Cephalic Disorders
Cephalic disorders are congenital conditions that stem from damage to, or abnormal development of, the budding nervous system. Cephalic disorders are not necessarily caused by a single factor but may be influenced by hereditary or genetic conditions or by environmental exposures during pregnancy. Most cephalic disorders are caused by a disturbance that occur very early in the development of the fetal nervous system.
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 a cephalic disorder that results from a neural tube defect that occurs when the rostral (head) end of the neural tube fails to close, usually between the 23rd and 26th days of conception, resulting in the absence of a major portion of the brain, skull, and scalp. Infants with this disorder are born without a forebrain - the largest part of the brain consisting mainly of the cerebrum, which is responsible for thinking and coordination. The remaining brain tissue is often exposed - not covered by bone or skin.
Infants born with anencephaly are usually blind, deaf, unconscious, and unable to feel pain. Although some individuals with anencephaly may be born with a rudimentary brainstem, the lack of a functioning cerebrum permanently rules out the possibility of ever gaining consciousness. Reflex actions such as breathing and responses to sound or touch may occur. The disorder is one of the most common disorders of the fetal central nervous system. Approximately 1,000 to 2,000 American babies are born with anencephaly each year. The disorder affects females more often than males.
There is no cure or standard treatment for anencephaly and the prognosis for affected individuals is poor. Most infants do not survive infancy. If the infant is not stillborn, then he or she will usually die within a few hours or days after birth. Anencephaly can often be diagnosed before birth through an ultrasound examination.
Colpocephaly
Colpocephaly is a disorder in which there is an abnormal enlargement of the occipital horns - the posterior or rear portion of the lateral ventricles (cavities or chambers) of the brain. This enlargement occurs when there is an underdevelopment or lack of thickening of the white matter in the posterior cerebrum. Colpocephaly is characterized by microcephaly (abnormally small head) and mental retardation. Other features may include motor abnormalities, muscle spasms, and seizures.
Although the cause is unknown, researchers believe that the disorder results from an intrauterine disturbance that occurs between the second and sixth months of pregnancy. Colpocephaly may be diagnosed late in pregnancy, although it is often misdiagnosed as hydrocephalus (excessive accumulation of cerebrospinal fluid in the brain). It may be more accurately diagnosed after birth when signs of intellectual disability, microcephaly, and seizures are present.
There is no definitive treatment for colpocephaly. Anticonvulsant medications can be given to prevent seizures, and doctors try to prevent contractures (shrinkage or shortening of muscles). The prognosis for individuals with colpocephaly depends on the severity of the associated conditions and the degree of abnormal brain development. Some children benefit from special education.
Holoprosencephaly
Holoprosencephaly is a disorder caused by the failure of the prosencephalon (the embryonic forebrain) to sufficiently divide into the double lobes of the cerebral hemispheres. The result is a single-lobed brain structure and severe skull and facial defects. In most cases of holoprosencephaly, the malformations are so severe that babies die before birth. In less severe cases, babies are born with normal or near-normal brain development and facial deformities that may affect the eyes, nose, and upper lip.
There are three classifications of holoprosencephaly. Alobar, in which the brain has not divided at all, is usually associated with severe facial deformities. Semilobar, in which the brain's hemispheres have somewhat divided, causes an intermediate form of the disorder. Lobar, in which there is considerable evidence of separate brain hemispheres, is the least severe form. In some cases of lobar holoprosencephaly the baby's brain may be nearly normal.
The least severe of the facial anomalies is the median cleft lip (premaxillary agenesis). The most severe is cyclopia, an abnormality characterized by a single eye located in the area normally occupied by the root of the nose, and a missing nose or a proboscis (a tubular-shaped nose) located above the eye. The least common facial anomaly is ethmocephaly, in which a proboscis separates closely-set eyes. Cebocephaly, another facial anomaly, is characterized by a small, flattened nose with a single nostril situated below incomplete or underdeveloped closely-set eyes.
