History: 15 years old female domestic short hair cat
Diagnoses: Thoracal serosal linings (pulmonal pleura, mediastinum, pericard): Metastasizing malignant mesothelioma
Lung: moderate, multifocal to coalescent atelectasis; multifocal, moderate, acute alveolar emphysema
Description: At necropsy the animal had mild anaemia and 50 ml of a clear serosanguineous pleural effusion. The thoracical lining including the diaphragm and cranial mediastinum was covered with multifocal to coalescent firm, whitish, smooth, up to 6 × 5 × 3 mm nodules. These nodules were most striking on the sternal surface of the pleura, especially within and around the sternal lymph nodes. Cross sections of the masses were homogenously whitish and nodules attached firmly to the underlying tissue. The right cranial pulmonary lobe contained identical nodules. Additionally, the cranial and the ventral parts of the caudal lung lobes were atelectatic. The dorsal aspects of the caudal lobes had moderate, multifocal, acute, alveolar emphysema. Additionally, a 7 × 7 × 6 mm mass was present in the right caudal lung lobe.
Comments: Fibrosarcoma was the preliminary diagnosis of the tumour according to its histological features. To ascertain the diagnosis, immunohistochemical stains for cytokeratin (pancytokeratin antibody, clone AE1/AE3, DAKO, Hamburg, Germany) and vimentin (clone Vim 3B4, DAKO, Hamburg, Germany) were performed using standard procedures. Neoplastic cells stained positive for both the epithelial marker cytokeratin and mesenchymal marker vimentin, except some multinucleated cells that had only weak staining for cytokeratin. Interestingly, spindle cells displayed more prominent cytokeratin staining than the polygonal cells. However, both cell types stained equally for vimentin.
Due to the immunohistochemical features of the tumour the final diagnosis of a predominantly fibrous malignant mesothelioma was made.
Authors: Afonso da Costa and Alexander Weiss, Department of Veterinary Pathology, Freie Universitaet Berlin, Germany