Objective: To describe two patients with posterior fossa arachnoid cysts later diagnosed with suspected multiple system atrophy – cerebellar type (MSA-C).

Background: The diagnosis of MSA requires core features of autonomic failure with a predominant parkinsonian or cerebellar syndrome [1]. MRI findings include cerebellar peduncle and pontine atrophy. Pathologically, MSA is due to α-synuclein aggregation with neuronal loss [2]. Arachnoid cysts are incidental findings found in 1.4% of the population [3]. There is limited evidence whether posterior fossa cysts with mass effect may be associated with the development of a neurodegenerative disease [4].

Method: Case series.

Results: Case 1. A 67-year-old woman with inactive MS presented with 3 years of progressive ataxia, dysarthria, and dream enactment behavior. Other symptoms included emotional lability (sudden crying), urge incontinence, and constipation. Surveillance imaging over 6 years revealed a posterior fossa arachnoid cyst and severe progressive olivopontocerebellar atrophy with a “hot cross bun” sign. There was no evidence of infratentorial inflammatory lesions attributed to MS. Examination showed ataxic dysarthria, nystagmus, mild parkinsonism, with severe truncal and moderate appendicular ataxia. Thermoregulatory sweat test was abnormal with widespread anhidrosis (63.8%). Autonomic reflex screen showed neurogenic orthostatic hypotension. 

Case 2. A 50-year-old man presented with 3 years of progressive ataxia and dysarthria. Other symptoms included resting tremor, erectile dysfunction, nocturia, and dream enactment behavior. He was trialed on carbidopa-levodopa with partial response. Examination showed ataxic dysarthria, saccadic intrusions, and appendicular ataxia. Imaging revealed a posterior fossa arachnoid cyst and cerebellar atrophy. Thermoregulatory sweat test and autonomic reflex screen were normal. 

Workup for other etiologies of ataxia was unremarkable in both patients, and they met MDS criteria for clinically established (case 1) and clinically probable (case 2) MSA-C.

Conclusion: We present two patients with suspected MSA who also had posterior fossa arachnoid cysts. The coexistence of two rare disorders suggests there may be a shared mechanism such as susceptibility to neuronal loss from an alpha-synucleinopathy in the setting of cerebellar and brainstem compression from an arachnoid cyst.

References: [1] Wenning GK, Stankovic I, Vignatelli L, Fanciulli A, Calandra-Buonaura G, Seppi K, Palma JA, Meissner WG, Krismer F, Berg D, Cortelli P, Freeman R, Halliday G, Höglinger G, Lang A, Ling H, Litvan I, Low P, Miki Y, Panicker J, Pellecchia MT, Quinn N, Sakakibara R, Stamelou M, Tolosa E, Tsuji S, Warner T, Poewe W, Kaufmann H. The Movement Disorder Society Criteria for the Diagnosis of Multiple System Atrophy. Mov Disord. 2022 Jun;37(6):1131-1148. doi: 10.1002/mds.29005. Epub 2022 Apr 21. PMID: 35445419; PMCID: PMC9321158.

[2] Monzio Compagnoni, G., Di Fonzo, A. Understanding the pathogenesis of multiple system atrophy: state of the art and future perspectives. acta neuropathol commun 7, 113 (2019). https://doi.org/10.1186/s40478-019-0730-6

[3] Al-Holou WN, Terman S, Kilburg C, Garton HJ, Muraszko KM, Maher CO. Prevalence and natural history of arachnoid cysts in adults. J Neurosurg. 2013 Feb;118(2):222-31. doi: 10.3171/2012.10.JNS12548. Epub 2012 Nov 9. PMID: 23140149.

[4] Bachstetter AD, Garrett FG, Jicha GA, Nelson PT. Space-occupying brain lesions, trauma-related tau astrogliopathy, and ARTAG: a report of two cases and a literature review. Acta Neuropathol Commun. 2021 Mar 23;9(1):49. doi: 10.1186/s40478-021-01152-3. PMID: 33757579; PMCID: PMC7986305.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/posterior-fossa-arachnoid-cysts-in-two-patients-with-suspected-multiple-system-atrophy-cerebellar-type/