2d:I[856015,["/_next/static/immutable/chunks/1xzisbplk9czp.js","/_next/static/immutable/chunks/3j2i1faptc_-9.js","/_next/static/immutable/chunks/0fma7nlq6immz.js","/_next/static/immutable/chunks/08tq8rmv423j5.js","/_next/static/immutable/chunks/1chr5wkk3j58k.js","/_next/static/immutable/chunks/37kmmh_zm4dov.js","/_next/static/immutable/chunks/311zvdjfxff-f.js","/_next/static/immutable/chunks/1a_hqhrsle_n_.js"],"default"] 2e:T6791,

Summary Table

Category	Details
Risk Factors	Folate deficiency (most important), maternal use of valproic acid or carbamazepine, maternal diabetes mellitus, maternal obesity, prior child with neural tube defect, maternal hyperthermia in the first trimester
Etiology	Failure of the posterior (caudal) neuropore to close during the 4th week of embryogenesis (days 21 to 28)
Patient Presentation	Ranges from incidental finding on imaging (occulta) to a visible midline back mass at birth with lower extremity weakness, bowel/bladder dysfunction, and sensory loss below the level of the defect
Classic Physical Exam	Cystic midline lumbosacral mass (myelomeningocele), lower limb flaccid paralysis, absent deep tendon reflexes below the lesion, clubfoot deformities, patulous anus, a tuft of hair or dimple overlying the lumbosacral spine (occulta), increasing head circumference (hydrocephalus from Chiari II malformation)
Key Diagnostic Results	Elevated maternal serum alpha-fetoprotein (MSAFP) on second-trimester screening; prenatal ultrasound showing the "lemon sign" (frontal bone scalloping) and "banana sign" (cerebellar compression); elevated amniotic fluid AFP and positive acetylcholinesterase on amniocentesis; postnatal MRI of the spine and brain
Management	Prevention with folic acid (0.4 mg/day for all women; 4 mg/day for high-risk women), surgical closure of open defects within 24 to 72 hours of birth, ventriculoperitoneal shunt placement for associated hydrocephalus, clean intermittent catheterization for neurogenic bladder, long-term multidisciplinary follow-up
Keywords	"Midline lumbosacral mass," "tuft of hair over the spine," "elevated MSAFP," "lemon and banana signs," "Chiari II malformation," "folate deficiency," "neural tube defect," "lower extremity paralysis at birth"

1. Pathophysiology

Neural tube closure is one of the earliest and most critical events in human embryogenesis. The process begins around day 21 and is completed by day 28 of gestation. The neural plate folds inward and fuses in a bidirectional, zipper-like fashion from the center toward both ends. The anterior (rostral) neuropore closes around day 25, while the posterior (caudal) neuropore closes around day 28. Spina bifida results from a failure of this caudal closure.

The underlying biochemistry centers on folate metabolism. Folic acid serves as a one-carbon donor in the synthesis of purines and thymidylate, which are essential building blocks for DNA replication. It also participates in methylation reactions that regulate gene expression during neural tube closure. When folate is deficient, the rapidly dividing cells of the neural plate cannot replicate their DNA efficiently, and the caudal neuropore fails to fuse. This explains why folate supplementation before conception is the single most effective preventive measure.

Valproic acid and carbamazepine are teratogenic because they interfere with folate metabolism through inhibition of folate absorption and increased folate catabolism. This is why women on these medications require higher-dose folate supplementation and ideally a switch to a less teratogenic antiepileptic before conception.

The neurological deficits in spina bifida correlate directly with the level of the vertebral defect. Because the spinal cord and nerve roots are exposed or herniated through the bony defect, all motor and sensory function below that level may be compromised. A lesion at L3 to L5 causes flaccid paralysis of the lower limbs, loss of sensation, and dysfunction of bowel and bladder (both are innervated by sacral nerve roots S2 to S4). Higher lesions produce more extensive deficits.

A key associated anomaly is the Chiari II malformation (also called Arnold-Chiari malformation), which is present in nearly all cases of myelomeningocele. During fetal development, cerebrospinal fluid (CSF) leaks out through the open spinal defect, reducing intracranial pressure and causing the posterior fossa to be underdeveloped. The cerebellar tonsils and vermis herniate downward through the foramen magnum, obstructing CSF flow and leading to obstructive hydrocephalus. This is why infants with myelomeningocele are monitored closely for a rapidly increasing head circumference.

