Imaging normal pressure hydrocephalus: theories, techniques, and challenges

Abstract

<jats:p>The pathophysiology of NPH continues to provoke debate. Although guidelines and best-practice recommendations are well established, there remains a lack of consensus about the role of individual imaging modalities in characterizing specific features of the condition and predicting the success of CSF shunting. Variability of clinical presentation and imperfect responsiveness to shunting are obstacles to the application of novel imaging techniques. Few studies have sought to interpret imaging findings in the context of theories of NPH pathogenesis. In this paper, the authors discuss the major streams of thought for the evolution of NPH and the relevance of key imaging studies contributing to the understanding of the pathophysiology of this complex condition.</jats:p>

Cerebral Autoregulation, CSF outflow resistance and outcome following CSF diversion in Normal Pressure Hydrocephalus

“…High R out , despite criticism 1-5,10,25 , seems to be a major component of NPH, highlighting the importance of a disturbed CSF circulation 1,5,15 . However, when R out is used as a sole predictor of shunt response in large cohorts of patients, it fails to provide an accurate indication for surgery, as negative predictive power of R out remains too low 1,36 .…”

“…It appears that the age-autoregulation relationship (higher age associated with dysautoregulation) may be magnified by general anesthesia. On the other hand, R out is known to positively correlate with age 8,15 . A strong relationship was successfully replicated in our cohort of NPH patients; a possible investigation of different Rout thresholds for different ages remains to be performed separately, for better future directions.…”

Does the Presence or Absence of DESH Predict Outcomes in Adult Hydrocephalus?

“…The authors chose not to classify Sylvian fissure enlargement by measurement, to avoid inconsistencies with previous reports describing the DESH classification. [3][4][5] In an effort to include a pure sample of DESH cases and controls negative for DESH, we excluded patients who had partial features of DESH without fulfilling all criteria from this study. Excluded patients were those with either tight highconvexity and medial subarachnoid spaces without enlarged Sylvian fissures or patients with enlarged Sylvian fissures in the absence of tight high-convexity and medial subarachnoid spaces.…”

“…As described by the NPH guidelines study group, there is no single standard for the imaging evaluation of idiopathic NPH (iNPH). [3][4][5] The Study of Idiopathic Normal Pressure Hydrocephalus on Neurologic Improvement (SINPHONI) developed MR imagingbased diagnostic criteria for adult hydrocephalus, termed "disproportionately enlarged subarachnoid-space hydrocephalus" (DESH). 2 DESH is defined as "tight high-convexity and medial subarachnoid spaces, and enlarged Sylvian fissures with ventriculomegaly."…”

“…A scaled measurement of the Sylvian fissure is provided to illustrate the extent of fissure enlargement in this representative case. However, consistent with the defining features of DESH in the literature,[3][4][5] quantitative measurement was not used as scoring criterion during blinded neuroradiologist review.…”