Letter to the Editor: Optic nerve sheath diameter as ICP marker

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TO THE EDITOR: We read with great interest the article by Maissan et al.6 (Maissan IM, Dirven PJAC, Haitsma IK, et al: Ultrasonographic measured optic nerve sheath diameter as an accurate and quick monitor for changes in intracranial pressure. J Neurosurg 123:743–747, September 2015), in which the authors measured intracranial pressure (ICP) and optic nerve sheath diameter (ONSD) before, during, and after tracheal suctioning in adult head injury patients with Glasgow Coma Scale (GCS) scores of 9 or less and found the ultrasonographic measurement of ONSD to be an accurate and quick method of identifying changes in ICP. We would like to address a few points that we believe warrant discussion. The authors did not describe the position of their patients (i.e., supine-horizontal, head elevated 30°, or other), orientation of the ultrasound probe (along the transverse or longitudinal axis or both), the distance of the site of measurement from the globe (e.g., 3 mm posterior), the use of sedatives and/or muscle relaxants prior to tracheal suction, the timing of the last dose of mannitol, timing of the test (i.e., day or night), the status of patients with a GCS score of E1M1V1 (i.e., brain dead or not), the association with cervical trauma (cervical collar use) or polytrauma, status of autoregulation (impaired vs intact), or cerebral perfusion pressure (CPP) and mean arterial pressure (MAP) before, during, and after tracheal stimulation. We had studied ONSD in 100 patients with head injuries, as published (Goel et al.)3 in the journal Injury in 2008. In that study, we compared the data with CT findings instead of ICP. We obtained false-positive results in 2 patients who had frontal extradural hematomas (EDHs). Frontal EDH with pressure on the optic nerve could be the reason for these false positives. We also had 1 false-negative result. This case involved an elderly patient, and we hypothesize that the false negative could be due to brain atrophy. There may be subarachnoid septations around optic nerves, and these septations could increase with age. We realize that it is not possible to discuss or quote all papers, but discussion of specific findings could be helpful in interpreting results.

After publication of our article, many studies were done to correlate ONSD as a marker of ICP in different conditions. These studies showed differing results. In sharp fluctuation of ICP, ONSD correlated with change in ICP in the study by Maissan et al.6 but not in the study by Rajajee et al.8 Autoregulation status; CPP and MAP before, during, and after tracheal stimulation; and muscle relaxant use were not described by Maissan et al.6 Perhaps these details could help to identify the cause of sharp fluctuations in ONSD and ICP after tracheal stimulation. Studies involving patients with endoscopic third ventriculostomy failure,7 ventriculoperitoneal shunt failure,2,4 and aneurysmal subarachnoid hemorrhage without raised ICP1 as well as studies of brain-dead patients9 show interesting results. Further studies of patients with hypothalamic and cervical injury are needed, as cervical sympathetic block has been found to cause an increase in ONSD.5 Patients with diffuse axonal injury (DAI) may show interesting results, as DAI is not associated with elevated ICP.

The upper limit of normal ONSD is 5 mm for adults, 4.5 mm for children aged 1–15 years, and 4.0 mm for infants up to 1 year of age.3 It would be useful to assess ONSD in adults as Grade 0 (< 5 mm), Grade 1 (5mm), Grade 2 (> 5mm but < 7 mm), and Grade 3 (≥ 7mm) and discuss results according to these grades, especially with respect to the use of ONSD as a prognostic marker in neurosurgical patients. ONSD grading should be correlated with ICP grades and CT scan midline shift grades, and it could be standardized and used in formulating treatment protocols.

We believe that ultrasonic measurement of ONSD has the potential to be a useful ancillary tool in the neurointensivist's armamentarium—not only in caring for patients with head injuries but also in managing other neurosurgical and medical conditions. We also believe that a prospective, blinded study of the correlation between ICP and ONSD could be of great help in standardizing the use of this tool—particularly if the study were to include analysis of multiple factors. It is important to identify indications for, limitations of, and misunderstandings related to the ultrasonic measurement of ONSD in order to optimize patient care. To avoid mechanical and thermal side effects, the procedure should be performed quickly, and one can expect that there would be a learning curve; accuracy and efficiency are likely to improve with experience. In summary, we believe that this new technology is appealing and that further assessment is needed to evaluate the efficacy of the technique.

