Macrocephaly
Alexander J. Towbin, MD
DIFFERENTIAL DIAGNOSIS
Common
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Benign Extracranial Collections of Infancy
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Hydrocephalus
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Child Abuse
Less Common
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Neurofibromatosis Type 1
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Vein of Galen Aneurysmal Malformation
Rare but Important
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Tay-Sachs Disease
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Alexander Disease
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Canavan Disease
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Krabbe Disease
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Leigh Syndrome
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
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Measurement of head circumference is part of typical well child check
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Macrocrania is defined as head circumference > 95th percentile
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Determinants of head circumference: Brain size, cerebral spinal fluid volume, and subdural spaces
Helpful Clues for Common Diagnoses
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Benign Extracranial Collections of Infancy
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a.k.a. benign hydrocephalus of infancy or external hydrocephalus
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Characterized by excess cerebral spinal fluid (CSF) in subarachnoid space and macrocephaly
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Excess fluid is more abundant overlying frontal lobes
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Often family history of macrocephaly
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Normal long-term development and no additional risk for hydrocephalus
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Extraaxial collection resolves by age 2
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Hydrocephalus
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Incidence has declined along with decrease of open neural tube defects
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2 main types: Communicating and noncommunicating
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Communicating: Overproduction or underresorption of CSF
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Obstructive: Intraventricular hemorrhage, aqueductal stenosis, and migrational abnormalities
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Present with enlarging head, crossing percentiles
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May have signs of ↑ intracranial pressure
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Often treated with shunting
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Child Abuse
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Cranial trauma is most common cause of death in abuse
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Most common cause of head trauma in children < 2 years
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Mechanism of injury: Shaking and impact
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Evaluation includes skeletal survey and head CT
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Findings: Skull fracture, subdural hematomas of different ages, and brain edema
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Helpful Clues for Less Common Diagnoses
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Neurofibromatosis Type 1
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Autosomal dominant disorder
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Affects 1:3,000
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Characteristic features: Café-au-lait macules, benign neurofibromas, plexiform neurofibromas, and iris hamartomas
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Neurologic findings: Optic pathway gliomas, seizures, headache, hydrocephalus, and macrocephaly
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Risk for central nervous system tumors: Astrocytomas, optic pathway gliomas
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Vein of Galen Aneurysmal Malformation
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Account for 1% of all intracranial vascular malformations
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30% of vascular intracranial malformations in children
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Ectatic vascular structure is median prosencephalic vein, not vein of Galen
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Occurs due to direct communication between arterial network and median prosencephalic vein
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After birth, increase in blood flow through malformation
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Up to 80% of left ventricular output may supply brain
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Leads to increased cardiac output and heart failure
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Usually associated with other intracranial venous anomalies
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Helpful Clues for Rare Diagnoses
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Tay-Sachs Disease
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Autosomal recessive disorder
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More common in Ashkenazi Jews
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Cause: Deficiency of β-hexosaminidase
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Characterized by progressive weakness and loss of motor skills beginning at 2-6 months of age
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Findings: ↑ startle response, hypotonia, hyperreflexia, and cherry red macule
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Progressive neurodegeneration with macrocephaly
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Macrocephaly due to accumulation of GM2 ganglioside
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Alexander Disease
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Demyelinating disorder characterized by Rosenthal fibers
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Usually sporadic disorder
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Types: Infantile, juvenile, and adult
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Infantile form is most common
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Characterized by macrocephaly, psychomotor retardation, muscle weakness, pyramidal tract signs, seizures
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Average age of onset: 6 months
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Juvenile form characterized by progressive paresis, bulbar signs, and brisk reflexes
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Average age of onset: 9 years
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Adult form: Intermittent neurologic disorders similar to multiple sclerosis
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MR: Frontal lobe demyelination and cysts, ventriculomegaly, and poor gray-white differentiation
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Canavan Disease
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Autosomal recessive disorder
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More common in Ashkenazi Jews
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Cause: Inborn error of metabolism, deficiency of aspartoacylase enzyme
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Leads to increased N-acetyl L-aspartate
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Characterized by spongy degeneration of brain
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Findings: Poor head control, macrocephaly, mental retardation, optic atrophy, and seizures
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Krabbe Disease
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Autosomal recessive disorder
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Characterized by severe myelin loss
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Cause: Deficiency of lysosomal enzyme galactosylceramidase
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2 types: Early infantile or late onset
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Most common: Early infantile (90%)
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Leigh Syndrome
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