Hydranencephaly
Hydranencephaly is a rare condition in which the brain's cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal fluid. An infant with hydranencephaly may appear normal at birth. The infant's head size and spontaneous reflexes such as sucking, swallowing, crying, and moving the arms and legs may all seem normal. However, after a few weeks the infant usually becomes irritable and has increased muscle tone. After a few months of life, seizures and hydrocephalus (excessive accumulation of cerebrospinal fluid in the brain) may develop. Other symptoms may include visual impairment, lack of growth, deafness, blindness, spastic quadriparesis (paralysis), and intellectual deficits. Hydranencephaly is considered to be an extreme form of porencephaly (a rare disorder characterized by a cyst or cavity in the cerebral hemispheres) and may be caused by vascular infections or traumatic disorders after the 12th week of pregnancy. Diagnosis may be delayed for several months because early behavior appears to be relatively normal. Some infants may have additional abnormalities at birth including seizures, myoclonus (spasm or twitching of a muscle or group of muscles), and respiratory problems.
The outlook for children with hydranencephaly is generally poor, and many children with this disorder die before age 1. However, in rare cases, children with hydranencephaly may survive for several years or more. Treatment is symptomatic and supportive. Hydrocephalus may be treated with a shunt (a surgically implanted tube that diverts fluid from one pathway to another).
Iniencephaly
Iniencephaly is a rare neural tube defect that combines extreme retroflexion (backward bending) of the head with severe defects of the spine. The affected infant tends to be short, with a disproportionately large head. Diagnosis can be made immediately after birth because the head is so severely retroflexed that the face looks upward. The skin of the face is connected directly to the skin of the chest and the scalp is directly connected to the skin of the back. Generally, the neck is absent.
Most individuals with iniencephaly have other associated anomalies such as anencephaly, cephalocele (a disorder in which part of the cranial contents protrudes from the skull), hydrocephalus, cyclopia, absence of the mandible (lower jaw bone), cleft lip and palate, cardiovascular disorders, diaphragmatic hernia, and gastrointestinal malformation. The disorder is more common among females.
The prognosis for those with iniencephaly is extremely poor. Newborns with iniencephaly seldom live more than a few hours. The distortion of the fetal body may also pose a danger to the mother's life.
Lissencephaly
Lissencephaly, which literally means "smooth brain," is a rare brain malformation characterized by microcephaly and the lack of normal convolutions (folds) in the brain. It is caused by defective neuronal migration (cortical malformation), the process in which nerve cells move from their place of origin to their permanent location.
The surface of a normal brain is formed by a complex series of folds and grooves. The folds are called gyri or convolutions, and the grooves are called sulci. In children with lissencephaly, the normal convolutions are absent or only partly formed, making the surface of the brain smooth.
Symptoms of the disorder may include unusual facial appearance, difficulty swallowing, failure to thrive, and severe psychomotor retardation. Anomalies of the hands, fingers, or toes, muscle spasms, and seizures may also occur.
Lissencephaly may be diagnosed at or soon after birth. Diagnosis may be confirmed by ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI).
Lissencephaly may be caused by intrauterine viral infections or viral infections in the fetus during the first trimester, insufficient blood supply to the baby's brain early in pregnancy, or a genetic disorder. There are two distinct genetic causes of lissencephaly - X-linked and chromosome 17-linked.
The spectrum of lissencephaly is only now becoming more defined as neuroimaging and genetics has provided more insights into migration disorders. Other causes which have not yet been identified are likely as well.
Lissencephaly may be associated with other diseases including isolated lissencephaly sequence, Miller-Dieker syndrome, and Walker-Warburg syndrome.
Treatment for those with lissencephaly is symptomatic and depends on the severity and locations of the brain malformations. Supportive care may be needed to help with comfort and nursing needs. Seizures may be controlled with medication and hydrocephalus may require shunting. If feeding becomes difficult, a gastrostomy tube may be considered.
The prognosis for children with lissencephaly varies depending on the degree of brain malformation. Many individuals show no significant development beyond a 3- to 5-month-old level. Some may have near-normal development and intelligence. Many will die before the age of 2. Respiratory problems are the most common causes of death.
Megalencephaly
Megancephaly, also called macrencephaly, is a condition in which there is an abnormally large, heavy, and usually malfunctioning brain. By definition, the brain weight is greater than average for the age and gender of the infant or child. Head enlargement may be evident at birth or the head may become abnormally large in the early years of life.
Megalencephaly is thought to be related to a disturbance in the regulation of cell reproduction or proliferation. In normal development, neuron proliferation - the process in which nerve cells divide to form new generations of cells - is regulated so that the correct number of cells is formed in the proper place at the appropriate time.
