What are the implications of a high head circumference in an 18-month-old child?

High Head Circumference in an 18-Month-Old Child

A high head circumference (>97th percentile or >+2 SD) in an 18-month-old requires careful clinical evaluation with serial measurements compared to parental head size, followed by neuroimaging only if concerning features are present on history or physical examination. 1, 2

Initial Assessment Approach

Measurement Verification and Serial Tracking

• Obtain accurate measurement using a firm, non-stretchable measuring tape placed just above the supraorbital ridges anteriorly and around the occiput posteriorly to obtain maximum circumference, recorded to the nearest 0.1 cm 1
• Plot on appropriate growth charts (WHO or CDC) to confirm macrocephaly (head circumference above +2 SD or 97th percentile) 1, 3
• Review all previous head circumference measurements to determine growth trajectory—serial measurements are more valuable than a single measurement for identifying abnormal patterns 1, 2
• Measure both parents' head circumferences and compare with the same-sex parent, as familial macrocephaly (benign familial megalencephaly) is common and often overlooked 2, 4

Critical History Elements

• Assess for symptoms of increased intracranial pressure: rapidly enlarging head circumference (>2 cm in <7 days), increased splaying of cranial sutures, full/tense fontanel, worsening apnea and bradycardia, lethargy, feeding intolerance, or vomiting 5
• Screen for developmental concerns: motor delays, regression of previously acquired skills, asymmetric motor development, or development of handedness before 18 months (which is abnormal) 5
• Evaluate for seizure history: recurrent nonfebrile seizures may indicate underlying structural brain abnormalities 5
• Review growth parameters: compare head circumference trajectory with weight and length/height growth patterns to identify disproportionate growth 5, 6

Physical Examination Red Flags

• Neurologic examination: assess for altered level of consciousness, abnormal tone (increased or decreased), primitive reflex persistence, absent protective reflexes, cranial nerve abnormalities, or focal neurologic deficits 5
• Fontanel assessment: full, tense, or bulging anterior fontanel suggests elevated intracranial pressure 5
• Ophthalmologic findings: papilledema on fundoscopic examination indicates increased intracranial pressure requiring urgent evaluation 5
• Signs of abuse: scalp bruising or bogginess, subconjunctival hemorrhage, bleeding from nose or mouth, facial bruising, or petechiae on trunk/face/ears warrant consideration of abusive head trauma 5
• Dysmorphic features: evaluate for syndromic conditions including facial features, skin findings, and other congenital anomalies 5, 4

When Neuroimaging is Indicated

Proceed with MRI (preferred over CT) if:

• Symptomatic hydrocephalus signs: rapidly accelerating head growth with clinical symptoms of increased intracranial pressure 5, 7
• Abnormal neurologic examination: focal deficits, altered mental status, seizures, or developmental regression 5
• Papilledema or visual changes: suggests elevated intracranial pressure requiring urgent evaluation 5
• Disproportionate growth: head circumference increasing out of proportion to weight and length 5, 6
• Concern for structural abnormality: based on clinical features suggesting tumor, hydrocephalus, or metabolic disorder 5, 4
• Suspected abuse: any concerning features on history or physical examination 5

Neuroimaging NOT routinely indicated if:

• Benign familial megalencephaly: child is developmentally normal with proportionate growth and same-sex parent has large head circumference 2, 4
• Stable growth trajectory: head circumference tracking along same percentile curve without acceleration 1, 2
• Normal neurologic examination: no signs of increased intracranial pressure, normal development, and no concerning symptoms 5

Common Pitfalls to Avoid

• Failing to measure parental head circumference: this is the most commonly overlooked step and can prevent unnecessary imaging in cases of benign familial megalencephaly 2
• Relying on single measurement: one elevated measurement without serial tracking can lead to overdiagnosis 1, 2
• Ordering imaging without clinical correlation: neuroimaging should be guided by concerning history or physical findings, not isolated head circumference measurement 5
• Missing subtle signs of increased intracranial pressure: in infants, increased head circumference may be the only early sign of hydrocephalus, particularly in the first 10 months of life 7, 8
• Overlooking developmental assessment: macrocephaly associated with developmental delays warrants more aggressive evaluation for metabolic or genetic disorders 5, 4

Follow-Up Strategy

• Serial measurements every 2-4 weeks if initial evaluation is reassuring but head circumference remains elevated, to monitor growth trajectory 6, 2
• Developmental surveillance at each visit to identify emerging concerns that might warrant further evaluation 5
• Reassess if clinical status changes: new symptoms, developmental regression, or accelerating head growth require prompt re-evaluation 5, 7
• Consider genetics or neurology referral if syndromic features present, developmental delays emerge, or growth pattern remains concerning despite benign initial workup 5, 4