ONSD alternative tool for detecting raised ICP. It

 

ONSD measurement by ultrasound:

 

A review article by Rosenberg et al. concluded ONSD and Doppler flow as the best noninvasive modalities for determining raised ICP (3). Ultrasonographic measurement of ONSD at a fixed distance from retina has been defined as a standard method of measuring the presence of raised ICP (14). The method of measuring ONSD by sonography using B mode was standardized by Hansel et al. in 1994 (12). It’s a bed side procedure which can be easily done by 5 to 10 MHz linear ultrasound probe (3). It takes just 4 minutes to measure ONSD in both eyes (12). Measurement of ONSD requires trained personnel and sound experience to currently predict raised ICP (8). 

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A  study conducted by Rajajee et al. (4) found ONSD measurement by USG to be an accurate noninvasive method of detecting raised ICP of more than 20mm of Hg. Rajajee et al.(4) had conducted a prospective blinded observational study in which 536 ONSD measurements were performed on 65 patients with invasive ICP measurement side by side on these patients. Correlation between each ONSD measurement by USG and ICP measurement at the same time period was done in this study (4). This study also concluded that ONSD of 04.8mm as a cut off for raised ICP. Sensitivity with 4.8mm cut off value for ONSD was 96% and specificity was 94% for detecting ICP of more than 20cm of water. However, authors suggested that the ONSD values have to be validated for it to become true. They suggested discarding the risk of invasive monitoring and high cost technique of CT or MRI, and including noninvasive method of ultrasound as an alternative tool for detecting raised ICP. It is more cost-effective and less tedious (4).

 

A study performed by Kimberly et al. (15) identified the correlation of ONSD with direct measurement of raised ICP. They conducted a prospective observational study in which invasive intracranial monitors were placed and ocular ultrasound was performed by 10 to 5 MHz linear probe among 15 individual patients. This study found a significant correlation between ONSD and ICP which was 0.59 calculated by spearman rank correlation coefficient test (15). The authors performed Receiver Operating Characteristic (ROC) curve test to assess the ability of ONSD to detect raised ICP. Authors of this study claim ONSD of greater than 5mm for detecting ICP of more than 20cm of water. Furthermore, the authors demonstrated ROC curve detecting sensitivity of  88% and specificity of 93% (15). They further suggested USG guided ONSD can be used as an noninvasive tool for measuring raised ICP (15).

 

A systematic literature review and meta-analysis conducted by Ohle et al. (12) concluded both USG of ONSD and CT scan were equally effective in detecting raised ICP. The authors performed a full review on 45 articles out of 1214 available article searches until August 2013 and included 12 studies meeting inclusion criteria with a total of 478 participants. Quality assessment of papers was done by Quality assessment of diagnostic accuracy studies tool (12).  Their analysis shows sonography of ONSD was 95.6% sensitive with 95% confidence interval (CI) of 87.7-98.5%. Also, it had specificity of 92.3% (95% CI of 77.9%- 98.4%) and positive plus negative likelihood ratio comparable to that of computed tomography. They concluded USG as a good diagnostic test accuracy compared to CT with high sensitivity for ruling out raised ICP especially in low risk group. Similarly, it also had high specificity than CT scan (12).  Authors of this paper concluded that USG as a better modality as it is noninvasive, can be performed at bedside and saves time as there is no need to transport the patient to CT machine. This method provides more economic value and centers without CT machines could largely benefit through this technique (12).

 

