- Department of Neurosurgery, Henry Ford Hospital, Detroit, MI, USA
- University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
- Department of Diagnostic Radiology, Henry Ford Hospital, Detroit, MI, USA
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Department of Radiology, Henry Ford Hospital, Detroit, MI, USA
- Department of Public Health Sciences, Henry Ford Hospital, Detroit, MI, USA
Department of Neurosurgery, Henry Ford Hospital, Detroit, MI, USA
DOI:10.4103/2152-7806.154777Copyright: © 2015 Reinard K. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Reinard K, Basheer A, Phillips S, Snyder A, Agarwal A, Jafari-Khouzani K, Soltanian-Zadeh H, Schultz L, Aho T, Schwalb JM. Simple and reproducible linear measurements to determine ventricular enlargement in adults. Surg Neurol Int 09-Apr-2015;6:59
How to cite this URL: Reinard K, Basheer A, Phillips S, Snyder A, Agarwal A, Jafari-Khouzani K, Soltanian-Zadeh H, Schultz L, Aho T, Schwalb JM. Simple and reproducible linear measurements to determine ventricular enlargement in adults. Surg Neurol Int 09-Apr-2015;6:59. Available from: http://sni.wpengine.com/surgicalint_articles/simple-reproducible-linear-measurements-determine-ventricular-enlargement-adults/
Background:Recent studies have suggested that Evan's Index (EI) is not accurate and instead endorse volumetric measurements. Our aim was to evaluate the reproducibility of linear measurements and their correlation to ventricular volume.
Methods:Using magnetic resonance (MR) images of 30 patients referred for normal pressure hydrocephalus (NPH), EI, frontal-occipital horn ratio (FOR), third ventricular width and height, frontal horn width (FHW), and callosal angle (CA) at the foramen of Monro and the posterior commissure (PC) were independently measured by residents in neurosurgery and radiology, a neurosurgeon and radiologist, and a medical student. Intraclass correlation coefficients (ICC) were calculated to establish inter-rater agreement among the reviewers. Pearson's correlation coefficients were done to assess the relationship of the linear measurements with total ventricular volume. Kappa analyses were performed to assess the degree of agreement between cutpoints determined by the ROC analysis for the linear measurements and reviewers’ gestalt impression about ventricular size with volumetric abnormality.
Results:The overall inter-rater agreement among reviewers was almost perfect for EI (ICC = 0.913), FOR (ICC = 0.830), third ventricular width, FHW (ICC = 0.88), and CA at PC (ICC = 0.865), substantial for temporal horn width (ICC = 0.729) and CA at foramen of Monro (ICC = 0.779), and moderate for third ventricular height (ICC = 0.496). EI, FOR, third ventricular width, temporal horn width, and CA at PC measures correlated with total ventricular volume. There was fair-to-almost-perfect agreement of the individual reviewer's gestalt responses of abnormatility with volumetric abnormality. Gestalt responses were better for more senior raters.
Conclusion:Linear measurements are reliable and reproducible methods for determining ventricular enlargement.
Normal pressure hydrocephalus (NPH) is a progressive disease that was first described by Adams et al. in 1965.[
Evan's index (EI) was first described by William Evans in 1942 as an indirect linear measurement of ventricular size on pneumoencephalography in pediatric patients. EI is calculated by the ratio of the maximal transverse diameter of the frontal horns to the maximum internal diameter of the cranium.[
Recent studies have questioned the reliability of EI for assessment of ventricular size and, in light of modern brain imaging, have endorsed volumetric analysis of ventricular volume.[
Our Institutional Review Board (IRB) approved the collection of data for this retrospective study (IRB #6628). A board-certified neurosurgeon and neuroradiologist developed the measurement guidelines that were used by the other raters as a guide for calculating all linear measurements in this study [Figure
(a) Axial T1 MRI with the largest biparietal diameter demonstrating the midline (b) as well as the linear measurements that are perpendicular to it and parallel to one another (a, c); (b) Third ventricular height: midsagittal T1 MRI demonstrating the anterior commissure to posterior commissure (AC-PC) line (a) as well as the largest, height of the third ventricle from its floor to its roof perpendicular to the AC-PC line (b); (c) Third ventricular width: axial T1 MRI with the largest third ventricular diameter perpendicular to midline (a); (d) Temporal horn width: Axial T1 MRI with the largest temporal horn diameter perpendicular to midline (b); (e) Frontal horn width: coronal T1 MRI demonstrating largest frontal horn diameter that is perpendicular to midline (a); (f) Aial T1 MRI with the largest bifrontal distance demonstrating the callosal angle at the foramen of Monroe; (g) Coronal T1 MRI image demonstrating the callosal angle at the posterior commissure, which is confirmed by the localizer mode on the sagittal T1 image
We reviewed our database and selected 30 consecutive patients that had been referred for evaluation of possible NPH. The mean age was 77.4 years with a range from 43 to 90 and 67% were female. All subjects underwent coronal T1-weighted magnetic resonance (MR) imaging with a General Electric 1.5-T Signa system (GE Medical Systems, Milwaukee, WI) using a 3D spoiled gradient-echo sequence with TR/TI/TE = 7.6/1.7/500 ms, flip angle = 20 degrees, field of view (FOV) =200 × 200 mm2, matrix size = 256 × 256, pixel size = 0.781 × 0.781 mm2, slice thickness = 2.0 mm (voxel size = 0.781 × 0.781 × 2.0 mm3), number of slices = 124, bandwidth = 25 kHz, and scanning time of 5 min and 45 s.
