Arachnoid cyst

Case contributed by Dr Varun Babu


Emergency CT brain in the ER following motor vehicle accident.

Patient Data

Age: 20 years
Gender: Male

CT brain

  • no intra axial or extra axial hemorrhage.
  • no calvarial fracture.
  • large extra axial CSF attenuating lesion is seen occupying the left middle cranial fossa splaying the sylvian fissure and displacing the frontal, parietal and temporal lobes. 
  • secondary mass effect is seen in the form of effacement of left cerebral hemispheric sulci, mild midline shift to right,  effaced ipsilateral lateral ventricle. 
  • no transtentorial herniation.  

MRI brain

Contrast enhanced MRI confirms

  • non enhancing nature of lesion.
  • CSF attenuation. 
  • extra axial location
    • displaced cortical mantle and cortical vessels between lesion and calvarium
  • no underlying white matter changes in left cerebral hemisphere. 

Case Discussion

Most common site of origin of the arachnoid cyst is in the middle cranial fossa, splaying the Sylvian fissure. Depending on the size and extent, it is classified by the Galassi classification. This a type III variant. 

They tend to be asymptomatic and pounced upon incidentally. The larger ones may cause symptoms secondary to mass effect. 

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Case information

rID: 46791
Published: 17th Jul 2016
Last edited: 31st Dec 2019
Inclusion in quiz mode: Included

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