Right lateral thoracic radiographic metrics help discriminate cranial mediastinal masses and pleural effusion in cats.

Objective: Determine whether the tracheal bifurcation (TB) is displaced caudally in cats with a mediastinal mass compared to cardiogenic pleural effusion, noncardiogenic pleural effusion, and no significant thoracic disease.

Methods: Medical records between 2005 and 2017 at the Oklahoma State University Boren Veterinary Medical Teaching Hospital and University of Missouri Veterinary Health Center were reviewed retrospectively. Advanced imaging or necropsy was required for inclusion into mediastinal mass, cardiogenic pleural effusion, and noncardiogenic pleural effusion groups. Three evaluators blinded to diagnosis obtained the following measurements on a lateral radiograph: number of intercostal spaces from first rib to TB (ICS), distance from caudal aspect of the manubrium to TB (MTB), vertebral score by drawing MTB from the fourth thoracic vertebra and counting included vertebral bodies (VS), and distance from first rib to TB (RTB). A 2-factor ANOVA was used, and sensitivity and specificity for each evaluator accurately diagnosing the presence or absence of a mediastinal mass was calculated. Data were reported as mean ± SEM.

Results: 76 cats were included. The mediastinal mass group had significantly increased ICS (6.1 ± 0.16), MTB (8.9 ± 0.18 cm), VS (7.4 ± 0.16), and RTB (7.5 ± 0.17 cm) compared to other groups. An MTB ≥ 7.5 and RTB ≥ 6 had the best sensitivity for detecting the presence of a mediastinal mass.

Conclusions: An MTB ≥ 7.5 cm and/or RTB ≥ 6 cm indicated potential for a mediastinal mass and warranted further diagnostics.

Clinical relevance: Lateral radiographic measurements associated with position of the TB aided practitioners in determining when advanced imaging was warranted for diagnosis of a mediastinal mass.