Large arachnoid cyst

Case contributed by A.Prof Frank Gaillard



Patient Data

Age: 65
Gender: Female

A large lobulated cystic lesion within the left frontal lobe appears to be intrinsic, rather than extrinsic. It has not remodelled the inner table of the skull, suggesting that it is not congenital. It markedly distorts the frontal horn and the left side of the genu of the corpus callosum. It shows free diffusion of the fluid within it and no pathological contrast enhancement. It measures 47 mm in width, 61 mm in anteroposterior diameter and 53 mm in height. Apart from scattered small foci of abnormal signal within the white matter of both cerebral hemispheres and the pons, which most likely represent chronic small vessel ischemic lesions, no other abnormality seen.


The differential for this lesions includes:

  1. arachnoid cyst
  2. porencephalic cyst
  3. hydatid cyst cannot be completely excluded

Case Discussion

The patient went on to have surgery



"Superficial cyst wall": A cyst wall 10x5x1mm. Cyst wall is translucent. No focal nodules or excrescences.


The section shows a collapsed cyst. The cyst lining consists of a single layer of meningothelial type cells. Foci of meningothelial cell hyperplasia are also noted. The cyst wall consists of loose fibrous tissue. Granulomas are not identified. There is no evidence of tumor.


Arachnoid cyst.


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Case information

rID: 28515
Published: 9th Apr 2014
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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