A dilated pulmonary artery means the main blood vessel carrying blood from the heart to the lungs has widened beyond its normal diameter. In most cases, this signals elevated pressure in the lung circulation, a condition called pulmonary hypertension, though the list of possible causes is longer and more varied than many people realize. Some people learn about it after a CT scan done for an entirely different reason, and the finding can range from clinically meaningless to urgently important depending on context.
How Doctors Define and Measure It
The main pulmonary artery in a healthy person measures roughly 27 mm across, though that number depends on your sex. A large study using cardiac CT in the Framingham Heart Study established sex-specific reference values: about 29 mm for men and 27 mm for women mark the upper boundary of normal.1PubMed Central. Reference values for normal pulmonary artery dimensions by noncontrast cardiac computed tomography: the Framingham Heart Study An older but widely cited CT study found the average main pulmonary artery diameter in healthy subjects was about 27 mm, and proposed that anything above roughly 33 mm should raise suspicion for pulmonary hypertension, with high specificity at that cutoff.2PubMed. CT measurement of main pulmonary artery diameter A severity classification system grades dilation as mild, moderate, or severe: mild starts just above the sex-specific normal range and extends to about 31 mm, moderate covers 31 to 34 mm, and severe is anything above 34 mm.3Journal of Cardiovascular Computed Tomography. Severity classification of main pulmonary artery diameter on computed tomography for diagnosis and prognostic implications in pulmonary hypertension
Body size, age, and sex all influence what counts as “dilated” for a given individual. Pulmonary artery size varies with height, weight, and body surface area, so a tall, large-framed person may have a wider artery that is still perfectly normal for them.4European Respiratory Journal. Pulmonary artery diameter to predict pulmonary hypertension in pulmonary sarcoidosis This is one reason radiologists rarely rely on the artery’s absolute width alone.
The Pulmonary Artery-to-Aorta Ratio
Rather than looking at the pulmonary artery in isolation, many clinicians compare it to the aorta on the same CT slice. If the pulmonary artery is wider than the aorta, the ratio exceeds 1.0, and that is generally considered abnormal. This ratio helps control for differences in body size and scanning technique. In a study of patients with heart failure, the pulmonary artery-to-aorta ratio showed the strongest correlation with actual measured pressures in the lungs and was independently tied to survival outcomes.5PubMed Central. Pulmonary artery to aorta ratio for the detection of pulmonary hypertension: cardiovascular magnetic resonance and invasive hemodynamics in heart failure with preserved ejection fraction
The ratio is not foolproof, though. A recent population-based analysis found that the ratio is influenced by aortic diameter itself, and the aorta tends to widen with age, high blood pressure, and atherosclerosis. That means an older person with an enlarged aorta might have a falsely reassuring ratio even if their pulmonary artery is genuinely dilated.6Academic Radiology. Revisiting the Clinical Interpretation of CT-Measured Pulmonary Artery-to-Aorta Ratio—The Rotterdam Study Neither the raw diameter nor the ratio alone can confirm pulmonary hypertension with certainty. A comprehensive review noted that while pulmonary artery dilation is suggestive of pulmonary hypertension, available data remain inconclusive about its ability to accurately predict the condition on its own.7PubMed Central. Significance of Main Pulmonary Artery Dilation on Imaging Studies The gold standard is still right heart catheterization, an invasive test that directly measures pressures inside the lung vessels.
Pulmonary Hypertension as the Most Common Cause
The single most frequent reason for a dilated pulmonary artery is pulmonary hypertension, which simply means chronically elevated blood pressure in the lung circulation. When pressures rise, the artery walls experience greater stress. Over time, the vessel responds by remodeling: the walls thicken with extra collagen and elastin, smooth muscle cells change their behavior, and the artery gradually stretches wider.7PubMed Central. Significance of Main Pulmonary Artery Dilation on Imaging Studies This remodeling is the body’s attempt to cope with the extra mechanical load, but it eventually contributes to stiffening and dysfunction of the vessel.
Pulmonary hypertension itself is not a single disease. It has many causes: left-sided heart failure that backs pressure up into the lungs, chronic lung diseases like COPD or interstitial fibrosis, blood clots that never fully dissolved, autoimmune conditions that scar the small lung vessels, and a primary form where the small arteries narrow for reasons that are still not completely understood. All of these can produce the same downstream effect of a widened main pulmonary artery on a CT scan.
Chronic Blood Clots and Thromboembolic Disease
One cause that deserves its own mention is chronic thromboembolic pulmonary hypertension, or CTEPH. This develops when blood clots in the lung arteries fail to dissolve completely after a pulmonary embolism. The organized scar tissue left behind obstructs blood flow in the larger and mid-sized pulmonary vessels, forcing pressures higher in the remaining open circulation. The failure of clots to resolve may be related to problems with the body’s clot-dissolving system or underlying blood disorders.8European Respiratory Review. The pathophysiology of chronic thromboembolic pulmonary hypertension CTEPH is treatable, sometimes even curable with surgery to remove the organized clot material, which makes it especially important not to miss.
