CraniotomyOccipital BoneCerebellar DiseasesFourth VentricleNeurosurgical ProceduresDura MaterCranial Fossa, PosteriorArnold-Chiari MalformationNeuroma, AcousticPneumocephalusMeningiomaMeningeal NeoplasmsCerebellopontine AngleMicrosurgeryFrontal BoneCranial Nerve NeoplasmsCerebrospinal Fluid OtorrheaHematoma, Subdural, AcuteTomography, X-Ray ComputedSyringomyeliaIntracranial AneurysmTrephiningNeuroendoscopyMagnetic Resonance ImagingDecompression, SurgicalForamen MagnumHead Injuries, Penetrating