A lung mass is an abnormal growth of tissue discovered in the lung, typically during an imaging test like a chest X-ray or a Computed Tomography (CT) scan. Medically, these growths are classified by size: a lesion measuring 3 centimeters (about 1.2 inches) or less is called a nodule, while anything larger is termed a mass. While the discovery of a growth can cause immediate concern, a lung mass is not automatically cancer. Many of these abnormal areas are benign (non-cancerous) and can arise from infectious, inflammatory, or congenital causes.
Non-Malignant Causes of Lung Masses
Most small lung nodules are not cancerous. The most frequent non-malignant cause is infectious or inflammatory remnants, often appearing as granulomas. These are small clumps of immune cells that have walled off a past infection, most commonly from fungal diseases like histoplasmosis or bacterial infections like tuberculosis. The remaining scar tissue often calcifies, which is a sign of a benign, long-standing process.
Another common source of benign masses is a hamartoma. Hamartomas are the most frequent type of benign lung tumor in adults and are composed of a disorganized mix of tissues, such as cartilage, fat, and connective tissue. These growths are typically slow-growing and often present as solitary nodules that do not cause symptoms. Less common causes include vascular issues, such as arteriovenous malformations, or inflammatory conditions like rheumatoid arthritis, which can create nodules that mimic tumors on imaging.
What Makes a Lung Mass Suspicious
When evaluating a lung mass, doctors look at radiological characteristics and a patient’s medical background to assess the likelihood of cancer. Size is a major factor, as the probability of malignancy increases significantly with the lesion’s diameter. Lesions larger than 3 cm are classified as masses, and these have a higher chance of being malignant compared to smaller nodules.
The rate of growth is another important characteristic, since rapidly growing lesions are considered suspicious. Benign nodules generally remain stable in size over two years, whereas cancerous growths tend to enlarge more quickly. The shape and borders of the mass are also closely analyzed, as malignant lesions often display irregular, spiky margins, a feature called “spiculation.” In contrast, benign growths are more likely to have smooth, well-defined borders.
Calcification patterns provide clues, as dense, centralized, or laminated calcifications strongly suggest a benign process, often an old granuloma. Malignant tumors rarely have uniform calcification, though eccentric or scattered calcification can sometimes be seen in cancerous masses. The patient’s risk factors, including heavy smoking, older age, or certain occupational exposures, significantly increase the probability that a mass is cancerous.
How Doctors Determine the Diagnosis
The diagnostic process begins with a CT scan, which provides detailed cross-sectional images of the mass. For small, low-risk nodules, doctors may recommend active surveillance, involving repeat CT scans over several months to monitor for growth or change. If the mass shows concerning features or the patient has a high risk profile, a Positron Emission Tomography (PET) scan may be ordered. This scan involves injecting radioactive sugar, which cancer cells typically take up more readily due to their high metabolic rate, causing them to “light up” on the image.
While imaging techniques can estimate the probability of cancer, the only definitive way to confirm the diagnosis is through a biopsy. This involves taking a tissue sample from the mass, which a pathologist then examines under a microscope to look for cancer cells. Different methods exist for obtaining a sample, depending on the mass’s location. For masses near the chest wall, a CT-guided needle biopsy may be performed, where a needle is inserted through the skin and guided to the mass using CT imaging.
Alternatively, a bronchoscopy may be used for masses closer to the central airways, involving a flexible tube with a camera inserted through the mouth or nose. Advanced techniques, such as Endobronchial Ultrasound (EBUS), can be used with bronchoscopy to sample lymph nodes or more peripheral lesions. Ultimately, the combination of clinical history, advanced imaging, and cellular analysis determines the mass’s true nature and guides the subsequent treatment plan.