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Neurology India, Vol. 58, No. 5, September-October, 2010, pp. 812-813 Letter to Editor Optic nerve ultrasonography for detection of raised intracranial pressure when invasive monitoring is unavailable Venkatakrishna Rajajee, Prithiviraj Thyagarajan, Ram E Rajagopalan Department of Critical Care Medicine, Sundaram Medical Foundation, Shanthi Colony, 4th Avenue, Annanagar, Chennai 600040, India Correspondence Address: Date of Acceptance: 27-Jul-2010 Code Number: ni10233 PMID: 21045531 DOI: 10.4103/0028-3886.72202 Sir, In many parts of the developing word, invasive techniques for intracranial pressure (ICP) monitoring such as ventriculostomy catheters and intraparenchymal catheters are not easily available because of constraints of resources, familiarity and readily available expertise. A noninvasive technique that accurately detects the presence of intracranial hypertension, even if only qualitative, would be very useful in this setting. The optic nerve sheath is a continuation of the dura, and the subarachnoid space extends along the optic nerve. Dilatation of the optic nerve sheath on ocular ultrasound has been shown to correlate well with raised ICP by invasive monitoring in recent studies. [1],[2],[3] An optic nerve sheath diameter (ONSD) >5-5.7 mm seems to have the greatest accuracy in detecting ICP >20 mm Hg. [1],[2],[3] We present our experience with ONSD measurement in a limited-resource environment where invasive ICP monitoring is generally unavailable. The study setting was a 16-bed general ICU and traumatic brain injury (TBI) the most common neurological admission diagnosis. Approval was granted by the institutional review board. Patients suspected to have intracranial hypertension based on history and physical examination underwent measurement of ONSD, performed by a single ultrasonographer (VR). All patients had a Glasgow Coma Scale (GCS) score of <8 following acute brain injury. The technique was as previously described [1],[2],[3] : A Sonosite Titan™ ultrasound machine was used with a 10-5-MHz linear-array probe placed gently over the upper lateral aspect of the eyeball to avoid the intraocular lens. Measurement was performed 3 mm behind the retina. The mean of 3 measurements on each side was recorded. Correlation was made to signs of raised ICP on CT, as well as subsequent neurological progression. Eight patients underwent ONSD measurement. The diagnoses were severe TBI- 4, ischemic stroke- 2, intracerebral hemorrhage (ICH)- 1 and tuberculous meningitis (TBM)- 1. Four patients (ischemic stroke- 1, TBI- 1, TBM- 1 and ICH-1) had mean ONSD >5 mm (mean+SD, 5.4+0.44 mm) [Figure - 1]. All four patients had CT evidence of raised ICP (ischemic stroke, ICH and TBI - midline shift >5 mm with sulcal or cisternal effacement. TBM - hydrocephalus with sulcal effacement) and neurological deterioration with a >2-point drop in the GCS in the first 6 hours. Three patients had rapid decrease in mean ONSD to <5 mm following therapeutic intervention (decompressive hemicraniectomy for malignant infarction, hematoma evacuation for TBI and therapeutic lumbar puncture plus acetazolamide for TBM) with corresponding clinical neurological improvement. A follow-up scan could not be done on one patient (ICH). Four other patients (TBI- 3, ischemic stroke- 1) had mean ONSD <5 mm (mean+SD, 4.2+0.6 mm) on serial ultrasound. All 4 had no CT evidence of raised ICP and had unchanged neurological exams in the first 6 hours and at discharge (P=0.028, Fisher exact test). In our experience, ONSD measurement correlated well with CT evidence of raised ICP, clinical deterioration and response to therapeutic intervention. Our case series illustrates a very important potential role for a promising new diagnostic technique. Invasive ICP measurement is the gold standard for identification of high ICP as well as monitoring following treatment and can be performed effectively even in resource-constrained environments. [4] We believe that ICUs in developing nations that routinely care for patients with severe brain injury must attempt to perform invasive ICP monitoring as the standard of care for patients suspected to have raised ICP. Realistically, however, this is unlikely to happen in the near future. ONSD measurement is inexpensive, appears to have relatively low inter-observer variability and is a relatively simple technique to teach to junior physicians. [3],[5] Optic nerve ultrasonography is a promising tool for the detection of intracranial hypertension in resource-constrained environments. References
Copyright 2010 - Neurology India The following images related to this document are available:Photo images[ni10233f1.jpg] |
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