Screening and Diagnosis of Spina Bifida
Spina bifida screening during pregnancy should be performed using maternal serum alpha-fetoprotein (AFP) at 16-18 weeks gestation, with ultrasound examination of the fetal spine and posterior fossa being the primary diagnostic modality, while newborn screening relies on physical examination of the spine immediately after birth.
Prenatal Screening
First Trimester (11-14 weeks)
Ultrasound examination of the posterior fossa can detect open spina bifida with 100% sensitivity in expert hands 1. Key markers include:
- Intracranial translucency (IT): Complete absence detected in 18% of open spina bifida cases 1
- Cisterna magna (CM): Obliteration or non-visualization of the fourth ventricle is the most sensitive intracranial sign, with detection rates of 64% when absent and 73% using cut-off values 1
- Brainstem parameters: Less predictive but should be assessed 1
First trimester detection rates are 100% for open spina bifida but only 28.5% for closed spina bifida, as closed defects lack the characteristic intracranial signs 2.
Second Trimester (15-20.9 weeks)
Maternal serum AFP screening is optimal at 16-18 weeks gestation but acceptable between 15.0 and 20.9 weeks 3. This is a screening test, not diagnostic 3.
Critical Technical Requirements:
- Gestational age determination: Ultrasound dating (particularly biparietal diameter) is superior to last menstrual period dating and significantly improves detection of open spina bifida 3
- Express gestational age as weeks and days (e.g., 15.7 weeks) rather than rounded weeks to improve screening performance 3
- Adjust AFP values for maternal weight to optimize screening performance 3
Ultrasound Anatomy Scan:
The second trimester anatomy scan should evaluate for:
- Chiari type II malformation signs 4:
- Ventriculomegaly
- "Lemon sign" (scalloping of frontal bones)
- "Banana sign" (backward and caudal displacement of cerebellar vermis with obliteration of cisterna magna)
- Direct spine examination: Thorough evaluation of the entire spine for defects, including position and morphology of the conus medullaris 5
Important caveat: Closed spina bifida and spina bifida occulta will NOT show cranial or posterior fossa features because they lack cerebrospinal fluid leakage, making direct spine examination essential 4.
Advanced Imaging
Two-dimensional and three-dimensional ultrasound in tertiary centers can accurately determine the location, type, extent, and upper level of spinal defects 4.
Fetal MRI should be restricted to candidates for intrauterine surgery as part of the preoperative protocol 4. Antenatal ultrasound correlates better with postnatal findings than MRI for determining lesion level (67% vs 50%) and ventriculomegaly (100% vs 63%) 6.
Diagnostic Confirmation
When maternal serum AFP screening is positive, diagnostic testing includes 3:
- Genetic counseling
- High-resolution ultrasound
- Amniocentesis with measurement of amniotic fluid AFP and acetylcholinesterase (AChE)
The combination of amniotic fluid AFP, AChE, and ultrasound is diagnostic for open neural tube defects 3.
Newborn Screening and Diagnosis
Physical examination of the newborn spine immediately after birth is the primary method for detecting spina bifida in newborns 7.
For confirmed cases, the CDC protocol recommends:
- Immediate postnatal evaluation including renal ultrasound and urodynamic studies 7
- Surgical repair: 99.4% of eligible cases undergo postnatal surgical repair, with significantly improved survival in recent cohorts (95.8% vs 85.9% in earlier eras) 8
- Ventriculoperitoneal shunt placement: Required in approximately 60% of infants with open defects 8
Postnatal Imaging Protocol:
- Ultrasound and urodynamic studies to assess bladder function 7
- MRI to confirm lesion level and assess for associated anomalies 6
Clinical Outcomes
Low spinal lesions are associated with significantly increased bladder morbidity compared to high spinal lesions (odds ratio 10.0), with 80% requiring intermittent catheterization at 12 months 6. Modern management achieves normal or mild motor deficits in 50% of cases and normal or mild sphincter dysfunction in 37.8% of cases, with intelligence quotient ≥70 in 81.4% of children 8.