Spina bifida is the most common of the neural tube defects, which include myelomeningocele, encephalocele, and anencephaly. Spina bifida is a complex and multisystem birth defect, in which one or more vertebral arches may be incomplete. This article discusses the sensory and motor impairments, neurologic disorders, orthopedic and cognitive impairments, and skin and other problems associated with spina bifida. This article also summarizes some of the key clinical issues in the care of children with this complex birth defect.
Spina bifida is the most common of the neural tube defects (NTDs), which include myelomeningocele, encephalocele, and anencephaly. Spina bifida occulta is a common spectrum condition, present in approximately 5% of the population, in which one or more vertebral arches may be incomplete ( Fig. 1 ). The spinal cord is normal, and there are usually no associated neurologic abnormalities. Spina bifida occulta may be accompanied by localized skin abnormalities (dermal sinus, dimples, and pigmented or hairy skin). If there is an associated skin-covered swelling, with an intact spinal cord, the terms meningocele or lipomeningocele are used. Meningoceles are almost always present in the lumbosacral area. A lipomeningocele may be entirely asymptomatic, but intraspinal lipomas can impinge on the cord and lead to progressive weakness and/or deformity.
When spina bifida is open and associated with a malformed spinal cord and a sac, the terms myelomeningocele or meningomyelocele are used. Myelomeningoceles arise as a consequence of incomplete or disrupted neurulation during the fourth week of gestation, when the embryo is only 3 to 5 mm in length ( Fig. 2 ). The myelomeningocele includes the splayed-open malformed cord (neural placode) as well as the meninges and fatty tissue ( Fig. 3 ). Myelomeningoceles are often intact, with a meningeal sac enclosing cerebrospinal fluid (CSF), but in many cases the sac is disrupted and leaking CSF at birth. Myelomeningoceles vary in size and location, and the range of associated motor and sensory impairments depends on the level of the lesion.
Sensory and motor impairments
Spinal level is determined by careful examination of sensation and motor function, and is generally classified as thoracic, high lumbar (L1 or L2), midlumbar (L3), low lumbar (L4 or L5), or sacral. Asymmetry of sensory loss or weakness is common. Most children with low lumbar (L5) or sacral myelomeningocele have absent sensation around the anus, perineum, and feet, but some individuals with lower sacral lesions may have no detectable sensory loss. Children with L1 or L2 lesions may have some hip flexion and adduction but no quadriceps strength to extend the knees. Those with L3 lesions may have knee flexion but paralysis of ankles and feet. Children with L4 and L5 lesions have quadriceps strength (for knee extension) and may have some hamstring (for knee flexion) and anterior tibialis strength (for ankle dorsiflexion). Those with S1 lesions may have functioning glutei (involved in hip extension) and gastrocnemii (involved in ankle plantar flexion). Assessment of motor function is important in predicting mobility and the need for bracing and also serves as useful baseline information in determining whether neurologic deterioration from tethering is occurring.
Functional mobility outcomes for different levels of spina bifida and the need for bracing have been reviewed extensively. Children with sacral lesions usually walk by the age of 2 to 3 years and may require bracing at the ankles. Those with L3 paralysis usually require forearm crutches and bracing above the knees. Children with high lumbar or thoracic lesions may eventually stand upright and walk with extensive support of the hips, knees, and ankles. Most children with midlumbar spina bifida, who are able to ambulate with crutches and braces, rely increasingly on wheelchairs for mobility as they get older.
In addition to the disruption of motor and sensory nerves, myelomeningocele affects the sacral parasympathetic nerves that supply the muscular walls of the bladder, urethra, and rectum, and are critically important in sexual functions. Sympathetic nerves controlling the bladder outlet, which originate in the lumbar region of spinal cord, are also typically involved. Bladder and bowel dysfunctions are present in almost all children with myelomeningocele along with varying degrees of sexual dysfunction.
Hydrocephalus and Chiari malformation
Most babies with myelomeningocele have a complex brain malformation, Chiari type II, with associated hydrocephalus. Among patients with Chiari II malformations, 80% of those with sacral lesions and more than 90% of those with higher-level lesions receive a shunt. The Chiari II malformation consists of downward displacement of the cerebellum, elongation and upward displacement of the medulla and fourth ventricle, dysgenesis of the corpus callosum, a small posterior fossa, and associated hydrocephalus ( Fig. 4 ). This complex anomaly arises in the fifth week of gestation as a consequence of abnormal neurulation. The Chiari malformation is commonly asymptomatic, but may present with a spectrum of symptoms and signs related to brainstem compression and lower cranial nerve dysfunction. About 30% of infants with myelomeningocele have mild symptoms, including feeding difficulties and gastroesophageal reflux, whereas 5% have more severe symptoms, including stridor, weak cry, failure to thrive, apnea, and cyanosis (“Chiari crisis”).
Abnormal CSF dynamics leads to hydrocephalus, which may be present prenatally (the so-called lemon sign on fetal ultrasonography). Neonatal signs include large or rapidly enlarging head circumference, bulging anterior fontanel, and split sagittal suture. Ventriculoperitoneal (V-P) shunts are placed in newborns with myelomeningocele and hydrocephalus, allowing control of CSF pressure and ventricular volumes and prevention of progressive hydrocephalus.
