Idiopathic Intracranial Hypertension - Mechanism

Mechanism

The cause of IIH is not known. The Monro-Kellie rule states that the intracranial pressure (literally: pressure inside the skull) is determined by the amount of brain tissue, cerebrospinal fluid (CSF) and blood inside the bony cranial vault. Three theories therefore exist as to why the pressure might be raised in IIH: an excess of CSF production, increased volume of blood or brain tissue, or obstruction of the veins that drain blood from the brain.

The first theory, that of increased production of cerebrospinal fluid, was proposed in early descriptions of the disease. However, there is no experimental data that supports a role for this process in IIH.

The second theory posits that either increased blood flow to the brain or increase in the brain tissue itself may result in the raised pressure. Little evidence has accumulated to support the suggestion that increased blood flow plays a role, but both biopsy samples and various types of brain scans have shown an increased water content of the brain tissue. It remains unclear why this might be the case.

The third theory suggests that blood flow from the brain may be impaired or congested. Only in a small proportion of patients has underlying narrowing of the cerebral sinuses or veins been demonstrated. Congestion of venous blood may result from a generally increased venous pressure, which has been linked to obesity.