a rare but possible long-term complication. Excision of additional colon may be necessary if it is found to be enlarged and retaining feces. The majority of cats have a good prognosis after subtotal colectomy with return to normal or near normal enteric function.4

References

1. Rosin E, Walshaw R, Mehlhaff C, Matthiesen D, Orsher R, Kusba J Subtotal colectomy for treatment of chronic constipation associated with idiopathic megacolon in cats: 38 cases (1979-1985). J Am Vet Med Assoc. 1988 Oct 1;193(7):850-3.
2. Bright RM, Burrows CF, Goring R, Fox S, Tilmant L Subtotal colectomy for treatment of acquired megacolon in the dog and cat. J Am Vet Med Assoc. 1986 Jun 15;188(12):1412-6.
3. D. C. Sweet, E. M. Hardie, E. A. Stone Preservation versus excision of the ileocolic junction during colectomy for megacolon: A study of 22 cats. Journal of Small Animal Practice Volume 35, Issue 7, pages 358–363, July 1994
4. Gregory CR, Guilford WG, Berry CR, Olsen J, Pederson NC Enteric function in cats after subtotal colectomy for treatment of megacolon.Vet Surg. 1990 May-Jun;19(3):216-20.