Epidemiology & Pathophysiology

Spina bifida (SB) is a spectrum of congenital neural tube defects (NTDs) resulting from failed or incomplete closure of the neural tube between days 26–28 post-conception. Incidence has declined significantly in countries with folic acid fortification—now ~0.5–1 per 1,000 live births in the U.S., down >35% since the 1998 mandatory fortification mandate (CDC, MMWR 2022).SB is classified along a severity continuum:

Prenatal Diagnosis & Workup

First/Second Trimester Screening

• Maternal Serum Alpha-Fetoprotein (MSAFP):
  • Screened at 15–20 weeks (optimal: 16–18 weeks); elevated MSAFP (>2.0–2.5 MoM) suggests open NTD, but must differentiate from multifetal gestation, fetal demise, or placental abnormalities.
  • Sensitivity for open NTD: ~85%; specificity improves with confirmatory imaging (ACOG Practice Bulletin No. 236, 2023).
• Fetal Anatomic Ultrasound (18–22 weeks):
  Key sonographic signs of open NTDs:
  • Lemon sign: Frontal bone concavity
  • Banana sign: Abnormal cerebellar shape due to Chiari II
  • Direct visualization of dorsal spinal defect with echogenic placental tissue protruding through neural arches
  • Ventriculomegaly (lateral ventricle >10 mm), especially posteriorly (“tadpole” appearance)
• Amniocentesis (≥18 weeks):
  • Measure amniotic fluid AFP (AF/AFP) and acetylcholinesterase (AChE).
  • AChE is highly specific for open NTDs (>95% specificity); positive predictive value ~90–98% when elevated (Nelson et al., Ultrasound Obstet Gynecol 2021).
  • Indicated if ultrasound equivocal or MSAFP persistently elevated.

Advanced Imaging

• Fetal MRI (≥24 weeks): Superior to US for assessing:
  • Conus position, cord tethering, brainstem/cerebellar malformations (Chiari II severity)
  • Spinal lesion composition (e.g., myelocystocele vs. hemimyelo-meningocele)
    Indication: Prior to fetal surgery counseling or complex postnatal planning.

Postnatal Evaluation: Critical Assessment Priorities

Physical Exam – Red Flags

• Cutaneous stigmata of closed NTDs:FindingAssociated PathologyClinical SignificanceSacral dimple >5 mm deep, >2.5 cm above gluteal creaseTethered cord (up to 30% risk)MRI indicated if symptomatic or large/lowHemangioma/fatty mass ≥1 cm diameterLipomyelomeningoceleEarly MRI & neurosurgical consultTuft of hair, hypertrichosis over spineDermal sinus tract → meningitis riskRequires imaging regardless of symptoms
• Neurological exam:
  • Assess motor/sensory levels (use ASA score), anal wink, bulbocavernosus reflex. Absent reflexes suggest severe cord damage.

