Radiological markers of idiopathic normal pressure hydrocephalus: Relative comparison of their diagnostic performance

Variability of Normal Pressure Hydrocephalus Imaging Biomarkers with Respect to Section Plane Angulation: How Wrong a Radiologist Can Be?

“…More radiologic as well as research attention should be paid to those biomarkers, which are the least sensitive to angulationrelated differences such as DESH, ZEI, or CMW; in addition, these biomarkers have also shown high discriminatory power between iNPH and HCs in a recently published study. 21 If further research proves that these biomarkers show high diagnostic accuracy for iNPH as well as insensitivity to angulation-related bias, it would yield benefits for daily radiologic practice and potentially aid in designing the future versions of iNPH diagnostic guidelines.…”

“…Ten previously published radiologic measures as well as 4 calculated indexes [5][6][7]12,[16][17][18][19][20][21] were individually evaluated on transverse/coronal imaging sections of 4 different angulations (bicallosal, bicommissural, Hy-Fa, and PBSM) (Fig 2): The frontal horn diameter (FHD) was defined by the maximum distance between the lateral margins of the frontal ventricular horns on the respective transverse sections. 16,17 The inner skull diameter (ISD) was defined by the maximum lateral-to-lateral distance between the inner laminae of the parietal bones on the same transverse sections that were used for FHD measurements.…”

“…Besides, the FHD scored comparably with the EI in a recent study on the diagnostic performance of 15 iNPH biomarkers. 21 This finding has further raised the question of whether a simple linear measure such as the FHD could possibly replace the more complicated index measurement of the EI which, in addition, shows significant variability when measured on different transverse sections. The reason for the increased EI variability is that although its numerator (FHD) remains constant at the level of maximum frontal horn diameter, the denominator (inner skull diameter) varies on differently angulated sections, which all intersect at the FHD level.…”

“…Furthermore, the ZEI has shown better discriminatory power between subjects with iNPH and HCs than the EI in the recent study. 21 When comparing the CA 5 with the simplified CA 6 , the former (assessed at the posterior commissure) shows substantially increased variability at different angulations. This is because the angle formed by the medial walls of the lateral ventricles progressively varies near the ventricular trigones (and posterior commissure) but is relatively constant at the midportion of the corpus callosum, making the simplified CA at this location less susceptible to angulation-related deviations.…”

“…Considering that the PBSM serves as the standard coronal imaging section at many institutions, improper-yet-not-rare assessment of the CA on PBSM sections may induce significant bias (Table 2 and Fig 3 ) and should be avoided. This observation should certainly not discourage radiologists from using the CA in routine practice because the CA has shown high discriminatory power between HCs and iNPH, surpassing, for example, the EI or the simplified CA, 21 yet it emphasizes that complying with the proper measurement methodology is essential.…”