Cephalic Disorders
Overview
The term "cephalic disorders" refers to defects resulting from abnormal development of, or damage to, the brain and spinal cord. Cephalic disorders are present at or before birth. In most cases, the problem occurs early in the development of the fetal nervous system. In other cases, the problem occurs when the fibrous joints connecting the bones of the skull join prematurely.
Cephalic disorders may be caused by genetic conditions or by exposure of the mother and developing fetus to infections, toxic substances, medications, or radiation.
The severity of these disorders varies greatly. Some cause mild disabilities; others are profound, resulting in total lifelong disability, vastly reduced functional capacity, and sometimes death.
Anencephaly
Anencephaly is one of the most serious cephalic disorders and afflicts roughly 1000 to 2000 babies born in the United States annually. Female infants are affected more often than males. Infants born with this disorder have no forebrain-the main portion of the cerebrum, responsible for thinking and coordination. Brain tissue that does develop often is not covered by bone or skin.
Causes
The cause of anencephaly remains unknown. A developmental failure occurs between the 23rd and 26th days of pregnancy. The cephalic (or head) end of the neural tube fails to close, and major portions of the brain, skull, and scalp do not develop. Recent studies suggest the addition of folic acid to the diet of women in their child-bearing years may reduce the incidence of neural tube defects, suggesting that factors associated with diet and vitamins may play a role.
Signs and Symptoms
Anencephalic infants typically are born blind, deaf, unconscious, and insensitive to pain. Some may have a rudimentary brainstem that permits reflex actions such as breathing and, in some cases, responsiveness to sound or touch.
Diagnosis
Anencephaly often can be diagnosed before birth through an ultrasound examination.
Treatment
The condition is untreatable and incurable.
Prognosis
Without a functioning cerebrum, anencephalic infants cannot gain consciousness. Most anencephalic infants are stillborn or die within a few hours or days after birth.
Colpocephaly
In this disorder, there is abnormal enlargement of the occipital horns-the rear portion of the cavities or chambers of the brain. Colpocephaly results from underdevelopment or lack of thickening of the white matter in the posterior cerebrum.
Causes
The cause is unknown. Research suggests there may be a intrauterine disturbance between the 2nd and 6th months of pregnancy.
Signs and Symptoms
Infants with colpocephaly have abnormally small heads (microcephaly), profound mental retardation, motor abnormalities, muscle spasms, and seizures.
Diagnosis
Colpocephaly sometimes is discovered late in pregnancy but is often misdiagnosed as hydrocephalus-excessive cerebrospinal fluid in the brain. More often, colpocephaly is diagnosed after birth when symptoms appear.
Treatment
Treatment is symptomatic. Anti-convulsant drugs may prevent seizures and other medications may be prescribed to prevent muscle shrinkage or contractures.
Prognosis
Prognosis depends on the severity of microcephaly and brain malformation. In some cases, children with colpocephaly are able to participate in special education.
Holoprosencephaly
The face and forebrain (or prosencephalon) of an embryo normally begin to develop in the 5th and 6th weeks of pregnancy. If the forebrain fails to divide into normal right and left hemispheres, deformities in the face and brain, or holoprosencephaly, results.
Types
The most serious form is alobar holoprosencephaly, in which the hemispheres completely fail to separate. It is characterized by severe facial and brain abnormalities so profound that they often cause intrauterine death. In semilobar holoprosencephaly the brain's hemispheres develop only a slight separation. Lobar holoprosencephaly is marked by substantial, but still incomplete, separation of the hemispheres.
Causes
The cause of most cases of holoprosencephaly is unknown. Nearly half of all cases are linked to chromosomal factors, such as Patau's syndrome (trisomy 13) and Edwards' syndrome (trisomy 18). There appears to be an increased risk for holoprosencephaly in infants of diabetic mothers, but the significance of this is not well understood.
Signs and Symptoms
The most severe forms of holoprosencephaly produce seizures and mental retardation. Typical facial defects involve the eyes, nose, and upper lip. In some cases, the nose may be missing entirely or may develop above the eye in the form of a proboscis, a tubular appendage. Other facial anomalies include:
- ethmocephaly (rare): absent nose; a proboscis separates narrow-set, sometimes abnormally small, eyes
- cebocephaly: small, flattened nose with a single nostril beneath incomplete or underdeveloped narrow-set eyes
- premaxillary agenesis median (cleft lip)
- cyclopia: single eye located in the area normally occupied by the root of the nose
Treatment
Treatment is largely symptomatic.
Prognosis
Infants born with most forms of holoprosencephaly face a poor prognosis. Few who survive achieve significant mental development.
Iniencephaly
Iniencephaly is marked by extreme backward bending (retroflexion) of the head and severe spinal defects. Iniencephalic infants are short, with disproportionately large heads.
