The splenial angle: a novel radiological index for idiopathic normal pressure hydrocephalus

Abstract

Objectives To evaluate the utility of the splenial angle (SA), an axial angular index of lateral ventriculomegaly measured on diffusion tensor MRI color fractional anisotropy maps, in differentiating NPH from Alzheimer’s disease (AD), Parkinson’s disease (PD), and healthy controls (HC), and post-shunt changes in NPH, compared to Evans’ index and callosal angle. Methods Evans’ index, callosal angle, and SA were measured on brain MRI of 76 subjects comprising equal numbers of age- and sex-matched subjects from each cohort of NPH, AD, PD, and HC by two raters. Receiver operating characteristics (ROC) and multivariable analysis were used to assess the screening performance of each measure in differentiating and predicting NPH from non-NPH groups respectively. Temporal changes in the measures on 1-year follow-up MRI in 11 NPH patients (with or without ventriculoperitoneal shunting) were also assessed. Results Inter-rater and intra-rater reliability were excellent for all measurements (intraclass correlation coefficients > 0.9). Pairwise comparison showed that SA was statistically different between NPH and AD/PD/HC subjects (p < 0.0001). SA performed the best in predicting NPH, with an area under the ROC curve of > 0.98, and was the only measure left in the final model of the multivariable analysis. Significant (p < 0.01) change in SA was seen at follow-up MRI of NPH patients who were shunted compared to those who were not. Conclusions The SA is readily measured on axial DTI color FA maps compared to the callosal angle and shows superior performance differentiating NPH from neurodegenerative disorders and sensitivity to ventricular changes in NPH after surgical intervention. Key Points • The splenial angle is a novel simple angular radiological index proposed for idiopathic normal pressure hydrocephalus, measured in the ubiquitous axial plane on DTI color fractional anisotropy maps. • The splenial angle quantitates the compression and stretching of the posterior callosal commissural fibers alongside the distended lateral ventricles in idiopathic normal pressure hydrocephalus (NPH) using tools readily accessible in clinical practice and shows excellent test-retest reliability. • Splenial angle outperforms Evans’ index and callosal angle in predicting NPH from healthy, Parkinson’s disease, and Alzheimer’s disease subjects on ROC analysis with an area under the curve of > 0.98 and is sensitive to morphological ventricular changes in NPH patients after ventricular shunting.

Structural neuroimaging markers of normal pressure hydrocephalus versus Alzheimer’s dementia and Parkinson’s disease, and hydrocephalus versus atrophy in chronic TBI—a narrative review

“…Measures of WM structural deformation and integrity measured through DTI have also been shown to distinguish between NPH and PD. The SA introduced by Chan et al ( 30 ) was significantly higher in NPH versus PD. Kanno et al ( 65 ) found lower FA and higher MD in the supratentorial WM in NPH when compared to PD.…”

“…A novel measure called the Splenial Angle (SA), defined on Diffusion Tensor Imaging (DTI) MRI Fractional Anisotropy maps as the angle subtended by the forceps major of the corpus callosum (CC) on axial slices, to capture the effect of ventricular distention on the CC at the ML in probable NPH was shown to have high sensitivity in distinguishing it from controls ( 30 ). Left ear extinction in NPH possibly associated with the upward elevation and thinning of the CC was found to be alleviated among patients with NPH post shunting, indicating the range of impairments that may be reversed with surgery ( 59 ).…”

“…In the same year, another study found that higher MD coupled with lower FA in the supratentorial WM of the brain was indicative of NPH versus AD and PD ( 65 ). The SA which captures the effect of distention of LVs on the forceps major of the CC ( 30 ) was also shown to differentiate between NPH and AD.…”

Brain linear measurements for differentiating normal pressure hydrocephalus from Alzheimer's disease: an exploratory study

“…Kim et al [11] reported that the combination of the narrowing of the callosal angle (CA), the dilatation of the Sylvian fissure and the narrowing of superior parietal sulci could be useful in the differential diagnosis between iNPH and AD (AUC 0.89). Chan et al [12] reported that the splenial angle presented higher accuracy than EI and CA in differentiating iNPH from AD (AUC 0.98).…”

Value of MRI-based semi-quantitative structural neuroimaging in predicting the prognosis of patients with idiopathic normal pressure hydrocephalus after shunt surgery

“…Based on CT image features, it included seven items: the EI, Sylvian fissures, tight high convexity, CA, focal sulcal dilatation, temporal horns, and periventricular hyperintensities (PVH) [ 9 ]. However, the accuracy and practicability of traditional structural imaging in the diagnosis and prognosis of iNPH are still debated [ 10 – 13 ].…”