The utility of the low motion area ratio for the preoperative detection of pleural adhesions: dynamic chest radiography analysis

Background: Dynamic chest radiography (DCR) is useful for detecting preoperative pleural adhesions, predicting operation time and blood loss, and determining the surgical approach. However, since DCR evaluations are subjective, an objective index was needed. Therefore, we focused on the low motion area (LMA) ratio derived from the objective data obtained through DCR. The purpose of this study was to examine the relationship between the LMA ratio and pleural adhesions, as well as to evaluate its cutoff values, detectability, and overall utility.

Methods: The study encompassed patients who received DCR prior to thoracic surgery from January 2020 to December 2023. The LMA ratio was calculated using an analysis workstation for DCR. Pleural adhesions were defined as adhesions extending to >20% of the thoracic cavity and/or taking >5 min to dissect. The relationship between the presence of pleural adhesions and the LMA ratio was analyzed retrospectively.

Results: A total of 338 patients were analyzed, of whom 65 had pleural adhesions. The median LMA ratio for patients with adhesions was 56.0%, while that of patients without adhesions was 41.5%, which amounted to a significant difference (P<0.001). This was also true in the group of patients with pulmonary comorbidities (56.0% vs. 41.0%, P<0.001). When the analysis was limited to the group of patients with a large lung field change rate (>28.2%; n=169), the power of detection using the LMA ratio improved [52.0% vs. 36.9%, area under the curve (AUC) =0.748]. When the two groups were further divided according to the extent of adhesion, the LMA ratio was significantly higher for extensive adhesions (49.8% in grade 1, the narrow adhesion, and 66.1% in grades 2-4, the extensive adhesion).

Conclusions: The LMA ratio is a useful objective index for detecting pleural adhesions. Adding the cutoff value of the LMA ratio (approximately 50%) to the conventional criteria may allow for a more reproducible preoperative assessment.