Planimetric and Volumetric Brainstem MRI Markers in Progressive Supranuclear Palsy, Multiple System Atrophy, and Corticobasal Syndrome. A Systematic Review and Meta-Analysis.

Background: Various MRI markers-including midbrain and pons areas (M, P) and volumes (M, P), ratios (M/P, M/P), and composite markers (magnetic resonance imaging Parkinsonism Indices 1,2; MRPI 1,2)-have been proposed as imaging markers of Richardson's syndrome (RS) and multiple system atrophy-Parkinsonism (MSA-P). A systematic review/meta-analysis of relevant studies aiming to compare the diagnostic accuracy of these imaging markers is lacking.

Methods: Pubmed and Scopus were searched for studies with >10 patients (RS, MSA-P or CBS) and >10 controls with data on M, P, M, P, M/P, M/P, MRPI 1, and MRPI 2. Cohen's , as a measure of effect size, was calculated for all markers in RS, MSA-P, and CBS.

Results: Twenty-five studies on RS, five studies on MSA-P, and four studies on CBS were included. Midbrain area provided the greatest effect size for differentiating RS from controls (Cohen's = -3.10; < 0.001), followed by M/P and MRPI 1. MSA-P had decreased midbrain and pontine areas. Included studies exhibited high heterogeneity, whereas publication bias was low.

Conclusions: Midbrain area is the optimal MRI marker for RS, and pons area is optimal for MSA-P. M/P and MRPIs produce smaller effect sizes for differentiating RS from controls.