Lecture Notes: Spina Bifida

Overview

• Definition: Spina bifida is a birth defect where the tissue on the left and right side of the back doesn't fully meet to form a seal over the spinal cord, leaving an opening in the lower back.
• Development: Occurs during early fetal development when the neural tube fails to close properly.
• Cause: Defect or absence of vertebral arches due to mesoderm failure, possibly involving meninges and neural tissue.

Types of Spina Bifida

1. Myelomeningocele (Meningomyelocele)

• Severe form: Spinal cord and meninges protrude through an opening in vertebrae, forming a skin pouch or exposed nerves in severe cases ('open spina bifida').
• Symptoms: Loss of sensation, paralysis, bladder/bowel issues, seizures, leg/foot deformities.
• Association: Often linked with Arnold Chiari II malformation (cerebellum/brainstem tissue slips into foramen magnum).
• Risks: Hydrocephalus due to cerebrospinal fluid accumulation.

2. Meningocele

• Least common: Only meninges protrude through vertebral gaps; spinal nerves not involved.
• Symptoms: Typically mild as spinal cord is not damaged.

3. Spina Bifida Occulta

• Most common and mild: Small tissue deformities in lower back; often undiagnosed.
• Symptoms: Usually asymptomatic; possible back hair, dimple, or birthmark above lesion.

Causes and Risk Factors

• Unknown exact cause.
• Folate (Vitamin B9) deficiency: Critical, hence prenatal vitamins contain folic acid.
• Timing: Deformities occur in the 4th week of pregnancy, often before pregnancy is known.
• Preventative measures: Folic acid added to enriched grain products.
• Other risk factors: Obesity, poorly controlled diabetes, certain medications affecting folate metabolism.

Diagnosis

• Myelomeningocele diagnosis: Detected prenatally through increased alpha fetoprotein (AFP) levels in maternal serum.
• Additional tests: HCG, inhibin A, estriol blood tests, and ultrasound.
• Amniocentesis: Direct sampling from amniotic sac if needed.

Treatment

• Prenatal surgery: Can close a myelomeningocele but risky for mother and fetus.
• Postnatal surgery: Often performed within days of birth to prevent infections such as meningitis.
• Long-term care: May require urinary catheterization, crutches/wheelchairs due to nerve damage.

Quick Recap

• Types:
  • Spina bifida occulta: Most common, least severe.
  • Meningocele: Least common, mild symptoms.
  • Myelomeningocele: Most severe.

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