Subarachnoid SpaceEpidural SpaceSubarachnoid HemorrhageArachnoidAnesthesia, EpiduralCerebrospinal FluidDura MaterMeningesCisterna MagnaSpinal CanalInjections, SpinalCerebrospinal Fluid PressureNeedlesVasospasm, IntracranialInjections, EpiduralMyelographyArnold-Chiari MalformationArachnoid CystsPneumoencephalographyLigamentum FlavumHydrocephalusCerebral VentriculographyCerebral VentriclesMagnetic Resonance ImagingAnalgesia, EpiduralSubdural SpaceLumbosacral RegionSpinal CordIntracranial PressureTomography, X-Ray ComputedSyringomyeliaSpinal Nerve RootsLaminectomyArachnoiditisSpinal PunctureAnesthesia, SpinalCerebral AqueductIntracranial AneurysmCerebrospinal Fluid ShuntsMicroscopy, Electron, Scanning TransmissionLumbar VertebraeEpidural NeoplasmsMeningitisCerebral AngiographyBupivacaineAnesthetics, LocalBattered Child SyndromeForamen MagnumAneurysm, RupturedRadiculopathyLipomatosisAnalgesia, ObstetricalCatheterizationAnesthesia, ObstetricalCoccyxVentriculostomyMeningeal NeoplasmsChloral HydrateThoracic VertebraeMeningitis, PneumococcalBrainSpinal DiseasesOptic NerveCerebral ArteriesBasilar ArteryTissue AdhesionsCranial Fossa, PosteriorFiber Optic TechnologyCerebrospinal Fluid ProteinsSpinal Cord CompressionMathematical ConceptsIntracranial HypotensionIntervertebral Disc DisplacementFluoroscopyBrain DiseasesBlood Patch, EpiduralEpidural AbscessSpinal NeoplasmsCerebrospinal Fluid RhinorrheaAnesthesia, CaudalAnatomy, Cross-SectionalFentanylCerebrovascular CirculationBlood-Brain BarrierSubarachnoid Hemorrhage, TraumaticTime Factors