Ilya saw a patient last week with ongoing headaches post MVA in January. Headaches were worst in the morning with nausea and vomitting.
Ilya did the following optic nerve US to confirm bilateral papilloedema.
Images of the optic nerve entering into the globe posterior of the left and right eyes (labelling!! Ilya!!) show optic nerve sheath diameter (ONSD) >5mm indicating elevated ICP. Note that Ilya appropriately measured the nerve diameter 3mm posterior to the retina.
Studies vary from 4.8-6.5mm in the cut off diameter for ONSD on US. This may be due to inconsistencies in insinuating angle and measurement, as well as individual variation. However, a diameter >5mm is usually used as the cut off suggestive of ICP >20mmHg. BMJ is currently conducting a systematic review on ONSD US for elevated ICP (1).
It can be tricky to find the optic nerve due to its oblique entry into the globe. Holding the probe transverse and moving the probe laterally and fanning superiorly and inferiorly usually helps. Shrestha et al showed that the learning curve for accurate measurement requires at least 20 scans(2).
Nevertheless, getting good at this beats having to look for papilloedema with the ophthalmoscope!!
Ilya's patient went on to have an LP: opening pressure >34cmH2O.
1. Koziarz A, Sne N, Kegel F et al Optic nerve sheath diameter sonography for the diagnosis of increased intracranial pressure: a systematic review and meta-analysis protocol.BMJ Open. 2017 Aug 11;7(8):e016194.
2. Shrestha GS, Upadhyay B, Shahi A et al Sonographic Measurement of Optic Nerve Sheath Diameter: How Steep is the Learning Curve for a Novice Operator? Indian J Crit Care Med. 2018 Sep;22(9):646-649.