Background: Idiopathic normal pressure hydrocephalus (iNPH) is a neurological condition where the symptoms include disturbed gait, balance, cognition and continence. The diagnostic guidelines are based on typical symptoms combined with imaging showing enlarged ventricles. Several scales for evaluating symptoms exist, but no corresponding tool is in use for imaging. The aim of this thesis was to construct a radiological scoring system, the iNPH Radscale, to facilitate radiological evaluation and systematic reporting of changes. Further, to test the reliability and accuracy of the scale and evaluate the usefulness for longitudinal monitoring.

Methods: In paper I 168 individuals over 65 years of age from the general population underwent computed tomography (CT) of the brain and a neurological examination, and the same cohort was followed up 2 years later in paper IV. The iNPH Radscale was developed in these papers and further validated in papers II and III. Papers II and III included surgically treated iNPH patients with preoperative imaging of the brain. Thirty-five patients were included in paper II comparing preoperative CT and magnetic resonance imaging (MRI) using the iNPH Radscale. Paper III included 75 shunt responsive patients and 55 asymptomatic controls to evaluate the accuracy of the iNPH Radscale.

Results: In paper I, seven parameters summarized as a total iNPH Radscale score were significantly associated with clinical iNPH symptoms (r = 0.55, p < 0.001). In paper II, the agreement between CT and MRI was substantial to almost perfect (kappa and intraclass correlation, 0.60–0.91, p < 0.001) for all parameters except periventricular white matter changes. In paper III the iNPH Radscale score was significantly higher in the iNPH group than the control group (p <0.001). Receiver operating characteristics analysis yielded an area under the curve of 99.7 %, and an iNPH Radscale score £ 4 identified those without iNPH (sensitivity 100 %, specificity 96 % and overall accuracy 98.5 %). In paper IV, symptomatic participants had significantly higher iNPH Radscale scores at baseline and follow-up.

Conclusions: The iNPH Radscale summarizes seven imaging features from the diagnostic guidelines and is applicable to both CT and MRI. INPH is very likely in patients with an iNPH Radscale score ³ 8 and corresponding clinical symptoms. On the other hand, the diagnosis should be questioned when the iNPH Radscale score is less than the cut-off of 4. In summary, the iNPH Radscale may become a relevant diagnostic tool for standardized evaluation in the workup of patients with suspected iNPH, as a diagnostic checklist and as a screening tool for detection with the potential for ruling out the disease.

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is typically manifested in people over 65 years. The condition of gait disturbances, incontinence, and cognitive dysfunction can be reversed in up to 80% of the cases by ventricular shunting. Neuropsychological testing and standardized brain imaging of signs of iNPH are essential to detect and define the progression. The aims of this thesis were to develop a radiological iNPH scale, examine how morphological features relate to symptoms of iNPH, investigate if dual-task testing (e.g., walking and talking) is helpful in detecting iNPH, and monitor developing symptoms over two years.

METHOD: The studies include 168 participants (median [range] age 73 [66–92]) at baseline (2014/2015) and 104 participants (age 75 [68–91]) at follow-up (2016/2017) from the general population. Neuropsychological tests of executive functions, memory, and motor performance, and computed tomography (CT) for brain imaging were used.

RESULTS: Seven morphological features were combined into a scoring scale for iNPH. The total score correlated with clinical symptoms (r = -0.40, p <.001). All core symptoms were associated to wider temporal horns (TH) (p <.01). Participants with iNPH stopped walking to talk more frequently (p = .044). Participants who developed iNPH during the study worsened more on declarative memory (ES -0.37).

DISCUSSION: The Radscale was related to symptoms of iNPH and the TH to all main clinical features. Difficulties walking while recalling a previous event, worsened declarative memory, and expanding ventricular space surrounding the hippocampus were noticeable signs of iNPH. Memory functions are important to recognize in iNPH.