Sarcoidlike reaction of neoplasia causing hypermetabolic thoracic adenopathy in setting of extrathoracic malignancy: Report of two cases and a review of the differential diagnostic considerations

The development of noncaseating granulomas in a patient with underlying malignancy and no symptoms or signs suggestive of systemic sarcoid is often referred to as a sarcoidlike reaction and is estimated to occur in a small but significant portion of cancer patients. The pathogenesis is poorly understood, but the entity is hypothesized to be an immune phenomenon representing a host defense mechanism against the spread of tumor cells. Sarcoidlike reactions can occur at any time from the time of diagnosis to several years afterward and may occur in lymph nodes draining a malignant tumor, in the tumor itself, and even in nonregional tissues. Like sarcoid, sarcoidlike reactions of neoplasia can demonstrate hypermetabolic lymph nodes on ¹⁸F-FDG PET imaging and thus be readily confused with metastatic disease. We describe 2 cases of a sarcoidlike reaction of neoplasia presenting as hypermetabolic thoracic lymph nodes on ¹⁸F-FDG PET/CT obtained for follow-up of extrathoracic malignancies: one a 73-y-old woman with a history of stage III head and neck squamous cell carcinoma and the other a 34-yold woman with recurrent giant cell tumor of the sacrum. In both instances, the differential diagnosis for the finding of hypermetabolic thoracic lymph nodes included the possibility of a sarcoidlike reaction, though tissue sampling was pursued to exclude the more worrisome presence of metastatic disease or, less likely, a new primary malignancy. We review the topic of sarcoidlike reactions of neoplasia as well as the analytic approach to hypermetabolic mediastinal and hilar lymph nodes encountered on ¹⁸F-FDG PET/CT.