Congenital colonic malformation (“short colon”) in a 4-month-old standardbred foal

Abstract

During exploratory laparotomy of a foal with colic, a congenital abnormally developed large colon was identified incidentally. Long-term follow-up showed that the colt was more prone to gas-colic with diet and exercise changes than were other horses, due possibly to the short colon.

A 4-month-old standardbred colt was examined by a private veterinary practitioner (KC) for mild colic, which responded to treatment with flunixin meglumine. No abnormalities were observed for the following 4 d. Suddenly, the colt started to show signs of severe colic. On physical examination, a heart rate of 80 beats per minute (bpm), hyperemic mucus membranes, and decreased gastrointestinal sounds were noted. No gastric reflux was obtained via nasogastric intubation. The colt was then treated with flunixin meglumine, xylazine, and butorphanol, IV. He continued to display severe colic signs and was referred within 1 h after onset of the signs to the Ontario Veterinary College, Veterinary Teaching Hospital, for further evaluation.

Case description

On presentation, the colt was in moderate, continuous pain and his abdomen was mildly distended. His heart rate was 88 bpm, respiratory rate 35 breaths per minute, and rectal temperature 37.5°C. Mucus membranes were hyperemic with a capillary refill time of 3 to 4 s. The distal extremities were cold to the touch. Based on the clinical examination, dehydration was estimated to be moderate. A jugular catheter was placed, IV, on the left side, and fluid therapy with lactated Ringer’s solution was initiated (50 mL/kg BW/h). On auscultation of the abdomen, decreased gastrointestinal sounds were noted in all 4 quadrants. Nasogastric intubation did not yield any gastric reflux. Initial packed cell volume, total plasma protein value, serum electrolyte levels, and venous blood gas levels were within normal reference ranges. On transabdominal ultrasonography, multiple loops of fluid-filled hypermotile small intestine were observed and a moderate amount of free peritoneal fluid was also identified. Abdominocentesis did not yield any peritoneal fluid. Within 1 h of admission, the colt received xylazine (Rompun; Bayer Agriculture Division Animal Health, Toronto, Ontario), 0.3–0.5 mg/kg body weight (BW), IV, q20min for 1 h and 1 dose of butorphanol (Torbugesic; Ayerst, Montreal, Quebec), 0.05 mg/kg BW, IV. However, the colt remained in pain despite the administration of analgesics and his heart rate increased from 88 to 100 bpm. Based on these findings, an exploratory laparotomy was recommended to the owner in order to further evaluate the origin of abdominal pain. Differential diagnoses at that time included small intestinal obstruction or small intestinal inflammation (proximal enteritis).

Sodium penicillin (Penicillin G Sodium; Novopharm, Toronto, Ontario), 20000 IU/kg BW, IV, q6h, and gentamicin (Gentamicin sulfate; The Veterinary Pharmacy, Guelph, Ontario), 6.6 mg/kg BW, IV, q24h, were administered pre-operatively. The foal was subsequently placed in dorsal recumbency under general inhalation anesthesia. A ventral midline celiotomy was performed and the peritoneal cavity explored. The small intestine was moderately hyperemic with several areas of petechiation (Figure 1), consistent with enteritis of the small intestine. The large intestine was exteriorized and found to be anatomically abnormal. The right ventral colon originated from the cecum and continued as the left ventral colon, which, in turn, continued as the transverse colon (Figure 1). The ventral colon was identified by its having a uniform diameter and 4 taeniae all the way through. Neither a pelvic flexure nor a dorsal colon was identified. The body of the cecum was attached along the right ventral colon and a short apex of the cecum was identifiable (Figure 2). Normally, the base of the cecum is attached, dorsally, by connective tissue and peritoneum to the pancreas and right kidney, and, retro-peritoneally, to the abdominal wall (1). In this case, there was an approximately 15-cm long mesentery-like attachment to the pancreas, right kidney, and abdominal wall. In normal horses, only about half of the cecal body and two-thirds of the ventral colon can be exteriorized through a midline laparotomy (2); in this case, most of these structures could be exteriorized, thus allowing complete evaluation of the ileocecal junction and the cecocolic junction. Mild edema was present in the wall of the cecum, but it was pink in color and good motility was present. No abnormalities were detected in the wall of the anatomically altered colon. Based on our surgical findings, a diagnosis of small intestinal enteritis with mild cecal inflammation was made. The anatomically abnormal colon was considered to be an incidental finding, whereas the macroscopic changes in the small intestine, indicative of proximal enteritis, were considered sufficient to explain the severe signs of colic. Whether the shortened colon would result in colic in the future life of the colt was unpredictable, but the owner was willing to give the colt a chance, so we proceeded to complete the surgery. The peritoneal cavity was thoroughly lavaged with warm lactated Ringer’s solution, and 1% sodium carboxymethylcellulose was instilled to decrease the risk of adhesion formation. The mid-line abdominal incision was closed in routine fashion. Assisted recovery from anesthesia was uneventful. Postoperatively, the foal was administered flunixin meglumine (Flunixin meglumine; The Veterinary Pharmacy), 1.1 mg/kg BW, IV, q12h; sodium penicillin (Penicillin G Sodium; Novopharm), 20 000 IU/kg BW, IV, q6h; gentamicin (Gentamicin sulfate; The Veterinary Pharmacy), 6.6 mg/kg BW, IV, q24h; and lactated Ringer’s solution (6 mL/kg BW/h). Ranitidine (Gen-ranitidine; Genpharm, Etobicoke, Ontario), 7 mg/kg BW, PO, q8h to prevent stomach ulcers and metronidazole (Metronidazole; The Veterinary Pharmacy), 15 mg/kg BW, PO, q6h, to treat the enteritis, caused possibly by Clostridium difficile, were also administered. Lidocaine (Xylocaine; AstraZeneca Canada, Mississauga, Ontario), in the form of a slow bolus (1.3 mg/kg BW, IV) was given immediately after surgery, followed by a constant rate infusion 0.05 mg/kg BW/min, IV, for 24 h, to prevent postoperative ileus.

