A case report of multiple cervical and mediastinal sialoceles in a dog: a rare differential for mediastinal masses with pleural effusion.

Mediastinal masses with pleural effusion in dogs typically raise suspicion for thymoma or mediastinal lymphoma, necessitating careful differentiation. This paper describes a 12-year-old neutered male dog presenting with acute-onset coughing. Radiographic imaging revealed mild pleural effusion with an expanded cranial mediastinum. Subsequent ultrasonographic and computed tomographic examinations identified multiple masses extending from the cervical region to the cranial mediastinum. Cytologic analysis of the pleural fluid revealed findings suggestive of a salivary origin, with mild inflammatory cell infiltration. The pleural effusion was repeatedly drained and monitored radiographically. All lesions regressed gradually without surgical intervention. This rare case highlights the need to consider differential diagnoses beyond thymoma and lymphoma when mediastinal masses with pleural effusion are present.