contributed by Roger J. Hudgins, M.D. and William R. Boydston, M.D., Ph.D.
Macrocephaly refers to a head circumference greater than two standard deviations above the mean for age, sex, race and gestation. Since macrocephaly is a statistical concept, a percentage of children with large heads will be normal. However, abnormal head size may be the first clinical sign of intracranial pathology. This is also true of serial measurements showing an increasing or decreasing rate of head growth still within the upper or lower second percentiles on the head growth curve.
Every child with macrocephaly or microcephaly or an increasing or decreasing rate of head growth should be evaluated. This should start with a careful history, cranial and neurological examination. As hydrocephalus, brain tumors, chronic subdural hematomas or other intracranial mass lesions may cause macrocephaly, symptoms and signs of increased intracranial pressure are extremely important in this evaluation. These symptoms may be progressive irritability, lethargy and vomiting in young children and intermittent headaches and vomiting in older children. Characteristic signs of elevated intracranial pressure are MacEwen's (cracked pot sound on thumping the head), prominent frontotemporal scalp veins, bulging anterior fontanel, impaired upward gaze (sunsetting eyes), unilateral or bilateral sixth cranial nerve paresis, papilledema and, later in the course, alteration of the level of consciousness. While the presence of any of these signs or symptoms in the child with macrocephaly would warrant immediate neurosurgical consultation, their absence does not preclude elevated intracranial pressure. With progressive hydrocephalus some children will have increased muscle tone, particularly in the lower extremeties, or difficulties with phonation or feeding.
If the child exhibits no signs of increased intracranial pressure but has developmental delay, metabolic and congenital abnormalties such as Alexander's disease and disorders of cerebral architecture must be excluded. Macrocephaly associated with primary abnormalities of bone such as achondroplasia and rickets are recognized primarily by the characteristic body habitus and/or laboratory abnormalities.
From a neurosurgical standpoint the key to evaluation of the infant or child with macrocephaly and suspected intracranial or cranial pathology is diagnostic imaging. For the infant with an open fontanel and suspected hydrocephalus, the cranial ultrasound is the imaging modality of choice. For evaluation of other suspected conditions, computed tomography (CT) and magnetic resonance imaging (MRI) are utilized. MRI is best suited for detailed imaging of the brain and, although more expensive than CT, does not use radiation. As MRI does not allow visualization of bone, CT is used if craniosynostosis is suspected.
One of the more common causes of macrocephaly is termed benign subdural hygromas of infancy. Characteristically, the infant has a normal head circumference at birth and for the first few months. The head growth then accelerates and may exceed the ninety-eighth percentile. Development is usually normal but there may be mild motor delay. The fontanel is sunken to flat. CT or MRI will reveal normal sized ventricles but an enlarged frontal subarachnoid space. These children do well without intervention. The head size usually normalizes by eighteen to twenty-four months and development catches up.