Newman et al. (16) conducted a study among shunted hydrocephalus children to evaluate the utility of ulrasonographic measurement of ONSD in children suspected of having raised ICP. In their study, 23 children who were shunted for hydrocephalus were included who gave clinical history suggestive of raised intracranial hypertension. ONSD of 102 control patient were also measured. The authors of this study (16) found that children with functioning VP shunt had lesser diameter of ONSD compared to those with non-functional shunt. This study showed the upper limit of ONSD was 4.5mm for children above 1 years of age. Similarly, children with functional VP shunt had mean ONSD of 2.9 (SD 0.5) mm and those with non-functional VP shunt had mean ONSD of 5.6 (SD 0.6mm) with p<0.0001. Newmen et al. (16) conclude USG guided ONSD as a tool to assess and monitor  ICP in children with hydrocephalus.     Zaidi et al. conducted a study to observe ONSD by USG as an screening tool for measuring raised ICP among shunt malfunctional patients (17). Authors mentioned that the most commonly used method to access the function of VPS is CT scan (17). CT scan causes radiation that has been found to cause harm resulting in lower cognitive test performances (17). Most patients with VPS undergo multiple CT scans. Malfunctioning VPS presents risk with very nonspecific symptoms such as sleepiness, vomiting, headache, and fuzziness among others (17). As MRI is not readily available, slow, expensive and may even require sedation specially for pediatric age group, this is still not the best screening tool for VPS malformation (17). Their study confirms ONSD is greater among the VPS malformation cases. Authors showed clinical correlation with signs and symptoms as equally important to diagnose malfunction and standardization of measurements by USG is important to minimize the inter-observer variation. They also showed ONSD as age and size dependent.   A prospective study was conducted by Komut et al. (5) among 100 patients to check for efficacay of ONSD in determining raised ICP among non-trauma patients. Their study found that ONSD among patients with cranial pathology in CT scan was 5.4 +/- 1mm and among patients without cranial pathology in CT scan was 4.1 +/- 0.5mm. This study determined ONSD value of 4.5mm as a cut off value which had sensitivity of 80% and specificity of 60% for detecting raised ICP (5). Authors claimed ONSD can be used for determining midline shift as well. ONSD cut off value for determining midline shift was 5.3mm with sensitivity of 80% and specificity of 60% with area under the curve 0.728, Confidence Interval  (95% 0.585 to 0.871). This study also showed ONSD to be larger in size at the corresponding lesion of brain with p<0.5 (5).  ONSD was found to be higher among patients with GCS score of less than 13 compared to that having GCS more than 13; p < 0.5. Their study reported ONSD as an important method to detect raised ICP and its severity (5). Authors claim ONSD can be used even for non-traumatic cases in which there is a suspicion of increased ICP (5). It is difficult to estimate raised ICP by history and physical examination specially among patients who are unconscious and intubated (5).   A study conducted by Pershad et al. analyzed cost effectiveness between CT, fMRI (fast sequence MRI) and USG measurement of ONSD. They found USG measurement of ONSD as cheaper and easier method (18). Pershad et al. mentioned clinical signs and symptoms of shunt failure are nonspecific and often neuroimaging is used as modality for the diagnosis (18). CT which is often being used for correctly diagnosing shunt failures. This results in exposure to ionizing radiation and has been linked with long term risk of malignancy (18). High negative predictive value of USG to detect raised ICP supports its use as screening tool (18). Preshad et al. suggested a screening test by USG as an intial method for detecting shunt failure and then to proceed for fMRI or CT scan (18). Toscano et al. conducted a retrospective study to analyze ONSD by USG among 21 critically ill patients with neurological disease who developed brain death during the course in ICU (2). Their study showed people with brain death had higher ONSD than normal control group even before having brain death. Authors concluded that daily ONSD measurement by USG among ICU patients could be useful to detect raise ICP earlier. They suggested this too to be very useful setup where invasive monitoring is not available (2).            ONSD measurement by ultrasound:   A review article by Rosenberg et al. concluded ONSD and Doppler flow as the best noninvasive modalities for determining raised ICP (3). Ultrasonographic measurement of ONSD at a fixed distance from retina has been defined as a standard method of measuring the presence of raised ICP (14). The method of measuring ONSD by sonography using B mode was standardized by Hansel et al. in 1994 (12). It's a bed side procedure which can be easily done by 5 to 10 MHz linear ultrasound probe (3). It takes just 4 minutes to measure ONSD in both eyes (12). Measurement of ONSD requires trained personnel and sound experience to currently predict raised ICP (8).    A  study conducted by Rajajee et al. (4) found ONSD measurement by USG to be an accurate noninvasive method of detecting raised ICP of more than 20mm of Hg. Rajajee et al.(4) had conducted a prospective blinded observational study in which 536 ONSD measurements were performed on 65 patients with invasive ICP measurement side by side on these patients. Correlation between each ONSD measurement by USG and ICP measurement at the same time period was done in this study (4). This study also concluded that ONSD of 04.8mm as a cut off for raised ICP. Sensitivity with 4.8mm cut off value for ONSD was 96% and specificity was 94% for detecting ICP of more than 20cm of water. However, authors suggested that the ONSD values have to be validated for it to become true. They suggested discarding the risk of invasive monitoring and high cost technique of CT or MRI, and including noninvasive method of ultrasound as an alternative tool for detecting raised ICP. It is more cost-effective and less tedious (4).   