Surgical Correction of Colonic Duplication in a Cat

Introduction

Colonic duplication is a rare condition that has been reported in humans, five dogs, and one horse.^1–4 In three of the five reported cases of colonic duplication in dogs, additional serious congenital cecal, vertebral, and urinary anomalies were also noted.^1–6 In two dogs, surgical correction was performed by removing the conjoined colonic duplicate via extension of a pre-existing communication between the colon and the colonic duplicate.^2,3

Intestinal duplication can occur at any level of the intestinal tract. A recent report described a subclinical jejunal duplication in a cat.⁷ In humans, the jejunum and ileum are the most common sites of alimentary tract duplication, and colonic duplication is reported less frequently.^8–10 In up to 80% of humans with colonic duplication, there is concurrent duplication of other organs.¹¹

The embryological mechanisms leading to colonic duplication have not been clearly delineated. The embryonic origin of the alimentary tract is the yolk sac endoderm, and the hindgut segment develops into the distal colon, rectum, and urogenital tract.¹² Potential causes for colonic duplication include interepithelial vacuolar persistence during intestinal development, duplicate formation of the early colon and rectum after cloacal division, and embryonic notochord division.^5,13–15

The clinical signs associated with colonic duplication vary according to the anatomical location of the duplicated segment, its size, and the presence or absence of communications.^8,10,11 The most common clinical signs reported in humans are nonspecific and include abdominal pain, abdominal distention, constipation, and vomiting.^8,10,11 Complications of colonic duplication may lead to perforation, volvulus, intussusception, obstruction, infection, ulcerative hemorrhage, and malignant transformation.^8,11,12,16

This report describes a challenging case of colonic duplication in a cat, a species in which the condition has not, until now, been reported.

Case Report

A 2-year-old, 4-kg, castrated male Manx cat was referred for anorexia, obstipation, and straining to defecate for 2 weeks. Referral radiographs showed a soft-tissue mass dorsal to the colon in the region of the pelvis. The cat was medically managed with oral lactulose^a and enemas. On physical examination, the cat was extremely uncomfortable on abdominal palpation and rectal examination. A complete blood count (CBC) and biochemical panel were normal. Abdominal ultrasononograhy identified a homogenous, 3-cm diameter mass in the caudal abdomen that was most consistent with an abscess. An ultrasound-guided fine-needle aspirate of the mass was performed, but cytology of the thick fluid aspirated from the mass was nondiagnostic.

An exploratory laparotomy revealed an intramural cystic mass of the dorsal wall of the distal colon. Needle aspirate samples were obtained, and the lesion was drained and omentalized by placing omentum into the defect and securing it to the serosa with simple interrupted sutures. Obstipated feces were massaged through the colon and into the rectum. The cat recovered from anesthesia uneventfully. Cytology of the aspirate was again nondiagnostic, and there was no growth on aerobic and anaerobic bacterial cultures. Within 2 days after surgery, the cat’s obstipation and abdominal discomfort were markedly relieved by the procedure.

The cat was reexamined 44 months after surgery. The cat was able to defecate normally until 2 to 3 weeks prior to presentation, at which time tenesmus, anorexia, and lethargy recurred. Abdominal radiographs showed a soft-tissue density in the sublumbar region, causing ventral displacement and luminal narrowing of the colon. Abdominal ultrasonography showed a fluid-filled, cystic structure dorsal to and in contact with the colon at the level of the lumbosacral junction. Computed tomography (CT) revealed a mass arising dorsal to the colon, caudal to the internal iliac bifurcation just left of midline and extending caudally to the level of the obturator foramen, with marked ventral displacement of the colon [Figure 1]. The mass did not enhance after intravenous (IV) administration of 2.2 mL/kg iodinated contrast medium (iothalamate sodium,^b 400 mg iodine per mL). Because the mass was not contrast enhancing, it was concluded the lesion was most likely a cyst or abscess.

A second exploratory laparotomy revealed an intramural, cystic mass of the dorsal colonic area. The outer wall of the cyst was excised, and copious amounts of viscous, opaque, yellow fluid were removed. Omentalization of the cyst cavity was repeated in a fashion similar to the previous surgery. No growth occurred on aerobic and anaerobic bacterial cultures of the fluid. Histopathology of the cyst wall was consistent with full-thickness sections of colon (i.e., mucosa, submucosa, and muscular wall) and mild, chronic inflammation. No evidence of a neoplastic process or an active infectious process was found. These findings were suggestive of congenital duplication of the colon or a colonic diverticulum.

The cat was again able to defecate normally after surgery. It was reexamined 17 months after the second surgery because of a 4-week history of obstipation and intermittent tenesmus. Upon physical examination, firm stool was palpable in the colon, and a firm, 1- to 2-cm, dorsally located mass was palpated 4 cm orad to the anus. No pain was noted during rectal examination. A CBC, biochemical panel, and urinalysis were normal. An abdominal ultrasound showed a poorly defined, 1-cm mass in the area of the dorsal colonic wall mass [Figure 2]. No evidence of colonic invasion or obstruction was detected.

