Bronchiectasis can cause lung nodules, and they show up frequently. In one lung cancer screening study, over 53% of patients with bronchiectasis had nodules on their CT scans, compared to just 18% of people without the condition. Most of these nodules are benign, caused by the chronic inflammation and infection that define bronchiectasis, but they still require careful evaluation.
Why Bronchiectasis Produces Nodules
The damaged, widened airways in bronchiectasis are a breeding ground for chronic infection and inflammation. Over time, this process creates small clusters of inflamed tissue around the airways. On a CT scan, these clusters appear as tiny nodules, typically described as “centrilobular” because they sit near the center of small lung structures called lobules. The nodules form when infected material from the airways spills into surrounding tissue, triggering an inflammatory response that walls off the debris in small granulomas.
A pattern called “tree-in-bud” often accompanies these nodules on imaging. It looks like branching lines with small buds at the tips, representing mucus and inflammatory material packed into the smallest airways. When a radiologist sees centrilobular nodules alongside tree-in-bud opacities in a patient with bronchiectasis, the most likely explanation is active infection spreading through the airway walls.
The Role of Nontuberculous Mycobacteria
One of the most important causes of nodules in bronchiectasis is infection with nontuberculous mycobacteria (NTM), a group of bacteria found in soil and water. The most common culprit is Mycobacterium avium complex, or MAC. This infection has become so closely linked with a specific pattern on CT scans that it has its own name: nodular bronchiectatic disease.
The hallmark of nodular bronchiectatic disease is a combination of widened airways and scattered small nodules, sometimes with small cavities. These findings tend to concentrate in the right middle lobe and the lingula, a tongue-shaped portion of the left upper lobe. Among patients whose CT scans show this characteristic pattern, 34 to 50% have active NTM infection. The nodules themselves represent granulomas and pockets of necrotic material that form around the infected bronchi as the immune system tries to contain the bacteria.
This form of the disease most commonly affects older women without prior lung disease. It progresses slowly, sometimes over years, and the nodules can wax and wane with treatment. Because NTM infections require specific antibiotic regimens that differ from standard bacterial pneumonia treatment, identifying this pattern early matters for getting the right care.
What These Nodules Look Like on a CT Scan
Not all nodules are the same, and the characteristics visible on imaging help determine what’s causing them. In bronchiectasis, the most common type is the centrilobular nodule, which is small (usually under 5 millimeters), clustered around airways, and often accompanied by the tree-in-bud sign. These are almost always inflammatory or infectious in origin.
Larger solitary nodules are less common but more concerning. A single round nodule with well-defined borders, especially one that grows over time, raises different questions than a scattering of tiny inflammatory nodules. The updated Fleischner Society guidelines from 2017 provide a framework for evaluating incidental pulmonary nodules, taking into account size, shape, whether the nodule is solid or partially solid, and the patient’s individual risk factors. In bronchiectasis patients, the challenge is distinguishing nodules caused by chronic inflammation from those that need further workup.
Bronchiectasis and Lung Cancer Risk
The high rate of nodules in bronchiectasis patients naturally raises concerns about cancer. In the screening study that found nodules in 53% of bronchiectasis patients, actual lung cancer was uncommon. Among 354 patients with bronchiectasis, five were diagnosed with lung cancer, including two adenocarcinomas, one squamous cell carcinoma, one small cell carcinoma, and one of unknown type. So while nodules are extremely common, the vast majority are not cancerous.
That said, chronic lung inflammation is a known risk factor for lung cancer, and the sheer number of nodules in bronchiectasis patients can make surveillance more complicated. A new nodule in someone who already has dozens of small inflammatory nodules is harder to spot and evaluate than one appearing in an otherwise clear lung. This is why regular imaging and close communication with a pulmonologist matter for anyone with bronchiectasis, particularly if new symptoms like unexplained weight loss, hemoptysis (coughing up blood), or a change in cough pattern develop.
How Nodules Are Evaluated
When a nodule is found on a CT scan in someone with bronchiectasis, the first step is characterizing it. Small centrilobular nodules in a pattern consistent with airway inflammation typically don’t need additional workup beyond treating the underlying infection. If sputum cultures reveal NTM or another specific pathogen, targeted treatment can reduce or resolve the nodules over time.
Larger or atypical nodules get more scrutiny. The key features that prompt further evaluation include size above 6 millimeters, irregular or spiculated borders, growth on serial imaging, and the presence of a solid component within a ground-glass opacity. Follow-up CT scans are the standard approach for monitoring borderline nodules, with the interval depending on nodule size and risk factors. For nodules that are growing or have suspicious characteristics, a biopsy or PET scan may be recommended to rule out malignancy.
The guidelines emphasize individualized decision-making. A 4-millimeter nodule in the right middle lobe of a patient with known NTM infection carries very different implications than a new 10-millimeter nodule in the upper lobe of a long-time smoker who also has bronchiectasis. Context shapes every decision about how aggressively to investigate.
When Nodules Resolve and When They Don’t
Inflammatory and infectious nodules often improve with appropriate treatment. In NTM-related nodular bronchiectatic disease, antibiotic therapy can reduce the number and size of nodules, though treatment courses are long, often lasting 12 months or more. Nodules caused by acute bacterial infections or mucus plugging may clear more quickly once the infection is controlled.
Some nodules persist even after treatment. Scarring and fibrosis from repeated cycles of infection and healing can leave behind stable nodules that don’t change over time. These stable, unchanging nodules are generally considered benign, but they establish a new baseline that makes future comparisons on imaging more complex. Keeping copies of prior CT scans accessible to your care team helps radiologists distinguish old, stable findings from new developments that need attention.