Defining a large head circumference (macrocephaly)
In medical terms, a big head circumference is formally known as macrocephaly. This diagnosis is typically made when a person's head circumference is greater than two standard deviations above the mean, which corresponds to being above the 97th percentile, for their age and sex.
For infants and children, this measurement is a standard part of routine well-child checkups up to age 24 to 36 months, as it is a key indicator of central nervous system development. Healthcare providers use specific growth charts from organizations like the World Health Organization (WHO) or Centers for Disease Control and Prevention (CDC) to plot the measurement and track growth over time. An abnormal finding often prompts closer monitoring and further evaluation.
In adults, while percentile charts still exist, the definition is less formal. Some sources consider head circumferences greater than 58 cm for men and 56 cm for women to be larger than average, though a definitive medical diagnosis of macrocephaly is less common and usually tied to specific symptoms or underlying conditions.
The varied causes of macrocephaly
The reasons for a large head circumference can range from completely harmless to indicative of a serious medical issue. It is crucial to determine the cause to understand the appropriate course of action.
Benign causes
- Benign familial macrocephaly: This is the most common cause of a large head and is simply an inherited trait. If a parent or other close family member has a large head and the child has no other symptoms or developmental delays, the condition is usually considered benign. The child typically follows a normal developmental trajectory.
- Benign enlargement of the subarachnoid space (BESSI): Also called benign external hydrocephalus, this condition involves a temporary excess of cerebrospinal fluid (CSF) in the space surrounding the brain. The condition often resolves on its own without intervention as the child gets older, usually by around 2.5 years of age.
Pathological (underlying medical) causes
- Hydrocephalus: A buildup of excess cerebrospinal fluid within the brain's ventricles can increase pressure on the brain tissue and cause the head to enlarge. This condition can lead to seizures and developmental delays if not treated promptly.
- Megalencephaly: This term refers to an actual overgrowth and enlargement of the brain tissue itself. It is a distinct condition from macrocephaly (large head), though it can cause it. Some forms can be benign, while others are associated with genetic disorders.
- Genetic syndromes: Many genetic disorders can cause a large head circumference, sometimes alongside other characteristic features. Examples include Sotos syndrome, Fragile X syndrome, and Neurofibromatosis Type 1 (NF1).
- Other conditions: In rare cases, macrocephaly can be caused by brain tumors, chronic hematomas (blood pockets), or infections like meningitis. These are typically accompanied by other distinct symptoms.
When to be concerned about a large head circumference
While benign familial macrocephaly requires only monitoring, other signs warrant immediate medical attention. When evaluating a child, healthcare providers look for signs beyond the head size itself.
- Rapid head growth: If a child's head circumference is rapidly crossing percentile lines on the growth chart, especially after 6 months of age, it could be a sign of a pathological condition like hydrocephalus.
- Developmental delays: Delays in reaching motor, social, intellectual, or language milestones can be a key indicator of an underlying issue, particularly in cases not attributed to benign familial traits.
- Neurological signs: Symptoms of increased intracranial pressure are a major red flag. For infants, this can include a bulging fontanelle (the soft spot on the head), unusually prominent scalp veins, excessive irritability, vomiting, or a downward gaze of the eyes. In older children, signs may include headaches, vision changes, or balance issues.
- Associated conditions: The presence of other features, such as those related to specific genetic syndromes like Sotos or Fragile X, will guide further investigation.
Benign vs. pathological macrocephaly: A comparison
| Feature | Benign Familial Macrocephaly | Pathological Macrocephaly |
|---|---|---|
| Family History | Yes, at least one other family member has a large head. | Usually no, or not consistently present. |
| Head Growth Pattern | Grows consistently along or slightly above the standard percentile curve. | May show a sudden acceleration, rapidly crossing multiple percentile lines. |
| Neurological Symptoms | Absent. The child is otherwise healthy and neurologically normal. | Often present, including irritability, vomiting, seizures, or vision changes. |
| Developmental Milestones | Reached on time or with minimal delay. Transient delays might occur but are not a defining feature. | Frequent and significant developmental delays or regression in skills. |
| Associated Conditions | None. The large head is an isolated finding. | Can be associated with genetic syndromes, tumors, or fluid buildup. |
The diagnostic and evaluation process
If a healthcare provider has concerns about a child's head circumference, they will follow a systematic process for evaluation:
- Serial Measurements: The head circumference will be measured and plotted on growth charts over several visits to monitor the rate of growth.
- Physical and Neurological Exam: A thorough examination will be performed to check for other signs like a bulging fontanelle, prominent scalp veins, or any neurological abnormalities.
- Family History: The provider will ask about the head size of family members to determine if the large head is simply an inherited trait.
- Imaging Studies: To rule out or confirm underlying conditions, imaging tests of the head may be ordered. These can include a head ultrasound (for infants), a CT scan, or an MRI, which can provide detailed images of the brain and surrounding structures.
- Genetic Testing: If a genetic syndrome is suspected based on other symptoms, genetic testing may be recommended.
Conclusion
A large head circumference is a medical finding that warrants careful attention, particularly in infants and young children. While the term macrocephaly can sound alarming, it is most often a benign, inherited characteristic with no associated health problems. However, because it can also be a sign of a serious underlying condition, distinguishing between these possibilities is paramount.
The diagnostic process, involving regular measurements, thorough physical examinations, and potentially imaging, allows healthcare professionals to accurately assess the situation and provide appropriate reassurance or treatment. Families who have questions or concerns about their child's head size should consult with their healthcare provider for a proper evaluation.
For additional information on childhood development and health concerns, resources like Nationwide Children's Hospital can be helpful.