2. Classification and Clinical Manifestation

Type	Defect	Neural Involvement	Skin Covering	Clinical Features
Spina Bifida Occulta	Incomplete fusion of the posterior vertebral arch (usually L5 or S1), no herniation	None; spinal cord and meninges remain in normal position	Intact skin; often marked by a tuft of hair, dermal sinus, dimple, or lipoma overlying the defect	Usually asymptomatic and found incidentally on imaging; occasionally causes tethered cord syndrome later in life
Meningocele	Bony vertebral defect with herniation of meninges only	No neural elements in the sac; the sac contains only CSF	Covered by a thin membrane or skin	Visible cystic midline mass; typically no neurological deficit because the spinal cord is not involved; transillumination of the sac is positive
Myelomeningocele	Bony defect with herniation of both meninges and spinal cord or nerve roots	Neural tissue (spinal cord and/or nerve roots) is present within the sac	Thin membrane, often ruptured or partially skin-covered	Motor and sensory deficits below the lesion level, neurogenic bladder and bowel, orthopedic deformities (clubfoot, hip dislocation), nearly always associated with Chiari II malformation and hydrocephalus
Myeloschisis (Rachischisis)	Complete failure of neural tube closure; open neural plate exposed directly to the surface	Unfused neural plate lies flat on the surface	No covering at all	Most severe form; profound neurological deficits; high risk of infection and CSF leak; often accompanied by other congenital anomalies

Spina bifida occulta is the mildest and most common form. It is often discovered incidentally on a lumbosacral X-ray obtained for another reason. The overlying skin markers (tuft of hair, dimple, hemangioma) are tested frequently as clues in vignettes. Despite its benign nature, occulta can occasionally cause a tethered spinal cord, presenting later in childhood or adolescence with progressive gait abnormality, back pain, scoliosis, and bladder dysfunction.

Myelomeningocele is the most clinically significant and most commonly tested form. A key teaching point: if you see a newborn with a lumbosacral cystic mass AND neurological deficits, the answer is myelomeningocele, not meningocele. Meningocele preserves neurological function because the neural tissue is not herniated.

3. Diagnostic Workup

Test	Purpose	Timing	Key Findings
Maternal serum alpha-fetoprotein (MSAFP)	Best initial screening test	Second trimester (15 to 20 weeks)	Elevated in open neural tube defects (myelomeningocele, myeloschisis); normal in spina bifida occulta and closed (skin-covered) meningocele
Prenatal ultrasound	Anatomical visualization; most common modality for detection	Second trimester (18 to 22 weeks, anatomy scan)	"Lemon sign" (frontal bone scalloping) and "banana sign" (curved, compressed cerebellum) indicate Chiari II malformation; direct visualization of the spinal defect and cystic mass
Amniocentesis	Confirmatory test when screening is abnormal	After abnormal MSAFP or equivocal ultrasound	Elevated amniotic fluid AFP and positive acetylcholinesterase (AChE) confirm an open neural tube defect
Fetal MRI	Detailed anatomical assessment	When surgical planning or confirmation is needed	Superior soft tissue contrast; evaluates the extent of the lesion, degree of Chiari II malformation, and presence of hydrocephalus
Postnatal MRI of spine and brain	Gold standard for postnatal evaluation	After birth	Defines the anatomy of the defect, location and extent of neural tissue herniation, presence of hydrocephalus, Chiari II malformation, tethered cord, or syringomyelia
Postnatal head ultrasound	Hydrocephalus screening	Immediately postnatal and in follow-up	Ventricular enlargement indicating developing hydrocephalus
Voiding cystourethrogram (VCUG) and renal ultrasound	Assess for neurogenic bladder complications	Early postnatal period	Vesicoureteral reflux, hydronephrosis, bladder wall thickening

The first clue in most exam vignettes is an elevated MSAFP on the routine second-trimester "quad screen." MSAFP is the best initial screening test for open neural tube defects. The AFP is produced by the fetal liver and yolk sac. When the neural tube is open, AFP leaks freely from exposed neural tissue into the amniotic fluid and then crosses into the maternal circulation. This is why closed defects (spina bifida occulta, skin-covered meningocele) do not elevate MSAFP, and why understanding the distinction between "open" and "closed" defects is critical.

When MSAFP is elevated, the next step is a targeted prenatal ultrasound. The ultrasonographer looks for intracranial signs of Chiari II malformation (lemon sign, banana sign, ventriculomegaly) and directly visualizes the spinal defect. Ultrasound is now highly sensitive for detecting myelomeningocele when performed at experienced centers.

If ultrasound findings are equivocal or need confirmation, amniocentesis is performed. The key finding is elevated amniotic fluid AFP combined with a positive acetylcholinesterase (AChE). AChE is released from exposed neural tissue and is more discriminating than AFP alone because AFP can be elevated for other reasons (abdominal wall defects such as gastroschisis and omphalocele, fetal demise, twin gestation). Positive AChE in the setting of elevated AFP is highly confirmatory for an open neural tube defect.

