The differential for a cavitating lesion most commonly includes malignancy and infection. This cavitating mass had grown between follow-up scans, had FDG avid walls on a PET-CT, and thus went for resection.
Cavitating malignancies include primary lung cancer (namely squamous cell carcinomas) and cavitating metastases, with the latter being the diagnosis in this case. Interestingly, histopathology demonstrated an endometrial primary of which the patient had a history of stage 2 endometrial carcinoma diagnosed three years earlier. Endometrial cancer is not on the usual list for causes of cavitating pulmonary metastases.