Arachnoid CystsArachnoidSpinal Cord CompressionSpinal CordSubarachnoid SpaceDura MaterSubdural SpaceSyringomyeliaSpinal Cord InjuriesArachnoiditisMeningesCranial SinusesSpinal Cord DiseasesHematoma, SubduralCentral Nervous System CystsCraniotomyCranial Fossa, PosteriorCranial Fossa, MiddleSubdural EffusionForamen MagnumMagnetic Resonance ImagingNeurosurgical ProceduresLaminectomyHerniaGranulation TissueDecompression, SurgicalCerebrospinal FluidSacrococcygeal RegionMeningiomaSpinal Cord NeoplasmsHydrocephalusPneumoencephalographyCerebral Ventriculography