Sirenomelia

Sirenomelia (also known as the mermaid syndrome) is a rare congenital malformation characterised by the fusion of lower limb structures.

Epidemiology

The estimated incidence is at ~1 in in 60,000-70,000 of pregnancies⁹. There may be greater male predilection (somewhat paradoxical given the usage of a mermaid).

Pathology

While it was previously thought as beloningbelonging the same spectrum as the caudal regression syndrome, this proposition is now heavily debated and it is now thought thought to result from a seperate pethogenesisseparate pathogenesis. A vascular steal phenomenon causing causing severe ischemia to the caudal portion of the fetus is often accepted.

Associations

• maternal diabetes
• renal agenesis
• single umbilical artery
• imperforate anus
• oligohydramnios
• congenital cardiac anomalies
• abdominal wall defects

Radiographic features

AntenetalAntenatal ultrasound

The lower extrametitiesextremities 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 ⁶

Treatment and prognosis

The condition of 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 appropriateinappropriate 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

For mild forms consider:

• caudal regression sequence: limbs not fused and often has polyhydramnios