Fact-sheet: Arachnoid cyst - intracranial
Updated on 09/17/2021 at 12:16 PM
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Definition
Cystic lesion of the pericerebral spaces bounded by arachnoid tissue, excluding post-traumatic scarring lesions, subdural hygromas, or post-infectious lesions. Possible associations: - temporal lobe agenesis or hypoplasia syndrome - Dandy-Walker complex - Neurofibromatosis - Marfan syndrome - chromosomal abnormalities - corpus callosum dysgenesis (interhemispheric form).
Clinical features
Most often asymptomatic.
Symptomatic forms result from compression of adjacent structures: headaches, intracranial hypertension, precocious puberty (suprasellar locations), oculomotor disturbances, mental retardation, epilepsy.
CT
Cystic formation with regular margins.
Mass effect: regular thinning of the calvaria, hydrocephalus (rare, midline locations).
Note the integrity of the cerebellar vermis and the absence of dehiscence of the roof of the fourth ventricle in posterior fossa locations.
Atypical forms: peripheral calcifications, intracystic hemorrhage, associated subdural hematoma.
MRI
As a second-line examination.
Useful for the assessment of midline or posterior fossa lesions and for detecting complicated forms.
Differential diagnosis
Consider a dermoid cyst in the presence of an atypical form with peripheral calcifications.
Diffusion-weighted imaging: diffusion hyposignal in arachnoid cysts vs. diffusion hypersignal in epidermoid cysts.