What are pulmonary nodules?

A pulmonary nodule is a small round or oval-shaped growth in the lung. It may also be called a “spot on the lung” or a “coin lesion.” Pulmonary nodules are smaller than three centimeters (around 1.2 inches) in diameter. If the growth is larger than that, it is called a pulmonary mass and is more likely to represent a cancer than a nodule.

How common are pulmonary nodules?

Countless pulmonary nodules are discovered each year during chest X-rays or CT scans. Most nodules are noncancerous (benign). A solitary pulmonary nodule is found on up to 0.2% of all chest X-rays films. Lung nodules can be found on up to half of all lung CT scans. Risk factors for malignant pulmonary nodules include a history of smoking and older age.

What causes pulmonary nodules?

There are two main types of pulmonary nodules: malignant (cancerous) and benign (noncancerous). Over 90% of pulmonary nodules that are smaller than two centimeters (around 3/4 inch) in diameter are benign.

Benign pulmonary nodules can have a wide variety of causes. Many are the result of inflammation in the lung as a result of an infection or disease producing inflammation in the body. The nodule may represent an active process or be the result of scar tissue formation related to prior inflammation. Benign developmental lesions may also appear as nodules.

  • Infections— Most infections that appear as with pulmonary nodules are relatively indolent and often not active. Examples include mycobacterium such as mycobacterium tuberculosis or mycobacterium avium intracellulare, and fungal infections such as aspergillosis, histoplasmosis, coccidiomycosis, and cryptococcosis. Inflammation related to infections often forms what is termed a granuloma. A granuloma is a small clump of cells that form when lung tissue becomes inflamed. Granulomas form when the immune system isolates substances that it considers foreign. Most of the time granulomas occur in the lungs, but they may also form in other parts of the body. They can become calcified over time, as calcium tends to collect in the healing tissue
  • Noninfectious causes of benign inflammatory lung nodules—Noninfectious disorders such as sarcoidosis, granulomatosis with polyangiitis (GPA), and rheumatoid arthritis also show themselves with granulomas forming in the lungs
  • Neoplasms—Neoplasms are abnormal growths that may be benign or malignant. Types of benign neoplasms include:
    • Fibroma (a lump of fibrous connective tissue)
    • Hamartoma (an abnormal grouping of normal tissues)
    • Neurofibroma (a lump made up of nerve tissue)
    • Blastoma (a growth made up of immature cells)
  • Types of malignant tumors include:
    • Lung cancer
    • Lymphoma (a growth containing lymphoid tissue)
    • Carcinoid (a small, slow-growing cancerous tumor)
    • Sarcoma (a tumor consisting of connective tissue)
    • Metastatic tumors (tumors that have spread to the lungs from cancer in another part of the body)

What are the symptoms of pulmonary nodules?

Usually there are no symptoms associated with pulmonary nodules. If present, symptoms would be related to the condition that led to the nodule developing. If the nodule is from a lung cancer, the patient is often without symptoms but may have a new cough, or cough up blood.

Most of the time, a patient is unaware that he or she has a lung nodule until a chest X-ray or computed tomography scan (CT scan) of the lungs is performed.

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