Congenital and Developmental Disorders

Neural Tube Defects - Tube Trouble Tales

• Failure of neural tube closure (3rd-4th week gestation).
• Key risk: Maternal folate deficiency. Others: valproate, maternal diabetes.
• Types:
  • Anencephaly: Anterior neuropore. "Frog-like" appearance. Polyhydramnios.
  • Spina Bifida (posterior neuropore):
    • Occulta: Vertebral defect, tuft of hair. AFP normal.
    • Meningocele: Meninges herniate.
    • Meningomyelocele: Meninges + neural tissue. Neurological deficits.
  • Encephalocele: Brain/meninges herniation through skull defect.
• Diagnosis: ↑ maternal serum AFP (MSAFP), ↑ amniotic fluid AFP & AChE (except occulta). Ultrasound.
• Prevention: Folic acid (0.4 mg/day; 4 mg/day high-risk).

⭐ Maternal folate deficiency is a major risk factor for Neural Tube Defects.

Forebrain Anomalies - Brain Building Blocks

• Holoprosencephaly (HPE): Failure of forebrain (prosencephalon) cleavage.
  • Spectrum: Alobar (severe) → Semilobar → Lobar.
  • Associations: Trisomy 13, SHH gene, maternal diabetes.
  • Facial: Cyclopia, proboscis.

  ⭐ Holoprosencephaly is strongly associated with Trisomy 13 (Patau syndrome).

• Lissencephaly (Smooth Brain): Agyria/Pachygyria.
  • Neuronal migration defect.
  • Type 1: LIS1, DCX. Type 2 (Cobblestone): e.g., Walker-Warburg.
• Polymicrogyria: Multiple small gyri; neuronal migration issue.
  • Causes: Genetic, CMV.
• Schizencephaly: Gray matter-lined clefts in hemispheres. EMX2 gene.
• Megalencephaly/Hemimegalencephaly: Enlarged brain/hemisphere; mTOR pathway.

Posterior Fossa Anomalies - Hindbrain Headaches

• Chiari Malformations: Cerebellar tissue herniation. Often cause occipital headaches.
  • Type I: Tonsils >5mm below foramen magnum. Adults. Syringomyelia, headaches.
  • Type II (Arnold-Chiari): Vermis, tonsils, medulla, 4th ventricle herniation. Infants. Hydrocephalus.

    ⭐ Chiari II malformation is almost invariably associated with a lumbar myelomeningocele.

  • Type III: Rare. Occipital/cervical encephalocele + cerebellar herniation.
  • Type IV: Severe cerebellar hypoplasia/aplasia.
• Dandy-Walker Malformation (DWM):
  • Agenesis/hypoplasia of cerebellar vermis.
  • Cystic dilation of 4th ventricle; enlarged posterior fossa.
  • Hydrocephalus common. 📌 DWM: Dilated 4th, Water (hydrocephalus), Missing vermis.
• Joubert Syndrome:
  • Vermis agenesis/hypoplasia.
  • "Molar tooth sign" on MRI (superior cerebellar peduncles).
  • Hypotonia, ataxia, developmental delay, abnormal breathing.

Hydrocephalus & Syringomyelia - Fluid Flow Faults

• Hydrocephalus: Increased CSF volume leading to ventricular dilation.
  • Communicating: Impaired CSF absorption (e.g., post-meningitis scarring).
  • Non-communicating (Obstructive): CSF flow blocked within ventricular system or its outlets (e.g., aqueductal stenosis).

    ⭐ Congenital aqueductal stenosis is the most common cause of non-communicating hydrocephalus in newborns.

  • Normal Pressure Hydrocephalus (NPH): Affects elderly; triad: Wet (urinary incontinence), Wobbly (gait ataxia), Wacky (dementia). 📌
  • Clinical (Infants): Bulging fontanelles, rapidly increasing head circumference, sunsetting eyes.
  • Clinical (Adults): Headache, nausea, vomiting, papilledema.
• Syringomyelia: Fluid-filled cavity (syrinx) within the spinal cord, typically cervical; involves central canal dilation.
  • Associations: Chiari I malformation, trauma, tumors.
  • Clinical: Classic "cape-like" bilateral loss of pain and temperature sensation in upper extremities (damage to spinothalamic fibers crossing in anterior white commissure); preserved touch. Late: motor deficits (LMN signs).

High‑Yield Points - ⚡ Biggest Takeaways

• Neural tube defects (NTDs) like anencephaly and spina bifida are linked to folate deficiency.
• Arnold-Chiari II involves cerebellar herniation, hydrocephalus, and myelomeningocele.
• Dandy-Walker malformation shows absent cerebellar vermis and a cystic 4th ventricle.
• Syringomyelia (spinal cord syrinx) is often associated with Chiari I and "cape-like" sensory loss.
• Holoprosencephaly (failed forebrain division) is linked to Trisomy 13 and SHH mutations.
• Lissencephaly ("smooth brain") results from defective neuronal migration.