Hemoperitoneum secondary to bilateral ovarian enlargement due to undiagnosed male cotwin pregnancy in a mare

A 17-year, Quarter Horse mare, was presented for colic symptoms that began the day prior to presentation; patient had no breeding history. Severe bilateral ovarian enlargement precluded transrectal palpation of the gastrointestinal tract and much of the uterus. Transrectal ultrasonography revealed severely enlarged ovaries with multiple, large, ovarian follicles, and structures with an echotexture consistent with hemorrhagic anovulatory follicles, corpora hemorrhagica, and hematoma formation. Transcutaneous abdominal ultrasonography revealed a large volume of peritoneal fluid. Abdominocentesis was performed that identified fluid consistent with frank blood (packed cell volume of 40% consistent with intraabdominal hemorrhage). Initial differential diagnoses included bilateral granulosa-theca cell tumors, other ovarian neoplasia, or ruptured ovarian corpora hemorrhagicum/hematoma resulting in hemoperitoneum. Repeat abdominal ultrasonography revealed a viable pregnancy (~ 70 days). Additional diagnostics obtained 5 days after admission had severely elevated serum testosterone (517.8 pg/ml), elevated inhibin B (160.7 pg/ml), and normal antiMüllerian hormone (0.12 ng/ml) concentrations. After misoprostal and dinoprost tromethamine treatment, manual termination was performed that resulted in the removal of 2 male cotwins. Ovarian size markedly reduced soon after pregnancy termination and serum hormonal concentrations decreased 1 week later to concentrations approaching the reference range for a mare in the first trimester of pregnancy.