Optic Nerve Sheath Diameter as a Predictor of Raised Intracranial Pressure Findings on Orbital Ultrasound

BACKGROUND Several studies have found an association between raised intracranial pressure (ICP) and optic nerve sheath diameter (ONSD) in conditions with severe head injury and intracranial bleeding. Idiopathic intracranial hypertension is also a cause of elevated ICP. Because the meninges and subarachnoid space around the optic nerve are continuous, a rise in ICP can be detected with an increase in ONSD. The objectives of this study were to correlate Optic Nerve Sheath Diameter (ONSD) with features suggestive of raised intracranial pressure on CT / MRI of the Brain and describe the features suggestive of raised intracranial pressure on CT/MRI Brain in clinically suspected patients. METHODS This was a case control study carried out in the Department of Radio-diagnosis at MGMCRI for suspected raised intracranial pressure evaluation. All these patients were subjected to ultrasound examination of the eye and the optic sheath diameter was measured while the patients were in supine posture. ONSD was measured on Mind ray DC8, and/or GE S7 Expert using High frequency linear probe on the closed upper eyelid with adequate aqueous gel as a coupling agent. ONSD was also measured in Philips 1.5T MRI and Ge optima 128 slice CT. Patients were followed up on whether they were treated surgically or medically and if they developed clinical signs of raised ICP such as headache, vomiting, raised blood pressure, double vision, confusion or loss of consciousness. RESULTS The raised ICP was observed in 30.67 % of study patients and the optic nerve sheath distension was observed in 37.33% of patients. The diagnostic accuracy of determining the optic nerve sheath diameter was equal such as area under curve, sensitivity and specificity as 0.833, 66.67% and 100 % respectively in both methods. CONCLUSIONS ONSD has emerged as an interesting option for measuring intracranial hypertension in brain-injured states, owing to its simplicity, non-invasive nature, and accessibility.