Noninvasive intracranial pressure estimation by orbital subarachnoid space measurement: the Beijing Intracranial and Intraocular Pressure (iCOP) study

Abstract

IntroductionThe orbital subarachnoid space surrounding the optic nerve is continuous with the circulation system for cerebrospinal fluid (CSF) and can be visualized by using magnetic resonance imaging (MRI). We hypothesized that the orbital subarachnoid space width (OSASW) is correlated with and can serve as a surrogate for intracranial pressure (ICP). Our aim was to develop a method for a noninvasive measurement of the intracranial CSF-pressure (CSF-P) based on MRI-assisted OSASW.MethodsThe prospective observational comparative study included neurology patients who underwent lumbar CSF-P measurement and 3.0-Tesla orbital magnetic resonance imaging (MRI) for other clinical reasons. The width of the orbital subarachnoid space (OSASW) around the optic nerve was measured with MRI at 3, 9, and 15 mm behind the globe. The study population was randomly divided into a training group and a test group. After adjusting for body mass index (BMI) and mean arterial blood pressure (MABP), algorithms for the associations between CSF-P and OSASW were calculated in the training group. The algorithms were subsequently verified in the test group. Main outcome measures were the width of the orbital subarachnoid space (OSASW) and the lumbar cerebrospinal fluid pressure (CSF-P).ResultsSeventy-two patients were included in the study. In the training group, the algorithms for the associations between CSF-P and OSASW were as follows: (a) CSF-P = 9.31 × OSASW (at 3 mm) + 0.48 × BMI + 0.14 × MABP-19.94; (b) CSF-P = 16.95 × OSASW (at 9 mm) + 0.39 × BMI + 0.14 × MABP-20.90; and (c) CSF-P = 17.54 × OSASW (at 15 mm) + 0.47 × BMI + 0.13 × MABP-21.52. Applying these algorithms in the independent test group, the measured lumbar CSF-P (13.6 ± 5.1 mm Hg) did not differ significantly from the calculated MRI-derived CSF-P (OSASW at 3 mm: 12.7 ± 4.2 mm Hg (P = 0.07); at 9 mm: 13.4 ± 5.1 mm Hg (P = 0.35); and at 15 mm: 14.0 ± 4.9 mm Hg (P = 0.87)). Intraclass correlation coefficients (ICCs) were higher for the CSF-P assessment based on OSASW at 9 mm and at 15 mm behind the globe (all ICCs, 0.87) than for OSASW measurements at 3 mm (ICC, 0.80).ConclusionsIn patients with normal, moderately decreased or elevated ICP, MRI-assisted measurement of the OSASW appears to be useful for the noninvasive quantitative estimation of ICP, if BMI and MABP as contributing parameters are taken into account.Trial registrationClinical trial registered with the Chinese Clinical Trial Registry: ChiCTR-OCC-11001271

Analysis of Cerebrospinal Fluid Pressure Estimation Using Formulae Derived From Clinical Data

“…Recently, a regression model to estimate CSFP using radiographic and physiologic parameters, such as optic nerve sheath width as determined by magnetic resonance imaging (MRI), body mass index (BMI), diastolic blood pressure (DBP), and age, was derived from a Chinese dataset in Beijing. 8 This model was reported to have an intraclass correlation coefficient (ICC) of 0.87 when the optic nerve subarachnoid space width was measured at 9 mm and 15 mm posterior to the globe. An equation excluding radiographic measurements that was derived from this set, but not described in the literature, determined an ICC of 0.71, still indicating a strong correlation between predicted and actual CSFP.…”

Non-invasive Evaluation of Cerebrospinal Fluid Pressure in Ocular Hypertension: The Beijing Intracranial and Intraocular Pressure Study

“…However, the fact that the difference between the study groups reached statistical significance suggests that the differences are real. We also accept that the CSFP and TLCPD were calculated using a formula that, while reported to be reliable, has not been fully validated and may not stand the test of time [18]. Direct measurement of the orbital CSFP is however currently impossible and till better methods become available this is all we have.…”

“…All measurements made by both observers were used to calculate inter-observer repeatability. The estimated CSFP (mmHg) value was calculated as 17.54 × MRI derived OSASW at 15 mm behind the globe +0.47 × body mass index +0.13 × mean arterial blood pressure-21.52 [18]. Compared to a lumbar spinal CSFP measurement, the mean estimated bias ± standard deviation (and the 95% limits of agreement) by the above formula was 0.08 ± 2.55 (-4.90-5.10) mmHg [18].…”

“…Scout images in the transverse and oblique sagittal planes were used to ensure optimal head positioning; oblique coronal images were used for quantification. Two basic FRFSE sequences were used [8,18]: -A T2-weighted fast recovery fast spin echo sequence (T2WI-FRFSE) provided good soft tissue contrast and morphologic data for planning (TR=2760 milliseconds; TE=120 milliseconds; number of excitations=2; echo train length=18; bandwidth=41.67 Hz/pixel; field of view=16 cm × 16 cm; matrix=512 × 256; slice thickness=3 mm; slice gap=0.3 mm; leading to a nominal spatial resolution of 0.2 mm × 0.2 mm). The sequence was applied twice with 12 contiguous slices in transversal and sagittal orientation.…”

“…Several publications have used MRI to evaluate CSFP by measuring the size of the optic nerve sheath or the optic nerve subarachnoid space [15][16][17]. We have previously reported the noninvasive estimation of CSFP using orbital magnetic resonance imaging (MRI) [18]. A recent study in dogs reported an algorithmic relationship between measured lumbar CSFP and orbital CSFP; while this study was in a different species and the relationship maintained only up to a breakpoint, it supports the use of estimated lumbar CSFP as a surrogate for orbital CSFP [19].…”