The term macrocephaly (from ancient Greek μακρός, macro, “long, large”; κεφαλή, kephalē, “head”), in human pathological anatomy, indicates a skull size greater than the 97th percentile of the comparison group of equal age and same sex. This abnormality may be evident in the newborn and may signal various conditions arising during embryonic development or in the first years of life.

Macrocephaly can be found, in particular, in the presence of hydrocephalus and megaloencephaly (excessive increase in encephalic mass). In turn, these pathological conditions may result from dysfunction of the encephalic circulation, cerebrospinal fluid alterations, arrested neuronal migration, and lissencephaly.

The most common causes of neonatal macrocephaly include hydrocephalus due to congenital malformations and infections acquired in utero (such as toxoplasmosis, rubella and cytomegalovirus) or in the perinatal period, such as viral or bacterial meningitis. In the first few months of life, the condition may depend on skeletal abnormalities (such as achondroplasia, Paget’s disease, or osteogenesis imperfecta) and space-occupying endocranial lesions (e.g., hemorrhages, subdural hematomas, and brain tumors).

Macrocephaly may also occur due to metabolic dysfunction, intoxication (e.g., exposure to certain drugs or fetal alcohol syndrome), storage diseases (such as mucopolysaccharidosis), or specific genetic defects (e.g., Simpson-Golabi-Behmel syndrome, Alexander syndrome, and Joubert syndrome). Macrocephaly may also be associated with neurofibromatosis, tuberous sclerosis, and progeria.

Diagnosis of macrocephaly

Before birth, the diagnosis of macrocephaly is sometimes made based on a prenatal ultrasound performed at the end of the second or beginning of the third trimester of pregnancy.

After birth, the physician measures the head circumference (measurement of the head at its widest point) of the baby during routine objective examinations. The diagnosis of macrocephaly is confirmed when the head circumference is significantly greater than normal for children of the same sex, age, and ethnicity in the region where the affected child resides. To make the diagnosis, physicians also consider the head circumference of the child’s parents and grandparents, because having a slightly larger head may be a family trait.

If macrocephaly is present, a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan of the head is usually performed to look for brain abnormalities. The doctor examines the infant and asks the parents to think about possible causes of macrocephaly, then performs some tests for any suspected causes. Sometimes the doctor may prescribe blood tests to determine the cause.

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