A third exploratory laparotomy revealed a 1-cm cystic structure in the dorsal wall of the distal descending colon. The cyst extended from approximately 1 cm orad to the pubis into the pelvic canal. The cystic mass was dissected from the colon using a combination of blunt and sharp dissection. During dissection, the wall of the cyst ruptured, and a thick, green, mucoid discharge was retrieved for cytological analysis and aerobic and anaerobic bacterial cultures. After the cyst ruptured, it became evident that the structure extended approximately 3 cm caudally within the seromuscular layer of the colonic wall. The lumen of the cyst was lined with mucosa-like tissue, and no connection to the colonic lumen was identified. The cystic structure was dissected from the colon without penetration of the colonic lumen, and it was resected in its entirety. The seromuscular defect was sutured with 4-0 polydioxanone^e in a simple continuous pattern. Prior to closing the abdomen, an assistant performed a rectal palpation and confirmed that no mass was digitally palpable and that no stricture had been created. The abdomen was lavaged thoroughly with warm isotonic saline and was closed routinely.

The cat made an uneventful postoperative recovery. Intravenous oxymorphone^d (0.05 mg/kg) and cefotetan^e (30 mg/kg q 6 hours) were started, and lactulose (1.5 mL per os [PO] q 8 hours) was also administered. The day after surgery, the antibiotics were changed to amoxicillin/clavulanic acid^f (62.5 mg PO q 12 hours). A CBC performed 24 hours after surgery was normal. No signs of tenesmus or fecal incontinence were noted. Because of occasional liquid feces, the lactulose dose was decreased to 1 mL PO q 12 hours. The cat was discharged from the hospital 3 days after surgery.

Histopathological examination showed that the wall of the resected cystic mass was similar to normal colon [Figure 3]. The wall was lined by colonic mucosa, with slightly disorganized glands, submucosa, tunica muscularis, and serosa. The tunica muscularis was incomplete and consisted of dispersed, small bundles of smooth muscle. Small numbers of lymphocytes and plasma cells were scattered in the lamina propria. In the absence of a communication with the lumen of the colon, colonic duplication was the most appropriate diagnosis.

Two weeks after surgery, the cat was defecating normally and the lactulose therapy was discontinued. Five months after surgery, the cat was still defecating normally and had soft to formed stools, with no recurrence of constipation. Physical examination at this time revealed no significant abnormalities. An abdominal ultrasound showed a fibrotic area located at the distal colon, consistent with the site of surgery. No new masses were observed. Abdominal radiographs showed a moderate amount of fecal material present in the descending colon, but no dilatation or constriction of the distal descending colon was noted. In follow-up telephone conversations 12 and 18 months after surgery, the owners reported the cat was able to defecate normally and the feces had a normal consistency.

Discussion

The cat in this report was a Manx, and the development of colonic duplication may have been associated with the caudal vertebral anomalies found in this breed. A classification system for colonic duplication in humans has been developed. Type I is partial and limited to the colon and rectum, and type II is complete and usually concurrent with other anomalies, such as vertebral malformations and urogenital duplications. Type I colonic duplication is further subdivided into type IA (spherical, noncommunicating), type IB (tubular, noncommunicating), type IC (tubular, communicating), type ID (loop with separate blood supply), and type IE (multiple duplications).¹⁷ On the basis of the human classification system, the cat in this report had a tubular, non-communicating type IB colonic duplication.

Clinical signs associated with colonic duplication in the dog have included tenesmus, constipation and fecal retention, increased frequency of defecation, and abdominal distention.^1,3,5 Clinical signs exhibited by the cat in this report were similar. Diagnostic imaging modalities that have been used in the diagnosis of colonic duplication include plain and contrast radiography, abdominal ultrasonography, CT, and magnetic resonance imaging.^1–3,8,16 In the case reported here, radiographs, ultrasonography, and CT showed the presence of a soft-tissue density dorsal to the colon; however, these modalities did not provide further information on the etiology of the mass. As in other reported cases, exploratory surgery with biopsies was ultimately required to characterize and diagnose colonic duplication.^3,8

Surgical excision of the duplicated colonic segment is the treatment of choice.¹⁷ The cat in this report experienced recurrence of clinical signs associated with reformation of the duplicate after incomplete excision and omentalization. Successful surgical resection was possible in this cat, because there were separate blood supplies to the colon and the duplicate segment, and there was no communication with the true colon.⁸ Although the cyst extended into the pelvic canal, it was completely excised by placing cranial traction on the colon during dissection, and the need for a pelvic osteotomy was eliminated.

Following excision, the resulting seromuscular defect was closed primarily. Potential complications of primary closure include stricture formation and obstruction from potential loss of serosal circumference. In this cat, a rectal examination was performed during surgery to verify adequate patency of the colon after seromuscular closure and to ensure there was no luminal obstruction. Alternative techniques for closure of the seromuscular defect include the application of a porcine small intestinal submucosal graft with an overlying omental flap, and serosal patching to reinforce primary repair of the seromuscular defect.²

Colonic duplication should be differentiated from a colonic diverticulum, which is bulging of the mucosa from a weakened muscular tunic. The lack of communication with the lumen of the colon and the presence of all layers of the colonic wall within the cystic structure were diagnostic for colonic duplication in the case reported here.

Conclusion

Colonic duplication was diagnosed in a 2-year-old Manx cat with chronic, persistent tenesmus and constipation. In this case, omentalization of the cyst was an inadequate surgical treatment, and complete excision of the duplicate colon was required to alleviate the cat’s clinical signs.