Macrocephaly
Anne Kennedy, MD
DIFFERENTIAL DIAGNOSIS
Common
Benign Familial
Macrosomia
Aqueductal Stenosis
Intracranial Cysts
Less Common
Holoprosencephaly Spectrum
CNS Tumors
Beckwith-Wiedemann Syndrome
Rare but Important
Hydranencephaly
Chiari II Malformation
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Ensure that measurements are obtained correctly
Biparietal diameter is measured at level of thalami and cavum septi pellucidi
Outer edge of near field skull to inner edge of far field
Head circumference in same axial plane,
Bone circumference only, does not include soft tissues
Repeat measurements for confirmation
Look at parents and consider measuring parental head circumference
Does the brain look normal?
Megalencephaly associated with abnormal gyral pattern and loss of architecture
Are the ventricles enlarged?
Where is the level of obstruction?
Look for mass or cyst obstructing flow of cerebrospinal fluid (CSF)
Is the posterior fossa normal?
Look for signs of Chiari malformation, Dandy-Walker continuum, posterior fossa cyst/mass
Is the falx present?
If absent, holoprosencephaly spectrum is most likely diagnosis
If present must differentiate hydranencephaly from severe hydrocephalus
Is there a cortical mantle?
MR may be necessary to make this determination
Helpful Clues for Common Diagnoses
Benign Familial
Measure parental head size
Underlying brain normal
Interval growth normal (i.e., no progressive enlargement)
Macrosomia
Estimated fetal weight > 90th percentile
Abdominal circumference may be larger than other parameters
Increased subcutaneous fat visible in third trimester
Often associated with polyhydramnios
Associated with overgrowth syndromes
Seen in infant(s) of diabetic mother(s)
Aqueductal Stenosis
Obstructive hydrocephalus
Moderate to severe lateral ventricular dilatation (> 15 mm)
3rd ventricle dilated
“Dangling” choroid
Cavum septi pellucidi may be absent
Posterior fossa structures look normal
No evidence of Chiari II or Dandy-Walker continuum as etiology of hydrocephalus
X-linked form: Adduction-flexion deformity of thumbs in male fetus
Intracranial Cysts
Arachnoid
Extra-axial
Simple
Typically stable in size but may enlarge and cause obstruction of CSF flow
Glioependymal
Extra-axial
Midline
Extend anterior to posterior
More likely to be multiloculated
High protein concentration: May show increased signal on T1WI MR
Helpful Clues for Less Common Diagnoses
Holoprosencephaly Spectrum
Lobar form more likely to be associated with significant ventriculomegaly and macrocephaly
Look for midline fused fornices
Look for gyral continuity across midline
Look for asymmetric falx placement
Small head size more likely with alobar/semilobar forms unless very large associated dorsal cyst
CNS Tumors
Solid intracranial mass with Doppler flow
Supratentorial but precise point of origin often hard to determine
May present with hydrocephalus before tumor visible
Exhibit rapid growth
Beckwith-Wiedemann Syndrome
Fetal overgrowth syndrome
Look for associated findings
Omphalocele
Macroglossia
Nephromegaly, hepatosplenomegaly, hemihyperplasia
Helpful Clues for Rare Diagnoses
Hydranencephaly
Head size usually normal but macrocephaly may be seen
Fluid-filled supratentorial space
Falx present
Normal posterior fossa
Medial temporal or inner occipital lobes also may be present
Perfused by posterior circulation therefore preserved
Chiari II Malformation
Although associated with ventriculomegaly, head size often normal
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