Prenatal ultrasound diagnosis of sirenomelia: A case report

Sirenomelia is an extremely rare and almost invariably lethal congenital malformation characterized by variable fusion of the lower limbs and severe associated visceral anomalies. We report a case prenatally diagnosed at 20 weeks of gestation in a 25-year-old nondiabetic, nonconsanguineous woman referred for suspected polymalformative fetal syndrome. Prenatal ultrasound demonstrated severe oligohydramnios, bilateral small hyperechoic kidneys suggestive of renal dysplasia, fused lower limbs, absent external genitalia, and a single umbilical artery, findings strongly supporting the diagnosis of sirenomelia. A suspected conotruncal cardiac anomaly was noted, though limited by the severity of oligohydramnios. Postnatal examination confirmed the prenatal findings; fetal karyotype was normal. Medical termination of pregnancy was performed following multidisciplinary counseling. This case highlights the central role of prenatal ultrasound in the early recognition of sirenomelia, and the importance of careful radiologic description, cautious classification, and multidisciplinary counseling in the management of this rare lethal condition.