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Three Part Question

In [patients suspected of having raised intracranial pressure] is [measurement of the optic nerve sheath diameter by ultrasound] accurate [at detecting raised intracranial pressure]

Clinical Scenario

A 35 year old man presents to the emergency department after falling off his bicycle while drunk. He has a large scalp laceration, some blood in his right ear canal and his GCS has dropped from 15 to 13 in the ambulance. He is now combative. His pupils are equal and reactive. Our concern is that his GCS is reducing because of a significant head injury with increasing intracranial pressure (ICP). How can you identify if the low GCS score is due to raised ICP, and initiate emergency treatment before the CT scan confirms the diagnosis.

Search Strategy

Medline 1950 – Week 31st March 2008 using NCBI/PubMed interface
Embase 1980– Week 31st March 2008 using Datastar interface
Cochrane Library

Medline/Embase: [(raised intracranial pressure) or (brain injury)] and [(optic nerve ultrasonography) or (transorbital sonography)] LIMIT to Human and English

Cochrane Library: Optic nerve sheath [MeSH] and Raised intracranial pressure [MeSH] 0 records.

Search Outcome

A total of 43 papers were found, of which 35 were irrelevant or insufficient quality. The table summarises the contents of the remaining 8 papers.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Kimberley et al, 2008, USA	Adults in the emergency department and neuro-intensive care department who had invasive intracranial monitors placed as part of their care. Ultrasound measurement of optic nerve sheath diameter was performed at the bedside by ED physicians blinded to ICP reading	Prospective observational study	Optic nerve sheath diameter measured by bedside ultrasound compared to direct ICP readings	Optic nerve sheath diameter of >5mm had sensitivity of 88% and specificity of 93% for diagnosis of ICP > 20cm H20 Spearman rank correlation coefficient 0.59 (p<0.0005)	Small study of 15 patients. Convenience sample so possible selection bias of patients easy to scan or who clinically had signs of raised ICP Ed physician performing ultrasound could not be blinded to patient condition
Geeraerts et al, 2007, France	Adult patients with severe traumatic brain injury, with GCS < or = 8, requiring ICP monitoring	Observational study	Optic nerve sheath diameter reading on admission to ED compared to initial invasive ICP reading	Spearman Rank correlation coefficient of 0.68 Sensitivity and negative predictive value of optic nerve sheath diameter >5mm detecting ICP >20 cm H20 100%	Small convenience sample of 31 patients. Selection bias
Tayal et al, 2007, USA	Adult ED patients with suspected raised ICP after head injury.	Observational study	Mean optic nerve sheath diameter from both eyes compared to CT findings suggestive of raised ICP	Sensitivity of 100% and Specificity of 63% for detecting signs of raised ICP on CT	Study of 59 patients CT poor indicator of raised ICP Convenience sample so possible selection bias
			Also compared to any CT diagnosis of any traumatic intra cranial injury ONSD >5mm taken as abnormal	Sensitivity of 84% and specificity of 73% for detection of any traumatic intra cranial injury on CT
Girisgin et al, 2007, Turkey	Adult ED population with elevated ICP from any cause diagnosed by emergency CT Control group of healthy volunteers	Case control study	Comparison between ONSD, measured by ultrasound, in both groups	Significant difference between study and control groups (p<0.001)	Small study of 54 patients Non blinded with CT diagnosis prior to ONSD measurement Patients with wide ONSD measurements but normal CT scans excluded from study
Karakitsos et al, 2006, Greece	CT and ONSD readings in 54 ITU patients with GCS <8 compared to control group.	Case control study	Brain death and a semiquantative CT neuroimaging scale used for outcomes	ONSD significantly increased in study group, compared to control, on admission (p<0.001) ONSD >5.9mm and ONSD increase of 2.5mm in serial readings associated significantly with brain death (p<0.01)	Difference between case and control groups in age. Control group had other significant pathologies and were not assessed for significant brain injury as controls, possibly confounding ONSD results Small study and comparison again made to CT
Blaivias et al, 2003, USA	Adult ED patients with a suspicion of elevated intracranial pressure from possible focal intracranial pathology	Observational Study	Mean optic nerve sheath diameter from both eyes compared to CT findings suggestive of raised ICP ONSD >5mm taken as abnormal	Sensitivity of 100% and specificity of 95% for detecting signs of raised ICP on CT PPV 93%, NPV 100%	Small study of 35 patients CT poor indicator of raised ICP Convenience sample so possible selection bias
Hansen et al, 1997, Germany	Adult patients undergoing neurological testing by means of intrathecal puncture.	Observational Study	ONSD taken by ultrasound during intrathecal fluid infusion compared to subsequent measurement of intrathecal CSF pressure	Mean linear regression correlation of 0.78 between ONSD and CSF pressures across all subjects	Small study Raised ICP due to intrathecal infusion so relevance to traumatic brain injury questionable
Goel et al, 2008, India	All adult patients admitted with head injury, who subsequently went on to have CT	Prospective, observational study of 100 patients	Mean ONSD reading compared to CT findings of raised ICP.	Sensitivity of 98.6% and specificity of 92.8%, PPV of 97.2% and NPV of 96.3% for raised ICP – compared to CT	CT poor indicator of raised ICP Selection bias
			Secondarily, compared ONSD with need for neurosurgical procedure	ONSD >0.5mm significant increase in need for neurosurgical intervention (P<0.0001)