Signs and Symptoms
Usually, the neck is absent, with the skin of the face connected directly to the skin of the chest and the scalp connected to the skin of the back. Other anomalies also may be present, such as anencephaly, cephalocele (part of the cranial contents protrude from the skull), hydrocephalus, cyclopia, absent lower jaw bone, cleft lip/palate, cardiovascular disorders, diaphragmatic hernia, and gastrointestinal abnormalities.
Diagnosis
The condition is readily diagnosed at birth by the prominence of its symptoms.
Prognosis
Newborns with iniencephaly seldom live more than a few hours. The mother is at risk during pregnancy and the birthing process because the distorted fetal body can cause her serious injury.
Lissencephaly
Lissencephaly means smooth brain. It is a rare disorder marked outwardly by abnormal smallness of the head (microcephaly) and inwardly by the lack of normal folds and grooves in the surface of the brain.
Cause
Lissencephaly results when nerve cells in the fetal neural tube fail to move to the proper location (called defective neuronal migration) as the fetus's central nervous system develops. This may be caused by intrauterine or fetal viral infections during the 1st trimester, insufficient blood supply to the brain early in pregnancy, or a genetic disorder.
Signs and Symptoms
Babies born with lissencephaly may present with an unusual facial appearance, difficulty swallowing, severe psychomotor retardation, muscle spasms, seizures, and/or deformities of the hands, fingers, or toes.
Diagnosis
The condition is diagnosed at or soon after birth. Doctors usually confirm the diagnosis with ultrasound, computed tomography (CT scan) or magnetic resonance imaging (MRI scan).
Treatment
Treatment for lissencephaly is symptomatic, depending on the nature and severity of the brain malformations. Supportive care and nursing may be needed. Medication may be prescribed to control seizures, and a shunt may be required to control hydrocephalus. When swallowing is a problem, a gastrostomy tube may be necessary.
Prognosis
Prognosis depends on the degree of brain malformation. While some have nearly normal development and intelligence, most show no significant development beyond that of a normal child who is 3 to 5 months old. Many lissencephalic children die of respiratory problems before age 2.
Megalencephaly
This condition is marked by an abnormally large, heavy, usually malfunctioning brain. The head may be enlarged at birth or become abnormally large in the early years. A rare variation on this condition, unilateral megalencephaly (also called hemimegalencephaly), involves enlargement of half of the brain. This results in a large, often asymmetrical head.
Causes
Megalencephaly may be caused by a disturbance in the process that controls the way nerve cells divide to form new cells (called nerve cell proliferation). Males are more likely to be afflicted than females.
Signs and Symptoms
Symptoms may include delayed development, convulsions, seizures, and brain cortex/spinal cord dysfunction. Unilateral megalencephaly usually results in mental retardation and severe seizures.
Treatment
Treatment is symptomatic.
Prognosis
Prognosis varies according to the severity of associated disorders. Prognosis for those afflicted with unilateral megalencephaly is poor.
Microcephaly
In microcephaly, the circumference of the head is markedly smaller than normal for the infant's age and sex. Microcephaly can be congenital or can develop during the first years of life.
Causes
The condition may be caused by factors related to abnormal brain growth or from chromosomal abnormalities.
Signs and Symptoms
At birth, the head of a microcephalic infant may be either normal or abnormally small. In many cases the head fails to grow as the face develops at a normal rate, resulting in the development of a small head with a large face, receding forehead, and scalp with loose, wrinkled, skin. The smallness of the skull becomes increasingly evident with age. The child's entire body may be underweight and dwarf-like. Motor functions often are poor, ranging from simple clumsiness to spastic quadriplegia (affecting all four limbs). Speech development often is subnormal. The child may suffer convulsions and be hyperactive or mentally retarded.
Treatment
Treatment for microcephaly is symptomatic and supportive.
Prognosis
Prognosis varies according to the severity of the child's associated abnormalities. Life expectancy usually is short.
Porencephaly
In porencephaly a cyst or cavity develops in a cerebral hemisphere. The disorder can occur before or after birth.
Causes
Porencephaly may have a number of different causes, including absence of brain development and lesions that destroy brain tissue.
Signs and Symptoms
Symptoms include delayed growth and development, slight or partial paralysis, decreased muscle tone (hypotonia), seizures or spasms, macrocephaly or microcephaly, epilepsy, hydrocephalus, shrinkage or shortening of muscles, and mental retardation. Speech development may range from poor to absent.
Diagnosis
Porencephalic cysts are sometimes detected in infancy. Severely affected infants usually display symptoms shortly after birth, and diagnosis usually is confirmed before age 1 by transillumination (passing light through) of the skull, CT scan, MRI scan, or ultrasonography.
Treatment
Treatment may include physical therapy, medication for seizures, and a shunt for hydrocephalus.
Prognosis
The location and extent of the brain damage determines the prognosis. Some patients develop normal intelligence and experience only minor neurological problems; others may be severely disabled. Many die before age 10.
