An aneurysm is a localized bulge or weakening in the wall of a blood vessel. A pulmonary artery aneurysm (PAA) is a specific, rare condition where this abnormal dilation occurs in the pulmonary artery, the main vessel connecting the right side of the heart to the lungs. This artery carries deoxygenated blood to the lungs to be refreshed with oxygen. While exceedingly rare, with an estimated prevalence of less than 0.008% in autopsy series, PAA is a potentially life-threatening condition due to the risk of rupture or dissection. Management is important because the mortality rate associated with rupture can be very high.
Defining a Pulmonary Artery Aneurysm
The pulmonary artery begins at the heart’s right ventricle and branches into the right and left pulmonary arteries, supplying blood to each lung. A true pulmonary artery aneurysm is defined as a focal dilation that involves all three layers of the arterial wall: the inner intima, the middle media, and the outer adventitia. This contrasts with a pseudoaneurysm (false aneurysm), which is a collection of leaking blood contained by surrounding tissue and does not involve all three vessel layers, often posing a higher and more immediate risk of rupture.
Physicians often define a PAA by its size, though a single universally accepted measurement is not yet established. While the upper limit of a normal main pulmonary artery diameter is about 29 millimeters on a CT scan, many experts consider a diameter exceeding 40 millimeters to be a true aneurysm, differentiating it from simple dilation. The majority of these aneurysms (approximately 89%) are located centrally, affecting the main pulmonary artery trunk rather than the smaller branches inside the lungs.
Primary Causes and Risk Factors
The development of a pulmonary artery aneurysm is categorized into congenital and acquired causes. Congenital causes are present at birth and often involve heart defects that alter blood flow and pressure. Increased blood flow from a left-to-right shunt, such as a patent ductus arteriosus or a ventricular septal defect, creates hemodynamic stress that weakens the arterial wall over time, leading to aneurysm formation.
The most frequently acquired cause is pulmonary hypertension, characterized by high blood pressure in the pulmonary arteries. This sustained, excessive pressure physically stresses the artery wall, causing it to stretch and dilate. Infections are another significant acquired cause, resulting in mycotic aneurysms, where bacterial or fungal agents like pyogenic bacteria or syphilis directly damage the vessel wall. Tuberculosis can also cause a specific type of pseudoaneurysm (Rasmussen aneurysm) in the lung branches. Other risk factors include inflammatory conditions like vasculitis (e.g., Behçet disease) and, less commonly, direct blunt or penetrating trauma to the chest, which typically results in a pseudoaneurysm.
Recognizing the Physical Signs
Many pulmonary artery aneurysms are asymptomatic and are often discovered incidentally during imaging for other issues. When signs do appear, they are often non-specific and related to the aneurysm’s size or the underlying condition, such as pulmonary hypertension. The most common manifestations include shortness of breath (dyspnea) and chest pain.
A large aneurysm can compress nearby structures, potentially leading to a persistent cough or hoarseness if the recurrent laryngeal nerve is affected. In severe cases, the patient may experience hemoptysis (coughing up blood), a serious sign that may indicate impending rupture. Other signs, such as palpitations or fatigue, are commonly associated with the heart failure that can result from the underlying cause.
Diagnosis and Treatment Approaches
The diagnostic process typically begins with advanced medical imaging. Computed Tomography Angiography (CTA) is the primary method, providing detailed, cross-sectional images that delineate the size, location, and extent of the aneurysm. Echocardiography is frequently employed to assess the heart’s function, especially the right ventricle, and to evaluate blood flow velocity and pressure within the pulmonary arteries. Magnetic Resonance Imaging (MRI) may be used as a supplementary tool to gather additional information, such as blood flow direction or the presence of inflammation.
Treatment decisions are highly individualized and depend significantly on the aneurysm’s size, the presence of physical signs, and the underlying cause. For small, asymptomatic aneurysms, a conservative approach involving watchful waiting and regular imaging follow-up may be recommended. The primary goal of this management is to monitor for any growth or the development of complications.
For larger aneurysms (generally exceeding 55 to 60 millimeters in diameter) or those causing significant symptoms like hemoptysis or compression, surgical intervention is often necessary due to the increased risk of rupture. Surgical repair typically involves resecting the affected portion of the pulmonary artery and replacing it with a synthetic graft or a patch. A key component of the treatment plan is managing the underlying cause, such as aggressive control of pulmonary hypertension or treating any infectious source. Endovascular therapy, a less invasive technique using catheters to deploy stents or coils, is sometimes an option, particularly for certain types of pseudoaneurysms.