Posterior fossa arachnoid cysts in multiple system atrophy

Multiple system atrophy (MSA) is an α-synucleinopathy characterized by prominent cerebellar or parkinsonian features. This is pathologically due to the deposition of α-synuclein in glial cells, the mechanism by which s not entirely clear. We describe three patients with posterior fossa arachnoid cysts later diagnosed with clinically established MSA, suggesting the co-existence of two rare pathologies through a shared mechanism versus by chance.

Patients ranged from 45 to 67 years of age at presentation, each describing 2-3 years of progressive symptoms. All displayed cerebellar findings and various non-motor features of orthostatic hypotension, genitourinary failure, and dream enactment behavior confirmed on diagnostic testing or on a clinical basis. All imaging demonstrated posterior fossa arachnoid cysts and supportive features of MSA, notably pontine and cerebellar atrophy.

The probability of having both MSA and a posterior fossa arachnoid cyst based on population study-derived point prevalence and assuming independence of the events is 1.09 e-6. We suspect that while uncommon, concurrence of the diseases is due to chance. It is plausible that space-occupying lesions, when already present, may contribute to neurodegenerative disease progression.