The third theory suggests that restricted venous drainage from the brain may be impaired resulting in congestion. Many people with IIH have narrowing of the transverse sinuses. It is not clear whether this narrowing is the pathogenesis of the disease or a secondary phenomenon. It has been proposed that a positive biofeedback loop may exist, where raised ICP (intracranial pressure) causes venous narrowing in the transverse sinuses, resulting in venous hypertension (raised venous pressure), decreased CSF resorption via arachnoid granulation and further rise in ICP.