After birth, MRI of the spine and brain is the gold standard. It precisely defines the level and extent of the defect, the presence and degree of Chiari II malformation, hydrocephalus, and any associated findings such as tethered cord or syringomyelia. A head ultrasound is performed early to monitor ventricular size, and urological evaluation (renal ultrasound and VCUG) is initiated to assess for neurogenic bladder and vesicoureteral reflux, which if untreated can lead to recurrent urinary tract infections, hydronephrosis, and renal damage.

4. Management and Treatment

Setting	Intervention	Details
Primary prevention	Folic acid supplementation	0.4 mg (400 mcg) daily for all women of childbearing age starting at least 1 month before conception and continued through the first trimester; 4 mg daily for women with a prior affected pregnancy, on antiepileptic drugs, or with diabetes
Prenatal surgical repair (select cases)	In utero myelomeningocele closure	Performed between 19 and 25 weeks of gestation at specialized centers; reduces the need for postnatal shunting and improves motor outcomes (based on the MOMS trial)
Immediate postnatal care	Wound protection and infection prevention	Cover the open defect with a sterile, saline-moistened, nonadherent dressing; position the infant prone or lateral to avoid pressure on the sac; administer prophylactic antibiotics
Definitive surgical closure	Postnatal repair of myelomeningocele	Within 24 to 72 hours of birth to reduce the risk of meningitis and further neural damage
Hydrocephalus management	Ventriculoperitoneal (VP) shunt or endoscopic third ventriculostomy (ETV)	Required in approximately 80% to 90% of myelomeningocele patients; monitor head circumference and fontanelle closely
Neurogenic bladder	Clean intermittent catheterization (CIC)	Started early in infancy; oxybutynin may be added for detrusor overactivity; regular renal ultrasound to monitor for hydronephrosis
Neurogenic bowel	Bowel program	Scheduled toileting, dietary fiber, stool softeners, rectal stimulation, or antegrade continence enema (Malone procedure) in refractory cases
Orthopedic care	Bracing and corrective surgery	Clubfoot correction (serial casting or surgery), hip stabilization, scoliosis monitoring, wheelchair and mobility aids
Long-term follow-up	Multidisciplinary clinic	Neurosurgery, urology, orthopedics, physical therapy, developmental pediatrics; monitor for tethered cord syndrome, shunt malfunction, latex allergy, and psychosocial needs

Prevention is the highest-yield management concept. All women of childbearing age should take folic acid 0.4 mg daily regardless of whether they are planning a pregnancy, because neural tube closure occurs by day 28, often before pregnancy is recognized. Women at high risk (prior pregnancy affected by a neural tube defect, maternal use of valproic acid or carbamazepine, pregestational diabetes) require a ten-fold higher dose of 4 mg daily, starting at least one month before conception and continued through the first 12 weeks of gestation.

Prenatal repair was validated by the Management of Myelomeningocele Study (MOMS trial), which demonstrated that fetal surgery performed between 19 and 25 weeks of gestation reduced the incidence of hydrocephalus requiring shunting (from 82% to 40%) and improved motor function at 30 months compared to postnatal repair. However, prenatal repair carries risks including preterm premature rupture of membranes and preterm delivery, and it is performed only at experienced fetal surgery centers with strict inclusion criteria.

At birth, the immediate priorities are wound protection and infection prevention. The defect must be kept moist with sterile saline-soaked nonadherent gauze. The infant is positioned to keep pressure off the sac. Broad-spectrum antibiotics are initiated to prevent meningitis. Definitive surgical closure is performed within 24 to 72 hours. Delay beyond this window significantly increases the risk of central nervous system infection and progressive neurological deterioration.

Hydrocephalus develops in the majority of myelomeningocele patients due to Chiari II malformation. Clinical signs include a bulging anterior fontanelle, rapidly increasing head circumference, sunsetting eyes, irritability, and poor feeding. The standard treatment is a VP shunt. Families are counseled on recognizing signs of shunt malfunction (headache, vomiting, lethargy, bulging fontanelle), which is a neurosurgical emergency.

Neurogenic bladder is managed with clean intermittent catheterization, typically performed every 3 to 4 hours. The goal is to prevent urinary stasis, reduce the risk of urinary tract infections, preserve renal function, and achieve social continence. Anticholinergic medications such as oxybutynin may be added to reduce detrusor hyperactivity. Regular urodynamic studies and renal ultrasound are part of long-term surveillance.

