Absence of Disproportionately Enlarged Subarachnoid Space Hydrocephalus, a Sharp Callosal Angle, or Other Morphologic MRI Markers Should Not Be Used to Exclude Patients with Idiopathic Normal Pressure Hydrocephalus from Shunt Surgery.

BACKGROUND AND PURPOSE: Several studies have evaluated the use of MR imaging markers for the prediction of outcome after shunt surgery in idiopathic normal pressure hydrocephalus with conflicting results. Our aim was to investigate the predictive value of a number of earlier proposed morphologic MR imaging markers in a large group of patients with idiopathic normal pressure hydrocephalus.

MATERIALS AND METHODS: One hundred sixty-eight patients (mean age, 70 ± 9.3 years) with idiopathic normal pressure hydrocephalus, subjected to standardized quantification of clinical symptoms before and after shunt surgery, were included in the study. Outcome was calculated using a composite score. Preoperative T1, FLAIR, and flow-sensitive images were analyzed regarding the presence of 13 different morphologic MR imaging markers.

RESULTS: The median Evans index was 0.41 (interquartile range, 0.37-0.44). All patients had an aqueductal flow void sign present and white matter hyperintensities. The median callosal angle was 68.8° (interquartile range, 57.7°-80.8°). Dilated Sylvian fissures were found in 69%; focally dilated sulci, in 25%; and widening of the interhemispheric fissure, in 55%. Obliteration of the sulci at the convexity was found in 36%, and 36% of patients were characterized as having disproportionately enlarged subarachnoid space hydrocephalus. Sixty-eight percent of patients improved after surgery. None of the investigated MR imaging markers were significant predictors of improvement after shunt surgery.

CONCLUSIONS: Disproportionately enlarged subarachnoid space hydrocephalus, a small callosal angle, and the other MR imaging markers evaluated in this study should not be used to exclude patients from shunt surgery. These markers, though they may be indicative of idiopathic normal pressure hydrocephalus, do not seem to be a part of the mechanisms connected to the reversibility of the syndrome.