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Original Research Paper ISSN : e- ISSN 2395-3950, p-issn 2395-440X
IRPMS | VOL-3 | No. 4 | OCT-DEC | 2017
20
OPTIC NERVE SHEATH DIAMETER (ONSD) MEASUREMENT
WITH OPTIC NERVE ULTRASOUND (ONUS) IN THE EVALUATION
OF ELEVATED INTRACRANIAL PRESSURE: A COMPARATIVE
STUDY WITH CT SCAN IN HEAD TRAUMA PATIENTS.
1Shreyas Patel, 2Krunalkumar Pancholi, 2Rahulkumar Humbal, 1Rina Parikh,
3A. K. Saxena
1Assistant Professor, 2Resident Doctor, 3Professor & Head, Department of Emergency Medicine,
Medical College, Baroda, Gujarat, India
Corresponding Author: Dr. Krunalkumar Pancholi, Resident Doctor, Department of
Emergency Medicine, Medical College, Baroda-390001, Gujarat, India.
Mail: shreyas384@gmail.com
ABSTRACT
BACKGROUND & OBJECTIVE: Elevated intracranial pressure (ICP) is a challenging
and potentially fatal complication of acute head trauma in patients who present to the
emergency department. Although computed tomography scanners are the most common
diagnostic tests for these patients in hospital, there are situations in which a rapid bedside
means of evaluating intracranial pressure would be advantageous. These situations include
unstable multiorgan-system trauma patients, remote settings with prolonged transport
time, or mass casualty occurrences. The optic nerve sheath diameter has been suggested as
a possible indicator of elevated intracranial pressure.1-9 Optic Nerve Ultrasonography
(ONUS) may help us to identify raised intracranial pressure. Our objective is to determine
whether a bedside ultrasonographic measurement of optic nerve sheath diameter can
accurately predict elevated intracranial pressure in adult head injury patients in the
emergency department (ED),taking CT scan as gold standard test. Methods: We
conducted a prospective, blinded observational study on adult patients in ED patients with
suspected intracranial injury. Using a 7.5-MHz ultrasonographic probe on the closed
eyelids, a single optic nerve sheath diameter was measured 3 mm behind the globe in each
eye. Cranial CT findings of midline shift, edema, or effacement suggestive of elevated
intracranial pressure were used to evaluate the accuracy of optic nerve sheath diameter.
RESULTS: The sensitivity of mean binocular ONSD >5mm measured by ONUS for raised ICP
was found to be 100% with specificity of 89%.The Positive predictive value was 68% & the
negative predictive value was 100%.
CONCLUSION: Bedside ONSD measurement, performed by ED physicians can provide
accurate, non-invasive method to identify raised ICP in patients with acute brain injury.
KEY-WORDS: ONSD, ONUS, Elevated ICP, Head Trauma, Emergency Department.
Original Research Paper ISSN : e- ISSN 2395-3950, p-issn 2395-440X
IRPMS | VOL-3 | No. 4 | OCT-DEC | 2017
21
INTRODUCTION
Raised intracranial pressure is a
complication of traumatic brain injury. Early
identification of elevated intracranial
pressure (ICP) is helpful to ensure timely
and appropriate treatment. Ultrasound is a
readily available imaging modality and
examination of optic nerve sheath by bedside
ultrasound allows detection of changes in
diameter which may indicate intracranial
hypertension.1, The optic nerve sheath
anatomy is identical to that of the brain
coverings (Dura, Arachnoid & Pia), and
therefore, it has potential to provide a
window on changes within the intracranial
cerebrospinal fluid space.2,3, 4, 5
THE ANATOMY OF OPTIC NERVE
SHEATH : The intra orbital section of
optic nerve extends from the globe,
where it inserts medially, to the optic
canal located in the lesser wing of
sphenoid bone. It is encased by a
meningeal sheath consisting of dura
mater, arachnoid mater and piamater.
Cerebro-spinal fluid is contained in the
trabeculated subarachnoid space and is
continuously and slowly filtered. As a
result, the optic nerve sheath is in direct
communication with the intracranial
subarachnoid space. It is this relationship
that forms the physiological basis for
using the optic nerve sheath as a
surrogate for intracranial pressure
measurement. The optic nerve sheath is
bound more loosely to the optic nerve
closer to the globe. This loose binding
creates a much larger and potentially
more distensible, subarachnoid space in
this region, which can appear bulbous on
ultrasound. While papilloedema may
take time to develop, dilation of the optic
nerve sheath occurs much earlier and
may be a near instantaneous
manifestation of elevated ICP. 6
Ultrasound Images of Globe and Optic
Nerve and its Sheath
The aim of this study is to determine
whether the bedside sonographic
measurement of ONSD can accurately
predict the CT scan results of elevated
intracranial pressure (ICP) in head injury
patients at the emergency department.
MATERIAL & METHODS
We conducted a cross sectional,
observational study over a period of two
months, enrolling 60 patients with head
injury. Patients or their relatives were asked
to give informed & written consent before
their inclusion in the study.
INCLUSION CRITERIA... Patients
presented to the ED with head injury.
EXCLUSION CRITERIA... Age
younger than 18 years.
Patients with penetrating ocular
trauma.
History of neurological or
hypertensive disease.
