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Causes of pulmonary nodules
Primary lung cancer and solitary metastasis from extrapulmonary malignancies are common causes of SPNs detected on chest radiography. Pulmonary granuloma and pulmonary hamartoma are other common causes.
Many other entities can cause SPNs or multiple pulmonary nodules, including malignancy (e.g., metastatic disease), infections, vasculitis, and inflammatory diseases (e.g., sarcoidosis, rheumatoid arthritis, or inhalational lung disease). Be careful about a “confluence of shadows” or overlap of normal vascular and skeletal structures that can mimic a nodule on a chest radiograph. Nipple shadows can also mimic nodules but often appear bilaterally and symmetrically.
Differential Diagnosis of Causes of Solitary Pulmonary Nodule (SPN)
Neoplastic
- Primary lung cancer (No. 1 cause of SPN detected on chest radiography)
- Metastasis
- Lymphoma/post-transplant lymphoproliferative disorder
- Carcinoid tumor
- Primary lung sarcoma
- Hamartoma (No. 3 cause of SPN detected on chest radiography, No. 2 cause of benign SPN)
Infections
- Granuloma (No. 2 cause of SPN detected on chest radiography, No. 1 cause of benign SPN)
- Bacterial infection
- Viral infection
- Fungal infection
- Mycobacterial infection
- Parasitic infection
- Septic emboli (often multiple, peripheral, and cavitary)
Vascular
- Pulmonary infarction (often peripheral and wedge-shaped, associated with pulmonary embolism)
- Vasculitis
- Arteriovenous malformation
- Pulmonary venous varix (tubular and avidly enhancing on CT)
- Pulmonary artery aneurysm
Inflammatory
- Sarcoidosis
- Inhalational lung disease
- Hypersensitivity pneumonitis
- Organizing pneumonia
- Bronchiolitis
- Langerhans cell histiocytosis (associated with upper lobe predominant cystic interstitial lung disease in smokers)
- Rheumatoid (necrobiotic) nodule
- Inflammatory pseudotumor
Congenital
- Intrapulmonary lymph node
- Pulmonary sequestration (solid or cystic opacity most often in lower lobes)
- Bronchial atresia
Traumatic
- Radiation therapy (typically has linear margins and known history of prior radiation therapy)
- Pulmonary contusion (associated with traumatic injury to the chest)
Pseudonodules
- Rounded atelectasis (“folded lung,” typically a subpleural opacity associated with pleural thickening or effusion and “comet-tail” sign of swirling bronchovascular structures central to opacity)
- Pulmonary scarring
- Mucoid impaction
- Fluid in interlobar fissure (often lenticular in shape on lateral chest radiograph in the location of a fissure)
- Healing rib fracture
- Bone island
- Spinal osteophyte
- Skin lesion
- Nipple shadow
- Pleural lesion
- Mediastinal lesion
- Overlap of vascular and osseous structures
