Objective: To evaluate the diagnostic utility of a computer-assisted elliptical fitting tool for standardized measurement of the midbrain and pons in differentiating progressive supranuclear palsy (PSP), multiple system atrophy (MSA), idiopathic Parkinson’s disease (IPD), and essential tremor (ET).

Background: Differential diagnosis among parkinsonian syndromes remains clinically challenging. While MRI-based brainstem morphometry is a validated marker, clinical adoption is hindered by time-intensive manual measurement and inter-observer variability. We developed a semi-automated tool using elliptical fitting to standardize analysis while maintaining researcher control over anatomical boundary identification.

Method: We analyzed midsagittal T1-weighted MRI from 62 patients (PSP: n=7; IPD: n=20; MSA: n=14; ET: n=21). Using a custom program, researchers fitted ellipses to midbrain and pons boundaries, which then automatically calculated nine variables (length, width, area, and ratios). Group differences were assessed via one-way ANOVA with Tukey HSD post-hoc testing. Results were validated against established benchmarks in current literature.

Results: All nine morphometric variables demonstrated statistically significant group differences (p<0.05). PSP patients showed markedly reduced midbrain measurements compared to all other groups (midbrain area: PSP 25.46±2.84 mm² vs IPD 38.98±3.97 mm², MSA 38.19±6.52 mm², ET 39.79±9.29 mm²; all p<0.001). MSA patients exhibited significantly smaller pons measurements versus IPD and ET (pons area: MSA 88.55±19.10 mm² vs IPD 135.83±17.06 mm², ET 125.51±17.57 mm²; both p<0.001). Midbrain-to-pons ratios effectively discriminated all parkinsonian subtypes, with PSP showing the lowest ratios (ratio_l: PSP 38.79±4.22 vs IPD 53.58±6.48, MSA 69.15±12.78, ET 55.40±6.84; all pairwise p<0.001). Our computer-assisted measurements align closely with literature-reported manual measurement patterns while demonstrating comparable discriminative performance to established benchmarks.

Conclusion: Computer-assisted elliptical fitting successfully replicates established diagnostic patterns, identifying severe midbrain atrophy in PSP and pons atrophy in MSA. This semi-automated approach offers standardized, efficient, and accurate brainstem morphometry, supporting its utility as a robust tool for the differential diagnosis of parkinsonian disorders.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/computer-assisted-morphometric-analysis-of-midbrain-and-pons-for-differential-diagnosis-of-parkinsonian-disorders/