What is megalencephaly?
Megalencephaly is a condition in which your brain is abnormally large. An
average adult brain weighs between 1,300 and 1,400 grams, or between 2.87
pounds and 3.09 pounds. According to The Gale Encyclopedia of Neurological
Disorders, the brain of an adult with megalencephaly weighs more than 1,600
grams, or 3.53 pounds.
Megalencephaly may be present at birth. It can also develop over time. In
some cases, your brain may reach twice the normal weight.
Megalencephaly can occur alone. It may not occur with any symptoms. It can
also occur with a wide range of neurological problems or birth defects. It’s
sometimes confused with macrocephaly. This is a condition in which your head is
large but not necessarily abnormal.
Three broad types of megalencephaly exist:
- primary megalencephaly, or benign familial
- secondary megalencephaly, which occurs as the result of
- unilateral megalencephaly, or hemimegalencephaly, which
occurs when half of your brain is enlarged
are the symptoms of megalencephaly?
If you have megalencephaly, your symptoms can range from mild to severe.
They depend on the underlying cause of your condition. If you have benign
familial megalencephaly, you may have no symptoms. You may have normal to
advanced intelligence. In other cases, your facial features may have an
abnormal size or shape. If another disorder causes megalencephaly, you may have
cognitive impairment, seizures, or other symptoms.
Common neurological symptoms include:
- delayed development of your gross motor skills,
including your ability to hold your head upright, change position, roll
over, sit, and stand
- delayed speech development
- corticospinal dysfunction, in which your brain doesn’t
send impulses to your spinal cord properly
- intellectual disability
- defects in your muscle tone
- body asymmetry
- an inability to coordinate and control your movements
- visual irregularities
What causes megalencephaly?
Defects in the way that your brain controls cell production cause
megalencephaly. In normal brain cell growth, your body produces the correct
number of brains cells. It produces them in the right place at the right time.
Megalencephaly occurs when your brain produces too many new brain cells or cells
that are too large. It can also occur when metabolic byproducts and matter
build up in your brain.
Genetic factors and genetic disorders can cause megalencephaly. For example,
the condition can result from:
- Alexander disease
- tuberous sclerosis
- overgrowth disorders, such as Sotos syndrome and
- chromosomal disorders, such as Klinefelter’s syndrome
Non-genetic causes can also lead to megalencephaly. For example, disorders affecting
your cerebral spinal fluid can cause it.
Sometimes, the doctor can’t identify the cause.
is at risk of megalencephaly?
Megalencephaly is three to four time more common in males than females,
reports The Gale Encyclopedia of Neurological Disorders. It affects between 10
and 30 percent of patients with macrocephaly. Asymptomatic cases may not be
reported, so the incidence is unknown.
How is megalencephaly diagnosed?
Your doctor will perform a complete physical exam to diagnose
megalencephaly. They’ll measure the circumference of your head. They may also
measure the heads of your immediate relatives. They may also take your personal
and family medical history.
In some cases, your doctor might perform developmental and neurological
exams. For example, they may order MRI or CT scans. This can help them examine
the appearance and size of your brain. They may also order laboratory tests.
This can help them check for genetic and chromosomal disorders.
is megalencephaly treated?
No cure for megalencephaly is available. However, your doctor may prescribe treatments
for your symptoms, underlying disorders, or associated disabilities.
For example, your doctor may prescribe medications. Anti-epileptic drugs can help
control seizures. Physical, speech, and occupational therapy may help you
manage physical or neurological disabilities.
is the outlook for megalencephaly?
If you have megalencephaly, your long-term outlook depends on the severity
of your condition.
In some cases, your symptoms may be very mild. They may require little to no
treatment. They may have little impact on your life.
In other cases, your symptoms may be severe. For example, seizures,
paralysis, and cognitive impairments can be limiting. If you have these
symptoms, you may need physical, speech, or occupational therapies. Children
with these symptoms may also require special education classes.
If you have hemimegalencephaly, the long-term outlook is poor. This
condition is rare. It can lead to cognitive impairment, severe seizures, and
paralysis on one side of your body.
Ask your doctor for more information about your specific diagnosis and
Megalencephaly isn’t preventable. If you have a family history of the
condition, talk to your doctor about genetic counseling. This can help you
assess your risk of developing the condition. It can also help you assess the
risk for your children or future children.