Lung nodules are small, often spherical, growths found in the lungs. Most lung nodules do not cause pain and are frequently found by chance during imaging tests performed for unrelated reasons.
Understanding Lung Nodules
Lung nodules are small, distinct spots or lesions in the lung tissue, typically measuring less than 3 centimeters (about 1.2 inches) in diameter. These growths are often round or oval-shaped and can appear in any part of the lung. Their prevalence is quite high, with many individuals having them without ever experiencing symptoms.
It is important to distinguish lung nodules from larger masses, which are generally defined as being larger than 3 centimeters. While both are growths, the smaller size of a nodule often correlates with a higher likelihood of being benign.
The Pain Question: Why Nodules Often Don’t Hurt
The human lungs contain very few pain receptors, which explains why small lung nodules do not cause discomfort or pain. This lack of sensory nerves means the presence of a small growth goes unnoticed. Most people are unaware they have a lung nodule until it is identified on an imaging scan.
Pain from a lung nodule can occur under specific circumstances, usually when the nodule grows large enough to interact with surrounding structures that do possess pain receptors. For example, a large nodule might press against the chest wall, ribs, or nearby nerves, which can lead to localized pain. The pleura, the delicate membrane lining the lungs and the inside of the chest cavity, is rich in pain receptors.
If a nodule causes significant inflammation or irritation of the pleura, it can result in chest pain, often described as sharp and worsening with deep breaths or coughing. This type of pain is called pleuritic chest pain. Pain can also arise if a nodule is part of a more widespread condition causing inflammation or damage to surrounding tissues. However, in the vast majority of cases, especially with small nodules, pain is not a presenting symptom.
How Lung Nodules Are Discovered and Evaluated
Lung nodules are most frequently discovered incidentally when individuals undergo imaging tests of the chest for unrelated medical conditions. A routine chest X-ray or a computed tomography (CT) scan can reveal a nodule. This incidental finding prompts further investigation.
Upon discovery, medical professionals evaluate the nodule’s characteristics, such as its size, shape, borders, and any changes over time. Patient risk factors, including smoking history or exposure to certain substances, also play a significant role in the assessment. Depending on these factors, follow-up might involve watchful waiting with repeat CT scans at regular intervals to monitor for growth or changes.
In some cases, further diagnostic tests may be necessary to better characterize the nodule. These can include a positron emission tomography (PET) scan, which helps identify metabolically active areas, or more invasive procedures like a biopsy. A biopsy involves taking a small tissue sample from the nodule for microscopic examination, often guided by imaging, or a bronchoscopy, where a thin tube with a camera is inserted into the airways to visualize and sample the nodule.
What Causes Lung Nodules?
Lung nodules can develop for various reasons, broadly categorized into benign (non-cancerous) and malignant (cancerous) causes. The majority of lung nodules identified are benign, meaning they are not cancerous and typically do not pose a serious threat to health.
Benign causes often include infections, such as those caused by fungi, bacteria like tuberculosis, or even common respiratory viruses, which can leave behind scarred tissue or granulomas. Inflammatory conditions, like rheumatoid arthritis or sarcoidosis, can also lead to the formation of nodules within the lung tissue. Scarring from previous lung injuries or infections is another common benign cause.
Malignant causes, while less common, are a significant concern when a nodule is discovered. These can include primary lung cancer, which originates in the lung tissue itself. Alternatively, a lung nodule can represent metastatic cancer, meaning cancer cells have spread to the lungs from a primary tumor located elsewhere in the body.