A study performed by Kimberly et al. (15) identified the correlation of ONSD with direct measurement of raised ICP. They conducted a prospective observational study in which invasive intracranial monitors were placed and ocular ultrasound was performed by 10 to 5 MHz linear probe among 15 individual patients. This study found a significant correlation between ONSD and ICP which was 0.59 calculated by spearman rank correlation coefficient test (15). The authors performed Receiver Operating Characteristic (ROC) curve test to assess the ability of ONSD to detect raised ICP. Authors of this study claim ONSD of greater than 5mm for detecting ICP of more than 20cm of water. Furthermore, the authors demonstrated ROC curve detecting sensitivity of  88% and specificity of 93% (15). They further suggested USG guided ONSD can be used as an noninvasive tool for measuring raised ICP (15).   A systematic literature review and meta-analysis conducted by Ohle et al. (12) concluded both USG of ONSD and CT scan were equally effective in detecting raised ICP. The authors performed a full review on 45 articles out of 1214 available article searches until August 2013 and included 12 studies meeting inclusion criteria with a total of 478 participants. Quality assessment of papers was done by Quality assessment of diagnostic accuracy studies tool (12).  Their analysis shows sonography of ONSD was 95.6% sensitive with 95% confidence interval (CI) of 87.7-98.5%. Also, it had specificity of 92.3% (95% CI of 77.9%- 98.4%) and positive plus negative likelihood ratio comparable to that of computed tomography. They concluded USG as a good diagnostic test accuracy compared to CT with high sensitivity for ruling out raised ICP especially in low risk group. Similarly, it also had high specificity than CT scan (12).  Authors of this paper concluded that USG as a better modality as it is noninvasive, can be performed at bedside and saves time as there is no need to transport the patient to CT machine. This method provides more economic value and centers without CT machines could largely benefit through this technique (12).   Newman et al. (16) conducted a study among shunted hydrocephalus children to evaluate the utility of ulrasonographic measurement of ONSD in children suspected of having raised ICP. In their study, 23 children who were shunted for hydrocephalus were included who gave clinical history suggestive of raised intracranial hypertension. ONSD of 102 control patient were also measured. The authors of this study (16) found that children with functioning VP shunt had lesser diameter of ONSD compared to those with non-functional shunt. This study showed the upper limit of ONSD was 4.5mm for children above 1 years of age. Similarly, children with functional VP shunt had mean ONSD of 2.9 (SD 0.5) mm and those with non-functional VP shunt had mean ONSD of 5.6 (SD 0.6mm) with p<0.0001. Newmen et al. (16) conclude USG guided ONSD as a tool to assess and monitor  ICP in children with hydrocephalus.     Zaidi et al. conducted a study to observe ONSD by USG as an screening tool for measuring raised ICP among shunt malfunctional patients (17). Authors mentioned that the most commonly used method to access the function of VPS is CT scan (17). CT scan causes radiation that has been found to cause harm resulting in lower cognitive test performances (17). Most patients with VPS undergo multiple CT scans. Malfunctioning VPS presents risk with very nonspecific symptoms such as sleepiness, vomiting, headache, and fuzziness among others (17). As MRI is not readily available, slow, expensive and may even require sedation specially for pediatric age group, this is still not the best screening tool for VPS malformation (17). Their study confirms ONSD is greater among the VPS malformation cases. Authors showed clinical correlation with signs and symptoms as equally important to diagnose malfunction and standardization of measurements by USG is important to minimize the inter-observer variation. They also showed ONSD as age and size dependent.   A prospective study was conducted by Komut et al. (5) among 100 patients to check for efficacay of ONSD in determining raised ICP among non-trauma patients. Their study found that ONSD among patients with cranial pathology in CT scan was 5.4 +/- 1mm and among patients without cranial pathology in CT scan was 4.1 +/- 0.5mm. This study determined ONSD value of 4.5mm as a cut off value which had sensitivity of 80% and specificity of 60% for detecting raised ICP (5). Authors claimed ONSD can be used for determining midline shift as well. ONSD cut off value for determining midline shift was 5.3mm with sensitivity of 80% and specificity of 60% with area under the curve 0.728, Confidence Interval  (95% 0.585 to 0.871). This study also showed ONSD to be larger in size at the corresponding lesion of brain with p<0.5 (5).  ONSD was found to be higher among patients with GCS score of less than 13 compared to that having GCS more than 13; p < 0.5. Their study reported ONSD as an important method to detect raised ICP and its severity (5). Authors claim ONSD can be used even for non-traumatic cases in which there is a suspicion of increased ICP (5). It is difficult to estimate raised ICP by history and physical examination specially among patients who are unconscious and intubated (5).   A study conducted by Pershad et al. analyzed cost effectiveness between CT, fMRI (fast sequence MRI) and USG measurement of ONSD. They found USG measurement of ONSD as cheaper and easier method (18). Pershad et al. mentioned clinical signs and symptoms of shunt failure are nonspecific and often neuroimaging is used as modality for the diagnosis (18). CT which is often being used for correctly diagnosing shunt failures. This results in exposure to ionizing radiation and has been linked with long term risk of malignancy (18). High negative predictive value of USG to detect raised ICP supports its use as screening tool (18). Preshad et al. suggested a screening test by USG as an intial method for detecting shunt failure and then to proceed for fMRI or CT scan (18). Toscano et al. conducted a retrospective study to analyze ONSD by USG among 21 critically ill patients with neurological disease who developed brain death during the course in ICU (2). Their study showed people with brain death had higher ONSD than normal control group even before having brain death. Authors concluded that daily ONSD measurement by USG among ICU patients could be useful to detect raise ICP earlier. They suggested this too to be very useful setup where invasive monitoring is not available (2).     

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