Characterization of primary pulmonary adenosquamous carcinoma-associated pleural effusion

A 10-year-old, female spayed Shih Tzu was presented due to weight loss, increased respiratory effort and lethargy, determined to be secondary to a congenital para-esophageal diaphragmatic defect with partial herniation of the stomach and spleen. Four days following reduction surgery of the displaced abdominal organs thoracic effusion developed. Thoracic fluid evaluation revealed a cell-rich, protein-poor modified transudate with neutrophils, reactive mesothelial cells, and atypical epitheloid cells which occasionally appeared to be keratinizing, consistent with neoplastic exfoliation. Thoracic effusion recurred 2 days later, with similar characteristics as the initial sample. Computed tomography (CT) indicated consolidation and displacement of the right middle and accessory lung lobes. Exploratory thoracic surgery demonstrated a thickened, hyperemic right middle lung lobe, and thickened pericardial diaphragmatic ligament. Histologic evaluation of these tissues identified a primary pulmonary adenosquamous carcinoma with intravascular and pleural invasion. Based on these cytologic, histologic, and clinical findings, we conclude that primary pulmonary carcinomas may involve superficial thoracic structures and exfoliate into a thoracic effusion.