• On a frontal chest radiograph, the left heart border is typically formed by the appendage of the left atrium superiorly and the left ventricle inferiorly.
• A contour abnormality in the left atrial bay refers to a bulge or convexity in the expected location of the left atrial appendage, which can alter the normal straight or slightly concave appearance of this segment of the cardiac silhouette.

Comment

• A smooth enlargement along the superior left heart border, often referred to as a “third mogul sign,” is a key feature.
• While enlargement of the left atrial appendage (LAA) is a classic sign of rheumatic mitral valve disease, especially mitral stenosis, it can also be seen in other conditions.
• The differential diagnosis for a prominence in this region includes congenital aneurysm of the LAA, which is a rare anomaly.
• Other congenital conditions such as L-transposition of the great arteries (L-TGA) and juxtaposition of the atrial appendages can also produce an abnormal bulge along the upper left cardiac border.

Lipkin D, et al. British Heart Journal. 1983.

• Aneurysm of the LAA is an abnormal, localized, or diffuse dilatation of the left atrial appendage.
• It can be classified as congenital (more common) or acquired. It may also be classified as intrapericardial or extrapericardial.

• Congenital: Thought to be caused by dysplasia of the pectinate muscles within the LAA.
• Acquired: Often results from conditions that increase left atrial pressure, such as mitral valve disease. Other reported causes include syphilitic myocarditis and tuberculosis.

• The muscular wall of the appendage is weak, leading to dilatation. Histopathology often reveals fibrosis of the heart’s inner (endocardium) or middle (myocardium) layers.
• The enlarged, often dysfunctional, aneurysmal sac promotes blood stasis, which is a major risk factor for thrombus (blood clot) formation.
• Structural remodeling and electrical dissociation of the heart muscle cells within the aneurysm can create a substrate for arrhythmias.

• A saccular or diffuse enlargement of the LAA, which can vary significantly in size. The mean size has been reported as 7.8 x 5.9 cm.
• A large aneurysm can compress adjacent structures, such as the left ventricle or coronary arteries.

• Many patients are asymptomatic.
• When symptoms occur, they can include palpitations (most common), shortness of breath, and chest pain.
• The primary functional impacts are an increased risk of life-threatening complications like:
• Thromboembolism: Clots can form in the aneurysm and travel to the brain (causing a stroke) or other parts of the body.
• Arrhythmias: Atrial fibrillation or flutter are common due to the structural changes in the atrium.

• Chest X-ray: May show a bulge along the upper-left border of the heart silhouette or general heart enlargement (cardiomegaly).
• Echocardiography (TTE/TEE): This is a primary diagnostic tool. It shows a sac-like structure connected to the left atrium and can identify blood clots. Transesophageal echocardiography (TEE) often provides clearer images than transthoracic (TTE).
• CT Scan and MRI: These are used to confirm the diagnosis, precisely measure the aneurysm’s size, define its relationship to surrounding structures, and detect thrombi.

• Laboratory findings are generally within normal limits unless the patient is on anticoagulant medication.

• Surgical Resection: This is the most common treatment, even for asymptomatic patients, to prevent potentially fatal complications. The aneurysm can be surgically cut out (resected) or closed off (ligated).
• Medical Management: Anticoagulation (blood thinners) is used to prevent clot formation, especially in patients with arrhythmias or documented thrombus.
• Minimally Invasive Approaches: In some cases, catheter-based closure devices or minimally invasive surgery may be considered.

• The prognosis after surgical resection is generally excellent, with most patients showing improvement or remaining asymptomatic.
• Without treatment, the risk of life-threatening events such as stroke and lethal arrhythmias is significant.

• While rheumatic fever, the primary cause of mitral stenosis, is an inflammatory process, the enlargement of the LAA is predominantly a result of the hemodynamic consequences of the stenosis, not isolated inflammation of the appendage itself.

• This is the proposed pathophysiology for a congenital aneurysm of the LAA, not the enlargement seen in acquired mitral stenosis.

• Mitral stenosis creates a mechanical obstruction to blood flow from the left atrium (LA) to the left ventricle. This obstruction leads to a chronic elevation in LA pressure, causing the chamber, including its appendage, to dilate over time.
• Gupte, A. et al. StatPearls. 2023.

• This describes the mechanism of atrial enlargement in conditions like an atrial septal defect (ASD), which primarily causes right atrial and right ventricular volume overload. While some LA enlargement can occur, it’s not the primary mechanism associated with mitral stenosis.

• This defect results in a patent foramen ovale or an atrial septal defect, not the malpositioning of the entire atrial appendages.

