Caudal regression syndrome

Caudal regression syndrome


Caudal regression syndrome represents a wide spectrum of malformations which ranges from imperforate anus to sirenomelia. It occurs during the third week of fetal development and is caused by a wedge-shaped defect in the posterior axis caudal blastema, causing malformation or fusion of the early lower limb buds. The different degrees of severity are related to different length and width of the early caudal defect. Sirenomelia has been postulated as occurring in the presence of a single umbilical artery which diverts blood flow from the caudal portion of the embryo, producing malformation of caudal structures. Caudal regression syndrome is more frequent in monozygotic twins and shows a 200-fold increase in diabetic mothers, occurring in 0.2 to 0.5 percent of these infants. The incidence is reported to be approximately one in 47,000 to 60,000 live births. The syndrome includes distorted or absent vertebra below the thoracic level, rudimentary or absent pelvic bones and asymmetrically short lower limbs. Associated malformations include gastrointestinal, genitourinary, and cardiac anomalies.


Sonographic diagnosis of caudal regression syndrome has been reported from 17-34 weeks of pregnancy, and is frequently hindered by oligohydramnios. It has been suggested that the diagnosis of caudal regression syndrome includes lumbosacral agenesis of the spine, normal amniotic fluid volume and a three-vessel umbilical cord. Sirenomelia may be diagnosed in the presence of oligohydramnios, bilateral renal agenesis, lower extremity fusion, and a two-vessel cord. Sirenomelia also involves absence of urinary, genital or anal orifices and no external genitalia although a tail or phallus may occasionally be found. Other genitourinary structures such as the bladder may also be missing. There may be missing kidneys or cystic dysplastic kidneys. Amnioinfusion has been helpful in making a diagnosis in some cases with oligohydramnios.

Differential Diagnosis

Sacral agenesis includes the absence of the coccyx and sacrum without vertebral anomalies of the lumbosacral spine. VACTERL syndrome shows a wide overlap with caudal regression and may include vertebral, anal, cardiac, oesophageal, renal and limb anomalies.

Sonographic Features

Interruption of lower distal lumbar spine

Abnormal lower limb position or movement – or development Limb contracture

Absence of lower limb movement

Deformed foot/feet (clubbed or rocker-bottom) or lower limbs

Hypoplasia of sacrum and lower extremities

Hip malformation: dislocation or appoximation of both femoral heads with agenesis of the sacrum


Associated Syndromes

  • Bilateral renal agenesis (Potter’sSyndrome)
  • Diabetic embryopathy
  • Extra bisatellited minute chromosome (probably derivative 22, one case)
  • Posterior urethral valve syndrome
  • Vitamin A teratogenicity


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