Hydranencephaly
Hydranencephaly is a rare and extreme form of porencephaly. The hemispheres of the cerebrum are absent and replaced by sacs filled with cerebrospinal fluid (CSF). In most cases, the cerebellum and brainstem are formed normally.
Causes
Vascular injuries, infections, or trauma after the 12th week of pregnancy result in malformations of the brain.
Signs and Symptoms
Some infants with hydranencephaly may have seizures; sudden, rapid, involuntary twitches or jerks (myoclonus), and respiratory problems at birth. Most appear normal and have normal spontaneous reflexes (e.g., sucking, swallowing, crying, moving the arms and legs). Within a few weeks these infants become irritable and develop an abnormal increase in muscle tone (hypertonia). Seizures and hydrocephalus usually follow within a few months, and there may be symptoms of visual impairment, lack of growth, deafness, blindness, paralysis, and intellectual deficits.
Diagnosis
Because of the infant's relatively normal initial appearance and early behavior, diagnosis of hydranencephaly may take several months. Diagnosis is confirmed by means of a procedure in which light is passed through body tissues (transillumination), CT scan, and MRI scan.
Treatment
Treatment is symptomatic and supportive. A shunt may be installed to control hydrocephalus.
Prognosis
Prognosis is poor. Most infants die within their first year.
Schizencephaly
Schizencephaly is a form of porencephaly in which the brain's hemispheres are marked by abnormal slits or clefts. The clefts may occur in one hemisphere (unilateral) or occur in both hemispheres (bilateral).
Causes
Research strongly suggests schizencephaly occurs early in fetal development. The cause may be genetic or may stem from vascular injury or the mother's exposure to certain medications or toxins during pregnancy.
Signs and Symptoms
Individuals born with small, unilateral clefts have weakness on one side of the body and may have average or nearly average intelligence. Persons with bilateral clefts usually have serious developmental disabilities, delayed speech and language skills, and brain cortex/spinal cord problems.
Associated conditions include varying degrees of microcephaly, mental retardation, reduced muscle tone (hypotonia), seizures, and weakness or paralysis on one side of the body (hemiparesis) or in all four limbs (quadriparesis). Hydrocephalus also may occur.
Treatment
Individuals with schizencephaly may benefit from physical therapy and treatment to control seizures. Cases involving hydrocephalus may call for implantation of a shunt.
Prognosis
Prognosis depends on the size of the clefts and the extent of the neurological deficits.
Other Cephalic Disorders
Acephaly is usually associated with the development of a parasitic "twin" attached to an otherwise normal fetus, usually at the neck. The acephalic fetus has no head or heart and cannot survive independently; blood circulation comes from the heart of the otherwise normal "twin."
Exencephaly usually is found in embryos as an early stage of anencephaly. It is characterized by development of the brain outside the skull. In most cases, the brain tissue degenerates as pregnancy progresses. Exencephalic embryos rarely survive to term.
Macrocephaly is characterized by an abnormally large head circumference. It may be inherited and may or may not be associated with other disorders, such as dwarfism, neurofibromatosis, mental retardation, or tuberous sclerosis. Some cases may be caused by an enlarged brain or by hydrocephalus.
Micrencephaly is characterized by an abnormally small brain. It can be caused by a genetic factor but is more often associated with maternal alcoholism, diabetes, and exposure to German measles (rubella). Newborns with micrencephaly usually have profound neurological defects, seizures, and greatly impaired intellectual development. Motor function problems may appear later in life.
Octocephaly is characterized by agnathia, the total or virtual absence of a lower jaw, and a poorly functioning airway. This is a fatal condition that may occur alone or with holoprosencephaly.
Craniostenoses are an extremely rare group of cephalic disorders, characterized by skull deformities caused by premature fusion of various fibrous joints (cranial sutures) connecting the bones of the head.
- Scaphocephaly: fusion of the sagittal suture, the joint connecting the two parietal (top and sides of the head) bones of the skull, causing a long, narrow head. This is the most common of the craniostenoses.
- Plagiocephaly: unilateral fusion (joining of one side) of the fibrous joint between the occipital and parietal bones, causing asymmetrical (one side) flattening of the skull. It is thought to be caused by a brain malformation, an excessively small or tight intrauterine environment, or a spasm or tightening of the neck muscles.
- Brachycephaly: fusion of the joint between the skull's frontal and parietal bones, causing foreshortened front-to-back diameter of the skull.
- Trigonocephaly: fusion of the metopic suture, part of the frontal joint between the two halves of the skull's frontal bone, causing a V-shaped deformity at the front of the skull, a triangular prominence of the forehead, and closely set eyes.
- Oxycephaly: closure of the coronal suture and any other suture or fusion of all cranial sutures. This is the most severe form of craniostenoses.