Apical pleural parenchymal scarring forms at the tops of the lungs through a combination of mechanical stress, prior infections, inflammatory conditions, and sometimes no identifiable cause at all. It is one of the most common incidental findings on chest CT scans, turning up in a surprisingly large fraction of the population. The scarring itself is usually harmless, but certain underlying causes deserve attention, and telling the difference between a benign old scar and something progressive matters for what comes next.
How Common Is Apical Scarring
If you have ever been told about scarring at the tops of your lungs after a routine CT scan, you are far from alone. A study examining 780 chest CTs found that apical pleuroparenchymal scarring was present in roughly two-thirds of scans, with the vast majority classified as mild.1PubMed. Incidental Apical Pleuroparenchymal Scarring on Computed Tomography: Diagnostic Yield, Progression, Morphologic Features and Clinical Significance That number sounds alarmingly high, but it reflects how sensitive modern CT imaging has become at picking up subtle changes that older chest X-rays would have missed entirely.
A separate study looking specifically at a healthy screening population of nearly 2,900 people found a lower but still meaningful prevalence of about 5.5%. The rate climbed steadily with age: roughly 1.6% in those between 20 and 39, about 4% in the 40-to-59 group, and around 8% in people 60 and older.2PubMed. Clinical Characteristics and Prevalence of Apical Scarring at Chest CT in a Healthy Population The gap between the two studies largely comes down to who was being scanned and how strictly the scarring was defined, but the pattern is clear: apical scarring becomes more common as you age, and most people who have it never knew about it until someone happened to image their chest.
Why the Tops of the Lungs Are Vulnerable
The lung apex sits in a mechanically unusual position. It is wedged up behind the collarbone, pressed against the first rib, and suspended from the top of the chest cavity in a way that exposes it to forces the rest of the lung does not experience. Gravity pulls the bulk of the lung tissue downward, which stretches and distorts the uppermost portion. The alveoli at the apex end up larger and more inflated than those at the base, and the pleural lining that wraps the lung experiences higher stress in this region.
Research into the biomechanics of the apex has found that physical stress creates a negative circumferential force within the visceral pleura, enough to cause tissue tearing or destruction over time. The distortion of the lung under its own weight contributes to this, making the apex inherently prone to microscopic damage and repair.3Journal of Infectious Diseases and Epidemiology. Common Pathophysiological Pathways for Apical and Upper Lobe Lung Disease These pleural stress levels are not the same in everyone. They are highest in young men with low body mass index, whose taller, narrower chest walls amplify the forces acting on the apex. That mechanical vulnerability can promote the growth of air-filled blebs or bullae in the apex, which in turn can limit the clearance of inhaled material and set the stage for infection or rupture.4PubMed. A biomechanical hypothesis for the pathophysiology of apical lung disease
The blood supply to the apex adds another layer of vulnerability. Because the apex sits at the highest point of the chest, blood flow to this region is lower relative to other parts of the lung, particularly when a person is upright. Reduced perfusion means less efficient immune surveillance and slower clearance of pathogens. This is one reason tuberculosis classically sets up shop in the upper lobes: the apex offers a relatively oxygen-rich, low-blood-flow environment that favors certain organisms.
What the Scarring Actually Looks Like
When pathologists examine apical scarring under a microscope, they find a fairly consistent picture. The scars tend to be pyramid-shaped, sitting just beneath the pleural surface with adhesions and thickened patches of the pleura on top. Inside the scar, dense fibrosis replaces normal lung tissue, filling the air spaces with old, mature collagen. The underlying elastic framework of the lung gets compressed and folded, with the elastic fibers curling up in an accordion-like pattern.5PubMed. Pulmonary apical cap: a distinctive but poorly recognized lesion in pulmonary surgical pathology
This description applies to the “apical cap,” which is the most benign and common form of apical scarring. Apical caps are often bilateral and symmetric, becoming thicker with age. In some people, what looks like scarring on imaging actually includes a component of extrapleural fat that has descended because scarring has retracted the upper lobes slightly. The practical point is that the histology of a garden-variety apical cap looks like old, burned-out fibrosis with no active inflammation, which is why these findings are almost always left alone clinically.
