Sirenomelia

A rare congenital malformation characterized by fused lower limbs

Sirenomelia

[[File:Sirenomelia.svg|left|thumb|Classification of sirenomelia by the presence or absence of bones within the lower limb.
Sirenomelia, also known as mermaid syndrome, is a rare congenital developmental disorder characterized by anomalies of the lower spine and lower limbs. The condition results in the fusion of the legs, giving the appearance of a mermaid's tail, hence the name. Sirenomelia is associated with a range of other malformations, particularly affecting the genitourinary system, gastrointestinal tract, and skeletal system.

Epidemiology

Sirenomelia is an extremely rare condition, with an estimated incidence of 1 in 100,000 live births. It is more common in males than females, with a male-to-female ratio of approximately 3:1. The condition is often associated with maternal diabetes, which is considered a significant risk factor.

Pathophysiology

The exact cause of sirenomelia is not well understood, but it is believed to result from a disruption in the normal development of the caudal region of the embryo. This disruption may be due to abnormal vascular supply, specifically the "steal phenomenon," where the blood supply is diverted from the lower limbs to the upper body, leading to underdevelopment of the lower extremities.

Clinical Features

The primary feature of sirenomelia is the fusion of the lower limbs. The degree of fusion can vary, ranging from complete fusion with a single foot to partial fusion with two distinct feet. Other common features include:

• Absence or underdevelopment of the genitalia and urinary tract
• Anomalies of the gastrointestinal tract, such as imperforate anus
• Renal agenesis or dysgenesis
• Skeletal abnormalities, including sacral agenesis

Diagnosis

Sirenomelia can often be diagnosed prenatally through ultrasound imaging, which may reveal the characteristic limb fusion and associated anomalies. Postnatal diagnosis is based on physical examination and imaging studies such as X-ray and MRI to assess the extent of the malformations.

Management

There is no cure for sirenomelia, and management focuses on addressing the associated anomalies and improving the quality of life. Surgical interventions may be necessary to correct gastrointestinal and genitourinary malformations. In some cases, separation of the fused limbs may be attempted, although this is complex and depends on the individual anatomy.

Prognosis

The prognosis for individuals with sirenomelia is generally poor, with a high rate of stillbirth or early neonatal death due to severe malformations, particularly of the renal and respiratory systems. However, there have been rare cases of long-term survival with extensive medical and surgical management.

Related pages

• Congenital disorder
• Caudal regression syndrome
• VACTERL association

Classification	ICD-10: Q87.2 MeSH: D004480
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