A noninvasive method for the estimation of increased intracranial pressure in patients with severe traumatic brain injury using optic nerve sheath diameter measured on computed tomography head
- Departments of Neurosurgery, Arrowhead Regional Medical Center, Colton, United States.
- Departments of Neurosurgery, Riverside University Health System, Moreno Valley, CA, United States.
Departments of Neurosurgery, Arrowhead Regional Medical Center, Colton, United States.
Departments of Neurosurgery, Riverside University Health System, Moreno Valley, CA, United States.
DOI:10.25259/SNI-120-2019Copyright: © 2019 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Gohar Majeed, Samir Kashyap, Rosalinda Menoni, Dan Miulli, Raed Sweiss. A noninvasive method for the estimation of increased intracranial pressure in patients with severe traumatic brain injury using optic nerve sheath diameter measured on computed tomography head. 07-Jun-2019;10:97
How to cite this URL: Gohar Majeed, Samir Kashyap, Rosalinda Menoni, Dan Miulli, Raed Sweiss. A noninvasive method for the estimation of increased intracranial pressure in patients with severe traumatic brain injury using optic nerve sheath diameter measured on computed tomography head. 07-Jun-2019;10:97. Available from: http://surgicalneurologyint.com/surgicalint-articles/9350/
Background:Measurement of optic nerve sheath diameter (ONSD) using ocular ultrasonography has shown a promise in predicting increased intracranial pressure (ICP). However, this method is dependent on operator technique and equipment availability. We propose an alternative method of measuring ONSD and Marshall score grading by utilizing initial computed tomography (CT) head obtained on admission. We believe that such a technique could help predict patients requiring an invasive ICP monitor on admission.
Methods:Patients were retrospectively selected from the neurosurgery database of a level II trauma center. Control patients originated from a database of nontraumatic brain injury (TBI) patients with a negative CT head and no intracranial pathology. Study subjects included patients aged 18–90 years, who sustained a severe TBI requiring placement of an ICP monitor on admission. All patients had a non-contrast CT head before the placement of an ICP monitor. Patients receiving any intervention for decreasing suspected elevated ICPs and those with any documented orbital fractures before ICP monitor placement were excluded from the study. All measurements were performed by at least of two independent assessors.
Results:A total of 242 patients were reviewed, of which 204 (100 control and 104 intervention) met inclusion criteria for this study. T he average age in the control group was 49.1 ± 22.9 years old while the average age of the intervention group was 36.9 ± 15.1 years (P 0.0001). The average Glasgow Coma Scale was 7 in the intervention group. The average ONSD of the control group was 5.73 ± 0.58 mm compared to 6.76 ± 0.83 mm in the intervention group (P 0.0001). Linear regression analysis demonstrated a statistically significant correlation between ONSD and opening ICP (r = 0.40, P r = 0.31, P 0.0001). An ONSD ≥6.0 mm + Marshall score ≥3 on initial CT head demonstrated a 92.5% sensitivity, 92.6% specificity, and 96.1% positive predictive value for developing an ICP ≥20 mmHg during hospitalization.
Conclusion:Utilizing ONSD in combination with Marshall score grading on initial CT head is a strong predictor of elevated ICP. These criteria can be used in future studies to develop more objective criteria to guide ICP monitor placement.
Keywords: Intracranial pressure, Optic nerve sheath diameter, Traumatic brain injury
Traumatic brain injury (TBI) affects approximately 1.4 million individuals per year in the United States and is a major cause of disability, death, and economic cost to patients, their families, and society as a whole.[
Recent studies have examined the efficacy of various noninvasive methods to predict increased ICPs and measurement of the optic nerve sheath diameter (ONSD) using ultrasound or CT has accurately predicted increased ICP or intracranial pathology.[
This is a retrospective review of a prospectively collected database from two level II trauma centers. Study subjects included patients aged 18–90 years old who sustained a severe TBI (GCS ≤8) that had an ICP monitor placed on admission. All patients had a non-contrast CT head before placement of an ICP monitor. Patients receiving a craniotomy or craniectomy for decreasing suspected elevated ICPs before ICP monitor placement were excluded. Furthermore, patients with any documented orbitofacial trauma or concerns for cerebrospinal fluid leak were excluded from the study. The opening pressure after placement of the ICP monitor and peak ICP during hospitalization was recorded (mmHg). The same CT head was used to determine the Marshall score. We established a control group that consisted of 100 patients with negative CT head. McKesson Radiology PACS and Sectra PACS were used as the software for measuring ONSDs. The ONSD was measured by a team comprising of senior neurosurgery residents, staff neurosurgeon, and neuroradiologist at our respective institutions. The thickness of the CT slices was 5 mm in all subjects.