• Juxtaposition of the atrial appendages is thought to result from abnormal rotation of the primitive cardiac tube during embryogenesis. Overtorsion can cause the left atrial appendage to move to the right (right juxtaposition), while undertorsion can lead to the right atrial appendage moving to the left (left juxtaposition).
• Agarwal, A. et al. Journal of the American College of Cardiology. 2017.

• This embryological error is the proposed cause for congenital absence of the pericardium.

• This leads to defects like truncus arteriosus or transposition of the great arteries, but it does not directly cause malposition of the appendages themselves, although they are often associated.

• Mitral stenosis is unlikely in this demographic without a history of rheumatic fever and typically presents with dyspnea on exertion. The constellation of ECG and X-ray findings is not classic for mitral stenosis.

• While this can cause a prominent LAA, the specific combination of cardiac levoposition, ECG findings, and a lucent area between the great vessels is not characteristic.

• L-TGA can present with a prominent upper left heart border, but this is due to the left-sided ascending aorta. The X-ray and ECG findings described in the question are more specific for another condition.

• The clinical picture of atypical chest pain, combined with classic ECG (RBBB, right axis deviation) and X-ray findings (levoposition, prominent pulmonary artery, and interposition of lung tissue between the aorta and pulmonary artery) is highly characteristic of partial congenital absence of the left pericardium, which allows the LAA to bulge outwards.
• Shah, A. et al. Cureus. 2022.

• This is not a recognized late complication of pericardiectomy. The findings of biatrial enlargement and septal bounce point to a global filling issue.

• Post-pericardiotomy syndrome is an acute inflammatory process that typically occurs in the first few weeks or months after surgery, characterized by fever, pleuritic pain, and effusions. It is not a chronic process presenting 5 years later.

• Incomplete surgical resection of the pericardium can lead to recurrent or residual constriction. The persistent signs of impaired diastolic filling, such as septal bounce and biatrial enlargement due to elevated filling pressures, are classic for this condition.
• Klautz, R. et al. Circulation. 1966.

• While mitral regurgitation can cause left atrial enlargement, it does not explain the biatrial enlargement or the characteristic diastolic septal bounce, which is a sign of ventricular interdependence seen in constrictive physiology.

• Juxtaposition involves the malposition of both appendages and is usually associated with other complex congenital heart defects. The finding described is an isolated anomaly of the LAA itself.

• A congenital LAA aneurysm is a rare anomaly that characteristically presents as a well-defined, saccular enlargement of the appendage, often in an otherwise asymptomatic young adult. The imaging findings of a “third mogul” on X-ray and a confirmed isolated outpouching on CT are classic for this diagnosis.
• Pineda, AM. et al. Cureus. 2024.

• In mitral stenosis, the LAA enlargement is part of a generalized left atrial enlargement due to pressure overload. The patient would also likely be symptomatic, and other signs of mitral stenosis (e.g., pulmonary venous hypertension) would be expected.

• This condition causes the LAA to appear prominent because it herniates through the pericardial defect. However, it would not typically appear as a discrete, narrow-necked saccular aneurysm on CT and is often associated with other specific radiographic signs.

• The classic X-ray finding for supracardiac TAPVR is a “snowman” or “figure-of-eight” appearance, which is different from the description.

• L-TGA is characterized by atrioventricular and ventriculoarterial discordance. The classic radiographic finding is a straight or convex upper-left heart border caused by the malposed, left-sided ascending aorta. This differs from D-TGA, which often presents with an “egg-on-a-string” appearance.
• Donnelly, L. F. et al. Pediatric Radiology. 2003.

• This condition involves a single great vessel arising from the heart and typically presents with cardiomegaly and increased pulmonary vascular markings, but not the specific straight left heart border.

• The classic X-ray finding in Tetralogy of Fallot is a “boot-shaped” heart (coeur en sabot) with a concave main pulmonary artery segment and decreased pulmonary vascularity.

• This describes right juxtaposition, which is much less common than left juxtaposition.

• By definition, left juxtaposition of the atrial appendages is a congenital anomaly where both the morphologic right and left atrial appendages lie adjacent to each other on the left side of the great arteries.
• Thapar, M. K. et al. Annals of Pediatric Cardiology. 2013.

• This does not accurately describe the “juxtaposed” (side-by-side) nature of the anomaly. While the right appendage may course anterior or posterior to the aorta, both appendages end up on the same side.

• Atrial isomerism (or heterotaxy) refers to a condition where the atria have symmetric morphology (e.g., both appearing as right atria or both as left atria). This is a different anomaly from juxtaposition, although they can coexist.