Comparison of the Measurement of Optic Nerve Sheath Diameter(ONSD) with B Scan and MRI as a Surrogate for Patients with Idiopathic Intracranial Hypertension(IIH)

OBJECTIVE: To assess the ONSD with B Scan(10 MHz probe) and MRI(fat suppressed T2 weighted sequence) in patients with Idiopathic Intracranial Hypertension(IIH) and to compare the significance of ONSD in diagnosing raised intracranial pressure. BACKGROUND: The optic nerve sheath is in direct communication with the intracranial subarachnoid space which forms the physiological basis for using the Optic Nerve Sheath Diameter(ONSD) as a surrogate for intracranial pressure measurement. METHODS: 15 patients of IIH were selected according to Modified Dandy Criteria and were subjected to measurement of ONSD with MRI brain and B Scan separately. ONSD was measured in an axis perpendicular to the optic nerve, 3 mm and 5 mm behind the globe on both sides. Cut off values of ONSD to diagnose increased intra cranial pressure are taken as 5.8 mm and 6mm for MRI and B scan respectively. RESULTS: In B scan, 10 out of 15 patients are abnormal in 3 mm depth when compared to 5mm where 7 out of 15 patients are abnormal(p 0.010).In MRI, 11 out of 15 patients are abnormal in 3 mm depth when compared to 5mm depth where 7 out of 15 patients are abnormal(p 0.029). In 3 mm depth, 9 out of 15 patients are abnormal with MRI when compared to B scan where 8 out of 15 patients in right eye(0.004) and 6 out of 15 patients in left eye(0.017) are abnormal. In 5 mm depth, 6 out of 15 patients are abnormal with MRI when compared to B scan where 3 out of 15 patients in right eye(0.659) are abnormal. CONCLUSIONS: B scan and MRI measured at 3mm behind the globe from optic disc is statistically significant than 5 mm. MRI is statistically superior to B scan in measuring the optic nerve sheath diameter in diagnosing raised intracranial pressure. Disclosure: Dr. Kilji has nothing to disclose. Dr. Srinivasan has nothing to disclose. Dr. Bhanu has nothing to disclose. Dr. Samivel has nothing to disclose. Dr. Ranganathan has nothing to disclose.