Congenital Heart Defects
Certain heart defects present from birth can widen the pulmonary artery over years. The classic example is an atrial septal defect, a hole between the heart’s upper chambers. Blood shunts from the higher-pressure left side to the right side and then into the lungs, flooding the pulmonary circulation with more flow than it was designed to handle. That excess flow creates shear stress on the vessel lining, which triggers smooth muscle growth and progressive distortion of the pulmonary vessels. If left uncorrected long enough, the resistance in the lung vessels can climb so high that blood flow reverses direction through the defect, leading to low oxygen levels and a condition known as Eisenmenger syndrome.9PubMed Central. Atrial septal defects and pulmonary arterial hypertension
Connective Tissue and Valve Problems
People with Marfan syndrome, a genetic condition affecting the body’s connective tissue, frequently have a dilated pulmonary artery root. The widening tracks with the severity of aortic root dilation, reflecting the same underlying weakness in the elastic tissue of the arterial wall.10PubMed Central. Pulmonary artery root dilatation in Marfan syndrome: quantitative assessment of an unknown criterion In these patients, the dilation is not driven by high pressure but by structural fragility of the vessel itself.
Pulmonary valve stenosis, a narrowing of the valve at the exit of the right ventricle, causes a different kind of dilation. Blood accelerating through the tight valve opening hits the pulmonary artery wall in a high-velocity jet, and the artery balloons out downstream of the obstruction. This “post-stenotic dilation” can look dramatic on imaging, but its size does not always correspond to the severity of the valve narrowing.11PubMed Central. Pulmonary Valve Stenosis: From Diagnosis to Current Management Techniques and Future Prospects
Inflammatory and Infectious Causes
Inflammatory conditions that attack blood vessel walls can produce localized ballooning of the pulmonary artery, sometimes forming true aneurysms. Behçet’s disease, a chronic inflammatory condition affecting the vasculature, is a well-recognized cause, and pulmonary artery aneurysms are actually the leading cause of death in Behçet’s patients.12PubMed Central. Pulmonary Artery Aneurysm in Behcet Disease: Medical, Endovascular or Surgical Intervention Infections can also weaken the artery wall. In one documented case, a fungal lung abscess eroded into a lobar pulmonary artery, forming an aneurysm that ruptured fatally.13PubMed Central. Pulmonary artery aneurysm rupture These scenarios are rare but illustrate why clinicians take unexplained pulmonary artery dilation seriously.
When It Turns Out to Be Nothing
Not every dilated pulmonary artery signals disease. In a minority of patients, the artery is simply wider than average with no identifiable cause, a condition called idiopathic dilation of the pulmonary artery. Most of these individuals are asymptomatic, and studies suggest the condition is generally benign. In one series, about two-thirds of patients with idiopathic dilation had no symptoms at all, and all had normal heart and lung function. Most reported cases have seen patients surviving into their sixties or seventies without complications.14PubMed Central. Idiopathic dilatation of pulmonary artery: A review Management is primarily surveillance with periodic imaging. Surgery enters the conversation only if the artery grows beyond about 6 cm, at which point the risk of rupture or dissection becomes a concern.15CHEST. Idiopathic Dilation of the Pulmonary Artery
Athletes represent another population where a wider pulmonary artery may be perfectly normal. Endurance training enlarges the heart chambers and increases blood flow through the lungs, and the pulmonary artery appears to adapt accordingly. One study found that male athletes had significantly larger pulmonary arteries than sedentary controls, with about 22% of athletes exceeding 27 mm compared to just 7% of non-athletes.16Heart. Is pulmonary artery dilatation part of the athletic adaptation to exercise? Separate research confirmed that athletes of both sexes show increased pulmonary artery dimensions alongside the well-known enlargement of heart chambers, supporting the idea that the pulmonary vasculature remodels as part of the overall cardiopulmonary adaptation to regular intense exercise.17PubMed. Exercise-induced cardio-pulmonary remodelling in endurance athletes: Not only the heart adapts If you are a competitive endurance athlete and a radiologist flags your pulmonary artery as mildly enlarged, that context matters enormously.
Symptoms a Dilated Pulmonary Artery Can Cause
In the Framingham study, people whose pulmonary artery was at or above the 90th percentile were more likely to report shortness of breath with exertion.1PubMed Central. Reference values for normal pulmonary artery dimensions by noncontrast cardiac computed tomography: the Framingham Heart Study Most symptoms, however, come from whatever is driving the dilation rather than from the enlarged artery itself. If pulmonary hypertension is the cause, you might notice progressive breathlessness, fatigue, chest tightness, or lightheadedness during activity.
