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Background
Pulmonary masses initially raise the suspicion of neoplasms. This diagnostic approach leads to further studies, and a biopsy will be needed to definitively rule out malignancy. A pulmonary mass is defined as any opacities greater than 30 mm. It is generally solid or mostly solid, and its density and margins may be of diverse appearance; however, not every pulmonary mass has a neoplastic nature. Nonneoplastic pulmonary masses may have an infectious, inflammatory, congenital, or vascular etiology. We present the cases of various entities that meet pulmonary mass criteria but are not neoplastic.

Educational Goals / Teaching Points
Pulmonary mass on imaging should raise suspicion of a malignant neoplasm. Pulmonary mass not always related to a neoplasm, may be the manifestation of a broad spectrum of entities. Congenital masses: Lung sequestration, bronchogenic cyst or arteriovenous malformation. Immunocompromised patients with pulmonary mass: tuberculosis, nocardiosis, citomegalovirus, cryptococcosis or mucormycosis. Suspect silicosis or paraffinoma (lipoid pneumonia) in a proper clinical setting according to the patient's exposure history. Always rule out infectious etiology.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Infectious etiology includes round pneumonia, lung abscess, tuberculosis, bacteria (actinomycosis, nocardiosis), virus (CMV), and fungus (cryptococcosis, mucormycosis). Congenital etiology includes lung sequestration and bronchogenic cyst. Vascular etiology includes arteriovenous malformation, pulmonary infarction, pseudoaneurysm of the pulmonary artery, and Behcet's disease. Other miscellaneous etiology includes sarcoidosis, silicosis, organizing pneumonia pattern, granulomatosis with polyangiitis, paraffinoma, pulmonary hyalinizing granuloma, and inflammatory pseudotumor.

Conclusion
In the correct clinical context, radiologists facing a pulmonary mass should consider other differential diagnoses in addition to neoplasms.