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Normal Growth and Development of the Nervous System
- Growth and development of the brain occur most rapidly during fetal development and during the first year of life.
- The bones of the skull are joined by sutures, and the wide, membranous functions of the sutures known as fontanelles allow for brain growth and close by 18 months of age.
- At birth, neurologic function is primarily at the subcortical level with transition in reflexes as motor development progresses during the first year.
- Defects of neural tube closure include anencephaly (absence of part of the skull and brain), encephalocele (herniation of the meninges and brain through a skull defect), meningocele (a saclike meningeal cyst that protrudes through a vertebral defect, and myelomeningocele also known as spina bifida (failure of the vertebrae to close and the resulting protrusion of neural tube contents).
- Acrania is nearly complete absence of the cranial vault.
- Premature closure of the cranial sutures causes craniosynostosis and prevents normal skull expansion, resulting in compression of growing brain tissue.
- Microcephaly is lack of brain growth and retarded mental and motor development.
- Congenital hydrocephalus results from an overproduction, impaired absorption, or blockage of circulation of cerebrospinal fluid. Dandy-Walker deformity is caused by cystic dilation of the fourth ventricle and aqueductal compression.
- Static encephalopathies are nonprogressive disorders of the brain that can occur during gestation, birth, or childhood and can be caused by endogenous or exogenous factors.
- Cerebral palsy can be caused by prenatal cerebral hypoxia or perinatal trauma, with symptoms of motor dysfunction including increased muscle tone, increased reflexes, and loss of fine motor coordination, mental retardation, seizure disorders, or developmental disabilities.
- Inherited metabolic disorders that damage the nervous system include defects in amino acid metabolism (phenylketonuria) and lipid metabolism (Tay-Sachs disease) and result in abnormal behavior, seizures, and deficient psychomotor development.
- Seizure disorders are abnormal discharges of electrical activity within the brain. They are associated with numerous nervous system disorders and more often are a generalized rather than a partial type of seizure.
- Generalized forms of seizures include tonic-clonic, myoclonic, atonic, akinetic, and infantile spasms.
- Partial seizures suggest more localized brain dysfunction.
- Febrile seizures usually are limited to children ages 6 months to 3 years, with a pattern of one seizure per febrile illness.
- Reye syndrome is an encephalopathy with fatty changes in the liver associated with influenza B, varicella viruses, and aspirin ingestion. Progressive manifestations include lethargy, stupor, rigidity, seizures, and respiratory arrest.
- Accidental poisonings from a variety of toxins can cause serious neurologic damage.
- Bacterial meningitis is commonly caused by Neisseria meningitides or Streptococcus pneumoniae and may result from respiratory or gastrointestinal infections; symptoms include fever, headaches, photophobia, seizures, rigidity, and stupor.
- Viral meningitis may result from direct infection or be secondary to a systemic viral infection (i.e., measles, mumps, herpes, or leukemia).
Human Immunodeficiency Virus and Central Nervous System Involvement
- HIV may be transmitted to infants and children through the placenta, by exposure to infected blood or vaginal secretions, or by ingestion of infected breast milk.
- The incidence of HIV among children is increasing. AIDS is most prevalent among youth ages 15 to 24 years.
- The classic symptoms are related to progressive encephalopathy.
- Brain tumors are the most common tumors of the nervous system and the second most common type of childhood cancer.
- Tumors in children most often are located below the tentorial plate.
- Fast-growing tumors produce symptoms early in the disease, whereas slow-growing tumors may become very large before symptoms appear.
- Symptoms of brain tumors may be generalized or localized. The most common general symptom is increased intracranial pressure (headache, irritability, vomiting, somnolence, bulging of fontanelles).
- Localized signs of infratentorial tumors in the cerebellum include impaired coordination and balance. Cranial nerve signs occur with tumors in or near the brain stem.
- Supratentorial tumors may be located near the cortex or deep in the brain. Symptoms depend on the specific location of the tumor.
- Neuroblastoma is an embryonal tumor of the
- sympathetic nervous system and can be located anywhere there is sympathetic
- nervous tissue. Symptoms are related to tumor location and size of metastasis.
- Retinoblastoma is a congenital eye tumor that has two forms: inherited and acquired.