Figure 1.

Short colon as it was encountered during exploratory laparotomy. Notice that more than usual of the cecum and colon can be exteriorized from the abdomen.

c = cecum, co = colon, i = ileum, ↓ = indicates direction to transverse colon

Figure 2.

Most of the cecum is fused with the colon.

c = cecum, co = colon, ↓ = indicates the cecocolic ligament

Day 1 after surgery, the colt was quiet and did not show any signs of abnormal pain, but his heart rate was still elevated (around 60 bpm) and he was febrile (rectal temperature 39.2°C). Since no signs of colic were encountered, handfuls of food were gradually introduced. On day 2 after surgery, all vital parameters were within normal limits, except that the heart rate remained elevated (around 60 bpm), and the colt was bright and alert. The amount of hay was gradually increased. Lactated Ringer’s solution was discontinued and the doses of flunixin meglumine were decreased to 0.5 mg/kg BW, IV, q12h. On day 3 after surgery, the colt continued to do well, and his heart rate was within the normal range. The sodium penicillin, gentamicin, and flunixin were discontinued. A normal amount of hay was fed and well tolerated. The metronidazole was discontinued on day 4 after surgery. On day 5 after surgery, the colt was discharged with instructions to the owner to administer ranitidine (Gen-ranitidine; Genpharm), 7 mg/kg BW, PO, q8h for 3 more days.

During the first 6 mo after discharge, the private veterinary practitioner (KC) and the farm manager reported that the colt had reduced weight gain compared with other foals his age. He also had suffered from repeated episodes of mild colic, which responded to either hand walking or flunixin meglumine and were considered to be gas colics. He appeared to be very sensitive to any change in diet or decrease in exercise. He was given stanozolol (Stanozolol; Summit Pharmacy, Aurora, Ontario), 0.55 mg/kg BW, IM, weekly for 8 wk. This helped to improve his appetite and he started to gain weight more rapidly. Reportedly for the next year, the colt continued to have occasional episodes of mild colic every time there was a change in diet or decrease in exercise, but otherwise he remains healthy and is currently in training.

Congenital short colon has been described in humans (3) and cats and dogs (4), but not in horses. During fetal development, the distal part of the small intestine and the large intestine are formed through a complex mechanism of rotation and elongation of the primitive midgut (5). In humans, abnormalities in elongation have resulted in either malrotation of the colon with normal differentiation (6) or in deficient length of the small intestine with lack of differentiation into duodenum, jejunum, and ileum (7). Deficient length of the colon in humans is associated, often, with anorectal malformation and, sometimes, with a colourinary fistula. In these cases, surgical correction usually results in a satisfactory outcome (3). In the 2 cats and 1 dog with short colon (4), the cats had the cecum located on the left side, consistent with incomplete rotation (7). Congenital malformation of the mesocolon has been described in the horse (8,9): in 1 case, it was dysplastic (8), in the other, it was so distorted that it led to stellate formation of the colon (9). Another possibility for the development of short colon is transmural colitis, leading to a grossly distorted colon (10), but no signs of colitis were identified in this foal. Even though small intestinal enteritis and mild cecal inflammation were present, the inflammatory process did not affect the colon macroscopically.

Long-term management of cases of short bowel in carnivores entailed dietary modification to a highly digestible, low residue diet (4). The large colon of horses is the site for microbial digestion of dietary carbohydrates and a rapid change in diet in healthy horses can lead to disturbances in the digestive tract (11). The colt in this report appears to be more sensitive to diet changes than other horses, which is likely due to the short colon. CVJ