Prior Infections
Tuberculosis is probably the best-known cause of apical scarring and the one doctors think of first, particularly when the scarring is unilateral or asymmetric. TB preferentially attacks the upper lobes because of the combination of high oxygen tension and low blood flow described above. Once the immune system walls off the infection, it leaves behind calcified granulomas and bands of fibrosis that can persist for a lifetime. Even people who were successfully treated decades ago often carry visible scars at the apex.
Fungal infections can produce a nearly identical pattern. Histoplasmosis and coccidioidomycosis are the most common culprits in certain geographic regions, and like TB, they often resolve into scarred-over remnants in the upper lobes. Bacterial lung infections, including community-acquired pneumonia that happened to affect the upper lobes, can also leave behind focal scarring, though this is less typical than with mycobacterial or fungal disease.
The challenge is that the end result of all these infections can look the same on a CT scan: irregular pleural thickening and parenchymal fibrosis at the apex. Without a clear history of past infection, biopsy, or old comparison imaging to show stability, it can be difficult to pin the scarring to a specific organism. In many cases, it is treated as a presumptive post-infectious scar based on the clinical story.
Ankylosing Spondylitis
Ankylosing spondylitis, a chronic inflammatory condition that primarily affects the spine and sacroiliac joints, has a well-documented relationship with apical lung disease. The lung involvement typically takes the form of fibrobullous changes at the apices: fibrosis, nodules, and eventually cyst or cavity formation in the upper lobes. It was first described in 1941 and has been better characterized since chest CT became widely available. The condition overwhelmingly affects men, with a male-to-female ratio reported as high as 50 to 1, and it tends to develop in patients who have had the spinal disease for a long time.6PubMed Central. Apical fibrobullous lung disease in ankylosing spondylitis: case report and literature review
The fibrobullous lung disease in ankylosing spondylitis typically starts as unilateral or asymmetric scarring but progresses over time to involve both upper lobes. The nodules can coalesce, cavities can form, bronchiectasis can develop, and the fibrosis can spread.7PubMed. Pulmonary manifestations of ankylosing spondylitis The progression is usually slow, sometimes unfolding over decades, but it is clinically significant because the cavities can become colonized by fungi, particularly Aspergillus, creating a secondary infection problem on top of the structural damage.
Apical pulmonary fibrosis is estimated to affect somewhere between 1% and 5% of people with ankylosing spondylitis, with higher rates in smokers and those with longstanding disease.8American Journal of Respiratory and Critical Care Medicine. A40-14 Breathless at the Top: Apical Pulmonary Fibrosis in Ankylosing Spondylitis Because the imaging can closely mimic tuberculosis, there is a history of misdiagnosis in both directions: patients with TB being worked up for ankylosing spondylitis and vice versa. The clinical context, particularly the presence of chronic back pain, limited spinal mobility, or known HLA-B27 positivity, usually sorts it out.
Sarcoidosis
Sarcoidosis is a granulomatous inflammatory disease that can affect almost any organ but hits the lungs and lymph nodes most often. When sarcoidosis progresses to fibrosis, it tends to concentrate in the upper and central parts of the lungs rather than the bases. About 5% of patients with sarcoidosis develop pulmonary fibrosis, and it carries a significantly increased mortality risk compared to sarcoidosis that resolves or remains stable.9PubMed Central. Pulmonary fibrosis in sarcoidosis
On imaging, the fibrosis from sarcoidosis has a distinctive pattern. It develops along the bronchovascular bundles with reticulations, traction bronchiectasis, and sometimes honeycombing. As the fibrosis progresses, consolidation can form centrally in the direction of lymph flow and peripherally along the pleural surface, sometimes producing lesions that look remarkably like pleuroparenchymal fibroelastosis. Traction bronchiectasis can create peripheral cysts, and all of these changes together contribute to upper-lobe volume loss.10PubMed Central. Imaging Findings of Fibrosis in Pulmonary Sarcoidosis The result on a CT scan is apical scarring with architectural distortion, which can appear similar to the scarring caused by other upper-lobe-predominant diseases.
