|Year : 2021 | Volume
| Issue : 3 | Page : 89-95
Ultrasonographic measurement of optic nerve sheath diameter to detect raised intracranial pressure in adult head injury patients in the intensive care unit and its correlation with computed tomography scan findings
A Srilekha1, Ram Murti Sharma2, Shibu Sasidharan3, Babitha Manalikuzhiyil4
1 Department of Critical Care Medicine, Tata Memorial Hospital, Mumbai, Maharashtra, India
2 Department of Anaesthesiology and Critical Care, AHRR, New Delhi, India
3 Department of Anaesthesiology and Critical Care, Level III IFH, MONUSCO, Goma, DR Congo
4 Department of Radiology, Ojas Hospital, Panchkula, Haryana, India
|Date of Submission||13-Apr-2021|
|Date of Decision||07-May-2021|
|Date of Acceptance||05-Jul-2021|
|Date of Web Publication||25-Sep-2021|
Dr. Shibu Sasidharan
E3/601, GH-79, Sector-20, Panchkula - 134 117, Haryana
Source of Support: None, Conflict of Interest: None
Background: Our objective was to evaluate if ultrasonographic measurement of optic nerve sheath diameter can be used for early and accurate diagnosis of raised intracranial pressure as seen in cranial CT scan in patients of traumatic brain injury.
Methods: Prospective, observational study. 40 adult traumatic head injury patients with altered sensorium suspected to have elevated intracranial pressure admitted to the ICU. Single optic nerve sheath diameter was measured 3.0 mm behind the globe in each eye, and optic nerve sheath diameter from each eye were averaged to create a binocular optic nerve sheath diameter measurement. A binocular optic nerve sheath diameter or uni-ocular measurement in patients with single eye measurement greater than 5.00 mm was considered abnormal. A CT scan of the head was performed within 2 hrs of USG measurement. The radiologist was blinded to the USG measurement of optic nerve sheath diameter and patient's CT considered to be positive for raised ICP
Results: Mean age of the patients was 41.15 years. Mean ONSD recorded was 5.613. Highest ONSD was 6.300 and the lowest was 4.750. CT scan findings of raised ICT were present in 36 patients and mean ONSD was >5.00 mm in all the patients. CT scan finding of raised ICT was not present in 4 patients out of which raised ONSD was present in 1 patient. Hence study showed that USG of ONSD has 100% sensitivity and 75% specificity with a positive predictive value of 97.3% and a negative predictive value of 100%.
Conclusions: Bedside ultrasonographic measurement of optic nerve sheath diameter has the potential as a sensitive screening test for elevated intracranial pressure in adult head injury patients in ICU.
Keywords: Traumatic Brain Injury, ONSD, Optic Nerve Sheath Diameter, ICP
|How to cite this article:|
Srilekha A, Sharma RM, Sasidharan S, Manalikuzhiyil B. Ultrasonographic measurement of optic nerve sheath diameter to detect raised intracranial pressure in adult head injury patients in the intensive care unit and its correlation with computed tomography scan findings. MRIMS J Health Sci 2021;9:89-95
|How to cite this URL:|
Srilekha A, Sharma RM, Sasidharan S, Manalikuzhiyil B. Ultrasonographic measurement of optic nerve sheath diameter to detect raised intracranial pressure in adult head injury patients in the intensive care unit and its correlation with computed tomography scan findings. MRIMS J Health Sci [serial online] 2021 [cited 2022 Dec 6];9:89-95. Available from: http://www.mrimsjournal.com/text.asp?2021/9/3/89/326734
| Introduction|| |
Traumatic brain injury is a leading cause of mortality in patients younger than 45 years. Primary damage to the brain is a direct consequence of initial trauma. Secondary damage to the brain is due to elevated intracranial pressure (ICP), hypoxemia, hypotension, and hypercapnia. The combination of hypotension and elevated ICP seriously compromises blood flow to the brain., Hence, elevated ICP is a challenging and potentially fatal complication of head trauma in patients who present to the ICU.
Clinicians need an accurate tool to detect elevated ICP. The physical examination is limited in its ability to accurately detect elevated ICP. Although computed tomography (CT) scanners are the most common diagnostic tests for these patients, there are situations in which rapid bedside means of evaluating ICP would be advantageous. Increased ICP is transmitted to the subarachnoid space surrounding the optic nerve causing optic nerve sheath expansion. Hence, optic nerve sheath diameter (ONSD) can be used as a possible indicator of elevated ICP.
The objective was to evaluate if ultrasonographic measurement of ONSD can be used for early and accurate diagnosis of raised ICP as seen in cranial CT scan in patients of traumatic brain injury.
