Pulmonary Nodule – Causes of Nodules in the Lung

Lung nodules or pulmonary nodules may be routinely discovered on a chest x-ray or thoracic CT scan. A patient may be asymptomatic or sought medical attention for some other condition when a nodule is identified on follow-up imaging studies. Screening may also be done for immigration purposes, where a person from a high risk country may have to undergo a chest x-ray, to exclude possible TB infection.

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The detection of a lung nodule often elicits panic in many patients as the possibility of cancer comes to mind. However, there are various causes of lung nodules that also need to be considered. This may require follow up investigations like a percutaneous needle biopsy to conclusively identify the cause and reach a diagnosis. Certain radiological features, however, may raise the concern of cancer. This is discussed further under what is a lung nodule?

Causes of Pulmonary Nodules

Tumors

Lung cancer is among the more common causes of a pulmonary nodule and is often the primary tumor. Single metastasis from other sites may also be possible. The presence of other symptoms like a persistent cough, hemoptysis, unintentional weight loss and clubbing may raise the concern of lung cancer. However, the solitary lung nodule may exist without any other signs and symptoms being evident. Nodules greater than 3 cm in diameter are considered as masses and are usually indicative of a malignant tumor.

Benign tumors, lymphomas or pseudotumors, which are fluid filled gaps in the lung parenchyma, are uncommon causes of lung nodules.

Infections

Among the infectious causes of a lung nodule, localized pneumonia, a lung abscess and tuberculous granuloma (tuberculoma) which arises in response to Mycobacterium tuberculosis are the common causes.

Aspergilloma, also known as mycetoma, is an uncommon infectious cause of a lung nodule. It is of fungal origin and is characterized by a nodule surrounded by an air halo on x-ray. Another uncommon infectious cause is a hydatid cyst due to the Echinococcus parasite.

Infectious causes of a lung nodule may not present with the typical symptoms of an infection. With chronic and slow-progressing infections, patients may report bouts of persistent coughing, occasionally accompanied by hemoptysis, recurrent fever and night sweats.

Other Causes

A pulmonary infarct is among the other common causes of a lung nodule. It often occurs as a result of a pulmonary embolism where occlusion of the arterial blood supply to the lung results in death of lung tissue within a confined area. The symptoms are similar to a heart attack and the coughing up of blood or pink foamy mucus may be the only differentiating sign.

Other causes of a pulmonary nodule are uncommon and includes :

  • Arteriovenous malformation
  • Bronchogenic cyst
  • Rheumatoid nodule
  • Sarcoidosis
  • Pulmonary haematoma
  • Wegener’s granuloma

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