Intracranial Cysts: Lateral

Intracranial Cysts: Lateral
Anne Kennedy, MD
DIFFERENTIAL DIAGNOSIS
Common
  • Choroid Plexus Cyst
  • Arachnoid Cyst
Less Common
  • Schizencephaly
  • Arteriovenous Fistula
Rare but Important
  • Porencephaly
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
  • Assessment of fluid-filled intracranial structure
  • Could it be a prominent normal structure such as lateral ventricle?
    • Mild ventriculomegaly
      • Choroid displaced from medial wall
      • Atria of lateral ventricle measures 10-12 mm
      • Look for signs of trisomy 21
      • Look for additional brain abnormalities
    • Colpocephaly: Tear drop shape to dilated occipital horns seen in agenesis of corpus callosum
      • Ventricles parallel
      • Absent cavum septi pellucidi
      • Loss of normal branch pattern of anterior cerebral artery
      • Stenogyria
  • Once abnormal lateral ventricle excluded, determine location
    • Is it in the choroid plexus?
    • Is it in the brain substance (i.e., intra-axial)?
    • Is it outside the brain substance (i.e., extra-axial)?
  • Is it replacing normal brain tissue?
    • Porencephaly
    • Schizencephaly
  • Is it a space-occupying lesion displacing brain tissue?
    • Arachnoid cyst
    • Arteriovenous fistula
  • Is it vascular?
  • Could it be a thrombosed vascular structure?
    • Hypoechoic structure with increased through transmission
    • Often contains faint low level echoes
    • Usually tubular or round
Helpful Clues for Common Diagnoses
  • Choroid Plexus Cyst
    • Cyst > 2 mm with defined wall, within choroid plexus
    • Variable size
    • Variable number
    • May be unilateral or bilateral
    • May be single or multiple
    • Look for associated signs of trisomy 18
      • Abnormal posturing
      • Facial cleft
      • Congenital heart disease
      • Neural tube defects
      • Omphalocele
  • Arachnoid Cyst
    • Extra-axial cyst displaces brain parenchyma
    • Unilocular
    • Avascular
    • Most common over convexities
      • 1/3 fetal cases are in posterior fossa
    • May enlarge and cause hydrocephalus due to mass effect at foramen of Monro or aqueduct of Sylvius
Helpful Clues for Less Common Diagnoses
  • Schizencephaly
    • Wedge-shaped defect in brain parenchyma
    • Extends from lateral ventricle to inner table of skull
    • Edges of cleft are lined by gray matter
    • Unilateral or bilateral
    • Open lip or closed lip
      • Open lip: Wedge-shaped defect, edges separated by cerebrospinal fluid-filled cleft
      • Closed lip: Edges of defect are in contact; unlikely to be detected on prenatal ultrasound
    • Size varies from small to “giant”
    • Consider MR to look for associated heterotopia, polymicrogyria, pachygyria, septo-optic dysplasia
  • Arteriovenous Fistula
    • Hypoechoic structure on grayscale images
      • Blood flow on Doppler evaluation when patent
      • Thrombosed AVF is tubular/round structure with low level internal echoes but no flow on Doppler evaluation
    • MR will show blood product signal even when flow is absent
    • May be intra-axial, but dural (i.e., extra-axial) more common in fetus
    • May be associated with high output cardiac failure
    • May be associated with polyhydramnios
    • Look for associated intraventricular or parenchymal hemorrhage
    • Look for associated ischemic damage secondary to vascular “steal”
      • Cortical thinning, ventriculomegaly, microcephaly
      • MR more sensitive than ultrasound for detection of encephalomalacia
Helpful Clues for Rare Diagnoses
  • Porencephaly
    • Porencephalic cyst replaces damaged brain
      • Intracerebral cavitation due to injury
      • Usually connected with lateral ventricle
    • Look for associated intracranial hemorrhage
    • Destructive process may present with mild ventriculomegaly and progress to encephalomalacia/porencephaly over time
Other Essential Information
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Aug 10, 2016 | Posted by in OBSTETRICS | Comments Off on Intracranial Cysts: Lateral

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