• Medical textbook library - I have access to a curated library of authoritative medical textbooks that I can search and cite directly, covering pharmacology, pathology, anatomy, clinical medicine, and more.
• PubMed integration - I can search peer-reviewed literature in real time and pull abstracts, systematic reviews, RCTs, and guidelines.
• Clinical depth - I'm set up to prioritize medical sources before answering health questions, rather than just relying on general training data.

• I take medical questions seriously and cite sources
• I won't fabricate drug doses, guidelines, or study results
• I'll say "I don't know" when I'm uncertain rather than guess

Schizencephaly

Definition

Types: Open-Lip vs. Closed-Lip

• Grainger & Allison's Diagnostic Radiology

Pathogenesis

• Genetic: May occur as a Mendelian or sporadic genetic trait. Previously thought to involve the EMX2 gene, but this has been disproven (Tietjen et al., 2007); the exact genetic basis remains unknown.
• Fetal vascular insult: Can result from porencephaly due to fetal cerebral infarction.
• Intrauterine infection: CT may show subependymal or parenchymal calcification, suggesting a cause such as CMV (cytomegalovirus) infection.
• Bradley and Daroff's Neurology in Clinical Practice

Associated Cortical Abnormalities

• Polymicrogyria - multiple small, abnormal gyri along the cleft margins
• Lissencephaly/pachygyria - may coexist to a variable degree
• The contralateral hemisphere may also show developmental abnormalities such as polymicrogyria and subependymal heterotopia
• The cortex appears thicker than normal on MRI due to the presence of polymicrogyria
• Grainger & Allison's Diagnostic Radiology

Location

• Most commonly central - involving the pre- and post-central gyri (sensorimotor cortex)
• Can also occur in parasagittal, frontal, or occipital sites (often milder manifestations)
• Typically located in the general region of the Sylvian fissure, but it is not a true Sylvian fissure
• Unilateral in about half of cases

Clinical Features

• Seizures - common and often severe
• Spasticity
• Hemiplegia - especially with unilateral, narrow or closed-lipped clefts
• Severe intellectual and psychomotor developmental delay - particularly with bilateral clefts
• Wide clefts generally correlate with more severe neurodevelopmental impairment
• Grainger & Allison's Diagnostic Radiology

MRI Appearance

Diagnosis - Imaging

• MRI is the gold standard, especially coronal T1-weighted MRI (3D volume acquisition) - best for detecting closed-lip schizencephaly
• CT can diagnose most open-lip cases but may miss closed-lip variants
• MRI demonstrates the grey matter lining the cleft and the abnormal cortical mantle (polymicrogyria)
• CT may show subependymal/parenchymal calcification, raising suspicion for intrauterine CMV infection as a cause
• Grainger & Allison's Diagnostic Radiology

Differential Diagnosis

• Porencephaly (cavity lined by white matter/gliosis, not grey matter)
• Hydranencephaly
• Arachnoid cyst
• Holoprosencephaly
• Transmantle cortical dysplasia

Summary

A 2025 review in Brain (Russ et al., PMID 40048696) covers fetal malformations of cortical development including schizencephaly with updated clinical guidance - worth consulting for the most current management perspectives.

Neural Tube Defects (NTDs)

1. Definition and Overview

2. Embryological Basis

• Emery's Elements of Medical Genetics and Genomics

3. Classification and Types

A. Spina Bifida (Spinal NTDs)

• Isolated bony defect (failure of vertebral arch closure) with no herniation of neural contents
• Usually asymptomatic; skin overlies the defect
• AFP is typically normal (covered lesion)
• May have skin stigmata: tuft of hair, dimple, lipoma, birthmark

• Herniation of meninges and CSF only through the spinal defect - no neural tissue involved
• Uncommon
• Generally better prognosis than myelomeningocele

• Most severe and clinically significant form of spina bifida
• Sac contains spinal cord or other neural elements protruding through the posterior defect
• Neural tissue exposed to amniotic fluid → progressive injury throughout pregnancy
• Visible at birth as a midline back lesion
• Over 80% are located in the lumbosacral region, but can occur anywhere along the spine

• Open midline lesion with completely exposed neural elements flush with the skin - no covering sac
• Most severe form of open spinal NTD

Fig. - Sagittal T1-weighted MRI: myelocele (A) vs myelomeningocele (B). Goldman-Cecil Medicine

B. Cranial NTDs

• Failure of the cranial neural folds to close → vault of skull absent, brain exposed
• The malformed brain tissue is exposed to amniotic fluid, degenerates → leaves a mass of necrotic tissue (the brainstem remains intact)
• Associated with polyhydramnios (fetus lacks swallowing reflex in last 2 months)
• Occurs in ~1 per 5,000 births; more common in females
• Fatal - incompatible with survival for more than a few hours after birth
• Detectable on ultrasound (absent skull vault)

