History

A 7-month-old 41-kg (90-lb) American Miniature Horse gelding was admitted to a large animal referral hospital for evaluation of acute colic. The weanling had inappetence and was found recumbent 2 hours earlier in a field. The weanling received xylazine (1 mg/kg [0.45 mg/lb], IV) before transport to the hospital.

At the time of admission, the weanling was quiet, alert, and responsive and had no signs of colic. The patient was in good body condition but the abdomen had a distended appearance with a loss of concavity in the paralumbar fossa. The heart rate was 52 beats/min, consistent with mild tachycardia. On abdominal auscultation, gastrointestinal sounds were decreased but present in all quadrants. Nasogastric intubation yielded no net reflux. No abnormalities were detected on transabdominal ultrasonography.

Medical treatment for a presumptive large intestinal nonstrangulating lesion included IV administration of flunixin meglumine (1.1 mg/kg [0.5 mg/lb]) and enteral administration of mineral oil (250 mL) and psyllium (57 g [2 oz]) via a nasogastric tube. Several hours later, signs of colic were observed. At that time, the blood lactate concentration was 2.0 mmol/L (reference range, 0 to 2.0 mmol/L). Abdominocentesis yielded a grossly normal peritoneal fluid sample with a lactate concentration of 3.8 mmol/L. Maintenance IV fluid therapy was initiated. Administration of analgesic drugs included detomidine (0.025 mg/kg [0.01 mg/lb], IV) and butor-phanol (0.025 mg/kg, IV). After several more hours, signs of colic were again observed. The weanling was moderately tachycardic (64 beats/min) with progressive abdominal distention, as detected by serial abdominal circumference measurements.

Abdominal radiography was performed. Considering the patient's size and sedation caused by analgesic drug administration, standard small animal orthogonal abdominal radiographs were obtained by use of a vertically oriented x-ray beam (Figure 1).

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Right lateral radiographic views of the cranioventral (A) and caudoventral (B) aspects of the abdomen and ventrodorsal radiographic views of the cranial (C) and caudal (D) aspects of the abdomen of a 7-month-old 41-kg (90-lb) American Miniature Horse gelding that was admitted to a large animal referral hospital for evaluation of acute colic.

Citation: Journal of the American Veterinary Medical Association 253, 6; 10.2460/javma.253.6.711

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Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →

Diagnostic Imaging Findings and Interpretation

On the ventrodorsal projection, a rounded, mineral opaque mass with smooth margins is evident in the descending colon at the level of the pelvic inlet. In the aboral direction, the mass effect is causing the large intestine to be markedly distended with gas. In the cranial portion of the abdomen, the mass effect is causing the large intestine to contain formed material that is more mineral opaque than typical fecal material; the material has a desiccated appearance. The body wall is outwardly convex secondary to dilation of gas-filled viscera within the abdominal cavity. A nonstrangulating mechanical obstruction (ie, fecalith) of the descending colon was the primary differential diagnosis. In addition, a secondary nonstrangulating mechanical obstruction of the ascending colon was suspected.

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Same radiographic images as in Figure 1. A—A moderate amount of heterogenous soft tissue opacity with fecal-like material as well as a mild amount of mineral opacities is present in the large intestine, ventrally (white arrows) with gas dorsally, suggestive of a large intestinal impaction with sand causing abdominal distention. B—The large intestine has a moderate amount of fecal-like material with some mineralized opacities (white arrows) consistent with a large intestinal impaction. The cecum is compartmentalized, contains intraluminal gas, and appears normal (arrowhead). C—A moderate to marked amount of fecal-like material is present within the sternal and diaphragmatic flexures of the ascending colon, consistent with a large intestinal impaction. D—Radiopaque digesta and fecal material are present within the descending colon (circle) just cranial to the right ilium suggestive of mechanical intraluminal obstruction. Aborally from the obstruction, the mass effect is causing the large intestine to be markedly distended with gas. Orally from the obstruction, there is amassment of fecal-like material and marked gas distention (black arrows).

