What is myelomeningocele (also known as meningomyelocele)?

Myelomeningocele: Definition and Clinical Features

Myelomeningocele (MMC) is a serious congenital malformation where both meninges and spinal cord herniate through a defect in the vertebral arches, representing the most severe form of spina bifida compatible with life. 1 This condition results from failure of primary neurulation during embryonic development, specifically the failure of dorsal fusion of the neural tube.

Anatomical Features

Myelomeningocele is characterized by:

• A placode of neural tissue attached to surrounding skin at the edges
• The placode may be elevated on a dome or sac by cerebrospinal fluid (CSF)
• If the thin tissue on the dome tears, the CSF escapes and the malformation appears flat
• Whether domed or flat, there is always a placode on the skin surface, making it an "open" malformation 1

Epidemiology

• Birth prevalence in the United States: approximately 0.2 per 1000 live births 1
• Incidence varies by ethnicity:
  • Highest among Hispanic infants (1.12 per 1000 live births)
  • Lowest among African American and Asian infants (0.75 per 1000 live births)
  • Intermediate among non-Hispanic white infants (0.96 per 1000 live births) 1
• Geographic variation: incidence in continental European countries ranges from 1 in 1700 to 10,000 live births, while in the British Isles it ranges from 1 in 260 to 400 1
• Ireland has the highest rate in Europe at 1 in 200 live births 1

Associated Conditions

Myelomeningocele is frequently accompanied by:

• Hydrocephalus (70% of cases) 1, 2
• Chiari type II malformation (98% of cases) 1, 3
• Syringomyelia (40-80% of cases) 1
• Spinal cord tethering (virtually all cases) 1
• Brainstem dysfunction 3
• Scoliosis 3

Clinical Presentation

The severity of neurological impairment generally correlates with:

• Size of the defect
• Cranial location (higher lesions typically cause more severe impairment) 1
• Most commonly affects the lumbosacral region 4

Management Considerations

1. Initial repair: Closure of the spinal lesion is preferably undertaken in the first 48 hours after birth to minimize the risk of injury and central nervous system infection 4

2. Hydrocephalus treatment:

   • 71.4% of MMC patients with hydrocephalus are treated with ventriculoperitoneal shunts
   • 4.0% are treated with endoscopic third ventriculostomy 2

3. Long-term care:

   • MMC requires lifelong care and multiple surgical procedures 3
   • Multidisciplinary evaluations are crucial for early identification and management of associated conditions 3

4. Urological management:

   • Only 3-10% of MMC patients have normal urinary continence 5
   • Urodynamic problems are detected in approximately 85% of patients 5

Surgical Timing Considerations

While traditional teaching recommends surgery within the first 48 hours of life, some research suggests that late repair (after 48 hours) may not significantly differ from early repair in terms of:

• Hydrocephalus development
• Urodynamic functions
• Motor deficits 5

Anesthetic Challenges

Surgical repair of myelomeningocele presents several anesthetic challenges:

• Difficulty in securing airway
• Intra-operative prone positioning
• Accurate assessment of blood loss
• Prevention of hypothermia 6

In conclusion, myelomeningocele represents a complex congenital malformation requiring prompt diagnosis, timely surgical intervention, and comprehensive long-term multidisciplinary management to optimize outcomes and quality of life.