One unusual symptom worth knowing about is hoarseness. A significantly dilated pulmonary artery can compress the left recurrent laryngeal nerve, which loops around the aortic arch right next to the pulmonary artery. When the artery pushes upward into the space between itself and the aorta, it squeezes this nerve against the aorta. Because the nerve controls the muscles of the voice box, the result is a chronically hoarse voice, a condition called Ortner’s syndrome or cardiovocal syndrome.18PubMed Central. Ortner’s syndrome: Hoarseness of voice revealing severe secondary pulmonary hypertension In children with congenital heart defects, the same mechanism can cause hoarseness, breathing difficulty, and even feeding problems.19Journal of Pediatric Surgery Case Reports. Cardiovocal syndrome due to a dilated pulmonary artery The nerve gets trapped as the left pulmonary artery shifts upward, erasing the normal gap between the pulmonary artery and the aorta.20PubMed Central. Ortner’s Syndrome (Cardiovocal Syndrome): A Case Report It is rare, but if you have unexplained hoarseness alongside known heart or lung disease, it is worth mentioning to your doctor.
What It Predicts in People With COPD
For people with chronic obstructive pulmonary disease, a dilated pulmonary artery carries particular prognostic weight. A landmark study published in the New England Journal of Medicine found that a pulmonary artery-to-aorta ratio greater than 1 was the single strongest predictor of severe COPD exacerbations, outperforming other established risk markers. People with this ratio had roughly three to five times the odds of a severe flare-up compared to those with a normal ratio.21PubMed Central. Pulmonary arterial enlargement and acute exacerbations of COPD The finding held in both the original trial and an independent validation group. Beyond exacerbations, the ratio also predicts mortality in people without previously known heart or lung disease, suggesting that pulmonary artery enlargement is a broader marker of cardiovascular stress.22PubMed Central. Pathophysiology and clinical implications of pulmonary arterial enlargement in COPD
This is the kind of finding that can change clinical decisions. If your CT scan shows an enlarged pulmonary artery and you have COPD, your doctor might be more aggressive about preventing exacerbations with inhaler optimization, pulmonary rehabilitation, or closer follow-up.
Complications When the Artery Gets Very Large
Most dilated pulmonary arteries stay in the mild-to-moderate range and never cause structural emergencies. But when dilation progresses to aneurysm territory, the stakes change. A pulmonary artery aneurysm can compress nearby structures, cause blood clots to form along the abnormal wall, or in the worst case, rupture. Rupture of a pulmonary artery aneurysm is life-threatening and often fatal, as illustrated by case reports documenting sudden massive hemorrhage.13PubMed Central. Pulmonary artery aneurysm rupture
There are no universally agreed-upon guidelines for when to intervene surgically on a pulmonary artery aneurysm. In cases where severe pulmonary hypertension drives the dilation, the underlying pressure problem has to be addressed rather than the artery alone. For patients with very advanced disease combining a giant aneurysm, right heart failure, and severe valve leakage, combined heart-lung transplantation has been described as a viable option, though the rarity of the condition means treatment is decided case by case.23PubMed Central. Combined Heart-Lung Transplant for Pulmonary Artery Aneurysm Secondary to Pulmonary Arterial Hypertension
The Workup After an Incidental Finding
Many people first learn about a dilated pulmonary artery from a CT scan ordered for something else entirely, perhaps a scan to check for a blood clot, evaluate a lung nodule, or assess chest pain. The presentation can range from incidental and chronic to acute and life-threatening, depending on the underlying cause.24PubMed Central. Pulmonary Arterial Dilatation: Imaging Evaluation Using Multidetector Computed Tomography What happens next depends on the clinical picture. If you have no symptoms and no known heart or lung disease, your doctor may simply repeat imaging in six to twelve months and check for signs of pulmonary hypertension with an echocardiogram. If there are symptoms or other red flags, the workup typically escalates to include blood tests for autoimmune and clotting disorders, a ventilation-perfusion lung scan to look for chronic clots, pulmonary function testing, and potentially right heart catheterization.
The goal is always to figure out whether the dilation reflects a treatable condition. Chronic blood clots can be surgically removed. Congenital defects can be repaired. Autoimmune-driven pulmonary hypertension responds to targeted medications. Even idiopathic pulmonary arterial hypertension, the most mysterious form, now has a growing arsenal of drugs that lower lung pressures and improve quality of life. The dilated artery on the scan is the signpost, not the destination. What matters is what you find when you follow it.
Why the Imaging Method Matters
CT is the most common tool for spotting a dilated pulmonary artery, but measurements can differ between imaging methods. An interesting finding from veterinary research, which often explores imaging comparisons more freely than human studies, showed that pulmonary artery-to-aorta ratios measured on CT during inspiration consistently overestimated the ratio compared to echocardiography.25PubMed. Computed tomographic measurement of the main pulmonary artery to aortic diameter ratio in healthy dogs: a comparison to echocardiographically derived ratios While this particular study was in dogs, the general principle applies to human imaging as well: the depth of your breath, whether contrast dye was used, and which imaging modality produced the measurement all affect the number your radiologist reports. A borderline measurement on one scan does not necessarily mean the same thing as a borderline measurement on another, and comparing numbers across different scans or different imaging techniques requires caution. If your doctor tells you the artery looks slightly enlarged on CT but normal on echocardiography, the discrepancy may reflect the measurement method as much as any real change in the artery itself.