- ABSTRACT BACKGROUND Idiopathic intracranial hypertension (IIH), is characterized by elevated intracranial pressure (ICP) without a clear cause. Recently it was shown that in more than 90% of the IIH patients there is stenosis of the transverse dural sinuses. In this study we assessed the changes in diameter of cerebral veins after lumbar puncture, in order to have some more insight regarding the volume and pressure influence on cerebral veins. METHODS We prospectively included 13 patients suspected with IIH, admitted for investigation in the Soroka medical center. All the patients had a lumbar puncture (LP) with opening pressure measurement and CSF analysis, and two MRI–MRV studies: one before the LP and one after it. Measurements of the cerebral venous sinuses diameter were performed. RESULTS Significant stenosis of both transverse sinuses was found before LP in IIH patients with an average diameter of 1.77 mm of the right TS, and 1.57 mm of the left TS. After the LP, there was a significant increase in all venous sinuses diameters (P < .05). There was no correlation between the changes in diameter of the venous sinuses after LP and opening pressure measured or BMI. CONCLUSIONS Our results support other studies and demonstrated narrowing of the transverse sinuses in IIH patients. The main finding of this study is the increase in cerebral sinuses diameter after LP. This observation should be considered when evaluating cerebral venous sinuses after LP. A larger scale study is warranted to validate our findings.