Pulmonary lymphoma

By Michael Rozmanec

An 8yr old outdoor domestic shorthair cat with a history of chronic respiratory distress and anorexia. Radiographs/necropsy revealed a diffuse miliary interstitial lung pattern (Fig 1). Post-mortem samples of lung, liver and kidney were examined histopathologically.

Fig 1. Thoracic radiograph (Courtesy: Clare Johnson)

Fig 2. Histopathology. Note the randomly distributed miliary pattern of cellular infiltrate. H&E, subgross slide photograph.

Fig 3. Histopathology. A closer look at the pulmonary infiltrate. Note the uniform sheets of large neoplastic round cells that infiltrate not only the perivascular/peribronchiolar spaces but also expand the parenchymal interstitium. There is mild congestion of the adjacent interstitium and increased numbers of vacuolated macrophages. H&E, x 200.

Fig 4a. Histopathology. Strong positive cytoplasmic staining of the neoplastic round cells with CD3 indicates a T-cell lymphoma. CD3 immunohistochemistry, H&E, x400.

Fig 4b. Histopathology. The large neoplastic lymphocytes infiltrate and expand the pulmonary interstitium. H&E, x 400.

Final Diagnosis

Pulmonary lymphoma

Discussion

This is a large-cell, T-cell lymphoma. It is not entirely clear whether this represents primary or metastatic lymphoma in this lung. Given the apparent random distribution of the neoplastic infiltrate, I would not exclude metastatic disease. However, as no other primary lesions were observed/reported at the time of post-mortem and no neoplasia was evident in the submitted renal or liver samples, primary pulmonary lymphoma was considered a valid differential in this case.

Pulmonary involvement with lymphoma is very uncommon in cats but should be considered amongst the potential differentials for infiltrative miliary or consolidated lung lesions. Other clinical differentials worth considering would include other metastatic neoplasia, pulmonary infiltrates with eosinophils (PIE) and granulomatous or pyogranulomatous diseases (e.g. parasitic, fungal or mycobacterial).

Refs: J Feline Med Surg. 2011 Oct;13(10):772-5 and Vet Radiol Ultrasound. 2010 Jul-Aug;51(4):386-90).