Sirenomelie
Sirenomelia (also known as the mermaid syndrome) is a rare congenital malformation characterized by the fusion of lower limb structures.
Epidemiology
The estimated incidence is at ~1 in 60,000-70,000 of pregnancies . There may be greater male predilection (somewhat paradoxical given the usage of a mermaid).
Associations
- maternal diabetes
- renal agenesis
- single umbilical artery
- imperforate anus
- oligohydramnios
- congenital cardiac anomalies
- abdominal wall defects
Pathology
While it was previously thought as belonging to the same spectrum as the caudal regression syndrome, this proposition is now controversial and current thinking is it results from a separate pathogenesis. A vascular steal phenomenon causing severe ischemia to the caudal portion of the fetus is often accepted.
Radiographic features
Antenatal ultrasound
The lower extremities typically appear fused into a single limb and there can be sacral agenesis to varying degrees.
Ancillary sonographic features:
- presence of a single umbilical artery
- presence of oligohydramnios
Treatment and prognosis
The condition is often fatal and incompatible with life (contrary to popular fairy tales). Exceptional cases without renal agenesis may survive. Depending on the country you live in, a termination of pregnancy could be considered in appropriate situations.
History and etymology
Derives from the Latin words: 'siren' meaning "a partly female creature in Greek legend whose beautiful singing lured sailors to their deaths" and 'melia' meaning limb
Differential diagnosis
- amelia: particularly in the absence of one of the lower limbs
- caudal regression sequence: limbs not fused and often has polyhydramnios
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