Lung nodules are frequently discovered during medical imaging. These small abnormalities in the lung tissue are a common finding. While their presence can be concerning, most are not cancerous and represent benign conditions. This article clarifies how these nodules are evaluated, focusing on the criteria that guide biopsy decisions.
Understanding Lung Nodules
A lung nodule appears as a round area denser than normal lung tissue on imaging scans like X-rays or CT scans, often described as a “spot on the lung” or a “shadow.” They are quite common, observed in nearly one out of every three chest CT scans. Most lung nodules are benign.
These nodules often result from inflammation from past infections, such as tuberculosis or fungal infections. Other causes include scar tissue, inflammatory conditions like rheumatoid arthritis or sarcoidosis, and small collections of normal cells called hamartomas. Lung nodules typically do not cause symptoms unless large enough to press on airways.
Criteria for Lung Nodule Biopsy
The decision to biopsy a lung nodule is complex, involving several factors beyond just its size. While size is a significant indicator, it is not the sole determinant. A multidisciplinary team typically evaluates each case to determine the most appropriate course of action.
Nodule size is a key factor. Guidelines suggest nodules larger than 8 millimeters (mm) often warrant biopsy, especially if malignancy is suspected. Smaller nodules can also be biopsied under certain circumstances. For solid nodules less than 8 mm, immediate biopsy is not recommended; surveillance is preferred based on risk factors.
Changes in nodule size over time, particularly growth, are important indicators of malignancy. Cancerous nodules tend to grow, while benign ones remain stable. The shape and margins of a nodule also provide clues; irregular, spiculated (spiky), or lobulated (having rounded projections) shapes are more concerning than smooth, round ones.
The nodule’s density on a CT scan is another factor. Solid nodules appear as a dense, opaque spot, while subsolid nodules, including ground-glass or part-solid, warrant different management approaches. Pure ground-glass nodules less than 5 mm require no further evaluation, while larger ones need annual CT surveillance. Part-solid nodules, even if small, carry a higher risk of slow-growing cancer and require closer monitoring.
Patient-specific risk factors are also considered. These include age, with cancerous nodules rare in people younger than 35 and more likely in those over 50. A history of current or former smoking significantly increases the risk. Other risk factors include a personal or family history of cancer, exposure to substances like asbestos or radon, and occupational exposures. The nodule’s location, particularly in the upper lobes, can also influence assessment.
Lung Biopsy Methods
When a lung nodule requires tissue sampling, several biopsy methods are available, suited to different nodule characteristics and locations. These procedures aim to obtain a small piece of the nodule for laboratory analysis. The choice of method depends on factors like the nodule’s size, location, and accessibility.
One common approach is a CT-guided needle biopsy. During this procedure, a radiologist uses real-time CT scan images to guide a thin, hollow needle through the skin and chest wall directly into the lung nodule. Tissue samples are collected and sent for pathological examination. This method is performed under local anesthesia and is considered less invasive than surgical options.
Another method is bronchoscopy with biopsy, used for nodules located closer to the central airways. A thin, flexible tube called a bronchoscope, equipped with a camera, is passed through the airways into the lung. Once the nodule is visualized, instruments are inserted through the bronchoscope to collect tissue samples. Robotic bronchoscopy can also be used to biopsy lung nodules and sample lymph nodes.
For nodules hard to reach with a needle or bronchoscope, or when other methods are inconclusive, a surgical biopsy may be performed. Video-assisted thoracic surgery (VATS) is a minimally invasive technique where a surgeon makes small incisions in the chest and uses a thoracoscope, a thin tube with a camera, to view the lung. Instruments are inserted through these cuts to remove a piece of the nodule or the entire nodule. In some cases, open surgery (thoracotomy) is necessary, involving a larger incision to access the lung.
Managing Smaller Nodules
For many small, indeterminate lung nodules, immediate biopsy is not the first step. Instead, “watchful waiting” or active surveillance is recommended. This approach avoids invasive procedures, as most small nodules are benign and remain stable over time. It also ensures that any changes are detected early.
Active surveillance involves regular follow-up CT scans to monitor the nodule for growth or changes in its characteristics. The frequency of these scans varies depending on the nodule’s initial size, appearance, and the patient’s risk factors. For example, solid nodules less than 6 mm do not require routine follow-up, though an optional CT scan is considered in 12 months for high-risk individuals.
Nodules between 6-8 mm require a repeat CT scan at 6-12 months, with further follow-ups considered at 18-24 months. For subsolid nodules, especially those larger than 5 mm, annual CT surveillance for at least three years is suggested. If a nodule remains unchanged over a two-year period, it is considered benign and no longer requires further monitoring. This structured management plan provides a way to observe nodules, intervening only if there are signs of concern.