Idiopathic Intracranial Hypertension May Not Be Idiopathic

Abstract & Commentary 

Source: Farb RI, et al. Idiopathic intracranial hypertension: The prevalence and morphology of sinovenous stenosis. Neurology. 2003;60:1418-1424.

This is an elegant study, which examined whether sinovenous obstruction may play a role in idiopathic intracranial hypertension (IIH). Farb and associates carried out studies using elliptic-centric-ordered 3-dimensional gadolinium-enhanced MR venography. This is a very sophisticated and reliable technique for visualizing the venous system. They prospectively studied 29 patients with established IIH as well as 59 control patients. The MRI venography studies were read in a blinded, randomized fashion by 3 readers. A novel scoring system was used to grade the degree stenosis seen in the transverse and sigmoid sinuses of each patient. Farb et al found that there was excellent reproducibility between the 3 readers in the application of the grading system. They observed substantial bilateral sinovenous stenoses in 27 of 29 patients with IIH and only 4 of 59 control patients. They concluded that by using a novel grading system, as well as MR venography for quantifying sinovenous stenoses, that they can identify IIH patients with a sensitivity and specificity of 93%.

Commentary

The pathophysiology of elevated intracranial pressure in idiopathic IIH is unknown. Elevated intracranial pressure has been attributed in the past to cerebral venous sinus occlusion, as well as radical neck dissection with removal of the jugular vein. It also, however, occurs in other settings, such as hypoparathyroidism, vitamin A intoxication, systemic lupus erythematosus, and renal disease, as well as being a side effect of a number of medications. Most patients with IIH are young, obese women who present with chronic daily headaches and papilledema. They may not uncommonly have an empty sella. The disease can be associated with transient visual obscurations, pulsatile tinnitus, and eventual visual loss. The neurologic signs occasionally include sixth nerve palsies. On rare occasion, IIH can occur without papilledema. Previous authors have suggested that IIH may result from decreased CSF resorption. In a previous study of patients with IIH, 5 of 10 had dural venous outflow obstruction on venography and the other 5 had normal anatomy, while 10 had elevated superior sagittal sinus pressure.

Farb et al have convincingly shown that patients with IIH show venous abnormalities including narrowing. It, therefore, appears that most cases of IIH are at least predisposed to by venous sinus abnormalities and narrowing. This is an extremely interesting observation. It, however, cannot account for all cases of IIH, such as those associated with vitamin A intoxication and some drug reactions. Nevertheless, patients who have these venous abnormalities may be predisposed to interactions with other factors that may modulate CSF production and reabsorption. Unfortunately, although the present study was extremely elegant in showing the venous sinus abnormalities, this technology is not readily available. The present study also does not lead to any new insights about effective treatments for IIH. Nevertheless, the findings are of considerable scientific interest since they provide an explanation for most cases of IIH. — M. Flint Beal

Dr. Beal is Professor and Chairman; Department of Neurology; Cornell University Medical College, New York, NY.