Sitting Versus Horizontal Position on Craniotomies

Inclusion Criteria: * Patients 18 - 75 years old undergoing open posterior cranial fossa and pineal region surgery and diagnosed with space-occupying or vascular lesions willing consent to participate in the study. Exclusion Criteria: * Significant cardio-vascular comorbid conditions (cardiac insufficiency, recent infarction, advanced arterial hypertension) * Advanced chronic respiratory comorbid conditions * Uncorrected hypovolemia, anemia, hypoalbuminemia * De-compensated acid base and electrolyte disorders * Anticoagulated patients and patients with coagulation disorders, deep venous thrombosis (history of deep vein thrombosis or clinically established) * Preoperative evidence of spinal or peripheral nerve dysfunction that may interfere with patient positioning. * Cervical myelopathy * Cervical spine disorders (atlanto-occipital arthritis, previous fractures etc.)