Biapical pleural parenchymal scarring is a band or cap of fibrous tissue at the top of both lungs, involving both the lung’s outer lining (the pleura) and the lung tissue itself (the parenchyma). It shows up frequently on chest CT scans and X-rays, and in most cases it reflects old, healed injury from past infections, normal aging, or minor lung insults that resolved long ago. The term sounds alarming when it appears on a radiology report, but for the majority of people, it is a harmless finding that requires no treatment. The picture gets more nuanced when the scarring is unusually thick, progressing over time, or accompanied by symptoms like breathlessness or chronic cough.
Breaking Down the Terminology
Radiology reports pack a lot of information into compact phrases, and “biapical pleural parenchymal scarring” is a good example. “Biapical” simply means both apices, the pointed tops of the left and right lungs. “Pleural” refers to the thin double membrane that wraps around each lung and lines the inside of the chest wall. “Parenchymal” refers to the functional lung tissue itself, the spongy material where gas exchange happens. And “scarring” means that some of this tissue has been replaced by dense, fibrous connective tissue. So the full phrase describes scar tissue sitting at the tops of both lungs, straddling the boundary between the pleural lining and the underlying lung.
You may also see the term “apical cap” or “apical pleural thickening” used to describe the same or a closely related finding. An apical cap is a fibroelastic scar involving the visceral pleura and the lung parenchyma at the apex, and it is occasionally observed in healthy, asymptomatic people.1BioMed Central / Respiratory Research. Pleural thickening on screening chest X-rays: a single institutional study When the same kind of scarring appears at the top of both lungs rather than just one, it earns the “biapical” label.
How Common It Is and What It Looks Like on Scans
Apical pleural parenchymal scarring turns up on imaging far more often than most people realize. A study evaluating nearly 800 chest CT scans found that some degree of apical pleuroparenchymal scarring was present on about 65% of them. Among those cases, roughly half were classified as mild in the axial plane (less than 5 mm thick) and about 80% were mild in vertical extent (not reaching far down the lung). The predominant pattern was nodular and symmetric, meaning both sides looked similar.2PubMed. Incidental Apical Pleuroparenchymal Scarring on Computed Tomography: Diagnostic Yield, Progression, Morphologic Features and Clinical Significance That 65% figure is striking: it suggests that most adults walking around with normal lungs have at least a trace of scarring at the top of their lungs, and it just goes unnoticed until someone looks at a scan.
On a chest X-ray, biapical scarring typically appears as a thin, crescent-shaped opacity draped over the lung apices, sometimes called a “cap.” On CT, the detail is sharper. Radiologists can measure the thickness, assess whether the pattern is nodular (lumpy) or reticular (net-like), and judge how far down the lung the scarring extends. Most incidental findings are small, symmetric, and stable over time.
Why the Tops of the Lungs
The lung apices occupy a unique position. They sit above the first rib, tucked behind the collarbone, in a zone where blood flow is relatively low compared to the lung bases. Lower perfusion means the immune system’s ability to clear infections and inflammatory debris is slightly less efficient there. This is partly why tuberculosis, for instance, has a well-known preference for the upper lobes. The apices are also subject to slightly different mechanical stresses during breathing, and they receive less ventilation relative to their position. Over a lifetime, these minor disadvantages add up, making the lung tops a natural site for small scars to accumulate.
Common Causes
Biapical pleural parenchymal scarring has a long list of possible causes, but in practice a few categories account for most cases.
Aging
The single most common explanation is simply getting older. Apical caps, either on one side or both, are a well-recognized feature of advancing age and are usually the result of subpleural scarring unassociated with other diseases.3PubMed. The apical cap Over decades, minor lung insults, subclinical infections, tiny areas of inflammation from inhaled particles, and other small-scale events leave traces of scar tissue behind. By middle age, many people have accumulated enough of this to be visible on a scan. It is so common in older adults that radiologists often mention it as an expected finding rather than something requiring follow-up.
Past Infections
Tuberculosis is the classic infectious cause of upper-lobe scarring. Even after successful treatment, TB leaves a lasting footprint on the lungs. A study of patients who had completed TB treatment found that 90% showed parenchymal fibrosis and architectural distortion, with the most common pattern being bilateral upper-lobe involvement.4PubMed Central. Aftermath of pulmonary tuberculosis: computed tomography assessment The scarring left behind by healed TB can look nearly identical to age-related apical caps, which is why radiologists will sometimes note “changes consistent with old granulomatous disease” when they see biapical scarring in someone with a history of TB exposure. Other infections, including fungal diseases like histoplasmosis, can leave similar upper-lobe scars, though TB is the most studied culprit.
