Arachnoid CystsArachnoidSpinal Cord CompressionCystsSpinal CordSyringomyeliaSubdural SpaceArachnoiditisSubarachnoid SpaceCentral Nervous System CystsCranial Fossa, MiddleHematoma, SubduralCranial Fossa, PosteriorForamen MagnumSpinal Cord DiseasesMagnetic Resonance ImagingSpinal Cord InjuriesDura MaterCraniotomySubdural EffusionNeurosurgical ProceduresCyst Fluid