Utility of Optic Nerve Sheath Diameter as a Screening Tool in Detecting Raised Intracranial Pressure

Abstract

Introduction: Raised Intracranial Pressure (ICP) is one of the most important causes of morbidity and mortality in the setting of Intensive Care Unit (ICU). Identifying the raised ICP as early as possible correlates well with the positive outcome of patients, which as of now relies more on ocular fundoscopy/Computed Tomography (CT) of brain/invasive monitoring, which relies on professional expertise and/or radiation exposure which may not be available all the times at all the places. This study tries to rationalise the utilisation of the commonly available modality of ultrasound in the evaluation of raised ICP compared to CT of brain. Aim: To measure optic nerve sheath diameter in cases of suspected raised ICP and to assess suspected raised ICP using the reference standard of radiologic diagnosis by CT of brain. Also, to assess diagnostic accuracy of sonography of the ONSD compared to CT brain for predicting raised ICP. Materials and Methods: This is a hospital based prospective comparative study on 60 adults over a period from June to August 2016, divided into two groups A and B consisting of 30 each, Group A consisted of 30 healthy controls and Group B consisted of 30 test subjects with symptoms of possible elevated ICP. The test subject’s CT imaging result was considered to be positive if findings suggested radiologic diagnosis of raised ICP such as midline shift of >3 mm/effacement of ventricles/cisterns/significant cerebral oedema/sub arachnoid haemorrhage. Ocular ultrasound and CT-scan of brain was done in both group of patients. Results: Mean age was 31.9 years in the control group and 44.6 years in the test group. Median age was 30 years in the control group and 45 years in the test group. The upper limit of the normal ONSD in the control group was 4.9 mm and a mean of 4.7 mm, those patients in the test group had a mean ONSD of 5.5 mm and upper limit of 5.7 mm, which was significantly more than the control group. These results showed that patients with raised ICP have an ONSD in excess of the control data (p<0.05). The above results were confirmed with Levene’s test for equality of means (p< 0.005). Conclusion: Ocular ultrasonography for measuring ONSD can be used an early test for diagnosing raised ICP and can be repeated for re-evaluation. In addition, ONSD has the advantage of diagnosing raised ICP earlier than ocular fundoscopy. Utilising no radiation exposure and being portable, ultrasonography avoids dangers associated with transporting ill patients from ICU and enables repeated reassessment of ICP.

Keywords

• : intracranial tension
• ocular sonography
• resource-limited conditions