References

  • 1

    Bäuerle JNiesen WDEgger KButtler KJReinhard M: Enlarged optic nerve sheath in aneurysmal subarachnoid hemorrhage despite normal intracranial pressure. J Neuroimaging [epub ahead of print 2105]

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  • 2

    Choi SHMin KTPark EKKim MSJung JHKim H: Ultrasonography of the optic nerve sheath to assess intracranial pressure changes after ventriculo-peritoneal shunt surgery in children with hydrocephalus: a prospective observational study. Anaesthesia 70:126812732015

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  • 3

    Goel RSGoyal NKDharap SBKumar MGore MA: Utility of optic nerve ultrasonography in head injury. Injury 39:5195242008

  • 4

    Hall MKSpiro DMSabbaj AMoore CLHopkins KLMeckler GD: Bedside optic nerve sheath diameter ultrasound for the evaluation of suspected pediatric ventriculoperitoneal shunt failure in the emergency department. Childs Nerv Syst 29:227522802013

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  • 5

    Kim MSYoon KBYoon DMKim DH: Effect of cervical sympathetic block on optic nerve sheath diameter measured by ultrasonography. Ultrasound Med Biol 41:159916042015

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  • 6

    Maissan IMDirven PJACHaitsma IKHoeks SEGommers DStolker RJ: Ultrasonographic measured optic nerve sheath diameter as an accurate and quick monitor for changes in intracranial pressure. J Neurosurg 123:7437472015

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  • 7

    Padayachy LCKilborn TCarrara HFigaji AAFieggen GA: Change in optic nerve sheath diameter as a radiological marker of outcome from endoscopic third ventriculostomy in children. Childs Nerv Syst 31:7217282015

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  • 8

    Rajajee VVanaman MFletcher JJJacobs TL: Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocrit Care 15:5065152011

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  • 9

    Topcuoglu MAArsava EMBas DFKozak HH: Transorbital ultrasonographic measurement of optic nerve sheath diameter in brain death. J Neuroimaging 25:9069092015

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Disclosures

The authors report no conflict of interest.

Response

We thank Ravishankar S. Goel and Pooja Goel for their comments on our paper. We also believe that ultrasonographic measurement of ONSD has the potential to be a useful tool, especially in prehospital settings and at the emergency department, where invasive ICP monitoring is often impossible. We compared 2 tests to determine ICP: the noninvasive sonographic measurement and the invasive gold standard, use of an ICP probe. Furthermore, we were interested in a tool to be used in the prehospital setting to assess instantaneous changes in ICP more than static ICP measurements. In our prospectively designed study we found a strong correlation between ICP changes and ONSD changes. ONSD was measured 3 mm behind the retina in a transverse axis. We used the international definition of ONSD as the distance inside the hyperechoic dura mater.2

All patients who suffered severe brain injury were treated according to our hospital protocol “raised ICP after traumatic brain injury.” This includes elevated head position (20°–30°), heavy sedation and analgesia, and mannitol administration 6–12 times a day, depending on baseline ICP. Mean arterial pressure was titrated to 80–100 mm Hg in patients with a baseline ICP < 20 mm Hg to guarantee cerebral perfusion pressure of at least 60 mm Hg. If baseline ICP exceeded 20 mm Hg, the treatment was intensified. No additional sedatives or muscle relaxants were administered prior to suctioning the endotracheal tube. All study measurements were done during daytime shifts (8:00 am to 6:00 pm; Amsterdam time, i.e., Greenwich Mean Time + 1 hour).

