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Caudal Regression Syndrome (Sacral Agenesis): Causes, Spectrum & Management

Caudal regression syndrome (CRS), or sacral agenesis, is a rare congenital disorder (1:25,000 births) characterized by abnormal development of the caudal (lower) spine and associated structures. It represents a spectrum from mild sacral hypoplasia to complete absence of sacrum/lumbar vertebrae with lower limb anomalies.

Etiology & Risk Factors

  • Maternal diabetes (pre-gestational): Strongest association; 200–400× increased risk. Hyperglycemia disrupts mesoderm migration (weeks 4–7).
  • Genetic factors: HLXB9 (MNX1) mutations (Currarino syndrome); VANGL1, CELSR1 (neural tube closure); chromosomal anomalies (7q36, 17p13).
  • Environmental: Retinoic acid, hypoxia, teratogens (alcohol, smoking)—less defined.
  • Vascular disruption: Umbilical artery steal, aortic occlusion theories.

Clinical Spectrum (Renshaw Classification)

TypeFeatures
IUnilateral/bilateral sacral hypoplasia; normal lower limbs
IIBilateral sacral agenesis; femurs present, knees/feet deformed
IIILumbar + sacral agenesis; femoral hypoplasia, knee/ankle contractures
IVComplete caudal agenesis (thoracolumbar spine ends in iliac wings); "sirenomelia" spectrum

Associated Anomalies (Multisystem)

  • Genitourinary (90%): Neurogenic bladder, renal dysplasia, VUR, hypospadias, Müllerian anomalies.
  • Gastrointestinal: Imperforate anus, rectal atresia, malrotation.
  • Cardiac: VSD, ASD, TOF (up to 25%).
  • Neurological: Tethered cord, syringomyelia, Chiari malformation.
  • Musculoskeletal: Clubfoot, hip dislocation, knee contractures, limb deficiency.
  • VACTERL association overlap.

Diagnosis

  • Prenatal: Ultrasound (2nd trimester): absent/shortened sacrum, "fluttering" fetal legs, polyhydramnios, single umbilical artery. Fetal MRI for detail.
  • Postnatal: Clinical exam, spinal X-ray/MRI, renal US, echocardiogram, spinal ultrasound (infants).

Management (Multidisciplinary)

  • Neurosurgery: Tethered cord release, syrinx decompression.
  • Urology: Clean intermittent catheterization (CIC), anticholinergics, bladder augmentation, renal surveillance.
  • Orthopedics: Serial casting, tendon releases, osteotomies, prosthetics/orthotics for ambulation.
  • GI/surgical: Anorectal reconstruction, colostomy if needed.
  • Rehabilitation: PT/OT, mobility aids, adaptive equipment.
  • Nephrology: CKD monitoring.

Prognosis & Quality of Life

  • Highly variable by type and associated anomalies.
  • Type I–II: Often independent ambulation, normal lifespan, urologic management lifelong.
  • Type III–IV: Wheelchair-dependent; significant medical complexity; lifespan may be reduced by renal/urologic complications.
  • Early, coordinated care maximizes function and longevity.

CRS is a complex congenital condition requiring lifelong, multidisciplinary care. Advances in urologic management, neurosurgery, and rehabilitation have markedly improved outcomes.

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