What causes lung nodules? With 150,000 people being diagnosed with a lung nodule on a chest x-ray every year in the U.S., this is a common question. What are some of the benign (non-cancerous) and malignant (cancerous) causes?
First, it is important to define what a lung nodule is. A lung nodule is a “spot” on the lung that is less than 3 cm (or 1½ inches) in diameter. If a spot is larger than 3 cm, it is considered a lung mass, rather than a lung nodule. The overall chance that a lung nodule is cancer is 40%, but that risk varies a lot depending on factors such as your age, if you have smoked, and what the nodule looks like on x-ray.
For an indepth discussion about lung nodules, check this article:
Benign (Non-Cancerous) Lung Nodules
Benign lung nodules are responsible for 60% of “spots” seen on a lung x-ray. A nodule is more likely to be benign if:- You are young (in people less than 35 years of age, 99% of lung nodules are benign)
- You are a non-smoker
- You haven’t worked in occupations that raise the risk of lung cancer
- The nodule is slow-growing (or grows very rapidly)
- The nodule has calcifications
- The nodule is smooth and regular in appearance
- You don’t have a history of cancer in the past
- You have traveled outside of the United States
Causes of benign lung nodules include:
Inflammatory lung nodules (granulomas):
- Sarcoidosis
- Rheumatoid nodules
- Wegener’s granulomatosis
- Lipoid pneumonia
Bacterial infections:
Fungal infections:
Parasitic infections:
- Ascariasis (round worm)
- Echinococcus (hydatid cyst)
- Paragonimus (oriental lung fluke)
Benign lung tumors:
- Bronchial adenomas
- Hamartomas - Hamartomas are the most common cause of benign lung nodules.
- Fibromas
- Blastomas
- Neurofibromas
- Hemangiomas
Other benign lung nodules:
- Pulmonary infarcts (areas of lung tissue that have lost their blood supply)
- Blood vessel abnormalities
- Bronchogenic cysts
- Atelectasis (collapse of part of a lung) - This is a common cause in people who have had lung conditions or lung surgery.
- Anthracosilicosis
- Pulmonary fibrosis (fibrosing alveolitis) – scar tissue in the lungs
- Amyloidosis
Malignant (Cancerous) Lung Nodules
A lung nodule is more likely to be malignant if:- You are older – half of lung nodules in people over age 50 are malignant
- You have a history of cancer in the past
- You smoke or have smoked in the past
- You work in an occupation where you are exposed to substances that cause lung cancer
- The nodule is irregular or “spiculated”
- The nodule is not calcified
- The nodule is growing on repeat x-rays
Causes of malignant lung nodules include:
- Lung cancer
- Metastatic cancer to the lungs from other regions of the body
- Lymphoma
- Carcinoid tumors
- Sarcoma
- Plasmacytoma
As noted above, there are many possible causes of lung nodules. While the likelihood of cancer is less than 50%, it is very important to discuss a lung nodule carefully with your doctor. When lung cancer is found at an early stage, the chances of a cure is much higher than at later stages of the disease.
Further Reading:
Sources:
Cronin, P. et al. Solitary Pulmonary Nodules: Meta-analytic Comparison of Cross-sectional Imaging Modalities for Diagnosis of Malignancy. Radiology. 2008. 246:772-782.
Gould, M. et al. Evaluation of Patients With Pulmonary Nodules: When Is It Lung Cancer? ACCP Evidence-Based Clinical Practice Guidelines (2nd Edition). Chest. 2007. 132(no 3 suppl):108S-130S.
MacMahon, H. et al. Guidelines for Management of Small Pulmonary Nodules Detected on CT Scans: A Statement from the Fleischner Society. Radiology. 2005. 237:395-400.
Wahidi, M. et al. Evidence for the Treatment of Patients With Pulmonary Nodules: When Is It Lung Cancer? ACCP Evidence-Based Clinical Practice Guidelines (2nd Edition). Chest. 2007. 132(no 3 suppl):94S-107S.