Images were de-identified. They were not morphed into Talairach space. The T1-weighted (T1W) images were first converted from Digital Imaging and Communications in Medicine (DICOM) format to Analyze 7.5 format using Eigentool, an in-house software program (
All linear measurements were calculated independently by a medical student, a mid-level resident in neurosurgery, a neuroradiology fellow, a board-certified neurosurgeon, and a neuroradiologist. Ventricular volume was classified as normal, minimally enlarged, moderately enlarged, and grossly enlarged based on the overall impression or “gestalt” of each rater. The raters were unaware of the software calculations of intraventricular volumes.
To assess the consistency of measurements and evaluate inter-rater agreement among the reviewers, overall intraclass correlation coefficients (ICCs) were calculated for the linear measurements. Landis and Koch used the following cut points for interpreting the degree of agreement which range from less than 0 to 1 (i.e. <0 representing poor or no agreement, 0.01–0.20 slight agreement, 0.21–0.40 fair agreement, 0.41–0.60 moderate agreement, 0.61–0.80 substantial agreement, and 0.81–1.00 almost perfect agreement).[
Pearson's correlation coefficients were calculated to assess the relationships of the total ventricular volume measurement with each of the individual linear measurements. These correlation coefficients of the linear measurements with total ventricular volume were then compared with each other using methods described by Yu and Dunn, which take into account the dependency in correlations.[
Receiver operating characteristic (ROC) methods were used to determine values for EI, frontal-occipital horn ratio (FOR), and frontal horn width (FHW) in the coronal plane that would maximize sensitivity and specificity for determining volumetric abnormality defined as an intraventricular volume ≥ 60 ml.[
Overall inter-rater agreement was almost perfect for the measurements of EI, FOR, third ventricular width, FHW in coronal plane, and callosal angle (CA) at the posterior commissure (PC). Inter-rater agreement was substantial for the measurements of temporal horn width and CA at the foramen of Monro. Inter-rater agreement for third ventricular height was moderate [
Because the inter-rater agreement was good for most of the linear measurements, the mean values for each subject were used in all subsequent analyses. The relationships between total ventricular volume and the linear measurements were significant for all measures except for third ventricular height (P = 0.244). EI, FOR, third ventricular width, temporal horn width, and FHW in the coronal plane were all positively associated with total ventricular volume while the CA at the foramen of Monro, and the CA at PC were negatively associated with total ventricular volume [
Correlations of the individual linear measurements with total ventricular volume (TVV). For the linear measurements, the average over all reviewers was used. (a) Evan's index; (b) Frontal-occipital Ratio; (c) Third ventricular height; (d) Thrid ventricular width; (e) Temporal horn width; (f) Frontal horn width coronal; (g) CA for Monroe; (h) CA at PC
The results for the ROC analyses for the specific linear measurements identified cutpoints of 0.3 for EI, 0.42 for FOR, and 39 mm for FHW on coronal section. The kappa results for agreement with volumetric abnormality (>60 ml) along with sensitivity and specificity are given in
Idiopathic NPH has long been described as a progressive disease of the elderly who exhibit the classic triad of clinical findings (known as Hakim's triad) of instability, urinary incontinence, and dementia with ventriculomegaly.[
Current guidelines for diagnosis of NPH require evidence of ventriculomegaly, which has been historically defined by an EI of greater than 0.3. Recent studies have suggested that EI is not an accurate measure of ventricular volume and endorse volumetric measurements. Despite advances in modern brain imaging and computerized volumetric analysis, simple linear measurements such as EI continue to be fast, reimbursable, reliable, and reproducible methods for determining ventricular enlargement and feasible for general neurosurgical practice.
The authors would like to thank Sue MacPhee, M.A., for her editorial contribution.
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