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Arachnoid cyst - cerebellopontine angle

Case contributed by Assoc Prof Frank Gaillard


Headaches, nausea and vomiting.

Patient Data

Age: 30 years

A CSF density lesion in the right cerebellopontine angle, with moderate local mass effect with mild displacement of the brainstem but no effacement of the fourth ventricle. No widening of the adjacent porus acousticus. Remodelling of the adjacent bone is, however, present. 

Conclusion: Right cerebellopontine angle cystic lesion most likely represents an incidental arachnoid cyst with a differential diagnosis that includes epidermoid cyst or cystic acoustic neuroma (the latter two are thought less likely). 

As demonstrated on the preceding CT scan, within the right cerebellopontine angle is a well-circumscribed CSF intensity lesion with bony remodelling of the petrous apex and indentation of the middle cerebellar peduncle. Content follows CSF on all sequences including diffusion-weighted imaging. No abnormal enhancement. The seventh and eighth cranial nerves are displaced anteriorly. The ventricles are unremarkable in appearance with no evidence of a hydrocephalus.

Conclusion: Right cerebellopontine angle arachnoid cyst.

Case Discussion

The features, in this case, are pathognomonic of an arachnoid cyst, in a typical location for an epidermoid cyst. The absence of any significant diffusion restriction confirms the diagnosis. 

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Case information

rID: 59689
Published: 25th Apr 2018
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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