Idiopathic intracranial hypertension (IIH), or pseudotumor cerebri, is a debilitating neurological disorder characterized by elevated CSF pressure of unknown cause. IIH manifests as severe headaches, and visual impairments. Most typically, IIH prevails in overweight females of childbearing age and its incidence is rising in parallel with the obesity epidemic. The most accepted theory for the cause of IIH is reduced absorption of CSF due to elevated intracranial venous pressure. A comprehensive MRI study, which includes structural and physiological imaging, was applied to characterize morphological and physiological differences between a homogeneous cohort of female IIH patients and an age-and BMI-similar control group to further elucidate the underlying pathophysiology. A novel analysis of MRI measurements of blood and CSF flow to and from the cranial and spinal canal compartments employing lumped parameters modeling of the cranio-spinal biomechanics provided, for the first time, evidence for the involvement of the spinal canal compartment. The CSF space in the spinal canal is less confined by bony structures compared with the cranial CSF, thereby providing most of the craniospinal compliance. This study demonstrates that the contribution of spinal canal compliance in IIH is significantly reduced.