Strangulation of the small colon by ovarian pedicle in an adult broodmare
Kevin M. Claunch, DVM, DACVS-LA; Parker Wurst, DVM, Cari Chisholm, DVM
Weems & Stephens Equine Hospital; 5960 Hospital Rd. Aubrey, TX, 76227 USA
Summary
A 17-year-old Quarter Horse broodmare was taken to surgery for signs of colic unresponsive to medical management. The small colon was strangulated by a pendulous ovarian pedicle. The strangulation was freed, and the affected ovary was removed. The mare developed signs of a small colon obstruction 4 days after surgery. The mare was euthanized 6 days after surgery for signs of a GI rupture. A post-mortem examination revealed necrosis of the affected portion of small colon.
Keywords: Horse, Small colon strangulation, Ovarian strangulation, colic
Case History
A 17 year-old Quarter Horse broodmare presented to the hospital for signs of abdominal pain of 7 hours duration. The mare was given flunixin IV on the farm which did not reduce her abdominal pain. The mare presented with marked abdominal distension and severe abdominal pain. At admission the mare had a rectal temperature of 38.2C (100.8F), heart rate of 80 beats/minute, and respiration rate of 36 breaths/minute. Borborygmi was absent in all abdominal quadrants. The mare was sedated with 3 mL of xylazine (Anased1 0.55 mg/kg IV once) and was administered 3 mL N-butylscopolammonium bromide (Buscopan2 0.11 mg/kg). Transrectal palpation of the abdomen revealed severe GI distension that prevented full insertion of an arm. Trans abdominal ultrasound did not reveal any excess peritoneal fluid or small intestinal distension. The large colon was filled with gas and was of normal wall thickness. Nasogastric intubation yielded 2 liters of net reflux. The mare had a PCV of 32% and TP of 6.8 g/dL. An intravenous catheter was placed in the left jugular vein. The mare was taken to a stall and started on intravenous balanced electrolyte solution (Plasma-Lyte3) as a bolus. The mare was extremely painful and difficult to keep standing. The mare was taken to surgery due to unrelenting pain and concern for a large intestinal obstruction.
Surgery details
The mare was administered potassium penicillin (22,000 units/kg IV) and gentamicin (6.6 mg/kg IV). The mare was sedated with xylazine (Anased1 1 mg/kg) IV. She was then induced under general anesthesia with ketamine (Ketaset4 2.2 mg/kg IV once) and midazolam (.03 mg/kg IV once). The mare was positioned in dorsal recumbency and maintained on oxygen and isoflurane using mechanical ventilation. The ventral abdomen was clipped. The clipped area was aseptically prepped with chlorhexidine and alcohol and routinely draped. A 30 cm ventral midline incision was made, and the abdomen was entered. Exploration of the abdomen revealed a markedly gas distended cecum and the large colon was markedly distended with gas and ingesta. The small colon was firmly impacted with ingesta, and gas distended at its oral aspect. An aboral segment of the small colon was strangulated by the left ovary with an abnormally long mesovarium. The strangulation was manually corrected. A controlled high enema was performed to evacuate the small colon. The large colon was evacuated via pelvic flexure enterotomy. The enterotomy was closed with 2-0 polyglactin 910 (vicryl5) using a full thickness simple continuous pattern oversewn with a Cushing pattern. The strangulated portion of the small colon could not be exteriorized. When looking into the abdomen with a headlight, a portion of the small colon mesentery and serosal surface was light purple in color. The left ovary was dark purple to black in color and was mildly enlarged. The left ovary was considered non-viable. The left ovary was easily exteriorized through the midline incision. The mesovarium was grasped with Carmalt forceps and a vessel sealing device (Liga-sure6) was used to cauterize and transect the mesovarium. The ovary was sectioned, placed in formalin, and submitted for histopathology. The linea alba was closed with #3 polyglycolic acid (PGA7) using a simple continuous pattern, the subcutaneous tissues were closed with 0 polyglactin 910 (vicryl5) using a simple continuous pattern, and the skin was closed with 2-0 poliglecaprone (Monocryl5) using a simple continuous pattern. The incision was covered with a tightly rolled sterile Huck towel which was sutured to the skin with 0 nylon using large cruciate sutures. The mare recovered from anesthesia uneventfully with the aid of head and tail ropes.
