Prevalence and characteristics of minimal pleural fluid on screening chest MRI

Background

Minimal pleural fluid is often seen incidentally on chest MRI. However, its prevalence and clinical characteristics remain unknown.

Methods

This retrospective observational study included 2726 participants who underwent comprehensive medical check-ups for screening, including chest CT and MRI, and transthoracic echocardiography between March 2018 and February 2019. Pleural fluid on MRI was manually measured for maximum thickness. Its distribution, change over time, and relevance to participant characteristics were analyzed. The pulmonary function data of 82 participants and their associations with fluid were also analyzed.

Results

Of the 2726 participants (mean age ± standard deviation, 59 ± 11 years), 2009 (73.7%) had minimal pleural fluid (thickness, 1–9 mm) on either side, with right-sided fluid being more frequent than left-sided fluid (P < 0.001). Negligible changes in fluid thickness were observed one year later. The following parameters were associated with less fluid: age, ≥65 years (P < 0.001); male sex (P = 0.006); current smoking (P < 0.001); body mass index, ≥25 kg/m² (P < 0.001); and mean arterial pressure, ≥100 mmHg (P = 0.01), whereas a ratio between early mitral inflow velocity and mitral annular early diastolic velocity>14 was associated with more fluid (P = 0.01). The presence of fluid was an independent explanatory variable for a higher percentage of predicted vital capacity (P = 0.048).

Conclusions

MRI was highly sensitive in detecting minimal pleural fluid. Pleural fluid found on MRI for health screening was assumed to be physiological and fluid thickness at the steady state might be variable among participants depending on age, sex, smoking habits, body shape, blood pressure, and cardiac diastolic capacity.