Molecular characterization of benign intracranial glioependymal and arachnoid cysts suggest heterogeneous mechanisms of action.

Benign-appearing intracranial cysts may become symptomatic due to mass effect and require surgical treatment. Mechanisms underlying cyst formation and growth remain poorly understood. This study identified 16 patients who underwent surgical treatment for benign intracranial cysts. Cyst wall pathologic samples (n = 8) were characterized as arachnoid or glioependymal cysts using H&E and immunofluorescence staining. Five samples (62.5%) were found to be glioependymal while three (37.5%) were arachnoid cysts. Cyst fluid examined in 4 cases resembled cerebrospinal fluid (CSF) and showed no significant differences in composition between pathological subtypes. Single-cell sequencing and RNA expression profile comparisons between glioependymal and arachnoid cysts revealed distinct cellular profiles. Analyses of the innermost cell layer (ependymal cells versus arachnoid cells) suggested differing mechanisms of pathogenesis. Glioependymal cysts harbored upregulated expression of sodium transporters and aquaporin channels, which suggests possible CSF-like fluid production whereas arachnoid cysts may be associated with mechanical fluid accumulation. Thus, intracranial cysts represent multiple unique pathologic entities with differing cell types and RNA expression profiles. Further study into mechanisms of glioependymal cyst formation may allow for targeted interventions to reduce fluid production and avoid surgery.