Prenatal Diagnosis of Megacystitis and Hydronephrosis in an Equine Fetus: How Transabdominal Ultrasonography Can Help to Diagnose Fetal Abnormalities

Premature udder development constitutes an alarm signal in pregnant mares. The objective of this clinical case report is to highlight the importance of transabdominal ultrasound examination of the fetus in these cases and to report a unique case of prenatal diagnosis of obstructive uropathy based on the observation of severe fetal hydronephrosis and megacystitis in utero. A 4-year-old French chaser primiparous mare was referred for evaluation of premature udder development during the ninth month of pregnancy. The mare had clinical signs within normal limits, a developed and sensitive udder with secretions, and no vulvar discharge. Transrectal examination revealed the presence of an immobile fetus. Combined uteroplacental thickness was within normal limits. Transabdominal ultrasound revealed a single live fetus in posterior presentation with several abdominal abnormalities. Unilateral hydronephrosis and megacystitis lead to a hypothetical diagnosis of fetal multiple urinary tract malformation with outflow obstruction. Treatment was discontinued and the mare was monitored. Abortion occurred spontaneously a week later. Postmortem examination revealed a ruptured bladder of abnormally large dimensions and a severely distended left kidney without parenchyma (filled with free urine) and lack of permeability in the left ureter and urethra. Postmortem diagnosis was consistent with our prenatal ultrasonographic diagnosis. Even though described during human pregnancy with various etiologies and severity, prenatal diagnosis of fetal hydronephrosis and megacystitis has not been reported in equine veterinary medicine before. These malformations need to be characterized more precisely in the future. This case highlights the importance of transabdominal ultrasonography to detect equine fetal abnormalities.