Optimal Diagnostic Indices for Idiopathic Normal Pressure Hydrocephalus Based on the 3D Quantitative Volumetric Analysis for the Cerebral Ventricle and Subarachnoid Space

Fellows’ Journal Club

Editor’s Comment

Patients with suspected idiopathic normal pressure hydrocephalus (NPH) on the basis of the ventriculomegaly and a triad of symptoms underwent the CSF tap test. CSF volumes were extracted from a T2-weighted 3D spin-echo SPACE sequence on 3T MR imaging and were quantified semiautomatically. Twenty-four patients with tap-positive idiopathic NPH, 25 patients without response to the tap test, and 23 age-matched controls were included. The CSF volume of the parietal convexity had the highest area under the ROC curve in the discrimination of the tap-test response (0.768), followed by the z-Evans Index (0.758), and the upper-to-lower subarachnoid space ratio index (0.723). CSF volume of the parietal convexity of less than 38 mL, upper-to-lower subarachnoid space ratio of less than 0.33, and a z-Evans Index of greater than 0.42 are the newly proposed useful indices for idiopathic NPH diagnosis.

Abstract

Division of the subarachnoid space into the 4 parts. The subarachnoid space was divided into the following 4 parts: frontal convexity (yellow), parietal convexity (magenta), Sylvian fissure and basal cistern (sky blue), and posterior fossa (light green) in the 3D segmentation. The left, middle, right upper 3D volume-rendering reconstruction images show the axial, coronal, and sagittal dimensional views, respectively. Light green in the left lower axial MIP image indicates the segmented region of the parietal convexity of the subarachnoid space, and that in the middle and right lower MIP images indicates axial and coronal views of the Sylvian fissure and basal cistern.
Division of the subarachnoid space into the 4 parts. The subarachnoid space was divided into the following 4 parts: frontal convexity (yellow), parietal convexity (magenta), Sylvian fissure and basal cistern (sky blue), and posterior fossa (light green) in the 3D segmentation. The left, middle, right upper 3D volume-rendering reconstruction images show the axial, coronal, and sagittal dimensional views, respectively. Light green in the left lower axial MIP image indicates the segmented region of the parietal convexity of the subarachnoid space, and that in the middle and right lower MIP images indicates axial and coronal views of the Sylvian fissure and basal cistern.

BACKGROUND AND PURPOSE

Despite the remarkable progress of 3D graphics technology, the Evans index has been the most popular index for ventricular enlargement. We investigated a novel reliable index for the MR imaging features specified in idiopathic normal pressure hydrocephalus, rather than the Evans index.

MATERIALS AND METHODS

The patients with suspected idiopathic normal pressure hydrocephalus on the basis of the ventriculomegaly and a triad of symptoms underwent the CSF tap test. CSF volumes were extracted from a T2-weighted 3D spin-echo sequence named “sampling perfection with application-optimized contrasts by using different flip angle evolutions (SPACE)” on 3T MR imaging and were quantified semiautomatically. Subarachnoid spaces were divided as follows: upper and lower parts and 4 compartments of frontal convexity, parietal convexity, Sylvian fissure and basal cistern, and posterior fossa. The maximum length of 3 axial directions in the bilateral ventricles and their frontal horns was measured. The “z-Evans Index” was defined as the maximum z-axial length of the frontal horns to the maximum cranial z-axial length. These parameters were evaluated for the predictive accuracy for the tap-positive groups compared with the tap-negative groups and age-adjusted odds ratios at the optimal thresholds.

RESULTS

In this study, 24 patients with tap-positive idiopathic normal pressure hydrocephalus, 25 patients without response to the tap test, and 23 age-matched controls were included. The frontal horns of the bilateral ventricles were expanded, with the most excessive expansion being toward the z-direction. The CSF volume of the parietal convexity had the highest area under the receiver operating characteristic curve (0.768), the z-Evans Index was the second (0.758), and the upper-to-lower subarachnoid space ratio index was the third (0.723), to discriminate the tap-test response.

CONCLUSIONS

The CSF volume of the parietal convexity of <38 mL, upper-to-lower subarachnoid space ratio of <0.33, and the z-Evans Index of >0.42 were newly proposed useful indices for the idiopathic normal pressure hydrocephalus diagnosis, an alternative to the Evans Index.

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Optimal Diagnostic Indices for Idiopathic Normal Pressure Hydrocephalus Based on the 3D Quantitative Volumetric Analysis for the Cerebral Ventricle and Subarachnoid Space
jross
Jeffrey Ross • Mayo Clinic, Phoenix

Dr. Jeffrey S. Ross is a Professor of Radiology at the Mayo Clinic College of Medicine, and practices neuroradiology at the Mayo Clinic in Phoenix, Arizona. His publications include over 100 peer-reviewed articles, nearly 60 non-refereed articles, 33 book chapters, and 10 books. He was an AJNR Senior Editor from 2006-2015, is a member of the editorial board for 3 other journals, and a manuscript reviewer for 10 journals. He became Editor-in-Chief of the AJNR in July 2015. He received the Gold Medal Award from the ASSR in 2013.