Diagnosis and Imaging: Reading Your Reports
At a Glance
Bronchiolitis obliterans is diagnosed by combining medical history with PFTs and HRCT rather than relying on one test. Fixed airflow obstruction, increased air left in the lungs after exhaling, and expiratory air trapping can support the diagnosis, while biopsy is not always needed.
Navigating the diagnostic process for bronchiolitis obliterans can feel like solving a complex puzzle. Because the disease affects the microscopic airways, standard tests often need to be interpreted specifically to find the unique “footprints” of the condition. Understanding your Pulmonary Function Test (PFT) and High-Resolution CT (HRCT) reports will help you engage more effectively with your care team.
Deciphering Your Lung Function (PFTs)
Pulmonary Function Tests measure how much air your lungs can hold and how quickly you can breathe it out. In bronchiolitis obliterans, the hallmark finding is an obstructive defect [1].
- Fixed Obstruction: Your doctor looks at the FEV1/FVC ratio (the fraction of forced vital capacity that you can exhale in one second). In this condition, the ratio is typically low. Unlike asthma, this obstruction is often “fixed” or incompletely reversible, meaning it does not improve significantly after you use a bronchodilator (rescue inhaler) [2][3]. However, some bronchodilator response can occur, so one negative test doesn’t prove scarring is the sole cause.
- Air Trapping and Hyperinflation: Because the small airways are narrowed, air gets “stuck” in the lungs. This can cause your Residual Volume (RV)—the air left in your lungs after you breathe out as much as possible—to be higher than normal [4]. A high RV is supportive of air trapping but is not obligatory.
- Variable Patterns: It is important to know that PFTs are not always the same for everyone. Some patients may have normal results early on, or show a low DLCO (a measure of how well oxygen moves into the blood), or even a “restrictive” pattern where total lung volumes are low [1][5]. A low DLCO or restrictive pattern should prompt your doctor to consider a coexisting parenchymal or vascular disease.
The CT Scan: Looking for the “Mosaic”
A standard CT scan might miss the subtle signs of bronchiolitis obliterans. Specialists use High-Resolution CT (HRCT), which takes very detailed “slices” of the lung [5].
Mosaic Attenuation
The most famous finding on an HRCT for this condition is mosaic attenuation. This looks like a patchwork quilt on your scan, with some areas appearing darker (greyer) and some lighter [6].
- Darker areas: These often represent regions where air is trapped or blood flow is reduced [7].
- However, darker areas are not automatically diseased and lighter areas are not necessarily healthier. Regional perfusion, parenchymal disease, and scan technique can create this appearance. Patients should not self-interpret the scan without a specialist.
Why “Expiratory” Images Matter
To help support the diagnosis, your radiologist might evaluate images while you are breathing in (inspiratory) and after you have breathed all your air out (expiratory) [5]. If the “patchwork” pattern becomes more obvious on the expiratory images, it supports air trapping—a sign that the tiny airways are failing to let air escape [8][9]. Expiratory air trapping supports small airway disease but does not confirm bronchiolitis obliterans on its own, as asthma or hypersensitivity pneumonitis can also cause it.
The Role of Biopsy: Is it Necessary?
A lung biopsy involves taking a small piece of tissue to look at under a microscope. While this is the only way to see the scarring directly, it is not always required.
- Transbronchial Biopsy (TBB): This is done during a bronchoscopy (a camera down the airway). Because the scarring in this disease is “patchy,” these tiny samples often miss the affected areas, leading to inconclusive results [10][5].
- Surgical Lung Biopsy: This is a more invasive surgery that provides larger samples. However, yield varies by population and pathology expertise [10]. Because it carries patient-specific risks—such as a collapsed lung or a flare-up of symptoms—multidisciplinary teams often avoid it if your PFTs and CT scans already strongly point to the diagnosis [2][11].
Diagnostic Completeness Checklist
When reviewing your records, ensure these elements have been addressed to confirm the diagnosis and rule out “mimics” like asthma or hypersensitivity pneumonitis [6][5]:
| Test Component | What to Look For |
|---|---|
| PFTs | Evidence of obstruction that doesn’t fully “reverse” with an inhaler [2]. |
| Lung Volumes | Measurement of Residual Volume (RV) to check for air trapping [4]. |
| HRCT Imaging | Expiratory views are often helpful to accurately assess air trapping [5]. |
| Clinical History | Documentation of past infections, toxic exposures, or autoimmune symptoms [8]. |
| Differential | Confirmation that other diseases like COPD, DIPNECH (a rare neuroendocrine lung condition), or vascular disease have been ruled out [6]. |
Common questions in this guide
What does a low FEV1/FVC ratio mean in bronchiolitis obliterans?
What does a high residual volume mean on my lung function test?
Why does my CT report mention expiratory images or air trapping?
Is mosaic attenuation on a CT scan specific to bronchiolitis obliterans?
Do I always need a lung biopsy to diagnose bronchiolitis obliterans?
What other conditions should be ruled out before diagnosing bronchiolitis obliterans?
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References
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Various Bronchiolar Lesions Accompanied by Idiopathic Pleuroparenchymal Fibroelastosis with a Usual Interstitial Pneumonia Pattern Demonstrating Acute Exacerbation.
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This page explains PFT and HRCT findings in non-transplant-related bronchiolitis obliterans for informational purposes only and does not constitute medical advice. Your pulmonologist and radiologist should interpret your reports and discuss whether biopsy is appropriate.