Citation: Journal of the American Veterinary Medical Association 253, 6; 10.2460/javma.253.6.711

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Treatment and Outcome

Exploratory laparotomy via a ventral midline approach was elected because of the refractory discomfort, progressive abdominal distention, and suspected fecalithiasis. The weanling received perioperative flunixin meglumine (1.1 mg/kg, IV, q 12 h), and broad spectrum antimicrobial treatment was initiated prior to surgery (potassium penicillin, 22,000 U/kg [10,000 U/lb], IV, q 6 h; gentamicin, 6.6 mg/kg [3 mg/lb], IV, q 24 h). A fecalith was identified in the mid-descending colon and was softened and broken apart by use of an intraluminal infusion of fluids combined with massage, then manually decompressed in an aboral direction. A marked impaction of the ascending colon was evident at surgery; a pelvic flexure enterotomy was performed to evacuate the impacted digesta and a mild amount of sand from the ventral and dorsal colon. No other abnormalities were identified in the abdomen. The weanling recovered well, received standard postoperative treatment and supportive care, and was discharged from the hospital 3 days after surgery.

Comments

The radiographic diagnosis of nonstrangulating mechanical obstruction in the case described in the present report was supported by the progression of clinical signs. Surgical treatment was chosen because the weanling had signs of abdominal pain that was refractory to analgesia, increasing abdominal distention, and identification of the lesion on radiographs. The suspected diagnosis was confirmed intraoperatively. A fecalith was found in the mid-descending colon and the ascending colon was impacted with digesta; both lesions were managed routinely.

Signs of colic in miniature horses are similar to those in full-sized horses. They include signs of pain that are referred to the abdomen, abdominal distention, pawing, rolling, decreased fecal output, anorexia, and lethargy. Compared with full-sized horses, however, diagnostic evaluation can be limited because palpation of the abdomen per rectum is unsafe and not advised in small equids.^1–4 In the weanling of the present report, a lack of ultrasonographic abnormalities on serial evaluation was supportive of large intestinal disease,⁵ but yielded no further diagnostic information. Therefore, radiographic evaluation of the abdomen was elected.

Abdominal radiography is a routine diagnostic component of colic in horses in geographic regions known for a high prevalence of sand impaction and enterolithiasis⁶; however, the weanling of the present report was not in such a geographic location. The small stature of the miniature horse of this report allowed for not only the standard lateral abdominal projection, the reported technique of which highlights the 4 abdominal quadrants (craniodorsal, caudodorsal, cranioventral, and caudoventral),⁷ but also a ventrodorsal projection by use of a vertically oriented x-ray beam. Although severe gas distention and moderate to marked colon filling were identified on the lateral view, it was the ventrodorsal projection that allowed for the identification of an intraluminal obstruction in the descending colon and highlighted the impacted material specifically within the sternal and diaphragmatic flexures of the ascending colon. These findings, in conjunction with progressive colic signs and abdominal distention, dictated the recommendation for surgical management.

In the present report, the weanling recovered well from surgery with no postoperative complications, and no recurrent episodes of colic were reported at long-term follow-up. Although abdominal radiography is often used as a routine diagnostic test for horses with colic, limitation to lateral projections in standing equids and silhouetting of abdominal viscera with a large volume of ascending colon contents preclude routine thorough evaluation of the abdomen radiographically. Diagnostic imaging success in the weanling of the present report was owed to relative ease of patient positioning, use of a vertical beam, use of orthogonal views, and less contrast-reducing scatter radiation in a small patient. Additionally, a large amount of gas present in both the ascending and descending colons with relatively mineral opaque contents increased radiographic contrast and highlighted the abnormalities. On the basis of findings in this report, the usefulness of orthogonal abdominal radiographs in select small equine patients should be recognized. In petite miniature breed horses and miniature foals that receive chemical restraint, orthogonal abdominal radiography by use of a vertical beam should be considered as a useful diagnostic tool for colic evaluation.