Background and purpose Venous Sinus Stenosis is found in up to 90% of patients who present with pseudotumor cerebri. Presently, most operators who perform venous sinus stenting in patients with pseudotumor cerebri use a gradient threshold of 8 mmHg to determine whether stenting is indicated, hypothesizing that such a gradient indicates a physiologically significant stenosis.

This study assesses the anatomy of screened patients that have gradient negative pseudotumor cerebri; monitoring for degree of stenosis, co-dominance, and laterality.

Methods Patients in the prospectively maintained pseudotumor cerebri database were assessed to ascertain which patients with clinically diagnosed medically refractory pseudotumor cerebri had undergone venous pressure monitoring.

The anatomy was assessed looking at degree of co-dominance as well as minimal and maximal luminal diameter as assessed on post contrast SPGR MRI.

Results 71 patients were screened yielding 13 patients who had undergone venous pressuring monitoring with gradients of 8 mmHg or less. 2 were patients that had undergone re-measurements post stent and excluded from this study.

Of the 11 remaining patients, 9 were judged to be co-dominant, using the definition of a ratio of > 2:1 in diameter of the dominant vessel:non dominant.

Average maximal luminal diameter of the aggregate transverse sinuses was 7.8 mm, and the mean degree of stenosis was 40%.

Conclusions The degree of co-dominance in medically refractory, gradient negative pseudotumor cerebri, is higher than what is seen in historical gradient positive pseudotumor cerebri.

Further research is needed to see whether endovascular therapy or diagnosis is worthwhile in such patients.

Disclosures C. Chung: None. M. Luciano: None. S. John: None. G. Kosmorsky: None. L. Lystad: None. F. Hui: None.