something conceived in the mind : thought, notion.

One conventional Idiopathic Normal Pressure Hydrocephalus Definition includes this provision: “symptomatic improvement achieved by CSF shunt placement.” However, since this Idiopathic Normal Pressure Hydrocephalus outcome can only be measured postoperatively, the definition is unsuitable for the preoperative Idiopathic Normal Pressure Hydrocephalus diagnosis. Hence, Nakajima in the 2021 guidelines refer to the description above as a “concept” rather than a definition of diagnosis per se.

The implications of using a “concept” lead to the introduction of stage-like progress in the establishment of the final diagnosis after performing shunt intervention with positive outcome. Before establishing the final diagnosis, several stages are required that will allow the selection of potential candidates for shunt treatment based on best available evidence, and these stages have been designated as suspected, possible, and probable (before shunt intervention) iNPH ¹⁾