Cystic Brain Lesions

Cystic lesions of the brain have a number of causes but ventriculomegaly and choroid plexus cyst are the most common. Usually, the location and associated abnormalities are very helpful in the differential diagnosis. For example, interhemispheric cyst is commonly related to agenesis of the corpus callosum. Likewise, ventriculomegaly and dorsal sac in the case of holoprosencephaly are often associated with other abnormalities, whereas others are mostly isolated findings. The choroid plexus cyst is always a lateral cyst located in the choroid plexus and is often isolated and not difficult to diagnose. Cystic lesions of Dandy-Walker malformations are always located in the posterior fossa.

Fig 1, Fig 2, Fig 3, Fig 4

Fig1: Choroid plexus cysts  Transverse scan of the skull: bilateral large choroid plexus cyst (arrow)

Fig 2: Porencephaly Some part of cerebral tissue is absent (*)

Fig 3: Ependymoma  Complex cystic mass (*) in the skull combined with fluid collection and partial absence of brain tissue

Fig 4: Semilobar holoprosencephaly  Oblique coronal scan of the skull: common ventricle (*) with partial separation

Video clips of cystic brain lesions

Choroid plexus cyst: Transvere scan at the level of lateral ventricles: bilateral choroid plexus cyst (*) with lemon sign

Arachnoid cyst: Transverse scan of the head: isolated cystic, circular, thin-walled brain lesion (*)

Colpocephaly:  Transverse scan of the head: bilateral marked dilatation of occipital horn (*) of lateral ventricles

Differential diagnosis

The differential diagnoses of intracranial cystic lesion are as follows:

Midline cyst

  • prominent cavum septum pellucidi (very common)
  • dorsal sac of holoprosencephaly (common)
  • interhemispheric cyst of agenesis of corpus callosum (uncommon)
  • vein of Galen aneurysm (rare)
  • arachnoid cyst (rare)
  • enlarged cavum vergae interhemispheric cystic lesions

Lateral cyst

  • choroid plexus cyst (very common)
  • unilateral hydrocephalus (uncommon)
  • porencephaly/schizencephaly (uncommon)
  • arachnoid cyst (rare)
  • neoplastic cyst (very rare)
  • periventricular cyst formation secondary to CMV infection

Posterior fossa cyst

  • enlarged cisterna magna (>10 mm (very common)
  • Dandy-Walker malformation (common)
  • arachnoid cyst (very rare)
  • median retrocerebellar fluid collections remain the most difficult to prognosticate, retrocerebellar cysts often being difficult to differentiate from enlarged cisterna magna and Dandy-Walker complex.