Cognition, FDG metabolism, and amyloid accumulation in relation to intracranial arachnoid cysts.

Background: Though traditionally regarded as harmless, incidental findings, recent literature indicates neuropsychological symptoms associated with intracranial arachnoid cysts (AC). Pathogenesis is unknown, but compression of parenchyma and altered metabolism has been suggested. Patients suspected of dementia often undergo evaluation which can lead to identification of an AC. It is uncertain whether AC can be a primary or contributing cause to symptoms in these and AC have sometimes been raised as a differential diagnosis.

Methods: In this cross-sectional study, patients with AC ≥ 2 cm in a group of 2292 patients referred as part of evaluation for dementia for positon emission tomography (PET) scans with [¹⁸F]Fluorodeoxyglucose (FDG) and/or Pittsburgh compound B (PiB) were investigated. FDG metabolism, amyloid accumulation, and neuropsychological symptoms were studied when data were available.

Results: The prevalence of intracranial AC ≥ 2 cm was 21 (1%). For 16 (76%) patients, the lesion was supratentorial; for 8 (50%), it was in the left temporal fossa. Neuropsychological symptoms did not correlate with AC localization and did not improve post-surgically. Nineteen (90%) did not have FDG alteration associated with the AC; two (10%) had indication of crossed cerebellar diaschisis. Focal amyloid accumulation around the AC was not found.

Conclusion: In an elderly population of 2292 individuals referred for PET scans under dementia evaluation, 21(1%) had an intracranial AC ≥ 2 cm. Amyloid accumulation and neuropsychological symptoms did not correlate well with cyst localization; a few cases had indication of crossed cerebellar diaschisis on FDG scans. AC are not usually explanatory of cognitive decline in a population investigated for dementia.