Occupational and Environmental Exposures
Asbestos exposure is best known for causing pleural plaques and mesothelioma, but it can also produce fibrosis predominantly affecting the upper lobes. In a study following asbestos-exposed workers, 40 patients developed lesions mainly concentrated in the upper parts of the lungs. All were men, ranging from their early 40s to late 70s, with an average latency of 34 years from first exposure. The average thickness of their apical pleural thickening was about 21 millimeters, well beyond what you would see in a typical benign apical cap. Biopsies showed varying degrees of asbestosis and nonspecific pleuritis, and in nearly every case the upper-lobe changes were part of a more widespread pattern of diffuse pleural and parenchymal fibrosis.11PubMed. Pleural and parenchymal fibrosis mainly affecting the upper lung lobes in persons exposed to asbestos
Although upper-lobe-predominant asbestosis is relatively uncommon compared to the more typical basal and lower-lobe pattern, it is important to recognize because it can mimic post-infectious scarring or other causes of apical fibrosis. An occupational history going back decades is the key clue. Other inhaled dusts, including silica and coal dust, can also cause upper-lobe fibrosis, though these exposures produce their own recognizable patterns that usually involve visible nodules in addition to scarring.
Pleuroparenchymal Fibroelastosis
Pleuroparenchymal fibroelastosis, or PPFE, is a distinct form of lung fibrosis that primarily targets the upper lobes and the pleural surfaces, producing dense scarring with a characteristic elastic fiber component. Most cases are classified as idiopathic, meaning no clear cause is found, but the condition has been linked to a variety of predisposing factors including prior chemotherapy, bone marrow transplantation, recurrent infections, and autoimmune disease.12PubMed Central. The similarities and differences between pleuroparenchymal fibroelastosis and idiopathic pulmonary fibrosis
What makes PPFE relevant to anyone reading about apical scarring is that it can be the explanation for progressive upper-lobe fibrosis that does not fit neatly into the TB, sarcoidosis, or autoimmune categories. The clinical course resembles idiopathic pulmonary fibrosis in many ways, with gradual worsening of lung function over time. Pathologically, PPFE features intense fibrosis of the visceral pleura, prominent subpleural fibroelastosis that fills the peripheral lung tissue with dense collagen and elastic fibers, and relative sparing of the deeper parenchyma away from the pleural surface.13CHEST. Idiopathic Pleuroparenchymal Fibroelastosis: A Descriptive Study The affected patients often develop a flattened chest appearance as the upper lobes shrink, along with progressive breathlessness and weight loss.
PPFE is probably underdiagnosed because the imaging overlap with common apical scarring is significant. A radiologist seeing mild bilateral apical thickening might call it a benign apical cap when in fact the patient has early PPFE that will progress. The distinction usually requires either serial imaging showing interval worsening or, in some cases, surgical lung biopsy.
When Apical Scarring Warrants Further Investigation
Most apical scarring found incidentally on a CT scan does not require any treatment or even follow-up. The typical apical cap is thin, symmetric, and stable over time. But certain features should prompt your doctor to look more carefully:
- Asymmetry: Unilateral or markedly asymmetric scarring is more concerning for a prior focal process like TB, a fungal infection, or early fibrobullous disease from ankylosing spondylitis.
- Thickness over 5 mm: Apical pleural thickening greater than about 5 millimeters starts to push beyond the benign cap range and warrants at least comparison with prior imaging.
- Cavitation or cysts: Air-filled spaces within the scarring suggest either active or prior cavitary infection, or progressive fibrobullous disease that could become colonized by fungi.
- Progression on serial scans: Apical caps that are clearly enlarging over months or years raise the possibility of PPFE, progressive sarcoidosis, or, less commonly, a malignant process like a Pancoast tumor at the lung apex.