One often-overlooked point: patients with spina bifida and repeated surgical exposures have a high incidence of latex allergy (due to repeated mucosal and wound exposure to latex-containing equipment). All patients with myelomeningocele should be maintained in a latex-free environment from birth.

5. Differential Diagnosis and Distractors

Differential	Why It Is Similar	Key Discriminator
Sacrococcygeal teratoma	Presents as a mass in the lumbosacral or coccygeal region at birth	Located at the coccyx/buttock area rather than the midline spine; contains mixed solid and cystic components on imaging; elevated AFP is from the tumor (yolk sac component), not from an open neural tube; no intracranial lemon/banana signs
Encephalocele	Also a neural tube defect with elevated MSAFP	The defect is in the skull (occipital region) rather than the spine; the mass protrudes from the head, not the back
Gastroschisis	Elevated MSAFP on screening, just like an open neural tube defect	Abdominal wall defect with bowel herniation through a paraumbilical defect (to the right of the umbilicus); no spinal or intracranial findings; AChE on amniocentesis can also be elevated, but ultrasound clearly shows an abdominal wall defect, not a spinal one
Omphalocele	Also an abdominal wall defect causing elevated MSAFP	Herniated abdominal contents are covered by a membranous sac at the umbilicus; associated with trisomies (13, 18) and Beckwith-Wiedemann syndrome; no spinal defect
Tethered cord syndrome	Progressive lower extremity weakness, gait changes, and bladder dysfunction in a child	Typically presents later in childhood, not at birth; no visible back mass; MRI shows a low-lying conus medullaris (below L2 in older children); may be a late complication of repaired spina bifida occulta
Caudal regression syndrome (sacral agenesis)	Lower extremity weakness and bladder dysfunction in a newborn	Strongly associated with maternal diabetes; X-ray shows partial or complete absence of the sacrum; no cystic back mass or elevated MSAFP; lower limbs may show a characteristic "frog-leg" posture

6. Traps and High-Yield Pearls

The most common way students lose points on spina bifida questions is by confusing the prenatal screening pathway. When a vignette presents an elevated MSAFP, many students jump directly to amniocentesis. However, the correct next step after an elevated MSAFP is a targeted ultrasound, not amniocentesis. Ultrasound is noninvasive, readily available, and can often confirm the diagnosis. Amniocentesis is reserved for cases where the ultrasound is inconclusive.

Another frequent trap involves distinguishing meningocele from myelomeningocele. Both present as a back mass, but the vignette will include neurological deficits (paralysis, absent reflexes, bladder dysfunction) only in myelomeningocele. If the child has a back mass but normal neurological function, the answer is meningocele. If there are deficits, it is myelomeningocele.

Students also commonly forget that spina bifida occulta does not elevate MSAFP because the defect is closed (covered by intact skin). If a vignette describes an incidental finding of a tuft of hair or dimple over the lumbosacral spine in an otherwise normal child, the diagnosis is spina bifida occulta, and the MSAFP would be normal.

The folic acid dosing distinction is tested repeatedly: 0.4 mg for the general population versus 4 mg for high-risk women. Getting the dose wrong (or the timing wrong) is a common error. Supplementation must begin before conception because the neural tube has already closed by the time most women realize they are pregnant.

Finally, always think about Chiari II malformation and hydrocephalus when you see myelomeningocele. These are nearly inseparable associations. If a vignette describes a neonate with a repaired myelomeningocele who then develops irritability, vomiting, and a bulging fontanelle, the diagnosis is hydrocephalus (likely from shunt malfunction or progressive Chiari II obstruction), and the next step is imaging followed by neurosurgical intervention.

The core competency being tested across all spina bifida questions is the ability to link embryology to clinical presentation, correctly sequence the prenatal workup, and recognize the downstream complications that require lifelong multidisciplinary management.

1e:["$","$L2d",null,{"article":{"id":"2ed9b15f-0609-409e-a487-fdb0ad0b1dfc","title":"Spina Bifida","content":"$2e","category":"Neurologi","created_at":"2026-07-18T08:07:19.762151+00:00","status":"published","subcategory":null},"questionCount":2,"sections":[{"id":"section-pathophysiology","num":"01","title":"Pathophysiology"},{"id":"section-classification-and-clinical-manifestation","num":"02","title":"Classification and Clinical Manifestation"},{"id":"section-diagnostic-workup","num":"03","title":"Diagnostic Workup"},{"id":"section-management-and-treatment","num":"04","title":"Management and Treatment"},{"id":"section-differential-diagnosis-and-distractors","num":"05","title":"Differential Diagnosis and Distractors"},{"id":"section-traps-and-high-yield-pearls","num":"06","title":"Traps and High-Yield Pearls"}],"hasSummaryTable":true}]