Radiographs usually reveal structured interstitial densities within pulmonary parenchyma.38 These lesions may represent primary or metastatic lesions. Clinical signs are typically absent, although coughing is most common. Acute respiratory signs may occur secondary to generation of pleural effusion or bleeding from a lesion (ie, hemangiosarcoma metastasis). Depending on the extent of disease, anorexia, lethargy, and weight loss may be appreciated.39
Pulmonary neoplasia may, on occasion, have a more diffuse nature. This is common with pulmonary lymphoma40 and is sometimes seen with carcinoma (author experience). Pulmonary lymphoma can have a rapid clinical course and mimic acute disorders. A diffuse, unstructured interstitial pattern is typically appreciated. Additionally, bronchointerstitial, alveolar, and nodular patterns may be observed (Figure 7).40
Diagnosis of pulmonary lymphoma requires airway cytology, pulmonary fine-needle aspiration, and/or confirmation on nonpulmonary samples.41
Carcinoma frequently causes anorexia and weight loss and should be considered in older patients with refractory pneumonia.42