This study aims to evaluate if ultrasonographic measurement of ONSD can be used to detect raised ICP in patients of traumatic brain injury.
To find the association between ONSD and ICP.
To validate the findings on ultrasound by correlating it with CT scan findings.
| Materials and Methods|| |
- Study type: Prospective, observational study
- Study population: 40 adult traumatic head injury patients with altered sensorium suspected to have elevated ICP admitted to the ICU
- Study place: ICU of a large tertiary level teaching hospital
- Study duration: September 2013–September 2015.
- Patients of age >18 years
- Moderate to severe head injury
- Glasgow Coma Scale <12.
- Patients of age <18 years
- Bilateral ocular trauma.
Institutional Ethical Committee clearance was obtained for the study.
Written informed consent was taken from the patient's relatives.
Ultrasonographic measurement was performed with a Sonosite machine (using a 13–6 MHz linear probe) under the guidance of an experienced intensivist.
The subjects were examined in the supine position, the gel was placed on the eyelid and the linear probe was used to obtain the axial cross-sectional images of the optic disc [Figure 1].
|Figure 1: Ultrasonographic measurement of optic nerve sheath diameter in a head injury patient in our study|
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A single ONSD was measured 3.0 mm behind the globe in each eye, and then the ONSD measurements from each eye were averaged to create a binocular ONSD measurement [Figure 2] and [Figure 3].
|Figure 2: Ultrasonographic measurement of optic nerve sheath diameter using calipers|
Click here to view
A binocular ONSD or uni-ocular measurement in patients with single eye measurement >5.00 mm was considered abnormal.
A CT scan of the head was performed within 2 h of ultrasonographic measurement.
The radiologist was blinded to the ultrasonographic measurement of ONSD and the patient's CT considered to be positive for raised ICP if one or more of the following were present:
- Significant edema
- Midline shift
- Mass effect
- Effacement of sulci
- Collapse of ventricles
- Compression of cisterns.
| Results|| |
We conducted the study on 40 adult head injury patients of age >18 years with moderate-to-severe head injury admitted to the ICU [Table 1] and [Table 2]. The mean age of the patients was 41.15 years. Mean ONSD recorded was 5.613. The highest ONSD was 6.300 and the lowest was 4.750. 80% of the patients were male (n = 32) and 20% were female (n = 8) [Table 3], [Table 4], [Table 5].
In 72.5% of the patients, the mode of injury was due to road traffic accidents. In 20%, it was due to fall and in 7.5%, it was due to assault.
CT scan findings of raised ICT were present in 90% of the patients. No CT scan findings of raised ICT were present in 10% of the patients - Midline shift present in 75% of the patients, edema in 70% of the patients, effacement in 35% of the patients, collapse of ventricles was present in 32.5%, and compression of mesencephalic cisterns in 12.5% [Table 3] and [Table 4].
CT scan findings of raised ICT were present in 36 patients and mean ONSD was >5.00 mm in all the patients. CT scan finding of raised ICT was not present in 4 patients out of which raised ONSD was present in 1 patient. Hence, the study showed that ultrasonographic measurement of ONSD has 100% sensitivity and 75% specificity. It has a positive predictive value of 97.3% and a negative predictive value of 100%.
We also tried to infer the effect of gender on many of the variables. There was no significance for the effect of gender on the mode of injury. Gender had no influence on raised ONSD. Gender had no significant effect on CT scan findings of raised ICT [Table 6] and [Table 7].
| Discussion|| |
The findings of severe head injury with elevated ICP often alter the treatment for trauma patients. Such decisions include transfer to the operating room versus the CT suite, treatment with medications such as mannitol, and placement of ICP monitors or drainage catheters. This study suggests that a bedside ultrasonography is sensitive to detect elevated ICP. There are several other studies which show similar findings and suggest bedside ultrasonography as a sensitive means to detect raised ICP.,,,
The eyes often reflect disease states elsewhere in the body and optic nerve has a unique characteristic that by histology it is not really a nerve but a white matter tract of the CNS that extends into the orbit where it is surrounded by cerebrospinal fluid (CSF) throughout its entire length. If the CSF pressure in the optic nerve sheath constantly fluctuates, as it does in the brain, the sheath, such as the spinal dural sac, could function as an expansion vessel. Hence, the evaluation of ONSD can be useful to detect raised ICP.
