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Narrow Cerebrospinal Fluid Spaces at Convexity Predictive of Normal Pressure Hydrocephalus

March 8, 2008
Written by: , Filed in: Neuroradiology
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Background
Because ventricular enlargement can be due to other causes of hydrocephalus or atrophy from various degenerative diseases and aging, radiologic diagnosis can be difficult. In a paper published in the AJNR in August 1998, findings typical of NPH were described as enlarged ventricles, Sylvian fissures, and basal cisterns, but also showed decreased size of the supraventricular sulci and midline subarachnoid space. Visual inspection of these features was reported as having a high inter-rater reliability.

The objective of a recent study was to assess the reliability of visual evaluation of the high convexity CSF spaces in NPH on axial or coronal images independently.

The study has concluded that narrow cerebrospinal fluid (CSF) spaces at the high convexity sulci and midline are reliably assessed visually and able to distinguish patients with idiopathic normal pressure hydrocephalus (NPH) and healthy age-matched controls.

Design/Participants
Prospective study involving 14 patients with NPH and 12 age-matched controls.

Methods
Two experienced neuroradiologists rated the presence or absence of narrowing of the high-convexity CSF spaces on T1 images in the MRI of each patient. This was considered the gold standard for the presence of this finding. They then taught this finding to two radiologists, one neurologist, and two residents.

Each rater evaluated two axial images at the high convexity and, separately, evaluated two coronal images near the foramen of Monroe from each study. They used a visual rating scale to express their degree of confidence in the presence of narrowing of the CSF space and the presence of NPH. Each rater evaluated all of the scans three times separated by two weeks so that intra-observer and inter-observer agreement could be determined.

Neuroradiology Review

The Johns Hopkins University School of Medicine
Course Directors: David Yousem, MD, MBA and Doris Lin, MD, PhD Maintaining certification requires not only medical knowledge to deliver quality care but also other essential elements that must be developed and maintained throughout every radiologist’s career. Therefore, this program serves as a comprehensive review of neuro-radiology and prepares the participants to tackle imaging of the brain, spine, head and neck, as well as the vascular anatomy of the central nervous system. Click here to read more or order: Neuroradiology Review

Results of the Study
Twelve of the 14 patients with NPH had narrow CSF spaces near the convexity. None of the controls had this finding. Receiver operator characteristic curve analysis was performed on the data from each rater and demonstrated an area under the curve ranging from 0.92 to 0.98 for assessing narrowing of the CSF and between 0.85 and 0.90 in predicting the presence of NPH.

Using 50% confidence as a cutoff for a positive result, the sensitivity and specificity were 0.80 and 0.97 for the narrow CSF space on axial images, and 0.87 and 0.93 on coronal images. Sensitivity and specificity for detecting NPH were 0.71 and 0.97 on axial images, and 0.74 and 0.92 on coronal images. Correlation coefficients between any two raters ranged from 0.58 to 0.90 overall. Intra-rater coefficients were 0.82 to 0.98.

Conclusions
Visual inspection of the CSF spaces near the convexity on either axial or coronal MRI is a reliable and accurate way of distinguishing patients with NPH from healthy age-matched control subjects.

Reviewer’s Comments
Although the study does not add much to the 1998 AJNR study, it is a helpful confirmation to the utility of assessing the high convexity CSF spaces. It is unfortunate that the NPH patients were not compared to patients with other diseases such as Alzheimer’s disease.

Author: Yaron Lebovitz, MD

Reference
Sasaki M, Honda S, et al. Narrow CSF Space at High Convexity and High Midline Areas in Idiopathic Normal Pressure Hydrocephalus Detected by Axial and Coronal MRI. Diagn Neuroradiol; 2008; 50 (February): 117-122:

Neuroradiology Review

The Johns Hopkins University School of Medicine
Course Directors: David Yousem, MD, MBA and Doris Lin, MD, PhD Maintaining certification requires not only medical knowledge to deliver quality care but also other essential elements that must be developed and maintained throughout every radiologist’s career. Therefore, this program serves as a comprehensive review of neuro-radiology and prepares the participants to tackle imaging of the brain, spine, head and neck, as well as the vascular anatomy of the central nervous system. Click here to read more or order: Neuroradiology Review
.

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