Neural Tube Defects

Spina Bifida

Spina Bifida is a midline defect of the spine resulting in the exposure of the contents of the neural canal

Incidence: 3 per 1000 births
Pathogenesis

Occulta: Vertebral schisis covered by normal soft tissues Large defects are associated with pigmented & dimpled overlying skin & subcutaneous lipomas

Aporta Ful – thickness defect of the skin, underlying son Essues & vertebral arches. exposing the neural canal. Defect is usually covered by a thin meningeal membrane giving the appearance of a cystic tumor if the mass contains spinal fluid and meningeal tissue, it is Meningocele and if it contains neural tissue, it is Myelomeningocele.

Associated anomalies: Hydrocephalus, Amold-Chlari, Holoprosencephaly, Agenesis of the Corpus Callosum, Paymicrogyria, Clubfoot, Dislocation of the hip, chromosomal abnormalities

Diagnosis : Lateral processes are splayed apart and neural canal is exposed posteriorly on transverse view. Posterior line and overlying soft tissues are absent at the level of esion on sagittal scan: Disappearance of the central line and widening of the two external lines on coronal view

Bananasion – Flat and curved cerebellar hemispheres.

Lemon sign – Scalloping deformity of the frontal calvarium anomalies

Prognosis: Worst for the lesions localized high in the spine and with associated

Recurrence risk: 2-3 per 100 after first affected child, 6.7per 100 after two affected children

Hydrocephalus

Hydrocephalus is dilatation of the fetal ventricular system not secondary to brain atrophy associated with increased intraventricular pressure.

Incidence: 0.3-1.5 per 1000 births.

Pathogenesis: Communicating (Non obstructive): Commonest type of Hydrocephalus, secondary to either abnormality of the arachnoid vill or over production of CSF by choroid plexus beyond the ability of the arachnold villi to absorb it.

Non communicating (Obstructive): It is secondary to either aqueductal stenosis or impedance of CSF flow through the foramina of fourth ventricle. Usually progressive.

Associated anomalies: Spina bifida, Meningocele, Encephalocel, Arnold-Chiari malformation, Hydronephrosis, Dysplastic kidneys Ventricular septal defects, Tetralogy of Fallot, Hypoplastic left heart syndrome, Omphalocele Gastroschisis, Tracheo-esophageal fistula, Malrotation of the bowel, Downs syndrome.

Diagnosis: Atrial width of more than 15 mm in the second and third trimesters.Gross dilatation of lateral ventricles. Shrinkage of the normally prominent choroid plexus within the body of the Lateral ventricle (Dangling choroid). Ventriculomegaly can be seen as an isolated anomaly.

Prognosis: Unilateral communicating ventriculomegaly has good prognosis. Progressive Hydrocephalus and Hydrocephalus with associated anomalies has bad prognosis

Recurrence rate: 1-4% for communicating hydrocephalus.

Anencephaly

Anencephaly is absence of the brain with functional neural tissue associated with absence of cranial vault.

Pathogenesis: Failure of the neural tube to completely close at its cephalic end.

Incidence: 1 in 1000 births.

Associated anomalies: Meningocele, Myelomeningocele, Spinabifida, Cleft palate, Umbilical hernia.

Diagnosis: Inability to identify cranial vault by 12 to 14 wks. Absence of normal bony structure and brain tissue cephalad to the orbits.

Prognosis: Lethal.

Recurrence: 5% after one affected child.
3% after two affected children.