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 * __ALTERATIONS OF NEUROLOGIC FUNCTION IN CHILDREN__**


 * __//STRUCTURE AND FUNCTION OF THE NERVOUS SYSTEM IN CHILDREN//__**

The CNS develops from a dorsal thickening of the ectoderm known as the **neural plate**. This unfolds to form a **neural groove** and **neural folds**. The **neural groove** eventually deepens and folds to form the neural tube. Some neuroectodermal cells separate from the neural tube but remain between the tube and the surface ectoderm, creating the **neural crest**. This cellular band develops into the cranial and spinal ganglia, mor commonly referred to as the **peripheral nervous system**.

//Normal growth and development:// neurologic functioning is primarily at a subcortical level at birth. Absence of expected relflex responses at the appropriate age indicates general depression of central or peripheral motor functions.


 * __STRUCTURAL MALFORMATIONS__**

//Defects of neural tube closure:// there is a strong association of fetal death with neural tube defects. Posterior defects are more common; these include anencephaly and a group of disorders collectively referred to as the myelodysplasias. //Myelodysplasia// is defined as a defective formation of the spinal cord. Anterior midline defects are less common because the inductive processes occur in a relatively short period. The most extreme form is //cyclopia//, in which the child has a single midline orbit and eye with a protruding noselike appendage above the orbit. //Anencephaly// is an anomaly in which the soft, bony component of the skull and part of the brain are missing. //Encephalocele// refers to a herniation or protrusion of brain and meninges through a defect in the skull, resulting in a saclike structure. //Meningocele// in a sacklike cyst of meninges filled with spinal fluid, occurs when the neural tube fails to close completely. //Myelomeningocele// is a hernial protursion of a saclike cyst through a defect in the posterior arch of a vertebra.


 * __MALFORMATIONS OF THE AXIAL SKELETON__**

//Spina bifida occulta// - cause is unknown and it is a defect of the neural tube closure. Cranial deformities range from minor to major defects.
 * acrania - the cranial vault is almost completely absent and an extensive defect of the vertebral column often is present.
 * craniosynostosis is the premature closure of one or moare of the cranial sutures during the first 18 to 20 months of the infant's life.

Microcephaly is a defect in brain growth as a whole. //Congenital hydrocephalus// is characterized by an increased volume of CSF. //Dandy-Walker deformity// is a congenital defect of midline cerebellar structures in which hydrocephalus is caused by atresia of the foramina of luschka or Magendie, leading the ventricular flow of CSF into a "blind pouch." //Macewen sign// ("cracked-pot" sign) is the resonant note when the skull is tapped.


 * __ENCEPHALOPATHIES__**

//Encephalopathy//, is a disorder involving the brain; a general category that includes a number of syndromes and diseases.

//Static encephalopathies// may occur during gestation or at birth or at any time during childhood growth and development. Clinical manifestations depend on the site and extent of the injury, as well as the age of the child and state of development at the time of injury. //Cerebral palsy// is the term given to a diverse group of non-progressive syndromes that affect the brain and cause motor dysfunction beginning in early infancy. //Spastic cerebral palsy// is associated with increased muscle tone, prolonged primitive reflexes, exaggerated deep tendon reflexes, clonus, rigidity of the extremities, scoliosis, and contractures. //Dyskinetic cerebral palsy// is associated with extreme difficulty in fine motor coordination and purposeful movements. //Ataxic cerebral palsy// manifests with gait disturbances and instability.

//Inherited metabolic disorders of the CNS// - their manifestations usually occur in infancy and childhood.

//Defects in Amino Acid metabolism// may be classified as (1) those in which the transport of amino acid is impaired, (2) those involving an enzyme or cofactor deficiency, and (3) those grouped around certain chemical components, such as sulfur-containing amino acids. //Phenylketonuria (PKU)// is an unborn error of metabolism characterized by the inability of the body to convert the essential amino acid phenylalanine to tyrosine. //Defects in Lipid metabolism// are termed lysosomal storage diseases because each disorder in this group can be traced to a missing lysosomal enzyme. //Tay-Sachs disease// is an autosomal recessive disorder.

