Dynamic Ultrasound of the Optic Nerve Sheath Diameter in Spontaneous Intracranial Hypotension
Aim: Spontaneous intracranial hypotension (SIH) is an increasingly recognized condition that commonly presents as orthostatic headache. The syndrome is caused by spontaneous spinal loss of cerebrospinal fluid. There is some evidence that the optic nerve sheath diameter (ONSD) may be affected by this disease and we hypothesize that positional changes of the ONSD occur from supine to upright position and that these changes are more pronounced in symptomatic patients with orthostatic headaches than in patients without orthostatic headaches.
Methods: All patients with clinically suspected SIH received dynamic ultrasound as part of their workup. The change in ONSD was measured in transorbital B-mode ultrasound. All patients underwent dynamic, first in supine then in upright position, ultrasound of the optic nerve sheath (ONS). The primary endpoint was the change of ONSD while standing as compared with the diameter while lying supine.
Results: Dynamic ultrasound was performed in 44 consecutive patients with suspected SIH. In 18 patients the leading symptom was orthostatic headaches (Group A: 10 men, 8 women; mean age 51.9 years). The remaining 26 patients did not have orthostatic headaches (Group B: 15 men, 11 women; mean age 61.9 years).
Data from the two groups revealed no statistically significant difference of ONSD when measured in supine position only (p = 0.957). The mean ONSD was significantly smaller in upright position among patients with orthostatic headaches (mean 0.484 ±SD 0.095cm) as compared with patients without orthostatic headaches (0.549 ±SD 0.097cm, p = 0.036). The change of ONSD from supine to upright position with the dynamic measurement - the d-ONSD - was significantly larger in patients with orthostatic headaches (mean -0.053 ±SD 0.034cm) as compared with patients without orthostatic headaches (0.005 ±SD 0.038cm, p≤0.001). Receiver operator characteristics revealed an area under the curve of 0.886.
Conclusion: In this series the changes of ONSD that occurred during dynamic measurement from supine to upright patient position were significantly larger in patients with orthostatic headaches. The diagnostic accuracy was significantly improved as compared with measurements in either position alone. We call this method of comparing supine and subsequent upright ONSD “dynamic ultrasound of optic nerve sheath diameter.” Transorbital dynamic ultrasound may provide a novel, non-invasive test for patients with SIH.