Unusual primary lung tumors: a radiologic-pathologic overview.

Although the great majority of lung carcinomas are histologically characterized as adenocarcinoma, squamous cell carcinoma, large cell undifferentiated carcinoma, or small cell carcinoma, a variety of rare benign and malignant lung tumors may sporadically affect the lung. Several nonneoplastic tumorlike lesions are seen infrequently but are also part of the differential diagnosis for lung masses. Conventional radiographic findings, although of limited value in the diagnosis of these entities, should be examined carefully when lung tumors are suspected. Computed tomography (CT) is well suited for making a definitive diagnosis of some disease processes. CT helps determine the location and features of the lesions and depicts associated findings to help document the extent of disease. The differential diagnosis can be narrowed when there are typical CT features (eg, the presence of fat in lipoid pneumonia). Although unusual primary lung tumors are difficult to diagnose on the basis of imaging findings alone because such findings are nonspecific in the majority of cases, cross-sectional imaging can play an important role in the diagnostic work-up of these unusual tumors by delineating their extent and directing the radiologist or bronchoscopist to the appropriate biopsy site.