Perirectal abscess, colic, and dyschezia in a horse

Abstract

A quarter horse gelding with intermittent colic was diagnosed with a perirectal abscess and dyschezia. Rectal ultrasonography identified a multiloculated, fluid-filled mass. A perirectal abscess was diagnosed when the mass ruptured and drained into the rectum. The abscess was treated successfully with warm soapy water enemas and trimethoprim and sulfamethoxazole.

An 8-month-old, quarter horse gelding was presented to the Large Animal Clinic of the Western College of Veterinary Medicine (WCVM) with a 30-hour history of intermittent colic. The gelding had received 2 treatments with 240 mL of mineral oil and molasses and an enema, as prescribed by the referring veterinarian. His feed consisted of alfalfa, grass hay, sweet feed, and grain, and he was still eating and drinking. Vaccinations and deworming were current. Rectal temperature, pulse rate, respiration rate, capillary refill time, blood gas analysis, and borborygmi were all within normal limits. When the gelding attempted to pass feces, it would strain and was able to pass only a small amount of dry manure.

In-house physical examination revealed a firm out-pouching of the perineum, immediately dorsal to the anus, and a firm mass dorsal to the rectum, about 5 cm cranial to the anus. The mass decreased the diameter of the rectum and impeded the passage of feces. The rectal wall, just ventral to the mass, was roughened. A complete blood cell count revealed hyperfibrinogenemia and neutrophilia with reactive lymphocytes consistent with chronic inflammation. A low hematocrit was consistent with anemia of chronic inflammation. A blood gas analysis was within normal limits. A fine-needle aspirate of the mass was performed transrectally; however, the aspirate was nondiagnostic and contained too few cells. Ultrasonography per rectum identified an encapsulated, fluid-filled, multiloculated mass, dorsal to the rectal wall. This mass measured 6 cm in diameter and extended cranial from the anus for 10 cm. A perirectal abscess was the tentative clinical diagnosis. Differential diagnoses included anorectal lymphadenopathy, hematoma, neoplasm, or a gluteal abscess that had migrated. During palpation of the mass per rectum, the caudal aspect of the mass ruptured, draining bloody, mucopurulent fluid into the rectum, thus confirming the diagnosis of perirectal abscess. Treatment was aimed at relieving the impaction and preventing future impaction. Two enemas were given, each with 2 L of warm soapy water. The enemas lubricated and softened the impacted feces cranial to the mass and rapidly relieved the colic. The diet was changed to alfalfa cubes soaked in water. The fecal output and size of the perirectal abscess were monitored. Trimethoprim and sulfamethoxazole (Nu-Cotrimox; Nu-Pharm, Richmond Hill, Ontario) 30 mg/kg body weight (BW), PO, q12h, for 15 d was prescribed, and the horse was discharged. Follow-up consultation after 2 wk of therapy verified that there had been no colic or fecal impaction since discharge.

Possible causes of partial or total rectal obstruction include perirectal abscess (1), anorectal lymphadenopathy (1), and perirectal strictures (2). Perirectal abscessation can occur from a rectal puncture or tear, rectal inflammation and lymphadenopathy (1), dystocia (3), or formation and gravitation of a gluteal abscess following an IM injection (3). However, the etiology is often idiopathic. Anorectal lymphadenopathy has been reported to cause colic and perirectal abscesses in young horses (1). Perirectal strictures may develop after rectal tears have healed (2). Common signs of extraluminal obstruction of the rectum include abdominal pain, tenesmus, dyschezia, dysuria (from neuritis secondary to regional inflammation), lack of fecal production, and fever (1,2). Diagnosis of rectal obstruction should include rectal palpation, percutaneous or per rectum aspiration of the mass, and ultrasonographic examination (1).

The case presented here is consistent with other published cases of perirectal abscesses in the horse (1,3). Magee et al (1) reported on 5 young horses presenting with signs of colic due to anorectal lymphadenopathy, perirectal abscesses, or both. Sander-Shamis (3) reported on perirectal abscesses in 6 horses. The etiologies for these perirectal abscesses were not reported. The gelding in this case had no known trauma and had not been palpated rectally. We considered other etiologies. Stallions housed together will mount one another and anal penetration has been reported (4). Similar to the majority of published cases, the abscess was dorsal to the rectal wall (1,3). Perirectal abscesses or anorectal lymphadenopathy has also developed ventral and lateral to the rectum (1,3). Most rectal tears involve the dorsal aspect of the rectum, are located 15 to 55 cm from the anus, and are parallel to the longitudinal axis (3).

Rectal palpation and ultrasonography aid in diagnosing rectal abscesses and in monitoring response to therapy. A fine-needle aspirate provides definitive diagnosis (1). Conservative medical management of this case was appropriate. The impacted feces were removed, which decreased the distension of the rectum. Laxatives may be given, PO, to keep feces soft (1). Nonsteroidal anti-inflammatory drugs can be given to alleviate the signs of pain and decrease perirectal inflammation (1). Antibiotics are an important component of treatment. The organisms isolated from perirectal abscesses in other young growing horses have been Streptococcus zooepidemicus and Escherichia coli (1,3). Surgical therapy is warranted if medical management fails or if the abscess spreads into the peritoneal cavity (1,3). Dorsally located abscesses are drained into the rectum (3). Those located laterally are drained by an ipsilateral incision on the outside of the anal sphincter. Ventral abscesses can be drained into the vagina in mares or ventral to the anus in males (3). The abscess cavity is then flushed with a 10% povidone-iodine solution for several days (3). Horses with peritonitis require an exploratory celiotomy (3). The prognosis for adult horses with an uncomplicated abscess is good (2).