Spinal Dysraphism Overview

Overview

This lecture provides an overview of spinal dysraphism, focusing on embryology, epidemiology, diagnosis, management, surgical techniques, and the distinction between open and closed neural tube defects.

Pathophysiology & Embryology

• Spinal dysraphism refers to congenital defects of the dorsal midline spinal structures due to incomplete neural tube closure.
• Neural tube closure occurs during the 3rd–4th week of embryonic development.
• Primary neurulation forms the spine to the lower lumbar region; failure leads to myelomeningocele and related defects.
• Secondary neurulation forms distal spinal segments below the lumbar region, involving canalization and regression.

Classification & Epidemiology

• Spinal dysraphism is classified as open (spina bifida aperta) or closed (spina bifida occulta).
• Myelomeningocele is the most common open neural tube defect (98% of cases).
• Incidence of spinal dysraphism is 0.05–0.25 per 1,000 live births; myelomeningocele: 0.1–0.2%.

Diagnosis & Clinical Features

• Diagnosis includes maternal serum alpha-fetoprotein (AFP), prenatal ultrasound, and fetal MRI.
• Typical findings: lumbosacral involvement, lower extremity dysfunction, urinary/fecal incontinence, hydrocephalus, Chiari II malformation.
• Closed defects may present with subcutaneous masses, cutaneous signs, or neurological dysfunction.

Management & Treatment

• Open neural tube defects require surgical closure within 24–48 hours after birth to prevent infection and further neurological decline.
• Fetal surgery offers reduced hydrocephalus risk and better lower extremity function but carries higher maternal and fetal risks.
• Post-op care includes prone positioning, head circumference monitoring, and evaluation for hydrocephalus and urologic function.

Associated Conditions & Outcomes

• Hydrocephalus develops in 60–90% of myelomeningocele cases; may require shunt placement or endoscopic intervention.
• Chiari II malformation can cause brainstem dysfunction and respiratory issues.
• Tethered cord syndrome may arise congenitally or secondarily (trauma, tumor, infection); requires clinical and radiological correlation.
• Up to 50% are ambulatory with bracing; 75–85% achieve dryness with catheterization; a small percentage have normal continence.

Closed Neural Tube Defects

• Subclassified based on presence/absence of a dorsal mass (e.g., lipomyelomeningocele, meningocele, dermal sinus tract).
• Usually managed conservatively unless risk for infection or symptoms of spinal cord tethering are present.
• Typical signs: midline cutaneous stigmata (dimple, lipoma, hairy patch, hemangioma), scoliosis, limb discrepancies, and anorectal anomalies.

Key Terms & Definitions

• Spinal dysraphism — umbrella term for congenital spinal midline defects due to faulty neural tube closure.
• Myelomeningocele — open spinal defect with exposed neural tissue and meninges.
• Spina bifida occulta — closed spinal defect, often asymptomatic, with intact overlying skin.
• Tethered cord syndrome — abnormal fixation of the spinal cord causing neurological deficits.
• Chiari II malformation — herniation of cerebellar and brainstem tissue through foramen magnum.

Action Items / Next Steps

• Review embryological development and classification of spinal dysraphism.
• Read about the MOMS trial on fetal myelomeningocele surgery.
• Study the clinical presentation and management protocols for open and closed neural tube defects.