Essentials of Neurology and Neuromuscular Disorders

Multisystem Comorbidities

Most children with cerebral palsies have clinically significant oromotor dysfunction, and when associated with gastroesophageal reflux, it may lead to recurrent aspiration, decreased respiratory reserve, esophageal stenosis, and malnutrition. Frequently used procedures include fundoplication, gastrostomy, and esophageal dilatation. Immobility, underhydration, and poor diet predispose patients to bowel stasis and constipation and, if severe, may result in fecal impaction. Malnutrition may depress immune responses, and electrolyte imbalance and anemia are common. Preoperative assessment of these parameters is essential.

Pulmonary complications are common causes of death in cerebral palsies. Aspiration associated with gastroesophageal reflux is the leading cause, and it may be exacerbated by excessive oral secretions, bulbar dysfunction, recurrent respiratory infection, and chronic lung disease. Scoliosis may also restrict pulmonary function, with cardiopulmonary involvement depending on the curve pattern and the severity of the curve (see Chapter 32 ).

Orthopedic operations are the most frequently performed procedures in children with moderate to severe cerebral palsies. Procedures include tendon releases to ease contractures, femoral osteotomy, and hip adductor and iliopsoas releases. The trend in orthopedic surgery is to perform multiple procedures involving tenotomies or osteotomies at different levels of all extremities during a single general anesthesic, rather than staging them during multiple operations. Scoliosis often requires surgery to prevent further deterioration in lung function and to stabilize the spine to facilitate ambulation and sitting. Spinal fusion is considered in all children with progressive curves greater than 40 to 50 degrees.

Botulinum toxin is commonly used to reduce muscle spasticity in affected children, and it may be injected with or without sedation or, more commonly, in children under general anesthesia. The need for repeated treatments (every 3-6 months) and the use of a nerve stimulator to confirm correct placement of the needle should be taken into consideration when assessing the child's need for sedation or anesthesia.

Approximately 30% of children with cerebral palsies have epilepsy. It is more common in spastic hemiplegia and quadriplegia, especially with a history of neonatal encephalopathy (53% vs. 29%) and less common in the ataxic and choreoathetotic forms. Secondary generalized and focal seizures frequently occur. Anticonvulsants should be maintained until the surgery date (given the morning of surgery) and restarted as soon as possible in the postoperative period.

Anesthesia Considerations for Cerebral Palsies

The many multisystem comorbidities and therapies specific to children with cerebral palsies must be understood to minimize perioperative complications. Risk factors include an inability to walk, severe neurologic deficit, major cognitive dysfunction, severe scoliosis, malnutrition, and the presence of a gastrostomy or tracheostomy. Severely compromised children can be optimally managed postoperatively with admission to the pediatric intensive care unit to provide analgesia with comprehensive monitoring, maximum support, and aggressive respiratory care; after their conditions are stabilized, they can be transferred to a setting with less intense monitoring.

All medications that the child is receiving should be reviewed; they may include anticonvulsant, antireflux, and antispasticity agents. Baclofen should not be discontinued abruptly because it can produce acute withdrawal symptoms. Oral dantrolene has also been used to reduce spasticity. Baclofen and dantrolene cause weakness; therefore the dose of neuromuscular blocking drugs may need to be reduced as these antispasticity drugs can delay the return of adequate respiratory effort during emergence from anesthesia.

Most of these children have above-average intelligence. They have the same emotional and cognitive concerns as others about undergoing anesthesia, including preoperative anxiety that may require premedication. Children with contractures, especially in the upper extremities, may present a challenge for establishing IV access. If gastroesophageal reflux is not controlled, consideration should be given to rapid-sequence induction. Although these children have a peripheral motor disorder, IV succinylcholine yields only a normal release of potassium, despite evidence of proliferation of extrajunctional acetylcholine receptors. Maintenance of and emergence from anesthesia requires special considerations, including the possibility of a reduced minimal alveolar concentration (MAC), resistance to neuromuscular blocking agents, and reduced bispectral index (BIS) measurements. If vomiting is likely to occur, the airway must be protected.

These children have normal responses to pain, which should be managed as if they were unaffected by cerebral palsy. Caudal or epidural analgesia may be a reasonable approach for perioperative pain management if the child does not have a ventriculoperitoneal shunt. Management and assessment of perioperative pain in children with neurocognitive impairment is addressed in Chapter 44 .

Neural Tube Defects: Cranial and Spinal Dysraphism

The fetal incidence of NTDs is 17 per 10,000 pregnancies; the live birth incidence is 5.7 to 6.7 per 10,000. NTDs are a group of birth defects presumed to have a common origin in failure of the neural tube to develop properly during the embryonic stage. NTDs include anencephaly, encephaloceles, and spina bifida.

The cause of NTDs is multifactorial, with genetic and environmental factors the most important. Approximately 10% of NTDs are caused by chromosomal abnormalities such as trisomies (i.e., 18, 13, and 21), triploidy, and 22q11 microdeletion. Some of the environmental causes include folate deficiency, maternal antiepileptic drugs (valproate, phenytoin, carbamazepine, and polytherapy), retinoins, and maternal diabetes.

