Sirenomelia (also known as the mermaid syndrome) is a rare congenital malformation characterized by the fusion of lower limb structures. The exact etiology of this disease is unknown.
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Terminology
sirenomelia sequence
sirenomelia syndrome
Epidemiology
The estimated incidence is at ~1 in 60,000-70,000 of pregnancies 9. There may be greater male predilection (somewhat paradoxical given the usage of a mermaid).
Associations
Diagnosis
It is usually made antenatal during second semester by fetal ultrasonography.
Clinical findings
Affected individual may have characteristic partial or complete fusion of both lower legs. There may be one femur or two femur within one shaft of skin. They may have no feet, one foot or two feet which may be rotated facing forward.
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 6
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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