2015 Volume 55 Issue 6 Pages 1037-1044
Adenocarcinomas, squamous cell carcinomas, and small cell carcinomas, collectively referred to as primary lung carcinomas, account for over 90% of all primary lung tumors. Other lung tumors are uncommon and may have epithelial, tracheobronchial gland, neuroendocrine, lymphopoietic, hematopoietic, mesenchymal, or uncertain cell origin. With notable exceptions, the imaging appearances of these tumors are non-specific since most tumors demonstrate considerable overlap with their rare counterparts, as well as with more common primary lung cancers. Consequently, the diagnosis of unusual lung tumors is typically made retrospectively from a biopsy or pathological specimen. Nevertheless, the presence of certain clinical and radiological features may alert the radiologist to the possibility of an uncommon lung tumor. Low malignant potential tumors include carcinoids (typical and atypical), adenoid cystic carcinomas, and mucoepidermoid carcinomas, each of which originate near the central airway. Carcinoid tumors commonly show well-defined nodules with intense enhancement on contrast-enhanced CT, and adenoid cystic carcinomas have a striking tendency toward submucosal extension and manifest with circumferential and infiltrative growth. Benign pulmonary tumors include hamartomas and sclerosing pneumocytomas (formerly referred to as sclerosing hemangioma), each of which show well-defined and smooth marginated nodules. Intranodular fat and popcorn-like calcifications are reliable indicators of hamartomas. Sclerosing pneumocytomas have been described as well-defined nodules with intense enhancement without contact with the major bronchus and pulmonary vessels. MALT (mucosa-associated lymphoid tissue) lymphomas and diffuse large cell B-cell lymphomas are relatively common pulmonary lymphomas. MALT lymphomas are typically single or multifocal and comprise ill-defined nodules containing air bronchograms, which occasionally appear as focal consolidation. Mediastinal lymphadenopathy is uncommon in MALT lymphomas. On the other hand, diffuse large cell B-cell lymphomas, single or multiple solid pulmonary nodules or masses that mimic lung cancer, and mediastinal or hilar lymph node enlargement are usually present. Pulmonary sarcomas are very rare and typically present as solitary huge masses that mimic common primary lung cancers. Characteristic imaging findings of pulmonary sarcomas are pulmonary intimal sarcomas. The most characteristic finding is a vascular filling defect with varying enhancement or enhancement in a filling defect that virtually excludes thrombus.