Comment(s)

Some papers have used CT as an indicator of raised ICP but the results of these studies are supported by studies comparing ONSD with direct ICP measurement. At present CT scan is the diagnostic test used in most hospitals to dictate management of head injuries as intracranial monitoring is poorly available. Although all of these studies were small and likely had some selection bias, these are the patients most likely to benefit from early detection of raised ICP. Sensitivity, specificity, negative and positive predictive values are high across the studies. Larger studies recruiting a more general population of patients, with a clinical suspicion of raised ICP from all causes, are needed. There may also be a future role for ultrasound ONSD measurement to exclude raised ICP in non trauma patients eg. Prior to lumbar puncture

Clinical Bottom Line

In patients, with head injuries, a bedside ultrasound measurement of the optic nerve sheath diameter >5mm has high sensitivity and specificity for detecting raised intracranial pressure.

References

1. Kimberly HH, Shah S, Marill K, Noble V. Correlation of optic nerve sheath diameter with direct measurement of intracranial pressure. Acad Emerg Med. 2008 Feb;15(2):201-4.
2. Geeraerts T, Launey Y, Martin L, Pottecher J, Vigue B, Duranteau J, Benhamou D. Ultrasonography of the optic nerve sheath may be useful for detecting raised intracranial pressure after severe brain injury. Intensive Care Med. 2007 Oct;33(10):1704-11.
3. Tayal VS, Neulander M, Norton HJ, Foster T, Saunders T, Blaivias M. Emergency department sonographic measurement of optic nerve sheath diameter to detect findings of increased intracranial pressure in adult head injury patients. Ann Emerg Med. 2007 Apr;49(4):508-14.
4. Girisgin AS, Kalkan E, Kocak S, Cander B, Gul M, Semiz M. The role of optic nerve ultrasonography in the diagnosis of elevated intracranial pressure. Emerg Med J. 2007 Apr;24(4):251-4.
5. Karakitsos D, Soldatos T, Gouliamons A, Armaganidis A, Poularas J, Kalogeromitros A, Boletis J, Kostakis A, Karabinis A. Transorbital sonographic monitoring of optic nerve diameter in patients with severe brain injury. Transplant Proc. 2006 Dec;38(10):3700-6.
6. Blaivias M Theodoro D, Sierzenski PR. Elevated intracranial pressure detected by bedside emergency ultrasonography of the optic nerve sheath. Acad Emerg Med. 2003 Apr;10(4):376-81.
7. Hansen HC, Helmke K Validation of the optic nerve sheath response to changing cerebrospinal fluid pressure: ultrasound findings during intrathecal infusion tests. Neurosurg. 1997 Jul;87(1):34-40.
8. Goel RS, Goyal NK, Dharap SB, Kumar M, Gore MA. Utility of optic nerve ultrasonography in head injury. Injury 2008 May; 39 (5): 519-524 .