Autoimmune and Inflammatory Conditions
Ankylosing spondylitis, a form of inflammatory arthritis that primarily affects the spine and sacroiliac joints, is a recognized cause of apical fibrocystic lung disease. In ankylosing spondylitis, early lung involvement may start out unilateral or asymmetric, but most cases eventually develop bilateral apical fibrobullous lesions with progressive nodules, cyst and cavity formation, fibrosis, and bronchiectasis.5PubMed. Pulmonary manifestations of ankylosing spondylitis This particular complication is considered rare and tends to appear in advanced disease, but it is distinctive enough that lung apical scarring in a young person with back pain and stiffness should prompt further investigation.6PubMed Central. Apical fibrobullous lung disease in ankylosing spondylitis: case report and literature review
Radiation and Chemotherapy
Cancer treatments can also leave apical scarring as a long-term complication. A case documented in the chest medicine literature described a young adult treated for rhabdomyosarcoma with chemotherapy and radiation who developed progressive biapical pleural scarring over several years. Serial CT imaging showed the scarring starting as bilateral pleural-based thickening in the upper lobes, then gradually increasing with additional pleural thickening, new pulmonary nodules, and eventually paramediastinal opacities.7CHEST. Pleuroparenchymal Fibroelastosis as a Long-Term Complication of Chemotherapy and Radiation Therapy in a Young Adult With Rhabdomyosarcoma This kind of progressive post-treatment scarring is not the norm for most cancer survivors, but it illustrates how medical treatments that damage lung tissue can trigger an ongoing fibrotic response concentrated at the apices.
When Apical Scarring Might Be Something More Serious
The critical question with biapical scarring is whether it represents a stable, harmless scar or the early stage of a progressive fibrotic condition. The main concern is a disease called pleuroparenchymal fibroelastosis, or PPFE, which involves relentless thickening and stiffening of the pleura and upper-lobe lung tissue over months to years.
Telling the difference between a benign apical cap and early PPFE can be genuinely difficult, because the two look similar both on imaging and under a microscope. Several features help clinicians distinguish them. PPFE tends to exceed the expected size of a typical apical cap, which averages around 2.2 cm. It also tends to be progressive on serial scans, whereas a benign apical cap stays stable. And the progressive course of PPFE eventually leads to measurable loss of lung function and symptoms like breathlessness, chronic cough, and exercise intolerance, which starkly contrasts with the asymptomatic nature of a simple apical cap.8CHEST. Evolution of Pulmonary Apical Cap to Pleuroparenchymal Fibroelastosis After Surgical Lung Injury
There is also the question of whether a benign apical cap can sometimes evolve into PPFE. The same case report documented a patient whose initially unremarkable apical cap progressed to full-blown PPFE after a surgical lung injury, suggesting that in certain clinical contexts, existing apical scarring may serve as a “risk field” for more serious fibrotic disease. This is far from the usual outcome, but it does mean that a history of lung surgery or other significant lung insult alongside apical scarring may warrant closer monitoring.
What the Tissue Looks Like Under the Microscope
When pathologists examine apical cap tissue, they find a characteristic pattern. The scars are typically pyramid-shaped, sitting just beneath the pleural surface, with overlying pleural adhesions and dense plaques. The lung tissue within these scars has been replaced by dense, basophilic fibrosis (fibrosis that stains dark blue with standard dyes), with air spaces filled in by old, mature collagen. The underlying elastic framework of the lung is contracted in an accordion-like fashion, with curls of reduplicated elastic fibers stacked on top of each other.9PubMed. Pulmonary apical cap: a distinctive but poorly recognized lesion in pulmonary surgical pathology The fibrotic visceral pleura and pleural adhesions are also consistently present.8CHEST. Evolution of Pulmonary Apical Cap to Pleuroparenchymal Fibroelastosis After Surgical Lung Injury
What makes this pattern distinctive is how tightly the scarring bridges the pleura and the parenchyma. The scar is not just on the surface and not just deep in the lung; it spans both layers, which is why the radiological description uses the compound term “pleuroparenchymal.” This bridging architecture also explains why biopsy is occasionally needed to distinguish apical caps from other entities like mesothelioma or Pancoast tumors when the clinical picture is ambiguous.
Symptoms and Effects on Lung Function
Most people with biapical pleural parenchymal scarring have no symptoms at all. The scarring is discovered incidentally on a scan done for another reason, such as screening for lung cancer, evaluating chest pain, or checking for a pulmonary embolism. A thin cap of scar tissue at the lung apex simply does not take up enough functional lung tissue to affect breathing in a meaningful way.
Where symptoms come into play is when the scarring is extensive, progressive, or part of a broader disease process. If biapical scarring is accompanied by significant pleural thickening on both sides, the lungs may lose some of their ability to expand fully, particularly at the top. Over time, this can restrict lung volumes, a pattern called restrictive physiology. You might notice it as mild shortness of breath on exertion, or it might only show up on formal pulmonary function testing. In conditions like PPFE, the progression can eventually become severe enough to cause substantial breathing difficulty and reduced exercise tolerance.
