Sirenomelia: Mermaid deformity on fetal MR imaging

This case involves the rare congenital disorder Sirenomelia, a diagnosis initially suspected during prenatal ultrasound and later confirmed by prenatal MRI. Sirenomelia, or mermaid syndrome, is mainly characterized by variable fusion of the lower limbs and by genitourinary anomalies. The vast majority of cases of this disease result in death secondary to associated renal agenesis or hypoplasia. Imaging findings from the disease are discussed, in addition to the clinical implications and suspected etiologies of this entity.