Net optic nerve sheath diameter as a factor for predicting intracranial hypertension

The assessment of intracranial pressure (ICP) is crucial in the management of neurological emergencies. Although invasive ICP monitoring has been widely used for the early diagnosis of intracranial hypertension, its routine application remains controversial for various reasons. This study aimed to evaluate the correlations between optic nerve parameters measured using cranial magnetic resonance imaging (MRI) and ICP, and to assess their diagnostic value in predicting intracranial hypertension.

The data of 112 patients with clinically suspected intracranial infections who underwent lumbar puncture (LP) and cranial MRI between October 2020 and September 2022 were retrospectively collected. Several optic nerve-related parameters were measured via cranial MRI, including optic nerve diameter (OND), optic nerve sheath diameter (ONSD), and eyeball transverse diameter (EBTD). The net optic nerve sheath diameter (nONSD; calculated as ONSD - OND) and the ONSD:EBTD ratio (ONSD/EBTD) were also calculated. ICP was determined via LP, with elevated ICP defined as >250 mmH₂O. The correlation between ocular parameters and ICP, along with the predictive value of these parameters for intracranial hypertension, was determined.

Among the included patients, 41 were found to have elevated ICP. In comparison with patients with normal ICP, those with intracranial hypertension had a higher median ONSD {5.23 [interquartile range (IQR) 4.85-5.83] vs. 4.83 (IQR 3.54-5.17) mm; P<0.001}, nONSD [2.62 (IQR 2.60-3.07) vs. 2.22 (IQR 1.85-2.40) mm; P<0.001], and ONSD/EBTD [0.23 (IQR 0.21-0.24) vs. 0.20 (IQR 0.15-0.23); P<0.001]. Moderate significant linear correlations were found between ONSD and ICP (r=0.36; P<0.001), ONSD/EBTD and ICP (r=0.36; P<0.001), and nONSD and ICP (r=0.61; P<0.001). The nONSD showed relatively promising predictive accuracy among the whole patient group: at an nONSD threshold of 2.52 mm, the specificity was 88.7%, and the positive predictive value (PPV) was 80%.

nONSD demonstrates strong potential as a non-invasive predictor of elevated ICP. Nonetheless, further prospective studies in varied populations are needed to establish the generalizability and clinical application of nONSD.