Anterior Callosal Angle: A New Marker of Idiopathic Normal Pressure Hydrocephalus?

Objective: Diagnosing idiopathic normal pressure hydrocephalus (iNPH) still remains a clinical challenge. The callosal angle (CA) is a widely used neuroradiologic marker for iNPH. However, the relationship of the CA to clinical features has not been well investigated. We hypothesize that iNPH symptoms might better correlate with a variant of the CA (anterior callosal angle [ACA]). We aim to establish the validity of the ACA measurement for the diagnosis of iNPH and compare it with current radiologic parameters. Methods: The multidisciplinary BOLOGNA PRO-HYDRO Study Group performed a retrospective review of consecutive iNPH patients. Magnetic resonance imaging studies for these patients were collected, as well as magnetic resonance imaging studies from Alzheimer disease and healthy control patients. The CA, ACA, and Evans Index were measured by 2 blinded members of the study team based on magnetic resonance images for each of these populations. Results: The ACA shows high accuracy, sensitivity, and specificity in distinguishing iNPH patients from healthy control and Alzheimer disease patients. The optimal pathologic diagnostic cut-off value for the ACA is 119 degrees. The diagnostic accuracy of the ACA is not significantly different from the CA. Conclusions: The ACA could be a valid radiologic parameter in the diagnostic armamentarium for iNPH.