• Herniation of brain tissue and/or meninges through a defect in the skull
• Most commonly occipital region; may also be frontonasal
• Subtypes include meningocele (meninges only), meningoencephalocele (meninges + brain), and meningohydroencephalocele (meninges + brain + ventricle)
• Occurs in ~1 per 12,000 births
• Smaller defects may survive with surgery; degree of neurological deficit depends on amount of neural tissue lost

• Most severe NTD: anencephaly combined with a large defect of the cervical and thoracic spine
• Not compatible with survival
• Langman's Medical Embryology

4. Etiology and Risk Factors

Genetic Factors

• Chromosomal: Trisomy 13 and Trisomy 18 each carry ~5-10% NTD incidence; aneuploidy is present in ~10% of cases overall
• Syndromal: Meckel-Gruber syndrome (AR) - encephalocele + polycystic kidneys + polydactyly
• MTHFR gene mutations: 677C>T variant (OR = 1.34; 95% CI, 1.17-1.54)
• Associated syndromes: VATER/VACTERL (vertebral defects, imperforate anus, tracheoesophageal fistula, renal defects)
• Most isolated NTDs show multifactorial inheritance

Environmental / Maternal Risk Factors

• Creasy & Resnik's Maternal-Fetal Medicine

5. Diagnosis

Prenatal Screening

• Most open NTDs are associated with elevated MSAFP
• AFP may be normal in skin-covered lesions (spina bifida occulta)
• Elevated MSAFP should prompt detailed sonographic evaluation

• Defect in dorsal aspect of spine with overlying cystic mass (sagittal view)
• V- or U-shaped splaying of posterior vertebral elements (axial view)
• Absent posterior elements without cystic mass = myeloschisis

• Banana sign: Chiari II malformation with effacement of cisterna magna and caudal cerebellar retraction (50-100%)
• Lemon sign: Bifrontal scalloping/retraction of frontal bone (53-100%)
• Hypoplastic cerebellum (82-96%)
• Ventriculomegaly (atrial width ≥10 mm) - 45-89%
• Dolichocephaly, microcephaly, abnormal corpus callosum (70-90%)

• Abnormal posterior brain view in midsagittal plane (obliterated cisterna magna - only two rather than three fluid spaces visible) indicates high risk; should prompt early anatomy scan at 15-16 weeks

Fig. - Ultrasound (20 weeks GA) showing myelomeningocele. Yellow arrows indicate the posterior spinal defect with overlying cystic mass. Creasy & Resnik's Maternal-Fetal Medicine

• Adjunct to ultrasound; helps determine lesion level, extent of bony defect, and associated brain anomalies

Postnatal Diagnosis

• Open lesions (myelomeningocele, myeloschisis) are visible at birth as midline back lesions

6. Associated Anomalies

• Chiari II malformation (virtually universal with myelomeningocele)
• Hydrocephalus - common, often requiring ventriculoperitoneal shunting
• Scoliosis, clubfeet
• Bladder and bowel dysfunction (neurogenic bladder)
• Lower limb paralysis - severity depends on lesion level
• Cardiac, urogenital, craniofacial, and other structural anomalies in 15-30% of euploid fetuses
• Aneuploidy in ~10% (primarily trisomy 18, trisomy 13, triploidy)
• Creasy & Resnik's Maternal-Fetal Medicine

7. Prognosis

• Level and size of lesion (higher and larger = worse)
• Presence of ventriculomegaly and associated anomalies
• Aneuploidy
• Type and timing of surgical closure

8. Management

Prenatal (Fetal Surgery for Myelomeningocele)

• Prenatal repair was associated with improved motor skills, greater likelihood of independent walking, and reduced need for VP shunting at 30 months
• However, it carries significant risks: preterm labor, uterine bleeding, amniotic fluid leak
• Only performed in specialized centers with the experience and expertise - careful patient selection required
• Schwartz's Principles of Surgery

Postnatal Management

• Neurosurgery
• Urology (neurogenic bladder - clean intermittent catheterization)
• Orthopedics (scoliosis, clubfeet, hip dysplasia)
• Physiotherapy and rehabilitation
• Developmental/educational support

9. Prevention

• Evidence supports folic acid supplementation reducing NTD risk by approximately 50-70%
• Supplemental folic acid before conception reduces risk of recurrent open NTD by 70%
• Fortification of staple foods (bread, flour) with folic acid has contributed to falling NTD incidence worldwide

10. Genetic Counseling and Recurrence Risk

• First-degree relatives (siblings, offspring) of an affected individual have an empiric recurrence risk of 4-5% in high-prevalence populations
• NTDs occurring in the setting of chromosomal aneuploidy (trisomy 13/18) carry the recurrence risk associated with the chromosomal abnormality, not the isolated NTD risk
• Families should receive non-directive genetic counseling prior to future pregnancies
• Emery's Elements of Medical Genetics and Genomics

Summary Table