Neural Tube Defects - Paediatric Neurology

Neural Tube Defects

·        A neural tube defect – failure of closure of the neural tube (4 weeks gestation – often already happened by the time a woman knows she‟s pregnant)

·        At lower ends leads to spina bifida and at upper end anencephaly or encephalocele

·        Rate varies on population. High in Irish, Welsh, Scottish (3%) and those from poor backgrounds (poor nutrition, ¯folate, etc)

·        Multifactorial causes: · Genetic

o  Environmental (eg diet)

o  Drug associations (eg antiepileptics)

·        Any midline lesion of the skin overlying the CNS from the nose to the sacrum may indicate a lesion below the skin (same embryological origin) – eg hair, pigmentation, etc

Types

·        Myelomeningocele:

o  Most common: 90% of spina bifida, failure of caudal closure of neural tube ® failure of closure of skin and absence/leaking of the dura/meninges. 

o  Lumbar sacral (25%), lumbar or thoracolumbar (50%) or thoracic/cervical (11%).

o  Spinal cord opened out flat.  Variable neuro deficit below lesion.  Possible tethering

o  Leads to: 

§  Paraplegia: paralysis of knee and hip extensors with retained flexion. Talipes (club foot) – equinovarus is commonest

§  Variable loss of sensation 

§  Autonomic problems: faecal incontinence, dribbling urinary incontinence on lifting baby or spastic urethral sphincter (® urinary retention), spastic bladder (® reflux, hydronephros)

§  Open lesion ® risk of ascending infection 

§  Hydrocephalus: very common (Arnold-Chiari malformation). Dislocation of cerebella tonsils and medulla into cervical canal, aqueduct stenosis (?primary lesion or tethering). Signs of hydrocephalus and ­ICP: bulging fontanelles, rapid head growth, poor feeding, separation of sutures, „sun-setting eyes‟ (looking down), drowsiness, venous congestion of skull. If acute: vomiting, bradycardia, hypertension

o  Management:

§  Interdisciplinary team

§  Close back to prevent infection

§  Drain hydrocephalus (ventriculoperitoneal shunt)

§  Bladder and bowel management

§  Review motor and sensory function, prevent contractures and aid mobility

§  Etc

·        Spina Bifida Occulta: Range from failure of formation of dorsal spine (cord intact) to abnormal cord contents

·        Diastematomyelia: bone or cartilage spur into the cord ® progressive loss of spinothalamic function (pain and temperature) with growth (slices as spine elongates). Not common. Leads to regression of acquired skills.

·        Lipoma: fatty mass ® pressure effects

·        Tethered cord: complication of many types. Cord fixed lower down and gets stretched as spinal column grows ® loss of power, sensation and autonomic function (ie sphincter function, weakness in toes and forefoot, saddle anaesthesia)

·        Dorsal Dermal Sinus: Epithelium lined tube from skin (lumbar/sacral) to dura or into spinal canal. Risk of meningitis (coliform) and tethered cord

·        Meningocele: 

o  Rarer. Swollen lesion on back, full of CSF, brilliant translumination. Little neurological deficit, risk of tethering

o  Cranial meningocele: occurs on skull and contains CSF

·        Encephalocele: occurs on skull and contains brain.  Prognosis more guarded

·        Anencephaly: Failure of cephalic closure of neural tube ® absence of cranium. Frequent polyhydramnios. Most live births die within 24 hours. Also occurs in other syndromes (Þ always do karyotype)

Prevention

·        Folic acid levels in pregnant women only half the recommended

·        Recurrence after one affected child is 3 – 5% (?inborn error of folate metabolism)

·        Low dose folate prophylaxis highly effective – but 50% pregnancies unplanned

·        Adequate dietary intake hard (5 portions of broccoli a day!) 

·        Can detect with antenatal ultrasound or ­maternal or amniotic fluid alpha-fetoprotein