There are many other methods to detect elevated ICP but with many limitations. Although physical examination is the only other bedside means of detecting raised ICP, it is not accurate and is limited in its ability if the patient is unconscious, sedated, paralyzed, or intubated. Clinically, detectable papilledema is not usually present with acute elevations of ICP, and may take over a week to develop. Lumbar puncture can be useful, but in certain situations carries significant risk. Although the intraventricular catheters that are fluid coupled to an external strain gauge are ranked first and also carry a therapeutic significance, they are invasive and difficult. There are situations where cranial CT is unavailable making the early detection of raised ICP difficult. Such situations include disasters and multi-casualty occurrences where a rapid triage is required. In such situations, a rapid and noninvasive method like bedside ultrasonography would be useful to evaluate raised ICP.
History dates back to 1964 when Hayreh in 1964 said that there is a constant communication between optic nerve sheath, subarachnoid space, and cranial cavity.
Hansen and Helmke in 1996 used B-scan to measure ONSD 3 mm behind the globe. The optic nerve, ontogenetically part of the central nervous system, is surrounded by subarachnoid CSF and dura mater. Because of the connection with the intracranial subarachnoid space, CSF pressure variations influence the ONSD [Table 8] and [Table 9].
Dubourg et al. conducted a meta-analysis of 6 studies done in 236 patients which showed a pooled sensitivity of 90%, pooled specificity of 85% and a pooled diagnostic odds ratio of 51, that is, patients with elevated ICP are 51 times more likely to have an elevated ONSD.
Newman et al. in 2001 measured ultrasonographically ONSD of 23 patients with shunted hydrocephalus and found that the upper limit of normal for ONSD is 4.5 mm (measured 3 mm behind the globe) in patients over 1 year of age, and 4.0 mm in children <1 year of age. Those patients with functioning ventriculoperitoneal shunts had a mean ONSD of 2.9 mm; those with raised ICP had a mean ONSD of 5.6 mm. These results confirm that ONSDs in excess of the control data are strongly suggestive of raised ICP.
Mladen Siranovi et al. compared the ultrasonographic measurement of ONSD with direct measurement of ICP by intracranial catheter and found that ultrasonographic measurement of ONSD correlates with direct measurement of ICP [Table 5].
Wang et al. estimated the ONSD cut off point for the prediction if elevated opening pressure on LP in Caucasian population. Hence, they proposed that ethnic differences should be noted and appropriately applied to the corresponding ultrasonographic criteria.
On ultrasound examination, the optic nerve appears homogeneous with low internal reflectivity compared with the high reflectivity of the nerve sheath; this was utilized by Ossoinig when he performed the first ultrasound measurement of the optic nerve using an A-scan technique, and subsequently described standardized A-scanning. Using these echography techniques several groups have investigated the relation between the ONSD as measured by A-scan and the ICP.
The present study was conducted on 40 adult head injury patients which was based on the sample size of previous studies:
In our study, ONSD was measured 3 mm behind the globe. This was based on Hansen's and Helmke postmortem studies. They conducted histological studies which revealed a segment of the optic nerve in which maximal diameter fluctuations could be expected, namely the bulging dura mater region approximately 3 mm behind the papilla. They also examined 20 postmortem optic nerve preparations sonographically before and after dilatation of the optic nerve sheath by means of measurement from 3 different projections. After artificial widening of subarachnoid space using gelatin, they found that the mean diameter increased by 60% at 3 mm behind the optic nerve head, but only by 35% at 10 mm distance. They also found that the 3 mm position is reliably reproducible.
We considered a binocular ONSD of >5 mm to be indicative of raised ICP. A similar upper limit was used in most of the previous studies.
Highest cut-off point used in the literature was 6.0 mm. One such notable study was conducted by Strumwasser et al. When we used a cut-off of 5.00 mm, we got a sensitivity of 100% and specificity of 75%. Strumwasser et al. used a cut-off point of 6 mm and found a sensitivity of 26% and specificity of 38% [Table 8] and [Table 9].
We found that as the ONSD cut-off was increased to 5.5 mm and above sensitivity of the study decreased and the specificity of the study increased.,
80% of our patients were males. 20% were females. This correlated well with the previous studies which showed a gender distribution that is more common in males. According to previous epidemiological studies conducted in India, the males affected were 5.7 times than that of the number of females. This can be attributed to the fact that in the settings of our country, it is the male that is more involved in outdoor activities. According to a study by Sathiyasekaran BWC, 80% of patients involved in road traffic accidents in India were males [Table 6] and [Table 7].
- The centers with less experience with ultrasonography may find varying results
- Small sample size and convenience sampling technique were the major limitations
- The criterion standard used for evaluation, CT scan finding, is not the gold standard method for the detection of elevated ICP though it is the most widely used method of detecting raised ICP.
| Conclusion|| |
Bedside ultrasonographic measurement of ONSD has the potential as a sensitive screening test for elevated ICP in adult head injury patients in ICU.
The authors would like to thank all the subjects who consented to participate in this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9]