It is not entirely clear how it protects the eye from the raised pressure, but it may be the result of either diversion of the CSF into the orbit or the creation of an area of scar tissue that lowers the pressure. The effects on the intracranial pressure itself are more modest. Moreover, the procedure may lead to significant complications, including blindness in 1–2%. The procedure is therefore recommended mainly in those who have limited headache symptoms but significant papilledema or threatened vision, or in those who have undergone unsuccessful treatment with a shunt or have a contraindication for shunt surgery.Shunt surgery, usually performed by neurosurgeons, involves the creation of a conduit by which CSF can be drained into another body cavity. The initial procedure is usually a lumboperitoneal (LP) shunt, which connects the subarachnoid space in the lumbar spine with the peritoneal cavity. Generally, a pressure valve is included in the circuit to avoid excessive drainage when the person is erect. LP shunting provides long-term relief in about half the cases; others require revision of the shunt, often on more than one occasion—usually due to shunt obstruction. If the lumboperitoneal shunt needs repeated revisions, a ventriculoatrial or ventriculoperitoneal shunt may be considered. These shunts are inserted in one of the lateral ventricles of the brain, usually by stereotactic surgery, and then connected either to the right atrium of the heart or the peritoneal cavity, respectively.
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. Diagnosis
The diagnosis may be suspected on the basis of the history and examination. To confirm the diagnosis, as well as excluding alternative causes, several investigations are required; more investigations may be performed if the history is not typical or the person is more likely to have an alternative problem: children, men, the elderly, or women who are not overweight. Investigations
Neuroimaging, usually with computed tomography (CT/CAT) or magnetic resonance imaging (MRI), is used to exclude any mass lesions. In IIH these scans typically appear to be normal, although small or slit-like ventricles, dilatation and buckling of the optic nerve sheaths and "empty sella sign" (flattening of the pituitary gland due to increased pressure) and enlargement of Meckels caves may be seen. An MR venogram is also performed in most cases to exclude the possibility of venous sinus stenosis/obstruction or cerebral venous sinus thrombosis. A contrast-enhanced MRV (ATECO) scan has a high detection rate for abnormal transverse sinus stenoses. These stenoses can be more adequately identified and assessed with catheter cerebral venography and manometry. Buckling of the bilateral optic nerves with increased perineural fluid is also often noted on MRI imaging. Lumbar puncture is performed to measure the opening pressure, as well as to obtain cerebrospinal fluid (CSF) to exclude alternative diagnoses.