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Macrocephaly
Macrocephaly is a rare condition in which the head is
abnormally large. Spaces between the bones of the head
that hold the brain, known as fontanels, are very wide in
people with macrocephaly. Compare macrocephaly to
microcephaly, which is a rare condition in which the head is
abnormally small.
HOW LARGE DOES THE HEAD HAVE TO BE TO
QUALIFY AS MACROCEPHALY?
Technically, any head in which the skull is able to hold more
than 1450 milliliters qualifies as macrocephaly. A milliliter is
one thousandth of a liter, meaning that it takes one thousand
milliliters to equal one liter.
FEATURED BOOK: Principles of Neurology by Adams and Victor
One liter is equal to about one fourth of a gallon. Now that you know how much is in a
liter, you can tell that a milliliter is a very small amount of liquid. The normal range for the
amount of milliliters that can fit in the skull is 1350 to 1450 milliliters. Heads in this range
are known as mesocephalic.
The head of an individual with macrocephaly is two or more standard deviations above
the average head size of a normal individual that is the same age, race, and sex. A
standard deviation is a measure of the degree in which something varies from the
average. Not all people have the exact same head sizes.
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However, most people's head sizes fall within a normal range. The
normal range is typically defined as falling within one standard
deviation below the average and one standard deviation above the
average. The more standard deviations away from the average that
something gets, the more abnormal it is.
WHEN DOES MACROCEPHALY DEVELOP & WHAT CAUSES IT?
Macrocephaly can be present from birth, but it can also develop
during the first few years of life. Thus, it is possible for the head to
be normal in size at birth, but to grow at a more rapid rate
afterwards, causing it to be too large.
Macrocephaly can be due to the following causes:
HYDROCEPHALUS: A condition in which the head grows too large due to a big increase in cerebrospinal
fluid, and is usually accompanied by increased pressure within the bones that surround the brain.
Cerebrospinal fluid is a liquid that cushions and protects brain and the spinal cord. People with
hydrocephalus have a thin scalp (the skin that covers the skull). As a result, the veins in the scalp are
easily seen in people with hydrocephalus. Hydrocephalus can cause the sutures (places where two bones
join together) of the skull to separate. The eyes of people with hydrocephalus are usually turned
downwards and the whites of the top of the eyes are clearly seen. In addition, the front part of the head
appears swollen.
Hydrocephalus can be caused by infection when the mother is still pregnant, narrowing of a passageway
for cerebrospinal fluid, and an Arnold-Chiari malformation. An Arnold-Chiari malformation is an abnormal
condition in which parts of the back, bottom area of the brain, push down through the top of the opening
that contains the spine.
HYDRANENCEPHALUS: The combination of hydrocephalus (see above) and the destruction or failed
development of some parts of the top area of the brain (known as the cerebrum). This condition is often
associated with a large head. When a light is passed through the head of someone with
hydranencephalus in a dark room, the head glows like a jack-o'-lantern. This condition can be causes by
something that blocks the blood supply to the inside of the uterus. The uterus is a hollow organ in a
female's body where the egg is implanted and the baby develops. Hydranencephalus can also be caused
by diseases that destroy both sides of the brain, such as toxoplasmosis and cytomegalovirus (CMV).
In hydranencephaly, the brain and head become enlarged because the lack of tissue in the brain prevents
it from resisting the pressure of the ventricles. Ventricles are openings in the brain that produce the
cushiony fluid that protects the brain and spine. As the ventricles get bigger, they push outwards and the
brain gets larger, as does the head.
MACRENCEPHALY: Macrencephaly is excessive brain growth. This can be due to certain diseases that
make the brain larger, such as Alexander disease, later phases of Tay-Sachs disease, and spongy
degeneration of infancy.
SUBDURAL HEMATOMA: A collection of blood below the outer covering of the brain. This can cause to
head to get bigger because the pressure from the blood pushes the bones of the skull outwards. Subdural
hematomas can cause the sutures (places where two bones join together) of the skull to separate.
Children with this condition are often irritable, difficult to nourish, and have a lack of energy.
