Cardiac Masses: Tumors and Mimics

Differential diagnosis

Cardiac structural abnormalities are frequently identified incidentally during echocardiography or CT imaging, irrespective of whether the study was performed to assess cardiac symptoms.

Pseudomass

• The initial diagnostic consideration is to determine whether the finding represent a true cardiac mass, or if it is a pseudomass?

Tumor mimic

• If a true cardiac mass is confirmed, the differential diagnosis is heavily influenced by the patients age and medical history.
• Thrombus or vegetation should be prioritized in the differential, because they are the most common cardiac masses and tumor mimics, especially in the context of infarctions and indwelling devices (thrombus) or heart valves (vegetation).
  Thrombi are most commonly observed in characteristic locations, such as the left atrial appendage or a dilated left ventricle.
  

Cardiac tumor

• Primary cardiac tumors are exceedingly rare, with the majority of cardiac neoplasms representing metastatic disease.
• The incidence of benign cardiac tumors varies by age:
  • Myxoma is the most prevalent in adults (~50%)
  • Rhabdomyoma predominates in children (~45%)

Multimodality imaging enhances diagnostic accuracy.
The following two tabels summarize the diagnostic findings of cardiac tumors and mimics on different imaging modalities.

• Ultrasound (TTE/TEE) is first-line: accessible, non-invasive, high spatial/temporal resolution, but operator-dependent and limited by acoustic windows.
• CT offers rapid, high-resolution imaging with excellent assessment of calcification, fat, extent, origin, and vasculature, but involves radiation and contrast.
• MRI provides detailed tissue characterization and functional data, but is limited by availability, scan time, and contraindications (e.g., devices, claustrophobia).
• FDG-PET aids in differentiating malignant/benign lesions and staging, but is costly, involves radiation, and has lower resolution with potential false positives.
• Tissue sampling (biopsy/resection) remains the gold standard for definitive diagnosis when feasible.

Pseudomass - Cor triatriatum sinistra.

Case Presentation

Initial suspicion on CT pulmonary angiogram was for an atrial thrombus or possible cardiac mass (white arrows).

Further evaluation demonstrated delayed filling of the right-sided chamber within a septated left atrium (yellow arrow).
This is consistent with the diagnosis cor triatriatum sinistra.

Cor triatriatum sinistrum is a rare congenital cardiac anomaly characterized by the presence of a fibromuscular membrane that divides the left atrium into two chambers:

1. Proximal chamber: Receives pulmonary venous return.
2. Distal chamber: Contains the mitral valve and left atrial appendage.

The membrane typically has one or more openings, allowing blood flow between the chambers.

Pseudomass - Obstructive Hypertrophic Cardiomyopathy

Case Presentation

Initial suspicion on CT pulmonary angiogram was for an atrial thrombus or possible cardiac mass (white arrows).

Further evaluation demonstrated delayed filling of the right-sided chamber within a septated left atrium (yellow arrow).
This is consistent with the diagnosis cor triatriatum sinistra.

Cor triatriatum sinistrum is a rare congenital cardiac anomaly characterized by the presence of a fibromuscular membrane that divides the left atrium into two chambers:

1. Proximal chamber: Receives pulmonary venous return.
2. Distal chamber: Contains the mitral valve and left atrial appendage.

The membrane typically has one or more openings, allowing blood flow between the chambers.

Pseudomass - Thrombus mimic

Suspected left atrial appendage thrombus, which proved not present on a slightly later contrast phase series.
If present at the scanner, consider a late phase in prone position instead of a separate repeat examination later.    

Thrombus

Cardiac thrombi are the most common intracardiac masses, typically forming in the left atrial appendage or left ventricular apex due to blood stasis, endothelial injury, or hypercoagulability. Predisposing conditions include atrial fibrillation, prior myocardial infarction with left ventricular dysfunction, and indwelling cardiac devices/catheters. These thrombi may lead to systemic or pulmonary emboli.

Example
Post-MI, a left apical thrombus may be visualized on 4-chamber cine (yellow arrow). After anticoagulation, CT can show thrombus resolution, with fibrofatty infiltration and myocardial thinning indicating prior infarction (arrowheads).

Images
A systemic embolic event due to a left ventricular apical thrombus (arrow) in a patient presenting with acute right M1 occlusion.

Lipomatous hypertrophy of the interatrial septum (LHIS)

LHIS is a benign, non-encapsulated accumulation of adipose tissue within the interatrial septum.
Unlike cardiac lipomas, it is not a true neoplasm but rather a variant of fatty infiltration.
Typically the fossa ovalis is spared, resulting in a characteristic dumbbell shape.
Often an incidental finding in asymptomatic elderly or obese patients, recognition of this entity is mainly important to avoid misdiagnosis as malignant cardiac pathology, thereby preventing unnecessary further investigation or intervention.

Images and video
Typical LHIS with sparing of the fossa ovalis, showing bulky fatty tissue in the interatrial septum on CT and various MRI sequences (cine, T1 and nT1 mapping).

Continue with the PET-CT image...

LHIS (2)

Images

• Focal fat accumulation on nonenhanced CT (black arrow).
• Focal FDG uptake in interatrial brown fatty tissue, illustrating its potential for misdiagnosis (white arrow).    

Caseous mitral annular calcification (cMAC)

cMAC is a degenerative variant of mitral annular calcification, marked by liquefactive necrosis within a calcified annular mass.
It most commonly affects the posterior mitral annulus and is often an incidental finding in asymptomatic elderly patients.
Recognition is critical to avoid misdiagnosis as a cardiac tumor or abscess, which could lead to unnecessary investigations.
Rarely, it may serve as a source of embolic strokes or a nidus for infective endocarditis.

Example
Unenhanced CT and CTA in a patient with typical caseous mitral annular calcification.   

cMAC (2)

Video of a patient with cMAC.

Myxoma

Cardiac myxomas are the most common benign primary cardiac tumours in adults, although they remain rare overall.

75% arise in the left atrium, usually originating from the interatrial septum.
Many are detected incidentally on imaging, however, if symptomatic, they may present with obstructive cardiac symptoms, embolic events, and/or constitutional complaints related to cytokine release.
Their characteristic mobility and pedunculated attachment explains the possible intermittent obstruction of valvular inflow, particularly across the mitral valve.
Surgical resection is typically curative, although follow-up is recommended due to the possibility of recurrence.

Video example
A large hypoattenuating mass is observed in the right atrium, demonstrating mobility on the 4-chamber cine series.
Post-contrast imaging reveals no early enhancement but shows heterogeneous late enhancement.
These findings are consistent with an atrial myxoma, which was confirmed following surgical resection.

Myxoma (2)

Video example
Left atrial myxoma with intermittent transvalvular movement across the mitral valve. 

Myxoma (3)

Video example
Another patient with an incidental left atrial myxoma, presenting in the ER due to obstructive symptoms.
Interstitial thickening due to cardiogenic edema and small pleural effusions (not shown) were present.    

Myxoma (4)

Images
A patient presented to the ER with obstructive symptoms and was found to have an incidental left atrial myxoma.
Imaging revealed interstitial thickening due to cardiogenic edema and small pleural effusions (not shown).

A right atrial mass. Myxoma was considered, however, MRI showed no pedunculated connection to the septum but connection to an indwelling central venous catheter.
Absence of early and late enhancement.
Findings are consistent with thrombus.