New Radiographic Tool Enhances Detection of Mediastinal Masses in Cats

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

Adam B. Moore, Laura A. Nafe, Kaitlyn M. DeAngelis, Ryan D. Baumwart, R. Mackenzie Hallman, Mark E. Payton, Carol R. Reinero

Background:
Differentiating between cranial mediastinal masses and pleural effusion in cats using thoracic radiography is challenging due to overlapping radiographic signs. This study addresses the diagnostic difficulty by exploring objective lateral thoracic radiographic measurements that could help distinguish between these conditions without relying solely on subjective interpretation or advanced imaging.

Methods:
This retrospective study evaluated thoracic radiographs of 76 cats categorized into four groups: cranial mediastinal mass, cardiogenic pleural effusion, noncardiogenic pleural effusion, and no significant thoracic disease. Radiographic metrics included: number of intercostal spaces (ICS), manubrium-to-tracheal bifurcation distance (MTB), vertebral score (VS), and rib-to-tracheal bifurcation distance (RTB). Diagnoses were confirmed through advanced imaging, cytology, or necropsy. Three evaluators with differing levels of experience provided subjective assessments, and statistical analyses determined metric efficacy and interobserver performance.

Results:
Cats with cranial mediastinal masses had significantly higher ICS, MTB, VS, and RTB values than other groups. An MTB ≥ 7.5 cm and RTB ≥ 6 cm were the most sensitive indicators for a mediastinal mass (89% and 94%, respectively). Combining these measurements yielded a sensitivity of 89% and specificity of 59%. Subjective radiographic assessments varied: the cardiologist achieved the highest sensitivity (89%), while the radiologist had the highest specificity (98%).

Limitations:
Limitations include its retrospective nature, absence of body condition scoring, and reliance on right lateral radiographs alone. No general practitioner evaluator was included to assess clinical applicability across diverse practice settings. The proposed metrics suggest the presence but not confirmation of a mass, requiring further diagnostics.

Conclusions:
Objective radiographic measurements (especially MTB ≥ 7.5 cm and RTB ≥ 6 cm) on lateral views are effective for identifying cats likely to have cranial mediastinal masses. These tools support clinical decision-making when advanced imaging is unavailable and improve diagnostic confidence beyond subjective assessment alone.