Myxoma is the most common primary benign cardiac tumour in adults, and the left atrium is its most frequent location. Echocardiography often provides the first decisive information, but the report should characterize the mass rather than label every mobile left-atrial structure as a myxoma.
Learning objectives
- Recognize the typical attachment and motion of a left-atrial myxoma.
- Assess mitral obstruction, regurgitation, pulmonary pressure, and embolic morphology.
- Build a practical differential diagnosis.
- Know when TEE, CT, or CMR is needed.
Begin with the attachment
A classic left-atrial myxoma is pedunculated and attaches to the interatrial septum, often near the fossa ovalis. It may be smooth or villous, homogeneous or heterogeneous, and variably calcified. Mobility depends on the length and width of the stalk and the size of the tumour.
Document the attachment in at least two planes. A mass that seems septal in one view may arise from the roof, posterior wall, mitral valve, pulmonary vein, or left-atrial appendage when examined from another angle.
Characterize what the mass does
- Measure maximal dimensions in standardized views.
- Describe mobility and whether the mass prolapses through the mitral valve.
- Record the attachment site and stalk when visible.
- Assess transmitral gradients when obstruction is suspected, recognizing heart-rate and flow dependence.
- Evaluate mitral regurgitation, LA size, pulmonary pressure, and right-heart response.
- Describe surface irregularity or fragmentation, which may be relevant to embolic presentation.
A mean mitral gradient caused by a mobile mass is flow dependent. Report heart rate and avoid translating the number directly into rheumatic mitral-stenosis severity categories.
Use TEE when the question remains
TTE may be sufficient for a large, well-visualized mass. TEE offers higher spatial resolution for the stalk, interatrial septum, small lesions, valve interaction, and alternative attachment sites. It is especially useful when TTE windows are limited or surgical planning requires more precise anatomy.
CMR can characterize tissue, vascularity, and enhancement; CT can define calcification and extracardiac anatomy. Multimodality imaging is complementary when the diagnosis is atypical, invasion is suspected, or thrombus remains a concern.
Myxoma versus thrombus
| Feature | Favors myxoma | Favors thrombus |
|---|---|---|
| Typical location | Interatrial septum near fossa ovalis | LAA, posterior LA, low-flow recess |
| Clinical context | Constitutional or embolic symptoms; may occur without AF | AF, mitral stenosis, severe LA enlargement, low appendage velocity |
| Mobility | Often pedunculated and highly mobile | Variable; may be layered or sessile |
| Associated findings | Stalk, mitral prolapse/obstruction | Spontaneous echo contrast and other low-flow markers |
These are probabilities, not proof. Organized thrombus can be pedunculated, and myxoma can be broad based. Histopathology after excision establishes the definitive diagnosis.
Other important mimics
- Papillary fibroelastoma, usually valve associated and smaller.
- Vegetation in the appropriate infectious and valvular context.
- Nonbacterial thrombotic endocarditis.
- Normal variants such as the coumadin ridge.
- Invasive or metastatic tumour.
- Reverberation, near-field, or side-lobe artefact.
Urgency and surveillance
Once a myxoma is strongly suspected, prompt cardiology and surgical evaluation is customary because of obstruction and embolic potential. Echo should not delay management while attempting to make every tissue distinction.
After excision, document the operative site, residual or recurrent mass, valve function, and chamber response. Surveillance frequency is individualized; recurrence risk is higher with familial syndromes, Carney complex, younger age, multiple tumours, or prior recurrence.
Knowledge check
1. What is the most typical attachment site for an LA myxoma?
Answer: The interatrial septum near the fossa ovalis.
2. Which findings make thrombus more likely?
Answer: LAA/posterior LA location, AF or mitral stenosis, spontaneous echo contrast, and low-flow physiology.
3. Can echocardiography prove histology?
Answer: No. Echo defines morphology and haemodynamic consequences; pathology establishes the tissue diagnosis.