Preconceptual folic acid supplementation has reduced the prevalence of NTDs by 30% to 50%. Along with antenatal ultrasound examination, screening is done for increased maternal serum levels of α-fetoprotein, reduced human chorionic gonadotropin levels, and reduced unconjugated estriol levels; termination of pregnancy in cases with positive test results has further reduced the prevalence of NTDs.

Anencephaly is a lethal disorder resulting from the neural tube failing to close between the 23rd and 26th day following conception. This leads to disorganization of neural elements and the absence of skull formation. Some deep cerebral structures may remain intact, and the brainstem may develop normally. With the latter situation, normal respiration and cardiovascular functions may develop, enabling the infant to survive for hours or days after birth. Other structures in the head and brain, including the eyes, face, and pituitary gland, may not develop normally. An infant with anencephaly is usually blind, deaf, and unable to feel pain.

Encephalocele is a herniation of neural tissue and meninges out of the skull through deficient skin and bone (see Fig. 26.12A ). They may be associated with other cerebral malformations. Encephaloceles found anteriorly are associated with underlying brain, orbital structures, or pituitary gland anomaly. Posteriorly, encephaloceles are associated with cerebral or cerebellar tissue that herniates through a bony defect in the posterior cranium. Intranasal encephaloceles may be difficult to detect. These defects carry a poor prognosis for long-term survival. The only treatment is reparative surgery; occasionally shunts are placed for resulting hydrocephalus. Most infants die, and in survivors, severe neurodevelopmental disability is common. Most of these children have hydrocephalus.

Spina bifida refers to a group of conditions in which there is abnormal or incomplete formation of the midline structures over the back (see Fig. 26.12B ). Skin, bony, and neural elements may be involved singly or in combination. Congenital malformations of the spinal cord may exist in isolation or in association with brain anomalies. These defects may present at birth, as in the case of the more severe and open lesions (i.e., spina bifida) or be identified later in childhood if the skin overlying the spinal defect is intact (e.g., spina bifida occulta). Those who develop a Chiari malformation may present with cervical cord or bulbar deficits, placing them at risk for respiratory embarrassment (see Figs. 26.13 , and 26.14 ). Children with spinal cord lesions are at increased risk for sensory deficits, making meticulous skin care and positioning essential to prevent pressure sores and damage to neuropathic joints.

Spina bifida occulta occurs in the absence of herniation of neural tissue or coverings so that the overlying skin appears to be intact and normal. In many cases, a hairy patch or a dermal sinus (i.e., sacral dimple) may communicate with the meninges or attach to the spinal cord or a lipoma that causes a fatty swelling overlying the bony defect. The spinal cord may be tethered by internal connection to such structures, making it vulnerable to trauma at surgery and during growth, especially at puberty. The spinal cord may be abnormally formed, with cartilaginous or bony spurs that damage or divide the cord during growth as the neural tissue grows at a slower rate than the surrounding bone (i.e., diastematomyelia). These infants may not be candidates for a caudal block because the spinal cord may end at an unusually low position.

Spina bifida cystica, the most common type of spinal dysraphism, manifests as an obvious lesion on the back. The defect may be diagnosed antenatally or at birth. The abnormally developed spinal cord may be covered by a layer of meninges (i.e., meningocele) or remain uncovered (i.e., myelomeningocele). The spinal level of the lesion is the major determinant of morbidity. Myelomeningoceles need to be repaired within a few days of birth to prevent infection and further damage to the neural tissues. A cerebrospinal fluid (CSF) leak or frank dural rupture may develop, leading to intravascular volume and electrolyte abnormalities that should be treated preoperatively.

When the defect is identified at birth, it is optimally managed in a specialist center by a multidisciplinary team (i.e., pediatrician, neurologist, neurosurgeon, orthopedic surgeon, and others) who can anticipate, prevent, and treat complications and assist in the child's long-term care. Children with dysraphism often develop postoperative hydrocephalus because of disrupted CSF flow and require a ventriculoperitoneal shunt. Long-term complications, including paraparesis, neurogenic bladder and bowel, renal insufficiency, trophic limb changes, pressure sores, joint contractures, and scoliosis may require surgical repair and future intervention. Children with NTDs may acquire latex allergy if they are exposed repeatedly to latex products (they do not have a genetic predisposition toward latex allergy). To prevent latex allergy, these children should be cared for in a latex-free environment. The anesthesia considerations for NTDs are presented in Chapter 26 .

Chiari Malformation

Chiari malformations of the nervous system may coexist with other anomalies and manifest in the neonatal period or later in the early decades of life ( Table 24.3 ).

