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Fetopathology and developmental pathology of the embryo and fetus
Marta Ježová, Josef Feit et al.
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Sirenomelia (Mermaid syndrome)
Introduction

A very rare complex congenital malformation syndrome, in which the legs are fused together (the name comes from mythical mermaids — sirens). Always accompanied by urogenital malformations with oligo/anhydramnion.

Etiology, pathogenesis
  • sporadic occurence, incidence 1 : 60 000 – 100 000
  • patogenesis is unknown, these mechanism are possible:
    • inadequate vascular supply of the caudal end of the embryo
    • a defect in the development of caudal somites
    • effect of compression
Clinical signs

Sirenomelia is always lethal. Congenital renal malformations with oligo/anhydramnion inevitably lead to pulmonary hypoplasia (Potter's sequence).

Macroscopic appearance
  • single lower limb (sympus) with various degrees of involvement: from the fusion of the soft tissues of two relatively well developed limbs to an atrophic stub
  • anal and rectal atresia
  • bilateral renal agenesis, or (less frequently) cystic renal dysplasia
  • urinary bladder agenesis
  • sacral and coccygeal agenesis, rudimental pelvis
  • agenesis or malformation of external genitalia
  • internal genital organs — testes undescended in the small pelvis, or even testicular agenesis
  • congenital malformations of other organs are frequent (skeletal, pulmonary, heart, esophageal atresia etc.)
  • single umbilical artery

Sirenomelia (73336)

Pictures

Sirenomelia: Sirenomelia, Macro, autopsy (73336) Sirenomelia, Macro, autopsy (73337)

Sirenomelia: Sirenomelia, Macro, autopsy (74566) Sirenomelia, Macro, autopsy (74567) Sirenomelia, Macro, autopsy (74568) Sirenomelia, Macro, autopsy (74569) Sirenomelia, Macro, autopsy (74570) Sirenomelia, Macro, autopsy (74571) Sirenomelia, Macro, autopsy (74572)

Case study
Sirenomelia
Marta Ježová
History

23-week male fetus, anhydramnion.

Pictures

Single rudimental lower limb, agenesis of the external genitalia, imperforate anus: Sirenomelia, Macro, autopsy (72534) Sirenomelia, Macro, autopsy (72535)

Rectal atresia, bladder agenesis: Sirenomelia, Macro, autopsy (72536)

Bilateral renal agenesis: Sirenomelia, Macro, autopsy (72538)

Agenesis of the right lung: Sirenomelia, Macro, autopsy (72537)