NEUROFIBROMATOSIS: A condition present at birth in which numerous benign tumors (known as
neurofibromas) and light tan spots are on the skin are present on the nerves and skin, and the bones,
muscles, and certain organs inside the body develop abnormally. Tumors are tissues that grow more
rapidly than normal. Benign tumors are tumors that are not immediately harmful.
ACHONDROPLASIA: A disorder in which the skull and cartilage (a type of tissue) in the ends of long
bones grows abnormally.
OSTEOGENESIS IMPERFECTA: An inherited disorder in which connective tissue does not develop
properly. Hydrocephalus (see above) seems to be responsible for the enlargement of the head in this
condition.
DESTRUCTIVE BRAIN DISEASES: Diseases that destroy parts of the brain, such as Greenfield's
disease and Schilder's disease, which both destroy myelin in the brain. Myelin is a fatty nerve covering
that sends impulses quickly.
AGENESIS OF THE CORPUS CALLOSUM: When the corpus callosum (a group of nerve fibers that
connect both sides of the brain) is not present. This condition is sometimes inherited.
DEFECTIVE FORMATION: A defect in formation during while the baby is developing during the first 8
weeks of pregnancy.
CAN MACROCEPHALY BE INHERITED FROM PARENTS?
Yes. There are some causes of macrocephaly that are inherited from the genes of parents. For example,
see agenesis of the corpus callosum and osteogenesis imperfecta in the last section. Genes are units of
material contained in a person's cells that contain coded instructions as for how certain bodily
characteristics (such as eye color) will develop. A cell is the smallest, most basic unit of life, that is
capable of existing by itself. All of a person's genes come from his/her parents. This is why people have
physical characteristic of their parents.
HOW IS MACROCEPHALY DIAGNOSED?
Macrocephaly is diagnosed by examining the size of the head. The specific cause of macrocephaly can
be examined by using a technique known as an ultrasound, which uses types of sound waves to produce
images of the body. Other advanced imaging techniques such as computerized axial tomography (CT)
scans and magnetic resonance imaging (MRI) can detect if there are abnormal levels of blood or fluid in
the head. A CT or MRI can also produce pictures of the size of the ventricles in the brain. Ventricles are
openings in the brain that produces the cushiony fluid that protects the brain and spine.
WHAT ARE THE BRAINS AND INTELLIGENCE LIKE OF PEOPLE WHO HAVE MACROCEPHALY?
In macrocephaly, the brain is abnormally large and brain functioning is usually abnormally slow. This
generally results in some degree of mental retardation (slowness), and thus many individuals with
macrocephaly have low intelligence.
CAN SOME PEOPLE WITH MACROCEPHALY HAVE BIG HEADS AND BRAINS BUT BE OTHERWISE
NORMAL?
Yes. There are a small percentage of people who have large heads and large brains, but are normal in all
other ways. These people tend to come from families of people with large heads, and in these cases the
condition appears to be inherited.
WHAT ARE THE FACIAL FEATURES LIKE OF PEOPLE WITH MACROCEPHALY?
The facial features of people with macrocephaly are usually normal. This is because the face grows at a
normal rate in people with macrocephaly.
WHAT DOES THE REST OF THE BODY LOOK LIKE IN PEOPLE WHO HAVE MACROCEPHALY?
The growth of the rest of the body, in people who have macrocephaly, is often slowed. Thus, the head
appears large in comparison to the rest of the body.
CAN MACROCEPHALY BE TREATED?
Unfortunately, there is no form of treatment for macrocephaly. Nursing care generally focuses on treating
specific symptoms, providing support, help, and education to parents so they can learn how to take care
of a brain-damaged child.
WHAT OTHER WORDS ARE RELATED TO MACROCEPHALY?
Macrocephaly is also known as leontiasi ossea, megacephaly, megacephalia, megalocephaly,
megalocephalia, macrocephalia, cephalomegaly, and Virchow disease. Macrocephalic and
macrocephalous means pertaining to macrocephaly. Compare macrocephaly to mesocephaly (a normally
shaped head), microcephaly (an abnormally small head), dolichocephaly (an abnormally long head), and
brachycephaly (a head that is too short and broad).
WHY IS IT CALLED MACROCEPHALY?
Macrocephaly comes from the Greek word "makros" meaning "large," and the Greek word "kephale"
meaning "head." Put the two words together and you get "large head."
A child with macrocephaly.