What Are Cephalic Disorders?
Cephalic disorders are congenital
conditions that stem from damage to, or abnormal development of, the budding
nervous system. Cephalic is a term that means "head" or "head end of the body."
Congenital means the disorder is present at, and usually before, birth. Although
there are many congenital developmental disorders, this article briefly
describes only cephalic conditions.
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.
What Are the Different Kinds of Cephalic
Disorders?
ANENCEPHALY is a neural tube defect that occurs
when the cephalic (head) end of the neural tube fails to close, usually between
the 23rd and 26th days of pregnancy, 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.
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 also are 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.
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 often is
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.
HOLOPROSENCEPHALY is a disorder characterized by the
failure of the prosencephalon (the forebrain of the embryo) to develop. During
normal development the forebrain is formed and the face begins to develop in the
fifth and sixth weeks of pregnancy. Holoprosencephaly is caused by a failure of
the embryo's forebrain to divide to form bilateral cerebral hemispheres (the
left and right halves of the brain), causing defects in the development of the
face and in brain structure and function.
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. Although it is
possible that improved management of diabetic pregnancies may help prevent
holoprosencephaly, there is no means of primary
prevention.
HYDRANENCEPHALY is a rare condition in which the
cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal
fluid. Usually the cerebellum and brainstem are formed normally. 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 (hypertonia). After several
months of life, seizures and hydrocephalus may develop. Other symptoms may
include visual impairment, lack of growth, deafness, blindness, spastic
quadriparesis (paralysis) and intellectual deficits.
Hydranencephaly is
an extreme form of porencephaly (a rare disorder, discussed later in this
article, characterized by a cyst or cavity in the cerebral hemispheres) and may
be caused by vascular insult (such as stroke) 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 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.
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 also may pose a danger to the mother's
life.
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,
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 also may
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 that 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, 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 article). 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 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 also may 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 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
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.
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, often are 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 also may 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.
What Are Other Less Common
Cephalies?
ACEPHALY literally means absence of the head. It is
a much rarer condition than anencephaly. The acephalic fetus is a parasitic twin
attached to an otherwise intact fetus. The acephalic fetus has a body but lacks
a head and a heart; the fetus's neck is attached to the normal twin. The blood
circulation of the acephalic fetus is provided by the heart of the twin. The
acephalic fetus cannot exist independently of the fetus to which it is
attached.
EXENCEPHALY is a condition in which the brain is located
outside of the skull. This condition is usually found in embryos as an early
stage of anencephaly. As an exencephalic pregnancy progresses, the neural tissue
gradually degenerates. It is unusual to find an infant carried to term with this
condition because the defect is incompatible with
survival.
MACROCEPHALY is a condition in which the head
circumference is larger than average for the age and gender of the infant or
child. It is a descriptive rather than a diagnostic term and is a characteristic
of a variety of disorders. Macrocephaly also may be inherited. Although one form
of macrocephaly may be associated with mental retardation, in approximately
one-half of cases mental development is normal. Macrocephaly may be caused by an
enlarged brain or hydrocephalus. It may be associated with other disorders such
as dwarfism, neurofibromatosis and tuberous
sclerosis.
MICRENCEPHALY is a disorder characterized by a small
brain and may be caused by a disturbance in the proliferation of nerve cells.
Micrencephaly also may be associated with maternal problems such as alcoholism,
diabetes or rubella (German measles). A genetic factor may play a role in
causing some cases of micrencephaly. Affected newborns generally have striking
neurological defects and seizures. Severely impaired intellectual development is
common, but disturbances in motor functions may not appear until later in
life.
OCTOCEPHALY is a lethal condition in which the primary
feature is agnathia — a developmental anomaly characterized by total or virtual
absence of the lower jaw. The condition is considered lethal because of a poorly
functioning airway. In octocephaly, agnathia may occur alone or together with
holoprosencephaly.
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.
BRACHYCEPHALY occurs when the coronal suture fuses
prematurely, causing a shortened front-to-back diameter of the skull. The
coronal suture is the fibrous joint that unites the frontal bone with the two
parietal bones of the skull. The parietal bones form the top and sides of the
skull.
OXYCEPHALY is a term sometimes used to describe the
premature closure of the coronal suture plus any other suture, or it may be used
to describe the premature fusing of all sutures. Oxycephaly is the most severe
of the craniostenoses.
PLAGIOCEPHALY results from the premature
unilateral fusion (joining of one side) of the coronal or lambdoid sutures. The
lambdoid suture unites the occipital bone with the parietal bones of the skull.
Plagiocephaly is a condition characterized by an asymmetrical distortion
(flattening of one side) of the skull. It is a common finding at birth and may
be the result of brain malformation, a restrictive intrauterine environment or
torticollis (a spasm or tightening of neck muscles).
SCAPHOCEPHALY
applies to premature fusion of the sagittal suture. The sagittal suture joins
together the two parietal bones of the skull. Scaphocephaly is the most common
of the craniostenoses and is characterized by a long, narrow
head.
TRIGONOCEPHALY is the premature fusion of the metopic suture
(part of the frontal suture which joins the two halves of the frontal bone of
the skull) in which a V-shaped abnormality occurs at the front of the skull. It
is characterized by the triangular prominence of the forehead and closely set
eyes.
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