Abnormal Brain Parenchyma
Karen Y. Oh, MD
DIFFERENTIAL DIAGNOSIS
Common
Exencephaly, Anencephaly
Destructive Lesions
Intracranial Hemorrhage
Encephalomalacia
Cytomegalovirus
Toxoplasmosis
Less Common
Schizencephaly
Lissencephaly
Gray Matter Heterotopia
Pachygyria-Polymicrogyria
Tuberous Sclerosis
Rare but Important
CNS Tumors
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Define recognizable brain parenchymal structures
If no discernible brain structures or skull present, consider exencephaly or anencephaly
Decide whether normal brain developed initially
Look for presence of basic structures: Gray/white matter, thalamus, ventricles/choroid, cerebellum/vermis, falx, corpus callosum
If suspect abnormal development, consider entities listed in less common diagnoses
If suspect normal development with later insult, consider destructive lesions
Characterize focal injury versus diffuse abnormality such as calcifications
If intracranial mass present displacing brain parenchyma, consider CNS tumor
Use color Doppler to evaluate for vascularity
Helpful Clues for Common Diagnoses
Exencephaly, Anencephaly
No calvarium and no recognizably normal neural tissue above orbits
Exencephaly
Dysmorphic neural tissue may be present initially
Usually “wears away” during gestation due to exposure to amniotic fluid and mechanical trauma
Anencephaly
No organized neural tissue remaining
Protuberant “frog-like” eyes due to shallow orbits
Polyhydramnios common due to impaired swallowing
Fluid often echogenic due to dissolved neural tissue
Intracranial Hemorrhage
Echogenic intracranial “mass” without vascularity
Most commonly intraparenchymal
Use fetal MR to clarify anatomy and confirm location of clot(s)
If flow voids on T2WI, consider underlying vascular malformation
Encephalomalacia
Result of various destructive brain processes
Sonographic findings often subtle
Look for associated ventriculomegaly as first clue
Periventricular lucencies due to cystic degeneration (later)
Porencephaly can occur due to parenchymal destruction
Intra-axial, avascular, round or irregular cavitary lesion without mass effect
Cytomegalovirus
Widespread (non-shadowing) calcifications
Most commonly affects brain
Results in ventriculomegaly, microcephaly
Even in absence of sonographic findings, with known fetal infections, at least 20% have neurologic sequelae
Toxoplasmosis
Non-shadowing intracranial and intrahepatic calcifications
Intracranial: Periventricular or random, may be very subtle and easily missed
Helpful Clues for Less Common Diagnoses
Schizencephaly
CSF cleft extending from surface of brain to underlying ventricle
Open-lip is most common type identified in utero
Can be bilateral
Absent cavum septi pellucidi (CSP) in up to 70%
Search for associated developmental brain anomalies
Lissencephaly
Smooth contour to brain surface
Lack of normal gyral and sulcal development
Cannot assess until third trimester after sulcation begins
Sulcation normally starts around 23-24 weeks
Brain continues to appear “smooth” until approximately 26 weeks
Look specifically for shallow, poorly formed Sylvian fissures
May be linked to genetic defect or syndrome
Chromosome 17 mutation
X-linked lissencephaly – mothers have band heterotopia
Walker-Warburg syndrome
Gray Matter Heterotopia
Gray matter cells in an abnormal location
Due to arrested neuronal migration to cortex
Subependymal: Nodules of gray matter along ventricular wall
Subcortical: Heterogeneous masses in subcortical location
Band: Homogeneous bands of gray matter between lateral ventricles and cortex
Pachygyria-Polymicrogyria
Pachygyria
Much more common than complete lissencephaly
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