Optic nerve subarachnoid space area may be an accurate marker for intracranial pressure

1. In a study of 90 patients, optic nerve subarachnoid space area (ONSASA) measured by transorbital ultrasound had a sensitivity of 100% and specificity of 92% for predicting elevated ICP.

2. ONSASA measurement outperformed ultrasonographic measurement of optic nerve sheath diameter and optic nerve subarachnoid space width in predicting ICP.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Intracranial pressure (ICP) must be monitored in many patients with acute neuropathology, and is currently measured using invasive methods such as intraparenchymal probes or lumbar puncture. However, ICP causes papilledema and visible changes in optic nerve anatomy, meaning that noninvasive markers for ICP using transorbital ultrasonography have shown promise in past studies. This validation study in 90 patients aimed to assess the performance of optic nerve subarachnoid space area (ONSASA) measurement in diagnosing ICP elevation compared to a standard of intraparenchymal ICP measurement. The correlation coefficient for ICP and ONSASA was 0.953. Using a linear model for calculating ICP from ONSASA and a cutoff of 20 mmHg for ICP elevation, the sensitivity and specificity of ONSASA were 1.00 and 0.92, respectively. Noninvasive ICP measurement has many potential clinical and research uses, and the high diagnostic performance of this measure is certainly interesting and encouraging. However, the necessity for trained transorbital ultrasonographers as well as a reliable image processing and calculation workflow means that this method would be challenging to implement in acute neurologic care settings. ONSASA may represent a valuable proxy for ICP in monitoring idiopathic intracranial hypertension or studying glaucoma pathophysiology.

Click to read the study in BJO

Relevant Reading: Invasive and noninvasive means of measuring intracranial pressure: A review

In-Depth [prospective cohort]: Patients undergoing intraparenchymal ICP monitoring at a single hospital in China were included. Patients with ICP greater than 30 mmHg, known history of ocular disease including glaucoma, or traumatic cerebrospinal fluid leak were excluded. Transorbital ultrasounds were obtained by experienced investigators and analyzed using image processing software. ONSASA was measured from 3 mm to 7 mm behind the globe. ICP was elevated in 17.8% of the study patients. ICP was significantly correlated with mean arterial blood pressure and body mass index. The correlation coefficients for ICP with optic nerve sheath diameter and optic nerve subarachnoid space width, other ultrasonographic parameters, were 0.672 and 0.691, respectively. Receiver operating curve analysis showed an area under the curve of 0.960 for ONSASA. The optimal cut-off value for prediction of ICP elevation using the ONSASA model was calculated as 19.96.

Image: PD

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