//Seizure disorders in Children://

//Epilepsy// is repeated recurrence of seizure activity. //Partial seizures// are characterized by seizure activity that begins in and usually is limited to one part of either the left or right hemisphere. //General seizures// are those in which the first clinical manifestations indicate that the seizure activity starts in or involves both cerebral hemispheres. //Infantile spasms// are a severe form of epilepsy characterized by a variety of clinical manifestations. The infant may have episodes of sudden flexion or extension movements involving the neck, trunk, and extremities. They are also common in those with //tuberous sclerosis complex//. Lennox-Gastaut syndrome is an epileptic syndrome characterized by an onset of seizures early in childhood, usually in males and around 1 to 5 years of age. //Juvenile myoclonic epilepsy// is a primary generalized epilepsy that usually affects adolescents and young adults. //Benign febrile seizures// occur in 3-4% of children younger than 5 years of age. They are usually brief and self-limited. //Status epilepticus// is defined as the state of continuing or recurring seizure activity in which the recovery from seizure activity is incomplete.
 * simple partial seizure refers to seizure activity that occurs without loss of consciousness.
 * complex partial seizure refers to seizure activity that occurs with impairment of consciousness.

//Acute encephalopathies//:

//Reye syndrome// is characterized by encephalopathy and fatty changes in a variety of organs, especially the liver. //Intoxications of the CNS// - drug induced encephalopathies always must be considered a possibility in the child with unexplained neurologic changes. They may result from accidential ingestion, therapeutic overdose, intentional overdose, or ingestion of environmental toxins. Meningitis refers to the inflammation of the meningeal coverings of the brain. It can be bacterial or viral
 * Bacterial meningitis is one of the most serious infections to which infants and children are susceptible. It is caused by //Streptococcus pneumoniae// and //Haemophilus influenze// type B.
 * Viral meningitis - the hallmark of viral meningitis, or aseptic meningitis, is a mononuclear response in the CSF and the presence of normal blood glucose level.


 * __HUMAN IMMUNODEFICIENCY VIRUS AND CENTRAL NERVOUS SYSTEM INVOLVEMENT__**

HIV subjects the body to multiple, repeated infections. The end stage of this infection is called AIDS. The primary pathologic condition of HIV causes specific immunodeficiency that destroys the host's ability to withstand infection. HIV directly invades most major organ systems, including the CNS. HIV may be transmitted through the placenta, exposure to infected blood or vaginal secretions or by ingestion of infected breast milk.

__**CEREBROVASCULAR DISEASE IN CHILDREN**__

//Occlusive cerebrovascular// disease may result from embolism, sinovenous thrombosis, or congenital or iatrogenic narrowing of vessels, which lead to decreased flow of blood and oxygen to areas of the brain. //Moyamoya disease// is a rare, progressive vascular disease that results in the progressive stenosis of arterial flow to the brain. //Hemorrhagic cerebrovascular// disease are most commonly caused by congenital arteriovenous malformations.


 * __CHILDHOOD TUMORS__**

//Brain tumors// are the most common solid tumor oand the second most common primary neoplasm in children, second only to leukemia. The cause of brain tumors is largely unknown, although genetic, environmental, and immune factors have been implicated in some tumor development. //Types are//: medulloblastoma, ependymoma, astrocytoma, brain stem glioma, craniopharyngioma, and optic nerve glioma make up approximately 75-80% of all pediatric brain tumors. //Embryonal tumors// such as //neuroblastoma// originates in neural crest cells that normally give rise to the sympathetic ganglia and the adrenal medulla. //Retinoblastoma// is a rare congenital eye tumor of young children that originates in the retina of one or both eyes; it is treatable.

NEUROPATHOLOGY REFERENCES