Pectus excavatum in motion: dynamic evaluation using real-time MRI

Objectives The breathing phase for the determination of thoracic indices in patients with pectus excavatum is not standardized. The aim of this study was to identify the best period for reliable assessments of morphologic indices by dynamic observations of the chest wall using real-time MRI. Methods In this prospective study, patients with pectus excavatum underwent morphologic evaluation by real-time MRI at 3 T between January 2020 and June 2021. The Haller index (HI), correction index (CI), modified asymmetry index (AI), and modified eccentricity index (EI) were determined during free, quiet, and forced breathing respectively. Breathing-related differences in the thoracic indices were analyzed with the Wilcoxon signed-rank test. Motion of the anterior chest wall was analyzed as well. Results A total of 56 patients (11 females and 45 males, median age 15.4 years, interquartile range 14.3–16.9) were included. In quiet expiration, the median HI in the cohort equaled 5.7 (4.5–7.2). The median absolute differences (Δ) in the thoracic indices between peak inspiration and peak expiration were ΔHI = 1.1 (0.7–1.6, p < .001), ΔCI = 4.8% (1.3–7.5%, p < .001), ΔAI = 3.0% (1.0–5.0%, p < .001), and ΔEI = 8.0% (3.0–14.0%, p < .05). The indices varied significantly during different inspiratory phases, but not during expiration ( p > .05 each). Furthermore, the dynamic evaluation revealed three distinctive movement patterns of the funnel chest. Conclusions Real-time MRI reveals patterns of chest wall motion and indicate that thoracic indices of pectus excavatum should be assessed in the end-expiratory phase of quiet expiration. Key Points • The thoracic indices in patients with pectus excavatum depend on the breathing phase. • Quiet expiration represents the best breathing phase for determining thoracic indices. • Real-time MRI can identify different chest wall motion patterns in pectus excavatum.