Microcephaly
Susan I. Blaser, MD, FRCPC
DIFFERENTIAL DIAGNOSIS
Common
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Secondary/Acquired from
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Hypoxic Ischemic Encephalopathy
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TORCH Infections
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Nonaccidental Trauma
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Meningitis
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Fetal Alcohol Syndrome
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Less Common
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Primary/Genetic with
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Gyral Simplification
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Cortical Dysplasia
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Midline Anomaly
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Cerebellar Hypoplasia
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Hypomyelination
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Rare but Important
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Microlissencephaly
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Pseudo-TORCH
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Aicardi-Goutières
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Progeroid Syndromes
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Cockayne
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ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
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Was head circumference ever normal?
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Decreased cranio-facial ratio on sagittal view helpful, tape measure best
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Do not disregard nonaccidental trauma as cause of small head
Helpful Clues for Common Diagnoses
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Hypoxic Ischemic Encephalopathy
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Perinatal or birth asphyxia (asphyxia neonatorium)
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Patterns helpful, even if no history
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Profound: Atrophy, gliosis
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Posterior putamen
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Lateral thalami
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Rolandic cortex
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Prolonged progressive
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Typical watershed encephalomalacia
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Mixed
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Features of both, ± calcified thalami
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TORCH Infections
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Cytomegalovirus (CMV) (common) and rubella (rare, today) most likely to have microcephaly
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Toxo, CMV, HIV, and rubella may have intracranial Ca++, which may help in determining underlying etiology
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CMV: Parenchymal or periventricular Ca++
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HIV: Basal ganglia and subcortical calcifications
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Toxo: Parenchymal or periventricular Ca++
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Rubella and HSV cause lobar brain destruction/encephalomalacia
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CMV may also have cortical dysplasia, periventricular Ca++, hypomyelination
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Nonaccidental Trauma
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History is crucial
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Majority of abuse in children < 1 year old
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Most common in children 2-6 months old
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After trauma: Subarachnoid and subdural hemorrhages are common
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Subdural hemorrhage over convexity, interhemispheric, overlying tentorium
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Caution in attempting to determine age of subdural hemorrhage
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BUT look for evidence of trauma/fractures on ALL available films
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Brain imaging of microcephaly
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Global atrophy or hemiatrophy
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Hemosiderin
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Meningitis
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Early infancy: Group B strep most damaging
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Hypothalamus
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Chiasm
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Inferior basal ganglia
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Diffuse cortex, often asymmetric
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Fetal Alcohol Syndrome
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Microcephaly
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By tape measure
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Or MR volumetrics
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Anomalies may occur, but not specific
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Diffusion tensor imaging (DTI) reported to show abnormal connectivity
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Helpful Clues for Less Common Diagnoses
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Gyral Simplification
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Small, grossly normal brain
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Looks like “small but perfect” brain
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Corpus callosum may appear thick, lack isthmus
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Cortical Dysplasia
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Midline Anomaly
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Holoprosencephaly
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Most severe are smallest
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Agenesis of corpus callosum
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Assess corpus callosum presence, size, shape
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Is there isthmus?
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Cerebellar Hypoplasia
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In multiple syndromes
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Olivopontocerebellar degeneration
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Spinocerebellar ataxia
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Carbohydrate deficient glycoprotein syndrome type 1a
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May be clue to rare disorders
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Microlissencephaly
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TUBA1A mutations: Lissencephaly PLUS cerebellar hypoplasia
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Assess degree of deficiency
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Fastigial recess, primary fissure
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Degree of vermian lobulation
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Tegmento-vermian angle (is the inferior 4th ventricle open?)
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Hypomyelination
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May be a clue to rare disorders
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Early onset West syndrome with cerebral hypomyelination and reduced white matter
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3-phosphoglycerate dehydrogenase deficiency
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Progressive encephalopathy, edema, hypsarrhythmia, optic atrophy (PEHO)
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Helpful Clues for Rare Diagnoses
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Microlissencephaly
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Z-shaped brainstem
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Callosal agenesis
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Surface often totally smooth
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Very small brain
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Pseudo-TORCH
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Aicardi-Goutières
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CMV-like: Ca++
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Hypomyelinaton
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Atrophy
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Autosomal recessive, important to diagnose
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Elevated CSF α-interferon
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Early onset: TREX1 mutation
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Late onset: RNASEH2B mutation
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Progeroid Syndromes
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Cockayne
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Cachectic dwarfism with mental retardation
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Disorder of DNA repair: Several mutations known, but lack phenotype-genotype correlation
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Facies & neuroimaging progressive
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Basal ganglia/dentate Ca++
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Demyelination
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Atrophy
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Image Gallery
![]() Axial NECT in a 3-month-old infant shows fusion of the coronal sutures
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