ONSD measurement protocol
Measurements of ONSD were obtained by adhering to a strict protocol established by our team to minimize interobserver variability. The mediastinum window was used to obtain all measurements. The ONSD was measured 3 mm behind the posterior aspect of the globe on axial sequences [
All data points were entered into our study database. The average ONSD of the left, right, and both eyes was calculated, and a linear regression analysis was conducted to determine the relationship between ONSD and ICP. Sensitivity, specificity, and positive predictive value calculations were also conducted. Fisher’s exact test was used to determine significance, which was defined as P < 0.05.
A total of 242 patients from 2012 to 2018 were identified from our database, and 204 patients (104 intervention, 100 control) met the inclusion criteria for this study. The average age in the intervention group was 37.1 years old and median initial GCS was 6.6. All ICP monitoring was in the form of external ventricular drain (EVD) placement. The total number of males overall (58 control and 83 intervention) was statistically significant (P = 0.0008).
Our control group consisted of 100 patients (58 males and 42 females) with no evidence any intracranial abnormality or severe head injury. Mean ONSD in the control group was 5.73 ± 0.58 mm. Mean ONSD in the male population was 5.82 ± 0.53 mm and 5.60 ± 0.63 mm in the female population. The ONSD range was 4.25–7.15 mm [
The average ONSD of both the eyes was 6.72 ± 0.79 mm. The average ONSD of the left eye was 6.76 ± 0.83 mm and the right eye was 6.63 ± 0.79 mm. The average age in the intervention group was 36.9 ± 15.1 years [
Further analysis revealed differences in the sensitivity and specificity between the laterality and mean ONSD measurements [
Measurement of ONSD on CT is an alternative method of measuring ONSD that has been previously validated and was used in this study.[
We were able to show that an ONSD of 6.0 mm and Marshall score ≥3 were both highly sensitive markers of elevated ICP and, when combined, are reliable indicators of whether an ICP monitor should be placed. The ONSD of the left eye had a higher sensitivity for detecting elevated ICP. This was initially attributed to the effects of midline shift and laterality of lesions; however, we did not observe a pattern to support this. Our specificity of 92.5% and positive predictive value of 96.1% are among the highest in the literature utilizing CT-measured ONSD in TBI. Luyt et al. demonstrated 100% specificity with a cutoff of 5.0mm; however, their study was performed in non-traumatic patients.[
Several studies have found a correlation between ONSD on ultrasound and ICP measured through traditional monitoring. Robba et al. showed that ONSD measured on ultrasound had the strongest correlation in predicting increased ICPs in patients with invasive ICP monitoring.[
Another method of estimating ICP uses the ratio of the ONSD to the transverse diameter of the eyeball (eyeball transverse diameter), as described by Vaiman and Bekerman, who have conducted the largest studies to date analyzing ONSD on CT. The advantage of this technique is that it reduces variation that occurs from involuntary eye movements during CT scan.[
While these studies prove that this is a reliable noninvasive technique, generalizing such a method for measuring ONSD is difficult due to differences in operator experience, technique, and the modality used. This is evidenced by the great heterogeneity in the cutoff values as shown in
The retrospective nature of our study is an inherent limitation due to selection bias. Another limitation of our study and utilizing CT head for ONSD measurement is the heterogeneity in the measurements of the ONSD due to the gantry differences between each scan. Patients’ head positioning within the scanner, time from injury to CT scan, and presenting GCS also skew these measurements. Future studies utilizing this method should include appropriate cuts through the optic nerves so that the most accurate measurements of the ONSD can be obtained. An additional limitation is the variation in EVD placement as well as differences in measurement of the opening pressure as some measured opening pressure based on centimeters of water (cmH2O) above the external auditory canal while others utilized millimeters of mercury (mmHg) as measured by an electronic transducer. In addition, distention of the optic nerve sheath in response to changing ICP is dependent on the sheath’s elasticity. Individual variability in the sheath’s elastic properties makes establishing a quantitative relationship between ONSD and ICP difficult. The ICP values used in our study were the first recorded ICP numbers. Even though institutional protocol for placing ICP monitors warrants measurement of ICPs before any CSF drainage, it would be hard to reliably guarantee such practice in a retrospective study.
Our study’s main objective was to use ONSD on initial CT head to predict who would benefit from invasive ICP monitoring. We found that an ONSD >6.0 mm on CT in the setting of trauma strongly correlated with increased ICP and, when combined with Marshall scoring on admission, is a very sensitive and specific predictor for developing critical ICP (≥20 mmHg). This is the only large retrospective study to establish a large control group using CT measurement of ONSD. This cohort of individuals can be used as a control group in future studies. Although ONSD measured on ultrasound has been validated as a reliable indicator of rising ICP, operator experience and variability of measurements limit its generalizability. Further studies are needed to better stratify ONSD values in combination with individual parameters, which may include the utilization of both dynamic ONSD monitoring (US) and precise ONSD measurements (CT). This combination of dynamic, objective, and validated criteria will be an effective tool that changes the way we determine which patients need invasive ICP monitoring.
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