Post-operative care
Following surgery, the mare was maintained on 50mL/kg/day of balanced electrolyte IV fluids (Plasma-Lyte3) for 48 hours, 22,000 IU/kg potassium penicillin IV q6h, 6.6mg/kg gentamicin IV q24h, and 1.1 mg/kg flunixin meglumine IV q12h. The mare immediately became comfortable following surgery. She was started on a gradual refeeding program beginning 48 hours after surgery. The mare had a good appetite and had normal vital signs until 4 days after surgery when she developed signs of abdominal discomfort, abdominal distension, and tachycardia (64bpm). Transrectal palpation of the abdomen revealed firm ingesta packed within the small colon consistent with a small colon impaction. At this time there was concern that the mare could have delayed ischemic damage of the small colon. Feed was removed, the mare was maintained on IV fluids, and was administered laxatives via NG tube (alternating doses of mineral oil, magnesium sulfate, and electrolyte water). Over the next 48 hours the mare remained mild to moderately uncomfortable and failed to pass manure. Repeated rectal exams confirmed the small colon obstruction was unchanged. The mare developed sudden profound tachycardia, full body sweating, and purple mucous membranes 6 days post-operatively. Transrectal palpation of the abdomen revealed free gas in the abdomen. Transabdominal ultrasound revealed heterogenous free abdominal fluid ventrally and free gas in the abdomen dorsally. An abdominocentesis revealed dark green fluid and it was determined the mare had suffered a rupture of the gastrointestinal tract. The mare was humanely euthanized.
Post-mortem findings
A necropsy was performed which revealed ischemic damage of a 70 cm section of small colon which corresponded to the site of the ovarian strangulation. A full thickness rupture was present in the ischemic section of the small colon.
Histopathology
Histopathology revealed extensive hemorrhage throughout the ovarian stroma characterized by large pools of red blood cells as well as congestion of blood vessels. The changes were compatible with acute ovarian strangulation. No other abnormalities were observed.
Discussion
To the authors’ knowledge this is the only report of ovarian strangulation of the small colon in an adult mare. An almost identical lesion has previously been reported (Pilatii 2013) as an acquired condition in a seven-day old filly. Ovarian strangulation of the small colon has also been reported in a newborn filly (Evard 1988). In addition, primary ovarian torsion has been described in a neonatal foal (Valk 1998). Disease of the small colon is only responsible for 2%-18% of horses admitted for colic to referral centers (Prange 2019). More typical diseases include small colon impaction, enteroliths/fecaliths, strangulations from lipomas, volvulus, or neoplasia, and vascular injuries including tearing of the mesocolon. Some form of large intestinal obstruction was expected prior to exploratory celiotomy in this mare. However, the highly unlikely nature of this type of strangulation along with the location making visualization of the strangulation impossible resulted in delayed recognition of the true cause of the strangulation. In fact, it was originally thought that the mare had a strangulating lipoma of her small colon after preliminary exploration of the abdomen. This was due to a soft spherical structure connected to a band being palpated tightly wrapped around the small colon. It was not until after the strangulation was resolved and the ovary was exteriorized did the true cause of strangulation become apparent. Thankfully this strangulation was able to be resolved by manual manipulation of the ovary around the mesovarium. If the ovary had been blindly transected within the abdomen, severe hemorrhage could have been encountered that would have been difficult to locate and control. Although uncommon, ovarian strangulation should be considered as a differential diagnosis when an intestinal strangulation is discovered especially prior to blind transection of a strangulating band.
The cause of the pedunculated nature of this ovary was not readily apparent. Presumably the mesovarium could be stretched by the weight of the uterus associated with multiple pregnancies. However, the right ovary/mesovarium was within normal limits. Ovarian strangulation being reported in young foals may suggest that an elongated mesovarium could be a congenital abnormality. Histopathology did not reveal any predisposing causes for the elongated mesovarium.
Unfortunately, this mare was not able to survive due to ischemic damage to the strangulated portion of the small colon. Conceivably a colostomy could have been performed at the time of surgery as the location of the strangulation made it difficult to be certain of viability, however this was not a feasible option for this mare nor was a second abdominal surgery. The initial rapid improvement in clinical signs made for a hopeful initial prognosis. At the time that the mare developed post-operative signs of small colon obstruction it was unknown if obstruction was due to temporary dysfunction or delayed ischemic injury. Supportive care was necessary until it became clear that the mare had a hopeless prognosis. Similar to other strangulating lesions, the mare likely would have had a better chance of successful outcome with earlier surgical intervention. A definitive pre-operative diagnosis was not able to be obtained and all signs associated with the initial colic evaluation were commiserate with a large intestinal obstruction. The amount of gas distension precluded palpation of the reproductive tract. If the mare had presented early after the strangulation developed, prior to the development of severe gas distension it is conceivable that the ovarian strangulation may have been able to be palpated per rectum.
Conclusion
Ovarian strangulation has now been reported as a rare cause of small colon strangulation as a congenital and acquired condition in foals and in an adult broodmare. Ovarian strangulation should be considered in cases of small colon strangulation especially in the caudal abdomen.
Author declaration of interests
The author has no conflicts of interest.