15 Caudal Regression Syndrome

Clinical Presentation

An 8-month-old baby presents with anorectal malformation and sensorimotor deficit of the lower extremities.

Figure 15A

Radiologic Findings

The sagittal T1-weighted (Fig. 15A1) and T2-weighted (Fig. 15A2) MRI demonstrates agenesis of the lower sacrum and coccyx. The caudal spinal cord is dysplastic and wedge-shaped (arrow). This is due to the agenesis of the conus, which is metamerically consistent with the missing spine. There also is hydrosyringomyelia, and a lipoma of the filum terminale is noted (arrow) (Figs. 15A1 and 15A3). The axial T1-weighted MRI (Fig. 15A3) demonstrates a horseshoe kidney.

Diagnosis

Partial sacral agenesis, which is part of the so-called caudal regression syndrome

Differential Diagnosis

The terms sacral agenesis, or lumbosacral agenesis, or thoracolumbosacral agenesis (which are different degrees of the same defect) are purely descriptive and speak for themselves. The term caudal regression syndrome refers to a pathophysiology, which is only a postulate.
The “hemisacral agenesis,” or “scimitar sacrum,” is a sacral defect typically related to an anterior-lateral sacral meningocele. The expansion of the meningocele generates scalloping and lateral displacement of the sacral plate, but the sacral segments are present. The association of a scimitar sacrum, a presacral mass (meningocele or lipomeningocele, or teratoma), and ano-rectal malformation makes up the Currarino syndrome.
Sacral agenesis without spinal cord agenesis, or with tethered cord. The lower spine is lacking, whereas the cord is located below L1, its lower end being tapered instead of wedge-shaped. Although included in the group of caudal regression syndrome, this malformation may be a different entity, in which only the lower vertebral development is affected.
Other scalloping and deformity of the caudal spine may result from malformations primarily of the cord (terminal lipoma, terminal myelocystocele).
When the lower spine is off-midline, a false image of distal sacral agenesis is generated.

Discussion

Background

Caudal regression syndrome is a rare congenital defect, characterized by the absence of the caudal-most vertebrae and spinal cord. The defect may affect the caudal sacrum only, or it may extend upward as far as the thoracic spine, with functional defects and associated malformations in proportion with the extent of the agenesis. It may be associated with a fusion, and posterior rotation, of the lower limbs (“mermaid” appearance or sirenomelia). Other visceral malformations, especially of the pelvic organs, are common. The pathogenesis of the disorder is poorly understood. Maternal diabetes is a common factor, and insulin in excess has been shown to generate a similar malformation in the chick embryo. The role of segmentation gene defects is likely as well, as it is in other segmental spinal dysgeneses.