Myelomeningocele (Spina Bifida)

CHAPTER 62

Myelomeningocele (Spina Bifida)

Introduction/Etiology/Epidemiology

• Myelomeningocele (also called spina bifida) is a spectrum of major birth malformations of the spinal cord caused by failure of closure of the neural tube.

• Affected patients have varying degrees of paralysis and sensory changes in the lower extremities and bladder as well as central nervous system involvement (hydrocephalus and Arnold-Chiari malformation).

• Meningocele is a protrusion of the meninges through a defect in the posterior spinal elements, but the spinal cord and nerve roots remain in the spinal canal.

• Myelomeningocele is the most severe form of spina bifida, in which the spinal cord is exposed through the opening in the spine. It is associated with partial or complete paralysis of the parts of the body below the spinal opening.

• Lumbosacral lipoma includes lipomeningocele, an intraspinal lipoma, or a lipoma of the terminal filum. These are skin covered with a deficiency in neural arch. There are many variants, and they are associated with neurologic changes and frequently spinal deformity.

• Note: Spina bifida occulta is a developmental variant in which one or more vertebrae have defects in the posterior arch without any skin or spinal malformation. This incidental form of spina bifida does not cause disability or symptoms, and referral for evaluation is not required.

• Sacral dimple is a small dimple or pit in the midline of the lower back just above the gluteal crease. It is found in about 2% to 4% of infants and is usually benign. Rarely, it can be associated with spinal anomalies; an ultrasonographic examination is indicated if the dimple is deeper than 5 mm. Other concerning features include associated fatty lump, swelling, adjacent birthmark, patch of hair, and discoloration.

• Risk factors associated with spina bifida include

— Inadequate maternal intake of folic acid prior to conception

— History of previously affected pregnancy with the same partner

— Maternal diabetes (not gestational diabetes)

— In utero exposure to valproic acid or carbamazepine

Signs and Symptoms

• The level of neurologic deficit is the main determinant of functional disability and is also the method of classifying patients (Table 62-1).

• Hydrocephalus occurs in 80% to 90% of children with spina bifida. The occurrence of hydrocephalus is related to the neurologic level.

• Arnold-Chiari malformation involves caudal displacement of the posterior lobe of the cerebellum into the foramen magnum. Manifestations include dysfunction of the lower cranial nerves presenting as weakness or paralysis of the vocal cords and difficulty with feeding and breathing.

• Syringomyelia (a fluid-filled cyst within the spinal cord) can cause progressive scoliosis.

• Tethered spinal cord

— Seen on nearly all magnetic resonance imaging (MRI) scans of persons with spina bifida; however, clinical signs (tethered cord syndrome) only occur in 15% to 30% of patients.

— Manifestations of tethered cord syndrome include changes in neurologic function, spasticity in the lower extremities, leg weakness, foot deformity, scoliosis, back pain, increased lumbar lordosis, and sensory changes.

• Urinary incontinence and infections

• Musculoskeletal complications of spina bifida

— Scoliosis and kyphosis

■May be neurogenic (because of shunt malformation, Arnold-Chiari malformation, or tethered cord syndrome) or secondary to the paralysis or congenital bony defects

■Kyphosis occurs in approximately 8% to 15% of children with spina bifida.

■Occurrence of scoliosis is approximately 60% and is related to the neurologic level, affecting approximately 90% of patients at the thoracic level, 44% of patients at the L1-L3 level, and 12% of patients at the L4-L5 level.

■Curves greater than 50 degrees affect sitting balance, which can lead to skin breakdown; more severe curves lead to restrictive pulmonary disease.

— Hip complications

■Hip contractures are common because of muscle imbalance or spasticity. In children who use wheelchairs, they may be caused by prolonged sitting.

■Hip dislocations occur in nearly 50% of children with spina bifida.

— Knee flexion contractures

■More common in patients with thoracic or upper-lumbar–level involvement because of prolonged sitting positions.

■Less common in patients affected at the mid-lumbar level (L3, L4, L5), and can be a significant hindrance to ambulation

■Uncommon in patients affected at the sacral level; may be a sign of spasticity and tethered cord.

— Knee extension contractures

■May occur in patients with L3- and L4-level involvement because of unopposed quadriceps action

■Prevent proper sitting and inhibit walking

Table 62-1. Classification of Motor Function Disability