Macrocephaly is a condition in which circumference of the human head is abnormally large.[1] It may be pathological or harmless, and can be a familial genetic characteristic. People diagnosed with macrocephaly will receive further medical tests to determine whether the syndrome is accompanied by particular disorders. Those with benign or familial macrocephaly are considered to have megalencephaly.
Causes
Macrocephaly (right) vs. normocephaly (left)
Many people with abnormally large heads or large skulls are healthy, but macrocephaly may be pathological. Pathologic macrocephaly may be due to megalencephaly (enlarged brain), hydrocephalus (abnormally increased cerebrospinal fluid), cranial hyperostosis (bone overgrowth), and other conditions. Pathologic macrocephaly is called "syndromic", when it is associated with any other noteworthy condition, and "nonsyndromic" otherwise. Pathologic macrocephaly may be caused by congenital anatomic abnormalities, genetic conditions, or by environmental events.[2]
At one end of the genetic spectrum, duplications of chromosomes have been found to be related to autism and macrocephaly; at the other end, deletions of chromosomes have been found to be related to schizophrenia and microcephaly.[4][5][6]
Environmental events associated with macrocephaly include infection, neonatal intraventricular hemorrhage (bleeding within the infant brain), subdural hematoma (bleeding beneath the outer lining of the brain), subdural effusion (collection of fluid beneath the outer lining of the brain), and arachnoid cysts (cysts on the brain surface).[2]
In research, cranial height or brain imaging may be used to determine intracranial volume more accurately.[2]
Below is a list of conditions featuring macrocephaly from NCBI's MedGen:[7]
Macrocephaly is customarily diagnosed if head circumference is greater than two standard deviations (SDs) above the mean.[8] Relative macrocephaly occurs if the measure is less than two SDs above the mean, but is disproportionately above that when ethnicity and stature are considered. Diagnosis can be determined in utero or can be determined within 18–24 months after birth in some cases where head circumference tends to stabilize in infants.[9] Diagnosis in infants includes measuring the circumference of the child's head and comparing how significant it falls above the 97.5 percentile of children similar to their demographic. If falling above the 97.5th percentile then the patient will be checked to determine whether there is any intracranial pressure present and whether or not immediate surgery is needed.[10] If immediate surgery is not needed then further testing will be done to determine whether the patient has either macrocephaly or benign macrocephaly.
Diagnosis for macrocephaly involves the comparison of the infant's head circumference to that of other infants of the same age and ethnicity. If a patient is suspected of having macrocephaly molecular testing will be used to confirm diagnosis. Symptoms vary on the cause of macrocephaly on the child and if the child has any other accompanying syndromes which will be determined through molecular testing.
Benign or familial macrocephaly
Benign macrocephaly can occur without reason or be inherited by one or both parents (in which it is considered benign familial macrocephaly and is considered a megalencephaly form of macrocephaly). Diagnosis for familial macrocephaly is determined by measuring the head circumference of both parents and comparing it to the child's. Benign and familial macrocephaly is not associated with neurological disorders.[10] While benign and familial macrocephaly do not result in neurological disorders, neurodevelopment will still need to be assessed.[citation needed]
Although neurological disorders do not occur, temporary symptoms of benign and familial macrocephaly include: developmental delay, epilepsy, and mild hypotonia.[10]
Neurodevelopment is assessed for all cases and suspected cases of macrocephaly to determine whether and what treatments may be needed, and whether any other syndrome/s may be present or likely to develop.[citation needed]
Other forms
Other forms of macrocephaly include:
Macrocephaly at birth: congenital macrocephaly already present at birth.[11]
Postnatal macrocephaly: macrocephaly developed postnatally (after birth).[12]
Progressive macrocephaly: macrocephaly developed progressively over time.[13]
Relative macrocephaly: mild macrocephaly measured under 2 SD from mean, but larger in appearance due to other factors (ex. short stature).[14]
Treatment
Treatment varies depending on whether or not it occurs with other medical conditions in the child and where the cerebrospinal fluid is present.[9]
If benign and found between the brain and skull then no surgery is needed.[9][15]
If excess fluid is found between the ventricle spaces in the brain then surgery will be needed.[15]
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