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, such as medication taken by the mother, maternal infection, or exposure to radiation. Some cephalic disorders occur when the cranial sutures (the fibrous joints that connect the bones of the skull) join prematurely. Most cephalic disorders are caused by a disturbance that occurs very early in the development of the fetal nervous system.
The human nervous system develops from a small, specialized plate of cells on the surface of the embryo. Early in development, this plate of cells forms the neural tube, a narrow sheath that closes between the third and fourth weeks of pregnancy to form the brain and spinal cord of the embryo. Four main processes are responsible for the development of the nervous system: cell proliferation, the process in which nerve cells divide to form new generations of cells; cell migration, the process in which nerve cells move from their place of origin to the place where they will remain for life; cell differentiation, the process during which cells acquire individual characteristics; and cell death, a natural process in which cells die.
Damage to the developing nervous system is a major cause of chronic, disabling disorders and, sometimes, death in infants, children, and even adults. The degree to which damage to the developing nervous system harms the mind and body varies enormously. Many disabilities are mild enough to allow those afflicted to eventually function independently in society. Others are not. Some infants, children, and adults die, others remain totally disabled, and an even larger population is partially disabled, functioning well below normal capacity throughout life.
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 respiration (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.
The cause of anencephaly is unknown. Although it is believed that the mother's diet and vitamin intake may play a role, scientists agree that many other factors are also involved.
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.
Recent studies have shown that the addition of folic acid to the diet of women of child-bearing age may significantly reduce the incidence of neural tube defects. Therefore, it is recommended that all women of child-bearing age consume 0.4 mg of folic acid daily.
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 mental retardation, 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.
There are three classifications of holoprosencephaly. Alobar holoprosencephaly, the most serious form in which the brain fails to separate, is usually associated with severe facial anomalies. Semilobar holoprosencephaly, in which the brain's hemispheres have a slight tendency to separate, is an intermediate form of the disease. Lobar holoprosencephaly, in which there is considerable evidence of separate brain hemispheres, is the least severe form. In some cases of lobar holoprosencephaly, the patient's brain may be nearly normal.
Holoprosencephaly, once called arhinencephaly, consists of a spectrum of defects or malformations of the brain and face. At the most severe end of this spectrum are cases involving serious malformations of the brain, malformations so severe that they are incompatible with life and often cause spontaneous intrauterine death. At the other end of the spectrum are individuals with facial defects - which may affect the eyes, nose, and upper lip - and normal or near-normal brain development. Seizures and mental retardation may occur.
The most severe of the facial defects (or anomalies) is cyclopia, an abnormality characterized by the development of a single eye, located in the area normally occupied by the root of the nose, and a missing nose or a nose in the form of a proboscis (a tubular appendage) located above the eye.
Ethmocephaly is the least common facial anomaly. It consists of a proboscis separating narrow-set eyes with an absent nose and microphthalmia (abnormal smallness of one or both eyes). Cebocephaly, another facial anomaly, is characterized by a small, flattened nose with a single nostril situated below incomplete or underdeveloped closely set eyes.
The least severe in the spectrum of facial anomalies is the median cleft lip, also called premaxillary agenesis.
Although the causes of most cases of holoprosencephaly remain unknown, researchers know that approximately one-half of all cases have a chromosomal cause. Such chromosomal anomalies as Patau's syndrome (trisomy 13) and Edwards' syndrome (trisomy 18) have been found in association with holoprosencephaly. There is an increased risk for the disorder in infants of diabetic mothers.
There is no treatment for holoprosencephaly and the prognosis for individuals with the disorder is poor. Most of those who survive show no significant developmental gains. For children who survive, treatment is symptomatic. It is possible that improved management of diabetic pregnancies may help prevent holoprosencephaly, however there is no means of primary prevention.
Hydranencephaly is an extreme form of porencephaly (a rare disorder, discussed later in this fact sheet, characterized by a cyst or cavity in the cerebral hemispheres) and may be caused by vascular insult or injuries, infections, or traumatic disorders after the 12th week of pregnancy.
Diagnosis may be delayed for several months because the infant's early behavior appears to be relatively normal. Transillumination, an examination in which light is passed through body tissues, usually confirms the diagnosis. Some infants may have additional abnormalities at birth including seizures, myoclonus (involuntary sudden, rapid jerks), and respiratory problems.
There is no standard treatment for hydranencephaly. Treatment is symptomatic and supportive. Hydrocephalus may be treated with a shunt.
The outlook for children with hydranencephaly is poor. Death generally occurs before age 1.
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.
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 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.
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 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 mental retardation. 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.
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.
Another group of less common cephalic disorders are the craniostenoses. Craniostenoses are deformities of the skull caused by the premature fusion or joining together of the cranial sutures. Cranial sutures are fibrous joints that join the bones of the skull together. The nature of these deformities depends on which sutures are affected.