- Associated symptoms: Chronic cough, breathlessness, or weight loss in someone with apical scarring changes the clinical significance. An isolated finding on imaging is very different from a finding accompanied by symptoms.
The study examining incidental apical scarring in healthy individuals found age-stratified prevalence rates that help put a new finding in context: if you are over 60, mild bilateral apical thickening is common enough that it often needs nothing more than a note in your chart.2PubMed. Clinical Characteristics and Prevalence of Apical Scarring at Chest CT in a Healthy Population If you are 25 and have the same finding, it is less expected and deserves a closer look at the possible causes.
The Role of Smoking and Emphysema
Smoking contributes to apical scarring through a slightly indirect route. Paraseptal emphysema, a form of lung destruction that disproportionately affects the periphery and apex of the upper lobes, is strongly associated with smoking. The destroyed alveolar walls leave behind thin-walled air spaces along the pleural surface, and the surrounding tissue can develop reactive fibrosis as it attempts to stabilize. Over time, the combination of emphysematous destruction and fibrotic repair produces a mixed pattern of apical scarring and bullous change that can be difficult to untangle from other causes.
Smoking also independently increases the risk of apical fibrosis in people who already have predisposing conditions. In ankylosing spondylitis, for example, smokers develop apical fibrobullous disease at higher rates than nonsmokers.8American Journal of Respiratory and Critical Care Medicine. A40-14 Breathless at the Top: Apical Pulmonary Fibrosis in Ankylosing Spondylitis The mechanical damage that smoking inflicts on the already-vulnerable apex likely compounds whatever inflammatory or autoimmune process is happening underneath.
Radiation Therapy and Other Iatrogenic Causes
Radiation delivered to the chest, particularly for cancers involving the mediastinum or breast, can cause fibrosis in whatever portion of the lung falls within the radiation field. When the treatment targets structures near the top of the chest, the resulting scarring concentrates in the apex. Unlike the other causes discussed above, radiation fibrosis develops in a geographic pattern that corresponds to the radiation portal rather than following the natural anatomy of the lung. It typically appears within six months to two years after treatment and then stabilizes, though it can slowly progress over decades in some patients.
Chemotherapy agents, particularly alkylating agents and bleomycin, can also cause lung fibrosis, and PPFE has been reported as a late complication in patients who underwent bone marrow transplantation. These iatrogenic causes are usually straightforward to identify because the medical history points directly to the exposure, but they occasionally surface years later in a patient who has forgotten or not mentioned a distant treatment history.
Age-Related Apical Changes and the “Normal” Apex
One of the hardest things about interpreting apical scarring is deciding what counts as normal aging versus pathology. The lung apex changes over a lifetime. The mechanical stresses described earlier accumulate, minor inflammatory episodes come and go, and the pleura gradually thickens. The rising prevalence with age found in healthy populations, from under 2% in younger adults to about 8% in those over 60, reflects this cumulative process.2PubMed. Clinical Characteristics and Prevalence of Apical Scarring at Chest CT in a Healthy Population
Extrapleural fat deposition adds another variable. In some people, particularly those who are older or overweight, fat accumulates in the extrapleural space at the apex and can mimic or exaggerate the appearance of pleural thickening on CT. A radiologist experienced in chest imaging can usually distinguish fat from true fibrosis based on the density of the tissue on the scan, but the distinction is not always obvious, and it contributes to the high frequency with which apical “scarring” is reported.
The biomechanical hypothesis offers a useful framework for thinking about this. The apex is under the greatest mechanical stress, has the poorest blood flow, and sits in an anatomical corner that traps inhaled particles less efficiently than the well-ventilated middle and lower lobes. Every insult the lung experiences over a lifetime, whether from infection, inflammation, environmental exposure, or simple wear and tear, leaves its heaviest mark at the top. In most people, the result is a thin stripe of scarring that never causes symptoms and never progresses. In a smaller subset, the scarring reflects a more serious underlying process that deserves to be identified and monitored.