Our results are in contradiction with the suggestions made by Rajajee et al. in their retrospective analysis of their data.1 They observed a rapid response of ONSD to ICP increase but a delayed return to normal ONSD after ICP had already lowered to baseline levels. However, they included patients with raised ICP due to causes other than brain injury. Furthermore, the delayed return may be the result of brain edema in their patients, and this may explain the difference in results. In our study, we focused on the value of ONSD in brain-injured patients as a tool in the prehospital setting. We do realize that our population was rather specific and small but believe our study should be interpreted as a proof of principle. We fully agree that more studies should be done in larger groups and in different circumstances to assess the efficacy and the place of this noninvasive technique.

References

  • 1

    Rajajee VVanaman MFletcher JJJacobs TL: Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocrit Care 15:5065152011

    • Search Google Scholar
    • Export Citation
  • 2

    Topcuoglu MAArsava EMBas DFKozak HH: Transorbital ultrasonographic measurement of optic nerve sheath diameter in brain death. J Neuroimaging 25:9069092015

    • Search Google Scholar
    • Export Citation

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Article Information

INCLUDE WHEN CITING Published online January 15, 2016; DOI: 10.3171/2015.9.JNS152178.

© AANS, except where prohibited by US copyright law.

Headings

References

  • 1

    Bäuerle JNiesen WDEgger KButtler KJReinhard M: Enlarged optic nerve sheath in aneurysmal subarachnoid hemorrhage despite normal intracranial pressure. J Neuroimaging [epub ahead of print 2105]

    • Search Google Scholar
    • Export Citation
  • 2

    Choi SHMin KTPark EKKim MSJung JHKim H: Ultrasonography of the optic nerve sheath to assess intracranial pressure changes after ventriculo-peritoneal shunt surgery in children with hydrocephalus: a prospective observational study. Anaesthesia 70:126812732015

    • Search Google Scholar
    • Export Citation
  • 3

    Goel RSGoyal NKDharap SBKumar MGore MA: Utility of optic nerve ultrasonography in head injury. Injury 39:5195242008

  • 4

    Hall MKSpiro DMSabbaj AMoore CLHopkins KLMeckler GD: Bedside optic nerve sheath diameter ultrasound for the evaluation of suspected pediatric ventriculoperitoneal shunt failure in the emergency department. Childs Nerv Syst 29:227522802013

    • Search Google Scholar
    • Export Citation
  • 5

    Kim MSYoon KBYoon DMKim DH: Effect of cervical sympathetic block on optic nerve sheath diameter measured by ultrasonography. Ultrasound Med Biol 41:159916042015

    • Search Google Scholar
    • Export Citation
  • 6

    Maissan IMDirven PJACHaitsma IKHoeks SEGommers DStolker RJ: Ultrasonographic measured optic nerve sheath diameter as an accurate and quick monitor for changes in intracranial pressure. J Neurosurg 123:7437472015

    • Search Google Scholar
    • Export Citation
  • 7

    Padayachy LCKilborn TCarrara HFigaji AAFieggen GA: Change in optic nerve sheath diameter as a radiological marker of outcome from endoscopic third ventriculostomy in children. Childs Nerv Syst 31:7217282015

    • Search Google Scholar
    • Export Citation
  • 8

    Rajajee VVanaman MFletcher JJJacobs TL: Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocrit Care 15:5065152011

    • Search Google Scholar
    • Export Citation
  • 9

    Topcuoglu MAArsava EMBas DFKozak HH: Transorbital ultrasonographic measurement of optic nerve sheath diameter in brain death. J Neuroimaging 25:9069092015

    • Search Google Scholar
    • Export Citation
  • 1

    Rajajee VVanaman MFletcher JJJacobs TL: Optic nerve ultrasound for the detection of raised intracranial pressure. Neurocrit Care 15:5065152011

    • Search Google Scholar
    • Export Citation
  • 2

    Topcuoglu MAArsava EMBas DFKozak HH: Transorbital ultrasonographic measurement of optic nerve sheath diameter in brain death. J Neuroimaging 25:9069092015

    • Search Google Scholar
    • Export Citation

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