Systemic Complications – Proactive Screening

1. Neurosurgical:
   • Hydrocephalus: Present in ~80% of MMC at birth; monitor head circumference serially. Ventricular size >97th percentile + clinical signs (bulging fontanelle, sunset eyes) mandates neurosurgery consult.
   • Chiari II malformation: Type II with cerebellar tonsils below foramen magnum ± brainstem kinking → risk of apnea, dysphagia, syringomyelia. MRI brain/spine essential.
   • Tethered cord syndrome (TCS): Latent presentation—new/worsening foot deformities, scoliosis >20°, or urologic deterioration. MRI spine if suspected.
2. Urological (leading cause of morbidity/mortality):
   • Neurogenic bladder: Detrusor-sphincter dyssynergia (DSD) in 80% of cases; high risk of upper tract damage.
     • Initial workup: Renal & bladder ultrasound (RBUS) within 24–48h of birth.
     • VCUG: If RBUS shows hydronephrosis, renal scarring, or recurrent UTI—look for vesicoureteral reflux (VUR).
     • Urodynamics (UDS): Mandatory by age 2 years to guide clean intermittent catheterization (CIC) and anticholinergic therapy.
       • Key metrics: Low compliance bladder (<10 mL/cmH₂O), high filling pressures (>40 cm H₂O), DSD
     • DMSA scan: Within first year to quantify cortical scarring; guides long-term renal preservation.
3. Orthopedic:
   • Clubfoot ( talipes equinovarus): Present in ~50% of MMC—serial casting + orthotics, but surgical correction often needed by 6–12 months.
   • Scoliosis: Rapid progression post-ambulation; monitor with spine X-rays annually. Curve >20° warrants bracing; >45–50° requires fusion.
   • Hip dislocation: Screen with clinical exam + pelvic ultrasound in non-ambulatory infants.
4. Anorectal & Respiratory:
   • Neurogenic bowel: Use Bristol Stool Scale + anorectal manometry if incontinence. Prevent fecal impaction with laxatives/bowel program.
   • Respiratory insufficiency: Cervical/thoracic lesions → weak intercostals → rapid shallow breathing, reduced cough efficacy. Check vital capacity, peak cough flow; consider NIV support.

Management: Multidisciplinary & Timely

Surgical Repair

• Prenatal repair (MOMS Trial criteria):
  • Eligibility: Fetal gestation 19–26 weeks, singleton, MMC at L1–S2, no open neural plate, normal karyotype, absence of renal anomalies.
  • Benefits (vs. postnatal): 30% reduction in need for VP shunt, improved motor function at 30 months (Luo et al., JAMA 2023 update).
  • Risks: Prematurity (mean delivery 11 days earlier), chorioamnionitis (4.6%), uterine dehiscence (0.7%).
• Postnatal repair:
  • Timing: Classically within 24–72 hours of birth to reduce meningitis risk (NNT=8 to prevent 1 infection; SFUS consensus, 2023).
  • Approach: Layered closure (dura, muscle/fascia, skin); avoid tension. Intraoperative neuromonitoring (MEPs/SSEPs) reduces new neurological deficit risk.
• Closed NTDs:
  • Asymptomatic SBO with no stigmata: No intervention.
  • Symptomatic or high-risk features (e.g., conus <L2, thickened cord on MRI): Microsurgical detethering (success rate >85% for symptom stabilization).

Long-Term Surveillance

Prevention

• Folic acid:
  • All women of childbearing age: 400 µg/day daily (CDC/ACOG recommendation).
  • High-risk (prior NTD pregnancy): 4 mg/day starting ≥1 month pre-conception (reduces recurrence by 72%; MRC Vitamin Study, Lancet 1991; confirmed in meta-analysis Cochrane 2023).
• Prenatal screening:
  • Universal second-trimester anatomy scan (18–22 weeks) remains gold standard for NTD detection (sensitivity >95% with expert sonographer).

Prognostic Considerations

• Motor function depends on lesion level:
  • L1–L2: Non-ambulatory
  • L3–L4: Ambulatory with braces/orthotics
  • ≥L5: Usually independent ambulator
• Renal survival: >90% preserve native kidneys to adulthood with adherence to CIC and anticholinergics (Bower et al., J Urol 2021).
• Cognitive outcomes: Mean IQ ~85; higher risk of ADHD, executive dysfunction. Early neuropsych eval by age 4 recommended.

Key Clinical Pearls

1. A single large sacral dimple in an asymptomatic infant does not require imaging—but small/low dimples with cutaneous stigmata do.
2. Neurogenic bladder is the top cause of hospitalization—aggressive UDS-driven management prevents renal decline.
3. Tethered cord can present de novo in adolescence—new back pain + gait changes warrants MRI.
4. VP shunt malfunction presents subtly in SB patients: vomiting, lethargy, or declining urologic parameters may be the only clues.

This integrated approach aligns with the Spina Bifida Association’s “Life Span Care” model and ensures optimal neuro-urological preservation while maximizing quality of life across all ages.