The callosal angle (CA) is a useful biomarker in the diagnosis and management of idiopathic normal pressure hydrocephalus (NPH). Used incorrectly, CA measurements are variable, affecting its reliability as a clinical tool. Our objectives are to evaluate (i) reproducibility of established CA measurements between trained raters and (ii) impact of minor angular mal-rotations of the true coronal plane on CA measurements.
CAs were measured by two independent raters on three-dimensional isovolumetric T1-weighted brain MRI of NPH patients and healthy controls using the established true coronal plane reformatted orthogonal to the plane containing the anterior-posterior commissural (AC-PC) line at the level of the posterior commissure. CA changes were subsequently evaluated when the coronal plane was mal-rotated by ± 5° and ± 10° in anterior-posterior and clockwise-anticlockwise directions. Inter-rater reliability of CA measurements was assessed using the intraclass correlation coefficient (ICC).
On the true coronal plane, inter-rater ICC was excellent (0.973) for NPH patients and good (0.875) for controls. On mal-rotated coronal plane setups, ICC for CA was worse in controls (0.484–0.886) than NPH (0.879–0.981) groups and in clockwise-anticlockwise (0.484–0.956) than anterior-posterior (0.503–0.981) mal-rotations. CA changes secondary to mal-rotations from the true coronal plane were significant in NPH patients (P < 0.0001 to 0.0378) but not in controls (P > 0.1).
This is the first demonstration of how small angular mal-rotations of the coronal plane used for CA measurement affect its value and inter-rater reliability, highlighting the importance of a standardized protocol when measuring the CA in NPH workup.
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We are grateful to the Radiography fraternity in the Singapore General Hospital for their strong support in this collaborative work.
National Medical Research Council, Singapore (NMRC/TA/0024/2013; NMRC/CSI/0006/2006).
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in the studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the studies approved by the SingHealth Centralized Institutional Review Board (2016/2627 and 2015/2587).
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Lee, W., Lee, A., Li, H. et al. Callosal angle in idiopathic normal pressure hydrocephalus: small angular mal-rotations of the coronal plane affect measurement reliability. Neuroradiology (2021). https://doi.org/10.1007/s00234-021-02658-2
- Normal-pressure hydrocephalus
- Callosal angle
- Test-retest reliability