The appearances of multiple large rounded masses indicates metastatic disease is likely. Although isolated large lesions have a wide variety of aetiologies, multiple large pulmonary masses are unusual. Except for metastatic disease which is by far the commonest, occasional fungal disease (e.g. coccidioidomycosis in renal transplant recipients) or lymphoma may result in multifocal large masses.
The morphology of the very large lesions falls into the category of “cannonball metastases”. One could consider that the left apical lesion is a primary lung carcinoma. Indeed in isolation, despite the absence of rib erosion, a Pancoast type tumour would be a strong consideration. However, in this case one has to consider that lung carcinoma is not a common cause of cannonball metastases. Therefore, in this case the lesion in the left apical lesion is also likely to be metastatic.
What are the common causes of cannonball metastases? Traditionally these are considered to be renal cell carcinoma, choriocarcinoma, endometrial carcinoma, prostate carcinoma, and occasionally some GI malignancies (particularly colorectal carcinoma) or sarcomas. When we also factor in the relative incidence of tumours and their timing of presentation renal cell carcinoma, prostate, endometrial and colorectal become more important. In this case the patient had polycythaemia which is a clue that the metastases were from renal cell carcinoma but there is no way of specifically identifying this source without further imaging.