Macrocephaly refers to an abnormally large head circumference. This condition can be a harmless variation that runs in families, or it can indicate an underlying medical condition. Understanding the potential causes helps determine if medical evaluation is necessary.
Understanding Macrocrania
Macrocrania is clinically defined when the occipitofrontal circumference (OFC) of the head is significantly larger than expected for an individual’s age and sex. This means a measurement greater than two standard deviations above the mean, or above the 97th or 98th percentile on standardized growth charts. While some children with mild macrocephaly may have normal development, a measurement above three standard deviations is considered clinically relevant.
Macrocrania is distinguished between benign familial macrocrania and pathological macrocrania. Benign familial macrocrania is a common inherited trait where a child has a larger head size, often similar to a family member, and does not present with neurological symptoms or require treatment. In contrast, pathological macrocrania indicates an underlying medical condition. Macrocephaly should also be differentiated from megalencephaly, which refers to an oversized brain.
Causes of Macrocrania
Macrocrania can stem from various factors, including an increase in brain size, cerebrospinal fluid (CSF), blood, or bone within the skull, or from increased intracranial pressure. Benign familial macrocephaly is one common cause.
Hydrocephalus, where excessive CSF accumulates within the brain’s cavities, is a neurological cause of macrocephaly, particularly in infants whose skull bones have not yet fused. This buildup increases pressure inside the head, leading to ventricular enlargement and skull expansion. Another cause is benign external hydrocephalus, also known as benign enlargement of the subarachnoid spaces in infancy (BESS or BESSI). This condition involves a transient accumulation of CSF in the frontal region, often resolving spontaneously by age three.
Genetic syndromes are often associated with macrocephaly. Examples include Sotos syndrome, an overgrowth condition characterized by macrocephaly, a prominent forehead, and advanced bone age. Fragile X syndrome, a common genetic cause of intellectual disability, can also present with relative macrocephaly. Other genetic conditions include neurofibromatosis type 1, tuberous sclerosis, and certain leukodystrophies like Alexander disease and Canavan disease, which involve white matter degeneration.
Brain tumors, both benign and malignant, can also lead to macrocephaly by occupying space within the skull or obstructing CSF flow, thereby increasing intracranial pressure. Metabolic disorders, such as glutaric aciduria type 1 and mucopolysaccharidoses, can cause macrocephaly due to the abnormal accumulation of metabolic substances in brain cells or impaired CSF reabsorption. Additionally, some bone disorders, like cranial hyperostosis or osteopetrosis, can result in macrocephaly due to overgrowth or increased density of the skull bones.
Diagnosis and Evaluation
The diagnostic process for macrocephaly begins with a comprehensive evaluation, including a detailed medical history and physical examination. Precise measurements of the head circumference are taken and plotted on growth charts to assess if the size is significantly larger than expected for the individual’s age and sex. Reviewing the growth pattern over time is also important, as a rapidly increasing head circumference can be a sign of an underlying issue.
Imaging studies are a next step to identify any structural abnormalities within the brain or skull. Ultrasound is used for infants with an open fontanelle, while computed tomography (CT) scans and magnetic resonance imaging (MRI) provide more detailed views. MRI is useful for distinguishing between different causes, such as enlarged brain tissue, fluid collections, or tumors. Genetic testing may also be performed to identify specific gene mutations or chromosomal abnormalities contributing to macrocephaly, especially when a genetic syndrome is suspected.
Management and Outlook
The management of macrocephaly is tailored to its underlying cause. For cases of benign familial macrocephaly, no specific treatment is necessary, and children remain asymptomatic. Regular monitoring of head size and neurological development is sufficient to ensure a favorable outcome. Similarly, benign external hydrocephalus resolves spontaneously without intervention.
When macrocephaly results from an underlying pathological condition, treatment focuses on addressing that specific disorder. For example, hydrocephalus requires neurosurgical intervention, such as the placement of a ventriculoperitoneal (VP) shunt, to drain excess cerebrospinal fluid and relieve intracranial pressure. Brain tumors may necessitate surgical removal, while metabolic disorders might be managed with targeted medications or therapies. The prognosis for individuals with macrocephaly varies widely depending on the identified cause, underscoring the importance of early and accurate diagnosis to guide appropriate interventions.