Original Research Paper ISSN : e- ISSN 2395-3950, p-issn 2395-440X
IRPMS | VOL-3 | No. 4 | OCT-DEC | 2017
22
ONUS WAS PERFORMED BY USING
THE FOLLOWING PROTOCOL...
o Patient Position - The patient was placed
supine with 30° head up position.
o Probe Position - Gel was applied on the
upper eyelid with closed eyes and a
linear (7.5 MHZ) probe was lightly
placed horizontal over the closed upper
eyelid of the patient on both the sides.
The structures of the eye were visualized
align the optic nerve directly opposite the
probe. Sonographic measurement of ONSD
was Perpendicular to the vertical axis of the
scanning plane, 3.00 mm behind the globe in
each eye2,7,8. A single ONSD was measured
and then the ONSD from each eye were
averaged to create a Mean Binocular ONSD
measurement. Based on prior literature, an
ONSD above 5 mm on ultrasound
considering abnormal, binocular ONSD >
5.00 mm was considered abnormal4,5,6. CT
scan was performed in all patients and the
results evaluated by radiologists blinded to
the ONSD results. The CT scan result was
considered to be positive for elevated ICP if
the results like significant edema, midline
shift of 3 mm or more, mass effect,
effacement of sulci, collapse of ventricles, or
compression of cisterns.6
RESULTS
60 patients were enrolled in the study, with
an average age of 38±17 Years. The majority
of the patients in our study were having a
Original Research Paper ISSN : e- ISSN 2395-3950, p-issn 2395-440X
IRPMS | VOL-3 | No. 4 | OCT-DEC | 2017
23
history of motor vehicle crash & remaining
were having a history of blunt assault & fall.
Mean Binocular ONSD of All study
Patients..
No. Of
Patient
Mean Binocular
ONSD (mm) ± SD
ONSD
< 5mm
44
4.28 ± 0.6
ONSD
> 5mm
16
5.91 ± 0.7
Comparison Between Mean Binocular
ONSD & CT Scan results
CT
Positive
(No. Of
Patients)
CT
Negative
(No. Of
Patients)
Total
ONSD
> 5mm
11
5
16
ONSD
< 5mm
0
44
44
Total
11
49
60
The Sensitivity of mean binocular ONSD in
patients with elevated ICP detected by CT
scan results was 100% & the specificity was
89%. The positive predictive value(PPV)
was 68% & the negative predictive
value(NPV) was 100%.
DISCUSSION
Our study finds similar values of Sensitivity,
Specificity, PPV and NPV as the study
performed by Blavias M, Theodoro D et al. 6
in 2003, which showed 100% sensitivity,
95% specificity, 93% PPV and 100% NPV.
The study performd by Tayal VS, Neulander
M et al9. also yielded Sensitivity of 100%
and specificity of 63%.
The result of our study suggested that optic
nerve ultrasonography (ONUS) can serve as
an adequate screening tool for elevated
ICP.10,11 Same result was obtained in other
studies.
Sensitivity of our result is 100 %, which
suggests that ONUS can detect nearly all
patients with raised ICP, but Specificity is
89% which tells patients can be
misclassified as having elevated ICP.
Negative predictive value of our result is
100%, which suggests ONSD<5 mm
definitely rules out elevated ICP.
0
10
20
30
40
50
ONSD < 5mm ONSD > 5mm
No. Of Patient
0
10
20
30
40
50
60
70
ONSD > 5mm
ONSD < 5mm
Total
Original Research Paper ISSN : e- ISSN 2395-3950, p-issn 2395-440X
IRPMS | VOL-3 | No. 4 | OCT-DEC | 2017
24
Similar to the results of the study performed
by Goel R, Goyal N et al,1 Soldatos T,
Karakistos D et al,3 and Geeraerts T,
Merceron S et al,8 ONSD can be a good
guide for triage, early decision making for
management of patients with head injury.
ADVANTAGES OF STUDY...
o Help to diagnose the patient with
elevated ICP following head injury.
o In the setting of disaster, a rapid bedside
ONSD measurement would be helpful to
triage patients who urgently need to
undergo CT scan.
o ONUS can be helpful when CT is not
available.
o ONUS is radiation-free, non-invasive,
portable, bedside and easy to apply in
patients with unstable vital findings10,11.
LIMITATIONS
o The Sample Size in our study was small
& included convenience samples. So we
need to perform this study on larger scale
before extrapolating in the ED Setting.
o ONUS is highly operator dependent.
CONCLUSION
Our study demonstrates a close correlation
between optic nerve sheath dilation on
ocular ultrasound and evidence of elevated
intracranial pressure on head computed
tomography in patients with Head injury.
The ONSD of < 5 mm measured at distance
of 3 mm behind the globe definitely rules out
raised ICP. ONSD of > 5 is suggestive of
raised ICP and need to be further confirmed
with other tests. Thus, ONSD measurement
with ONUS can be a very useful screening
test to detect raised ICP in Head injury
patients and to start measures to reduce ICP.
ACKNOWLEDGEMENT
Authors acknowledge the immense help
received from the scholars whose articles are
cited and included in references of this
manuscript. The authors are also grateful to
Authors/Editors/Publishers of all those
articles, journal and books from where the
literature of this article has been reviewed
and discussed.
SOURCE OF FUNDING: Nil.
CONFLICT OF INTEREST: None.
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