Definition: Sirenomelia represents a severe developmental field defect of the posterior axis caudal blastema, resulting in partial or complete fusion of the lower limb buds.

Synopsis

 fusion of the lower extremities

• partial or total femoral fusion (common femur)
• common tibia without fibula
• rudimentary foot with oligodactyly

 incomplete development of the bony pelvis

Types

 sirenomelia dipus
 sirenomelia unipus

Associations

 caudal regression syndrome

• agenesis of the urinary system
• agenesis of the genital system
• anorectal atresia

 single large umbilical artery
 complete situs inversus (#8719727#)

References

 Stocker JT, Heifetz SA. Sirenomelia. A morphological study of 33 cases and review of the literature. Perspect Pediatr Pathol. 1987;10:7-50. PMID: #3588246#