Ultrasonographic evaluation of the equine placenta

Abstract

Placentitis is a common cause of equine abortions. In a majority of cases, the route of infection is believed to be ascending through the cervix, and an area of the chorion adjacent to the cervical star shows characteristic pathology in aborting mares. This area is depleted of chorionic villi, thickened, discolored, and covered by fibronecrotic exudate. Mares with placentitis due to a hematogenous infection show multifocal pathology of the chorionic surface of the placenta. Clinical signs include udder development, premature lactation, cervical softening, and vaginal discharge. Treatment is often unsuccessful once the mare has developed clinical signs. Ultrasonographic evaluation of the placenta in late gestational mares allows the clinician to detect preclinical signs of placentitis and premature separation, which then could be treated in its early stages. Transabdominal ultrasonography: Focal areas of utero-placental thickening and partial separation of the allantochorion from the endometrium in the uterine body and horns, can be observed by this approach. The combined thickness of the uterus and the placenta (CTUP) should not be more than 12 mm at any site. In addition to evaluating the placenta, a biophysical profile of the fetus can be performed by a transabdominal approach. Transrectal ultrasonography: This approach provides an excellent image of the caudal portion of the allantochorion adjacent to the cervical star. Using transrectal ultrasonographic evaluation of the placenta, we have observed abnormal thickness and partial separation of the allantochorion from the endometrium in mares with clinical signs of placentitis. In advanced stages, the space between the uterus and the placenta is filled with hyperechoic fluid. Normal values of the CTUP in an area immediately cranially and ventrally of the cervix was determined to be: <8 mm between day 271 and 300; <10 mm between day 301 and 330; and <12 mm after day 330. Increased CTUP suggests placental failure and pending abortion. Treatment of placentitis should be aimed toward elimination of the infectious agents, reduction of the inflammatory response, and reduction of the increased myometrial contractility in response to the ongoing inflammation. Broad spectrum antibiotics, anti-inflammatories (flunixin meglumine, 1.1 mg/kg BID; phenylbutazone, 4 mg/kg BID) and tocolytics (Altrenogest, 0.088 mg/kg SID; Clenbuterol, 0.8 μg/kg), are recommended for treatment of placentitis. Pentoxyfylline (7.5 mg/kg p.o. BID) has been suggested to increase oxygenation of the placenta through an increased deformability of red blood cells.