caudal regression syndrome

Caudal regression syndrome represents a spectrum of structural defects of the caudal region. Malformations vary from isolated partial agenesis of the coccyx to lumbosacral agenesis.


Caudal regression syndrome is rare, with an estimated incidence of 1:7500-100,000 .

The vast majority of cases are sporadic, however, familial cases occasionally occur. An association with VACTERL and Currarino triad syndromic complexes has been reported. Severe cases are usually identified in utero or at birth. Mild cases may not be identified until adulthood. There is no gender predilection.

Clinical presentation

Caudal regression syndrome may present with a broad range of symptoms:

  • neurogenic bladder and anorectal malformations
  • sensorimotor paresis (motor deficits > sensory deficits)
  • features of sacral agenesis: narrow hips, hypoplastic gluteal muscles, shallow intergluteal cleft
  • mild foot deformities and gait abnormalities


Caudal regression syndrome results from an insult in early pregnancy (< 4th week of gestation). Hyperglycemia, infection, toxic and ischemic insults have been implicated.

Two possible etiologies are suspected :

  • disturbance of the primary neurulation process
  • derailment of the process of degeneration and differentiation of an initially normally developed primary and secondary neural tube

In an antenatal setting there are also associations with:

  • maternal diabetes: type I or type II
    • ~20% of cases of caudal regression syndrome are associated with either type I or type II diabetes mellitus in the mother
    • CRS occurs in up to 1% of pregnancies of women with diabetes
  • polyhydramnios 

Radiographic features

Imaging appearances can significantly vary depending on the severity of regression. In general, the following may be seen:

  • lumbosacral vertebral body dysgenesis/hypogenesis
  • the level of atresia/dysgenesis is usually below L1 and often limited to the sacrum
  • truncated blunt spinal cord terminating above the expected level (wedged- or cigar-shaped conus medullaris)
  • severe canal narrowing rostral to last intact vertebra

Associated abnormalities may also be demonstrated (see above).

Antenatal ultrasound
  • a blunted sharp ending distal cord on a longitudinal sonogram is typical
  • the conus often ends way above the expected level (sometimes even higher than L1)
  • absent/hypoplastic sacrum 
  • hypoplastic extended lower extremities (limbs are separated c.f. sirenomelia)
  • may show a "shield sign": opposed iliac bones in absence of sacral vertebrae: typically seen on an axial scan
  • fetal extremities may be seen in a "crossed legged tailor" position or a "Buddha" position 
  • in an early scan (1st trimester), the crown-rump length may be less than expected for gestational age as an indirect feature
  • shows similar features to those on ultrasound but in more detail
  • useful to assess canal stenosis
  • a characteristic wedge-shaped cord terminus may be seen

Imaging allows the differentiation of two broad groups of patients with caudal regression syndrome :

  • group 1:
    • the conus medullaris is blunt and terminates above the normal level; there is sometimes an associated dilated central canal or a cerebrospinal fluid-filled cyst at the lower end of the conus
    • these patients have major sacral deformities
  • group 2:
    • the conus medullaris is elongated and tethered by a thickened filum terminale or intraspinal lipoma and ends below the normal level. Neurologic disturbances are more severe in this group

Treatment and prognosis

Both treatment and prognosis depend on the extent of regression. Morbidity is mainly of genitourinary and neuromuscular complications and management options are often centered around these with both urological and orthopedic input.

Differential diagnosis 

General imaging differential considerations include:

On antenatal ultrasound also consider:

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