Hydrocephalus in an American Miniature Horse Foal: A Case Report and Review

A 6-year-old multiparous American Miniature Horse mare was presented at 324 days of gestation for evaluation of vaginal bleeding. A manual obstetrical examination was performed and the cervix was found to be open with the fetus in transverse position. The mare was sedated and placed under general anesthesia. Attempts made to mutate the fetus were unsuccessful. A cesarean section was performed and the foal was noted to be in transverse position with marked enlargement of the cranium. The abdominal incision was closed in a routine manner, and the mare recovered from anesthesia without incident. Postoperative treatment consisted of flunixin meglumine, gentamicin sulfate, potassium penicillin, oxytocin, and intravenous fluid therapy. The mare was discharged to the owners 4 days after surgery. A lateral radiograph of the fetus was obtained and confirmed hydrocephalus. On necropsy, it was found that the calvarium measured 59 cm in circumference and was dome-shaped, the neuropil and leptomininges measured only 1 to 2 mm in thickness, the brainstem and cerebellum were reduced in size, and there was moderate distension of the third ventricle with stenosis of the mesencephalic aqueduct. Inflammatory and neoplastic causes of mesencephalic aqueductal obstruction were ruled out by histopatholgy. This represents a classic case of hydrocephalus because of stenosis of the mesencephalic aqueduct, which to our knowledge has not been previously reported in a miniature foal. Further investigation is warranted into the pathogenesis of mesencephalic aqueduct stenosis in foals, which has now been reported in several equine breeds.