Biopsy/methods; Brain; Critical Care/methods; Cyclophosphamide; Heart Arrest; Steroids; Vasculitis, Central Nervous System; Adolescent; Anti-Inflammatory Agents/administration & dosage; Brain/diagnostic imaging; Brain/pathology; Cerebral Angiography/methods; Cyclophosphamide/administration & dosage; Cyclophosphamide/adverse effects; Diagnosis, Differential; Fatal Outcome; Humans; Immunosuppressive Agents/administration & dosage; Magnetic Resonance Angiography/methods; Male; Paraplegia/diagnosis; Paraplegia/etiology; Spinal Cord/diagnostic imaging; Steroids/administration & dosage; Steroids/adverse effects; Urinary Retention/diagnosis; Urinary Retention/etiology; Vasculitis, Central Nervous System/diagnosis; Vasculitis, Central Nervous System/physiopathology; Vasculitis, Central Nervous System/therapy