Chronic cough is another symptom that occasionally accompanies apical scarring, though it is nonspecific and can have many other causes. One case report documented a patient with persistent cough whose follow-up high-resolution CT showed stable biapical pleuroparenchymal changes.10PubMed Central. HRCT Diagnosis of Pleuroparenchymal fibroelastosis: Report of two cases Whether the scarring itself was causing the cough or was coincidental remained an open question, as it often does in clinical practice.
What Happens After You See It on a Report
If a radiology report mentions biapical pleural parenchymal scarring and you have no symptoms, there is a good chance nothing needs to be done. Radiologists may describe the finding without recommending follow-up, especially if it looks thin, symmetric, and consistent with age-related change or old infection. Your doctor may ask about any history of tuberculosis exposure, past lung infections, autoimmune conditions, or occupational dust exposure to help contextualize the finding.
Follow-up imaging is more likely to be recommended when:
- The scarring is thick: anything over about 10 mm in axial thickness gets more attention than a 2-3 mm wisp.
- It is asymmetric: unilateral or notably lopsided scarring raises more concern than a symmetric bilateral pattern, because tumors like Pancoast tumors at the lung apex can mimic apical scarring.
- There are new symptoms: progressive breathlessness, unexplained cough, or chest wall pain alongside apical scarring may warrant further workup.
- It is growing: comparison with prior scans is one of the most useful tools. Scarring that was not present before or that has clearly increased suggests an active process rather than old, stable scar tissue.
When further evaluation is needed, the next step is usually a CT scan if the finding was initially seen on a chest X-ray, or a high-resolution CT if the initial scan was a standard CT. Pulmonary function tests can determine whether the scarring is affecting breathing mechanics. In rare cases where malignancy needs to be ruled out, a biopsy may be performed, though this is uncommon for classic-looking bilateral apical caps.
Apical Scarring in Former TB Regions
In populations where tuberculosis was historically widespread, biapical pleural parenchymal scarring carries a slightly different clinical weight. A person born in a country with high TB prevalence who now has bilateral apical scarring on a chest scan may well be looking at the footprint of a past infection, even one that resolved without formal treatment. The bilateral upper-lobe pattern seen in post-TB scarring, with fibrosis and architectural distortion, is so characteristic that radiologists often flag it specifically.4PubMed Central. Aftermath of pulmonary tuberculosis: computed tomography assessment
This matters for a practical reason: post-TB scarring can sometimes harbor residual organisms or create cavities that serve as a niche for secondary infections, including aspergilloma (a fungal ball that colonizes old TB cavities). It can also make future chest imaging harder to interpret, because new changes might be difficult to distinguish from old scarring. If you know you had TB or grew up in a region where it was common, keeping copies of your baseline chest imaging is genuinely useful. Having a comparison point lets radiologists more confidently call future scans “stable” versus “changed.”
Occupational and Environmental Considerations
While age and infection explain the majority of biapical scarring, occupational exposures can contribute. Long-term inhalation of mineral dusts, including silica and asbestos, can cause upper-lobe fibrosis, though these exposures more commonly produce their own distinctive patterns. Silicosis tends to cause nodules concentrated in the upper and middle lung zones, and asbestos-related disease is more associated with lower-lobe and pleural changes than with isolated apical scarring. Still, someone with decades of occupational dust exposure and biapical scarring may have a mixed picture in which environmental insults and age-related change overlap.
Cigarette smoking also deserves a mention. Smoking causes a range of upper-lobe-predominant lung diseases, including emphysema and respiratory bronchiolitis. While these are distinct from pleural parenchymal scarring, they can coexist with it, and the combination can complicate interpretation of imaging. A radiologist looking at a smoker’s CT with both emphysematous changes and apical scarring has to sort out which findings represent old scar, which represent smoking-related damage, and whether anything looks suspicious enough to warrant further evaluation.
Why the Distinction Between Pleural and Parenchymal Matters
Sometimes a radiology report will say “pleural thickening” without mentioning parenchymal involvement, or it will say “parenchymal scarring” without mentioning the pleura. The combined term “pleuroparenchymal” is reserved for scarring that genuinely spans both layers. This distinction is not just semantic. Isolated pleural thickening has a different set of associations, including asbestos exposure, prior empyema (pus in the pleural space), and prior surgery or chest tube placement. Isolated parenchymal scarring, on the other hand, points more toward old infection, inflammation, or radiation damage within the lung itself.
When both layers are involved, as in true pleuroparenchymal scarring, the bridging nature of the scar suggests a process that started at or near the pleural surface and extended inward, or one that began in the lung and reached outward to involve the pleura. The pathological studies showing pyramid-shaped scars anchored to the pleural surface with collagen-filled air spaces extending into the parenchyma support the idea that many of these scars grow from the outside in.9PubMed. Pulmonary apical cap: a distinctive but poorly recognized lesion in pulmonary surgical pathology For you as a patient, the practical takeaway is that “pleuroparenchymal” scarring is a specific descriptor, not a more alarming version of plain pleural thickening. It tells the radiologist where the scar sits anatomically, which helps narrow down the cause.