Symptoms of megalencephaly may include delayed development, convulsive disorders, corticospinal (brain cortex and spinal cord) dysfunction, and seizures. Megalencephaly affects males more often than females.
The prognosis for individuals with megalencephaly largely depends on the underlying cause and the associated neurological disorders. Treatment is symptomatic. Megalencephaly may lead to a condition called macrocephaly (defined later in this fact sheet). Unilateral megalencephaly or hemimegalencephaly is a rare condition characterized by the enlargement of one-half of the brain. Children with this disorder may have a large, sometimes asymmetrical head. Often they suffer from intractable seizures and mental retardation. The prognosis for those with hemimegalencephaly is poor.
Microcephaly
Microcephaly is a neurological disorder in which the circumference of the head is smaller than average for the age and gender of the infant or child. Microcephaly may be congenital or it may develop in the first few years of life. The disorder may stem from a wide variety of conditions that cause abnormal growth of the brain, or from syndromes associated with chromosomal abnormalities.
Infants with microcephaly are born with either a normal or reduced head size. Subsequently the head fails to grow while the face continues to develop at a normal rate, producing a child with a small head, a large face, a receding forehead, and a loose, often wrinkled scalp. As the child grows older, the smallness of the skull becomes more obvious, although the entire body also is often underweight and dwarfed. Development of motor functions and speech may be delayed. Hyperactivity and mental retardation are common occurrences, although the degree of each varies. Convulsions may also occur. Motor ability varies, ranging from clumsiness in some to spastic quadriplegia in others.
Generally there is no specific treatment for microcephaly. Treatment is symptomatic and supportive.
In general, life expectancy for individuals with microcephaly is reduced and the prognosis for normal brain function is poor. The prognosis varies depending on the presence of associated abnormalities.
Porencephaly
Porencephaly is an extremely rare disorder of the central nervous system involving a cyst or cavity in a cerebral hemisphere. The cysts or cavities are usually the remnants of destructive lesions, but are sometimes the result of abnormal development. The disorder can occur before or after birth.
Porencephaly most likely has a number of different, often unknown causes, including absence of brain development and destruction of brain tissue. The presence of porencephalic cysts can sometimes be detected by transillumination of the skull in infancy. The diagnosis may be confirmed by CT, MRI, or ultrasonography.
More severely affected infants show symptoms of the disorder shortly after birth, and the diagnosis is usually made before age 1. Signs may include delayed growth and development, spastic paresis (slight or incomplete paralysis), hypotonia (decreased muscle tone), seizures (often infantile spasms), and macrocephaly or microcephaly.
Individuals with porencephaly may have poor or absent speech development, epilepsy, hydrocephalus, spastic contractures (shrinkage or shortening of muscles), and intellectual disability. Treatment may include physical therapy, medication for seizure disorders, and a shunt for hydrocephalus. The prognosis for individuals with porencephaly varies according to the location and extent of the lesion. Some patients with this disorder may develop only minor neurological problems and have normal intelligence, while others may be severely disabled. Others may die before the second decade of life.
Schizencephaly
Schizencephaly is a rare developmental disorder characterized by abnormal slits, or clefts, in the cerebral hemispheres. Schizencephaly is a form of porencephaly. Individuals with clefts in both hemispheres, or bilateral clefts, are often developmentally delayed and have delayed speech and language skills and corticospinal dysfunction. Individuals with smaller, unilateral clefts (clefts in one hemisphere) may be weak on one side of the body and may have average or near-average intelligence. Patients with schizencephaly may also have varying degrees of microcephaly, mental retardation, hemiparesis (weakness or paralysis affecting one side of the body), or quadriparesis (weakness or paralysis affecting all four extremities), and may have reduced muscle tone (hypotonia). Most patients have seizures and some may have hydrocephalus.
In schizencephaly, the neurons border the edge of the cleft implying a very early disruption in development. There is now a genetic origin for one type of schizencephaly. Causes of this type may include environmental exposures during pregnancy such as medication taken by the mother, exposure to toxins, or a vascular insult. Often there are associated heterotopias (isolated islands of neurons) which indicate a failure of migration of the neurons to their final position in the brain.
Treatment for individuals with schizencephaly generally consists of physical therapy, treatment for seizures, and, in cases that are complicated by hydrocephalus, a shunt.
The prognosis for individuals with schizencephaly varies depending on the size of the clefts and the degree of neurological deficit.
