Differentiation of normal pressure hydrocephalus from alzheimer's and Parkinson's Diseases using the splenial angle measured on brain CT: diagnostic performance and reliability study.

BACKGROUND

Although MRI and diffusion tensor imaging (DTI) based studies have evaluated the Splenial Angle (SA) in distinguishing normal pressure hydrocephalus (NPH), its reproducibility and diagnostic utility on CT remain untested.

OBJECTIVE

To assess the diagnostic performance and intra/inter-observer repeatability of CT-derived SA measurements for differentiating NPH from Alzheimer's and Parkinson's diseases.

MATERIALS AND

METHODS

This retrospective study included 325 individuals: 87 with NPH, 71 with Alzheimer's disease, 66 with Parkinson's disease, and 101 healthy controls. Evans Index (EI), Callosal Angle (CA), and SA were measured on brain CT images. Two radiologists assessed intra- and inter-observer repeatability. Continuous variables were analyzed using ANOVA, categorical variables using Chi-square tests, and Receiver Operating Characteristic (ROC) analysis determined diagnostic performance.

RESULTS

EI, CA, and SA differed significantly between the NPH group and the other groups (p < 0.001). The SA showed the highest diagnostic accuracy for NPH (AUC = 0.999; cut-off = 49.5°; sensitivity = 0.996; specificity = 0.989; LR + = 86.63; LR- = 0.004). The CA also demonstrated strong performance (AUC = 0.993; cut-off = 87.5°). The EI achieved high accuracy (AUC = 0.928) but was less specific. In the Alzheimer's and Parkinson's groups, these measurements had limited discriminatory ability. Intra- and inter-observer agreement was high for all three parameters, with the SA showing the greatest repeatability.

CONCLUSION

The SA can be used as a reliable CT-based marker to help distinguish NPH from neurodegenerative diseases, serving as a supportive imaging parameter in clinical assessment.