A lung nodule is a small spot or abnormality found in the lung, often detected incidentally during imaging tests. While computed tomography (CT) scans are highly effective at identifying these nodules, they cannot definitively determine if a nodule is cancerous based solely on the scan itself. The evaluation of lung nodules involves assessing their characteristics on the scan and considering other factors to guide further steps.
Understanding Lung Nodules and CT Scans
Lung nodules are common findings, appearing as small masses of dense tissue on chest X-rays or CT scans. These spots are frequently benign, resulting from various causes like old infections, inflammation, or scarring. Infectious granulomas, often caused by fungal or bacterial lung infections, are a common type of benign nodule. However, a small percentage of lung nodules can be cancerous.
A CT scan produces detailed images by taking multiple X-ray measurements from different angles, creating cross-sectional views or “slices” of the body. This advanced imaging technique provides greater detail than standard X-rays, making CT scans particularly useful for precise detection and evaluation of lung structures, including small nodules.
Interpreting CT Scan Findings
Radiologists examine several specific characteristics of a lung nodule on a CT scan to assess its likelihood of being cancerous. The size of a nodule is a significant factor; larger nodules, such as those over 8 to 10 millimeters, are generally more concerning. Nodules smaller than 6 millimeters have a less than 1 percent risk of being cancerous. Any growth exceeding 3 centimeters is typically classified as a lung mass, which carries a higher suspicion for malignancy.
The shape and borders of a nodule also provide important clues. Nodules with irregular, spiculated (spiky), or lobulated (lumpy) borders are more frequently associated with cancer. In contrast, nodules that are smooth, round, or oval in shape are often found to be benign. While some benign nodules can have irregular margins, the presence of spiculations is a particular indicator of potential malignancy.
Changes in nodule size over time are another important indicator, with growth being a strong sign of potential malignancy. Comparing current scans to previous ones helps determine if a nodule has grown, shrunk, or remained stable. Cancerous nodules can double in size at varying rates.
The density or type of a nodule visible on a CT scan also aids in assessment. Nodules can appear as solid, subsolid (partially solid and partially hazy), or pure ground-glass opacities. Subsolid and pure ground-glass nodules can be subtle findings but may represent early forms of lung cancer. The presence and pattern of calcification within a nodule are also evaluated; certain patterns typically suggest a benign origin, often linked to old infections or benign tumors. However, some malignant lesions can exhibit atypical calcification.
When CT Scans Are Not Enough
Despite the detailed information provided by CT scans, they often cannot definitively confirm whether a lung nodule is cancerous on their own. This limitation arises because various benign conditions, such as infections, inflammation, or scar tissue, can mimic the appearance of cancerous nodules. Conversely, some early cancers might present with features that appear benign, making a clear distinction challenging.
When CT scan features are ambiguous or a definitive diagnosis is not possible from the imaging alone, active surveillance is a common approach. For many small or low-risk nodules, healthcare providers monitor them with a series of follow-up CT scans over time. This typically involves scans at intervals like 3, 6, 12, and 24 months. If a nodule remains stable in size and appearance over a period of about two years, it is a strong indicator that it is benign and usually requires no further intervention.
In addition to imaging findings, a patient’s overall clinical context is considered during the assessment. Factors such as smoking history, age, family history of lung cancer, and exposure to environmental elements like radon or asbestos play a role in evaluating the risk associated with a lung nodule.
Path to Definitive Diagnosis
When a lung nodule is suspicious or shows growth over time, further diagnostic steps are necessary to achieve a definitive diagnosis. One common advanced imaging technique is a Positron Emission Tomography (PET) scan, often combined with a CT scan. A PET scan identifies areas of increased metabolic activity within the body, which cancer cells often exhibit due to their rapid growth. This can help differentiate between benign and malignant nodules, especially when CT findings are borderline.
To obtain a definitive diagnosis, a tissue sample from the nodule is required for microscopic examination, a process known as a biopsy. Methods include CT-guided needle biopsy, where a needle is inserted through the chest wall, and bronchoscopy, where a flexible tube collects samples from airways. Specialized techniques like endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) can also be used to sample lymph nodes or nodules near airways.
For nodules that are difficult to access or when less invasive methods do not yield a diagnosis, surgical biopsy or removal may be necessary, often performed through minimally invasive techniques like video-assisted thoracic surgery (VATS). Once the tissue sample is obtained, a pathologist examines it under a microscope to confirm the presence or absence of cancer cells. Decisions regarding diagnosis and treatment are typically made through a multidisciplinary approach, involving a team of specialists like radiologists, pulmonologists, oncologists, and surgeons.