Elevated intracranial pressure and pseudotumor cerebri.

The development of papilledema requires high cerebrospinal fluid (CSF) pressure in the distal optic nerve sheath, elevation of the pressure in the central retinal vein, and impaired perfusion of the neurons as they traverse the lamina cribrosa. Pseudotumor cerebri (PTC) is a syndrome defined by four criteria: 1) Increased intracranial pressure, 2) normal or small ventricles on neuroimaging, 3) no evidence of an intracranial mass, and 4) normal CSF composition. Elevated intracranial venous pressure is thought by some authors to be the "universal mechanism" of PTC of varying etiologies. The reason obesity predisposes to idiopathic PTC is unclear, but one mechanism proposed is that central obesity raises intra-abdominal pressure, which increases pleural pressure and cardiac filling pressures, which impede venous return from the brain, leading to increased intracranial venous pressure and increased intracranial pressure. Both optic nerve sheath fenestration (ONSF) and lumboperitoneal shunting (LPS) may improve vision and prevent deterioration of vision in patients with PTC. Both procedures have their advantages and disadvantages, but until a prospective, randomized study comparing ONSF with LPS for PTC is performed, the question of which surgical procedure is best for the treatment of PTC remains unanswered.