CAUSES OF RECTAL TEARS

Veterinarians most commonly cause tears of the rectum during palpation of abdominal structures. Other less common causes include enemas, meconium extraction with forceps, sadism, dystocia, diverticulum formation, bite injuries, neurogenic fecal retention, inherent bowel weakness, vertebral fractures, ruptured small colon hematomas, impactions secondary to mural neoplasia, sand or stricture, penile misdirection during breeding, or thromboembolism. Occasionally, tears are idiopathic. There are recognized predilections for rectal tears to occur in certain horses during rectal palpation. These include Arabians, small horses, horses with a history of rectal injury, young horses, horses unaccustomed to rectal palpation, nervous horses, horses with colic, stallions, and geldings.

DIAGNOSIS

Clinical signs seen in horses with a rectal tear vary with the severity of the tear and duration of the problem. If a tear occurs during rectal palpation, the veterinarian may feel a sudden release in pressure, cessation of straining, an improved ability to palpate the abdominal structures, and possibly the presence of blood on the rectal sleeve. A horse with a rectal tear may strain to defecate, pass hemorrhagic feces, and become colicky. Depression, endotoxemia, and peritonitis may follow within a few hours.

Establishing the severity of a tear is of vital importance because it dictates treatment and prognosis. This is best achieved by preventing further straining using intravenous (IV) xylazine hydrochloride (0.1 to 0.2 mg/kg) in combination with IV butorphanol tartrate (0.1 mg/kg). Lidocaine (50 mL of 2% lidocaine per rectum) can be used to relax the rectum; however, IV butylscopolamine bromide (0.3 mg/kg) is more effective at reducing rectal pressure. Once the horse is sedated, an epidural anesthetic can be administered (0.2 mg/kg xylazine hydrochloride and 0.22 mg/kg mepivacaine chloride diluted in saline to 10 mL) to enable exploration of the tear.

The rectum should be evacuated of all feces. Digital inspection with a lubricant-covered, ungloved hand is the most effective means of determining the extent and severity of a rectal tear. Typically the redundant rectal mucosal folds prevent direct view of the injury, although some tears may be inspected using a vaginal speculum or an endoscope. Endoscopic evaluation of the rectum is commonly performed at referral facilities to facilitate therapeutic decision-making.

Tears are graded according to the involvement of the layers of the bowel wall as initially reported by Arnold and colleagues in 1978 (Table 101-1). Tears can be located at any distance from the anus; however, most are 25 to 30 cm from the anus at the junction of the rectum and small colon. This area is considered to be predisposed to injury because the blood vessels penetrate the intestinal wall acutely and directly rather than gradually, therefore causing weakening in the dorsal aspect of the wall. Iatrogenic tears are most commonly longitudinal, but idiopathic tears may be transverse.