Hydrocephalus and Chiari malformation
Most babies with myelomeningocele have a complex brain malformation, Chiari type II, with associated hydrocephalus. Among patients with Chiari II malformations, 80% of those with sacral lesions and more than 90% of those with higher-level lesions receive a shunt. The Chiari II malformation consists of downward displacement of the cerebellum, elongation and upward displacement of the medulla and fourth ventricle, dysgenesis of the corpus callosum, a small posterior fossa, and associated hydrocephalus ( Fig. 4 ). This complex anomaly arises in the fifth week of gestation as a consequence of abnormal neurulation. The Chiari malformation is commonly asymptomatic, but may present with a spectrum of symptoms and signs related to brainstem compression and lower cranial nerve dysfunction. About 30% of infants with myelomeningocele have mild symptoms, including feeding difficulties and gastroesophageal reflux, whereas 5% have more severe symptoms, including stridor, weak cry, failure to thrive, apnea, and cyanosis (“Chiari crisis”).
Abnormal CSF dynamics leads to hydrocephalus, which may be present prenatally (the so-called lemon sign on fetal ultrasonography). Neonatal signs include large or rapidly enlarging head circumference, bulging anterior fontanel, and split sagittal suture. Ventriculoperitoneal (V-P) shunts are placed in newborns with myelomeningocele and hydrocephalus, allowing control of CSF pressure and ventricular volumes and prevention of progressive hydrocephalus.
Associated neurologic disorders
Approximately 15% to 20% of children with spina bifida have seizures in childhood. Seizures are more likely in children with shunts, especially in those with previous shunt infections, and the onset of a seizure may indicate a shunt malfunction. The seizures are usually generalized tonic-clonic type and respond well to antiepileptic medications.
Oculomotor disorders, such as difficulty with visual tracking, are common in spina bifida and may be related to the effects of Chiari malformation and hydrocephalus on midbrain gaze centers. Strabismus occurs in 20% of the patients and may require surgery. Even in the absence of hydrocephalus and Chiari malformation, fine motor function may be impaired, probably because of cerebellar and cervical cord abnormalities.
Parents and clinicians need to remain vigilant for signs of neurologic deterioration in children with spina bifida. The signs of shunt failure (rapidly enlarging head circumference, swelling or redness along the shunt track) are usually clear in the infant and toddler. In young children, shunt failure may present acutely with headache, irritability, lethargy, and vomiting, but signs of shunt malfunction may be subtle and insidious, including mild drowsiness and impaired attention and coordination. Chiari II malformation or cervical hydromyelia may present with neck pain, progressive spasticity, or ataxia.
Another important cause of neurologic deterioration is tethered cord. During normal growth, the spinal cord ascends within the canal so that the conus moves from L4 to L2 between birth and puberty. In spina bifida, the abnormal cord may be tethered to the scar tissue or bony deformities, leading to ischemic damage. Associated spinal cord anomalies such as hydromyelia and cord lipomas may also cause neurologic problems. Clinical signs are most common around the age of 6 to 12 years, including deterioration of walking, back pain, leg pain, spasticity, increasing scoliosis, progressive foot deformity, and deterioration in bladder and bowel function. Progressive weakness over time on manual muscle testing and changes in bladder function are key clinical findings. The back pain is typically worsened with activity and relieved by rest. Tethering is generally diagnosed on clinical grounds, although magnetic resonance imaging of the spine, urodynamics, and electrophysiologic testing may provide additional data. Surgical release of the tethered cord effectively relieves pain and may arrest neurologic deterioration.
Orthopedic impairments
Muscle weakness leads to abnormal positioning in utero. Consequently, 50% of the babies with myelomeningocele have significant foot deformity at birth (“clubfoot”), including calcaneovalgus, equinovarus, and vertical talus ( Fig. 5 ). During early childhood, further deformity may occur from ongoing muscle imbalance, postural effects of gravity, and growth. A plantigrade foot in neutral position is essential for optimal walking, and a well-positioned foot may protect against skin breakdown. Hence physical therapy, casting, subcutaneous releases, and postoperative splinting are commonly needed in infancy. More definitive surgical reconstruction, including releases, tendon transfers, and bony surgery, may be required at the age of around 12 to 24 months, and bracing is usually required to maintain alignment and improve mobility.
Hip flexors and adductors are innervated by L1 and L2, whereas hip extensors and abductors are innervated by L5 and S1. Hence, muscle imbalance and hip instability are common in spina bifida. Subluxed or dislocated hips occur in 25% to 50% of newborns with high or midlumbar lesions, and another 25% become unstable during early childhood. The main concern is not the effects on walking but that asymmetric hips and associated pelvic obliquity may cause scoliosis, seating problems, and pressure sores.
Scoliosis may be congenital or acquired. Congenital scoliosis occurs in 15% to 25% of newborns with spina bifida, most commonly with thoracic lesions. Acquired (or “paralytic”) scoliosis is usually first noted in early school age, and the condition may progress rapidly, especially during puberty. Tethering and hydromyelia, pelvic obliquity, and asymmetric motor function may cause progressive scoliosis. Severe kyphosis may be present at birth, most commonly associated with lumbar myelomeningoceles, posing a challenge to the surgeons performing the primary closure. Severe scoliosis and kyphosis may interfere with sitting and walking, and may compromise respiratory function. Lightweight molded orthoses may prevent progression and/or delay the need for spinal fusion and stabilization with rods.
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