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

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).

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.

The lower extremities typically appear fused into a single limb and there can be sacral agenesis to varying degrees.

Ancillary sonographic features:

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.

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

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Article information

rID: 13421
Tag: cases
Synonyms or Alternate Spellings:
  • Mermaid syndrome
  • Sirenomalia sequence
  • Mermaid fetus

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Cases and figures

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