Object: The authors examined the role of venous sinus obstruction in the etiology of idiopathic intracranial hypertension (IIH) by reviewing more than 200 MR venograms performed in suspected cases of IIH.
Methods: Individual MR venograms performed in cases of suspected IIH at the Children's Hospital at Westmead in Sydney, Australia, were reviewed. The authors excluded cases in which an intervention was performed before the scan or a structural cause for venous obstruction was identified. Cases with confirmed hydrocephalus were also excluded. For each of the 145 remaining scans, the authors completed a detailed review on a slice-by-slice basis of the 2D source images used to compile the rendered 3D MR venogram. The anatomical configuration of the dural venous sinuses and any areas of decreased flow in circulation were then noted. Where possible, they correlated their radiological findings with evidence of raised intracranial pressure based on LP opening pressures. They also reviewed a control group of 50 MR venograms.
Results: Seventy-six (52%) of 145 scans showed evidence of venous obstruction in the dominant-side circulation. Substantial nonphysiological collateral circulation was seen in 68% of cases with dominant-sided obstruction, suggesting a process of recanalization. In contrast, in the absence of dominant-sided obstruction, collateral circulation was uncommon. In 27 cases, CSF opening pressure measurements were available. In 20 cases the opening pressures were in excess of 20 cm H(2)O. Of those, 17 demonstrated evidence of dominant-sided venous outflow obstruction. Among those cases, the median opening pressure was 34 cm H(2)O. Dominant-sided venous outflow obstruction was seen in only 2 of 50 MR venograms in the control group. Furthermore, evidence of collateral circulation was also uncommon in the control group. There was a highly statistically significant difference between rates of dominant-sided venous obstruction in the suspected IIH and control groups (p ≤ 0.001).
Conclusions: A majority of patients presenting for investigation of suspected IIH demonstrated evidence of dominant-sided venous obstruction on MR venogram. In addition there was a high correlation between elevated CSF opening pressures and dominant-sided venous sinus obstruction. This correlation was further supported by evidence of collateral recanalization in patients with elevated CSF pressures and dominant-sided venous obstruction. A control group of 50 MR venograms indicated that dominant-sided venous outflow obstruction is an unlikely incidental finding, and a highly statistically significant difference was found between rates of obstruction in the suspected IIH and control groups.