Paediatrics: CNS malformations

CNS malformations

Overall incidence 74–5/10 000 births. There has been a dramatic fall in last 50yrs.

Neural tube defects

•   Failure of primary neural tube closure during 4th week of gestation.

·  Prevalence decreasing due to:

•   prenatal diagnosis (iAFP, USS) leading to termination;

•   maternal periconceptual folate therapy

Anencephaly 

Lethal condition comprising absence of skull bones, fore-brain and upper brain-stem.

Encephalocele 

Midline skull defect with brain tissue herniation. The lesion is covered with skin and requires surgical excision and closure. Associated brain abnormality usually leads to poor neurodevelopment.

Spina bifida

Several types, all secondary to failure of midline fusion of dorsal vertebral bodies. All forms require specialist advice and treatment.

•   Spina bifida occulta: no herniation of neural tissue. Often overlying dermal sinus, dimple, lipoma, or hairy naevus is present (perform spinal US or MRI). Associated with diastematomyelia or cord tethering.

•   Meningocele: herniation of meninges and fluid only with skin covering. Requires surgical closure. Excellent prognosis.

Myelomeningocele: herniation of spinal neural tissue, which may be covered by meninges/skin or be open. Adjacent spinal cord is always abnormal. Usually thoraco-lumbar, lumbar, or lumbo-sacral.

•   problems include—flaccid paralysis below the lesion; urinary and faecal incontinence; urinary tract dilatation; hydrocephalus; bulbar paresis secondary to Chiari malformation; and vertebral anomalies (e.g. kyphosis);

•   treatment—surgical closure and hydrocephalus drainage;

•   prognosis —related to severity of associated problems. Prognosis worst if lesion very large or high. Palliative care may be appropriate.

Congenital hydrocephalus

Excessive head growth caused by CSF accumulation.

•   Causes: congenital (aqueduct stenosis, Dandy–Walker malformation, congenital infection, e.g. CMV, cerebral tumour); acquired (IVH, subarachnoid haemorrhage, CNS infection, e.g. meningitis).

•   Features: OFC above the 97th centile with wide cranial sutures and bulging fontanelle, ‘sun-setting’ sign of eyes.

·  Confirmed by cranial US or MRI.

·  Treatment: surgical insertion of indwelling drainage device, e.g. ventriculo-peritoneal shunt.

Dandy–Walker malformation

·  Cerebellar vermis hypoplasia associated with:

·  hydrocephalus;

posterior fossa CSF collection (‘cyst’) expanding into 4th ventricle.

·Associated with variety of syndromes: foetal alcohol, trisomy 13 + 18.

·Prognosis: depends on associated abnormalities/underlying condition.

Agenesis of the corpus callosum

·Non-specific feature of numerous conditions and is associated with a wide variety of conditions.

·May be total or partial.

·May be incidental finding.

·Prognosis depends on associated syndromes/features.

Hydrancephalus

·Absence of cerebral hemispheres with cavity filled with CSF. Brainstem and midbrain are usually spared.

·Cause: severe (vascular) cerebral insult leading to extensive cortical necrosis.

·Prognosis: usually lethal. Survivors have severe neurodevelopmental impairment.

Microcephaly

OFC progressively falls below 3rd centile.

·Primary defect is reduction in brain size.

·Causes: intrauterine infection, chromosomal defects, various syndromes, maternal drug/alcohol abuse, brain injury.

·Prognosis: generally poor neurodevelopmental outcome.

Holoprosencephaly

Severe developmental defect of the forebrain. There is a single central cerebral ventricular cavity with varying degrees of development and sepa-ration of the hemispheres. Midline facial defects are common. May be isolated or associated with chromosomal defects, particularly trisomy 13. Poor prognosis.

Neuronal migration defects

Includes lissencephaly (smooth brain), pachygyria (very few gyri), poly-microgyria (numerous underdeveloped gyri), schizencephaly (deep cere-bral cleft), neuronal heterotopia (foci of neurones in abnormal locations within the brain). All are associated with poor neurodevelopmental out-come and seizures, but eventual outcome is dependent on severity of malformation.