A solitary pulmonary nodule (SPN) is a single abnormality in the lung that is smaller than 3 cm in diameter. Generally, a pulmonary nodule must grow to at least 1 cm in diameter before it can be seen on a chest X-ray.
An SPN is surrounded by normal lung tissue and is not associated with any other abnormality in the lung or nearby lymph nodes (small, bean-shaped structures found throughout the body).
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People with SPNs usually do not experience symptoms. SPNs are usually noticed by chance on a chest X-ray that has been taken for another reason (referred to as an incidental finding). SPNs are one of the most common abnormalities seen on chest X-rays. Approximately 150,000 cases are detected every year as incidental findings, either on X-rays or CT scans.
Most SPNs are benign (noncancerous); however, they may represent an early stage of primary lung cancer or may indicate that cancer is metastasizing (spreading) from another part of the body to the affected lung.
Determining whether the SPN seen on the chest X-ray or chest CT scan is benign or malignant (cancerous) is important. Prompt diagnosis and treatment of early lung cancer that looks like an SPN may be the only chance to cure the cancer.
Causes of Solitary Pulmonary Nodules
Solitary pulmonary nodules may have the following causes:
Neoplastic (an abnormal growth that can be benign or malignant):
Metastasis (spread of cancer from other parts of the body to the lung)
Lymphoma (a tumor made up of lymphoid tissue)
Carcinoid (a small, slow-growing tumor that can spread)
Hamartoma (an abnormal mass of normal tissues that are poorly organized)
Fibroma (a tumor made up of fibrous connective tissue)
Neurofibroma (a noncancerous tumor made up of nerve fibers)
Blastoma (a tumor composed mainly of immature, undifferentiated cells)
Sarcoma (a tumor made up of connective tissue -- usually cancerous)
Infections caused by fungi -- Histoplasmosis, coccidioidomycosis, blastomycosis, cryptococcosis, or nocardiosis
Other infectious causes:
Lung abscess (an infection in which cells of a part of the lung die)
Round pneumonia (infection caused by virus or bacteria; air spaces of the lungs are filled with fluid and cells)
Hydatid cyst (a cyst formed by the larval stage of a tapeworm, Echinococcus)
Rheumatoid arthritis (a generalized disease of the connective tissues; joint pain is the main symptom)
Wegener granulomatosis (inflammation of the small blood vessels characterized by lesions that kill the cells in different organs of the body)
Sarcoidosis (a disease characterized by granular lesions of unknown cause that involves various organs of the body)
Lipoid (resembling fat) pneumonia
Arteriovenous malformation (failure of proper or normal development of arteries and veins)
Sequestration (a piece of lung tissue that has become separated from the surrounding healthy tissue)
Lung cyst (an abnormal sac that contains gas, fluid, or a semisolid material)
Pulmonary infarct (death of cells or of a portion of lung, resulting from a sudden insufficiency of blood supply)
Round atelectasis (decreased or absent air in a part of the lung)
Mucoid impaction (the filling of parts of the lung with mucus)
Progressive massive fibrosis, also called "black lung disease" (formation of fibrous tissue as a reactive process, as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue)
Occasionally, a shadow on the X-ray film may be mistaken for an SPN.