Chiari I. This is the mildest of the hindbrain malformations and is characterized by displacement of cerebellar tonsils more than 5 mm caudally through the foramen magnum. The brainstem and fourth ventricle retain a relatively normal position, although the fourth ventricle may be small and slightly distorted. Although the spectrum of Chiari I malformations is not usually associated with other cerebral abnormalities, syringomyelia is found in 20% to 70% of patients, depending on the degree and extent of disruption of normal CSF flow between the spine and cranium. Adequate surgical decompression at the foramen magnum and upper cervical spine is the treatment of choice for neuronal dysfunction, symptomatic syrinx, or hydrocephalus. Ventriculoperitoneal shunting may be required for hydrocephalus and syringostomy or syrinx shunting for cord drainage if the craniocervical decompression alone does not relieve the pressure in the syrinx.

Chiari II. This is a more extensive and complex abnormality than the Chiari I malformation, with infratentorial and supratentorial abnormalities. It affects 0.02% of births, females twice as often as males. The cerebellar tonsils, inferior vermis, fourth ventricle, and brainstem are herniated from a shallow posterior fossa through a wide foramen magnum with obstruction to CSF flow at the exit of the fourth ventricle. Occasionally the fourth ventricle becomes “trapped” or encysted and will enlarge to appear normal or dilated. There is virtually always a meningocele or meningomyelocele present, some with associated hydrocephalus.

Chiari III. This defect is very rare. There is herniation of the posterior fossa contents into an associated occipital or high cervical cephalocele with the other features of a Chiari II malformation. These patients have severe neurologic defects and a poor prognosis.

Chiari IV. This abnormality is controversial and extremely rare. Many authors consider the features of primary cerebellar agenesis as a Chiari IV malformation, but it must be differentiated from a Chiari II malformation associated with a “vanishing” cerebellum. In primary cerebellar agenesis, there are remnants of a residual cerebellum (for example, anterior quadrangular lobule), a normal brainstem, a normal-sized posterior fossa, and a normal spine. The lack of a meningomyelocele virtually excludes a Chiari II malformation.

Syringomyelia

Syringomyelia results from a glial cell–lined cavitation within the spinal cord. Diagnosis has been greatly simplified by the use of MRI, which provides images of the spinal cord and the tubular fluid-filled space within. Although the spectrum of Chiari I malformations is not usually associated with other cerebral abnormalities, syringomyelia is found in 20% to 70% of patients, depending on the degree and extent of disruption of normal CSF flow between the spine and cranium. Syringomyelia manifests with dissociated sensory loss, usually in the upper limbs, causing loss or impairment of pain and temperature sensation, which may cause trophic changes in the fingers and neuropathic joints. It may progress to paralysis and hyporeflexia later in life. The lower limbs may exhibit pyramidal signs; some lesions may extend upward (i.e., syringobulbia) and produce lower brainstem signs, such as stridor and laryngospasm (i.e., vocal cord palsy).

Treatment of syringomyelia is controversial, especially if the lesion is asymptomatic. Management may focus on associated disorders as syringomyelia may progress slowly or not at all.

Adequate surgical decompression at the foramen magnum and upper cervical spine is the treatment of choice for neuronal dysfunction, symptomatic syrinx, or hydrocephalus. Ventriculoperitoneal shunting may be required for hydrocephalus and syringostomy or syrinx shunting for cord drainage if the craniocervical decompression alone does not relieve the pressure in the syrinx.

Hydrocephalus

Hydrocephalus is defined as an increase in the volume of CSF in the brain, particularly the ventricles, associated with an increase in the intracranial pressure (ICP) with classical signs and symptoms. It results from overproduction or impaired drainage of CSF from the brain. In practice, overproduction is an uncommon source of hydrocephalus; these cases most often result from tumors of the choroid plexus. Obstructed drainage of CSF is the far more common source for hydrocephalus. The causes of hydrocephalus include intraventricular hemorrhage, Arnold-Chiari malformation, brain tumor, congenital obstruction, and myelomeningocele. Hydrocephalus may present with chronic or acute symptoms of ICP. Children typically present with a headache and irritability, but signs and symptoms can progress to lethargy, seizures, vomiting, and ophthalmoplegia as pressure within the brain increases. In infants, it presents as accelerated head growth, bulging fontanelle, poor feeding, sunsetting sign, and developmental delay. If left untreated, it may lead to a reduced level of consciousness, oculomotor palsies, sluggish pupillary light reactions, bradycardia, and eventually respiratory arrest. Diagnosis of hydrocephalus is confirmed by neuroimaging, often with computed tomography (CT) in the acute situation, followed by MRI.

Surgery is the definitive treatment for hydrocephalus. It usually involves inserting a drainage system to shunt CSF from the brain to another site in the body (see Fig. 26.11 ). After insertion of a shunt, children should be closely monitored for shunt complications; these include infection, blockage or fracture of the shunt, and overdrainage of CSF. The anesthesia considerations for treating hydrocephalus are discussed in Chapter 26 . An endoscopic cerebral aqueductoplasty or third venticulostomy may be helpful for obstructive hydrocephalus.