measurement by CT scan:
of raised ICP was performed during signs such as significant midline shift,
effacement of basal cisterns, sulcal effacement, ventricular compression, and
cerebral herniation as previously mentioned by Rajajee et al (4). Measurement of
ONSD by CT to accurately diagnose raised ICP has been proved by previous
studies (6) (13).
observational study was conducted by Luyt et al. (8) on 56 patients
to study relationship between ONSD measured on CT and raised ICP. Opening
pressure manometry was measured during LP for detecting raised ICP (8). 14 patients
had elevated ICP > 20 mm Hg and 42 had normal opening pressure. Their
results show ONSD cutoff of 4.8mm by CT measurement had sensitivity and
specificity of 92.9 % and 97.6%, respectively to detect the raised ICP.
Furthermore, authors of this study mentioned that increasing the cut off value
to more than 5mm decreased the sensitivity to 85%.
cohort study was conducted by Sekhon et al. (13) on 57 TBI patients by measuring ONSD in CT scan and by invasive
ICP. They found ONSD as better predictor of raised ICP than other parameters of
CT scan such as cisternal effacement, sulcal effacement, ventricular compression
and cerebral herniation. Linear and logistic regressions were used in study to
see correlation between ONSD and invasive ICP values. Strong correlation
between ICP and ONSD r = 0.74 p < 0.001 was found in the study. Liner regression between ICP and ONSD was R2 of 0.56 compared to R2 of 0.21 between CT features and ICP. Authors conclude ONSD has higher predictive value than other traditional signs for detecting raised ICP (13). Legrand et al. conducted an study among 72 patients to evaluate correlation between ONSD by CT scan and prognostic factors in traumatic brain injury patients (11). They found intial ONSD > 7.3mm to be independently associated with ICU mortality rate
among TBI patients. Authors of the article suggest ONSD to be included with
initial management of TBI patients along with other clinical, radiological and
laboratory parameters (11). However they
also say higher ONSD does not necessarily rule out good outcome.
measurement by MRI:
Kang et al. (1) conducted a
study to look for relationship between ONSD in brain MRI and elevated ICP. This
study showed that patients with raised ICP have significantly greater diameter
of ONSD compared to normal group. Out of 31 patients in the study, 13 patients
with mass effect had average ONSD of right and left to be 5.06mm and 5.13mm,
respectively. Similarly, patients without features of mass effect had ONSD of
4.545mm (Rt) and 4.35mm (Lt). Kang et
al. cited hemodynamic instability and time as a restrictive factor for
radiological examinations (1). Kang et al. concluded ONSD measurement by MRI
as an efficient tool to predict increased ICP in an unconscious patient.
conducted by Geeraerts et al. (10) showed ONSD as an excellent predictor of raised ICP.
38 patients with TBI had undergone MRI in which ONSD was measured and ICP
monitoring was done via parenchymal sensor. Results of the study showed ONSD to
be 6.31mm +/- 0.5mm among patients with ICP > 20mm of Hg and ONSD of 5.29mm
+/- 0.48mm among patients with ICP below 20mm of Hg. Authors say ONSD
<5.30mm was unlikely to be associated with raised ICP, whereas an ONSD above 5.82mm was associated with a 90% probability of raised ICP (10). Singhal et al. conducted a study looking for change in ONSD among paediatric population with hydrocephalus who had undergone neurosurgical intervention (7). They assessed ONSD pre- and post-surgery by MRI among 9 patients who had undergone endoscopic third ventriculostomy and 7 patients who had undergone tumour resection (8). Authors of this study found significant decrease in ONSD after the intervention. The mean pre-operative ONSD was 6.1mm compared to mean post-operative ONSD of 5.71mm. Serial change of ventricular size is not a good indicator of uncontrolled hydrocephalus as raised ICP can occur even in normal ventricle size and smaller ventricles (8). They also claim serial measurement of ONSD and its reduction can be taken as a sign of improved hydrocephalus after the surgical intervention (8). Authors further say there was improvement in clinical signs and symptoms after intervention (7).