Description
Atrial myxoma is the most common type of primary heart tumour, often arising in the interatrial septum, predominantly within the left atrium. It is a gelatinous, noncancerous growth that can vary significantly in size and may lead to serious complications due to its location.
Pathogenesis
The precise cause of atrial myxoma is unknown. The majority of these tumours occur sporadically, though a minority are associated with Carney Complex, an autosomal dominant syndrome. Histologically, myxomas are composed of stellate to plump, cytologically bland mesenchymal cells set within a myxoid stroma.
Epidemiology, Risk Factors & Associations
- Atrial myxomas account for approximately 50% of all primary heart tumours.
- Occur at any age but are most common in adults between the ages of 30 and 60 years, with a slight female preponderance (60%).
- Associated with Carney Complex (20-30% of cases), a.k.a. MEN1 variant 2 – characterised by multiple myxomas, spotty skin pigmentation, and endocrine overactivity secondary to neuroendocrine tumours.
Clinical Features
- Cardiac symptoms: including dyspnoea, orthopnoea, palpitations, or sudden death from cardiac tamponade.
- Systemic symptoms: such as fever, weight loss, and malaise.
- Embolic events: due to fragments of the tumour or associated thrombus becoming dislodged.
- Auscultation: A characteristic “tumour plop” sound may be heard, which is a noise heard early in diastole, after the opening snap of the mitral valve.
Complications
Potential complications of atrial myxoma include stroke, myocardial infarction, pulmonary embolism, heart failure, sudden cardiac death, and recurrence if not fully resected.
Pathological Features
Histopathology
- Gross: Atrial myxomas are usually polypoid, gelatinous, and vary in size (1 cm to 10 cm). They are often pedunculated and attached to the interatrial septum.
- Microscopic: They are composed of scattered cells within a myxoid stroma. The cells can be multinucleated or fusiform and the stroma is often vascularised.
Genetics
A small subset of atrial myxomas are associated with Carney Complex, an autosomal dominant condition associated with mutations in the PRKAR1A gene.
Radiological Features
General Features
- Typically appear as a mass in the left atrium attached to the interatrial septum (left- to right-atrium ratio of 4:1). Stalk may be visualised.
- Calcification is seen in 50% of right atrial myxomas, but rarely seen in left atrial myxomas.
- May cause enlargement of the atrium and can obstruct blood flow, leading to functional mitral or tricuspid stenosis.
XR
- Cardiomegaly with left atrial enlargement: double-density sign (enlarged left atrium projects over the right atrium), splaying of the carina (tracheal bifurcation angle > 90°)
- Intracardiac tumoural calcification
- Mitral obstruction: Enlarged left atrium, pulmonary vascular congestion and cephalisation
Echo
- Transthoracic Echocardiogram (TTE): Typically shows a mass in the left atrium, often attached to the interatrial septum. The mass is typically heterogenous with areas of echolucency.
- Transesophageal Echocardiogram (TEE): Provides a more detailed assessment, helpful in defining the size and extent of the tumour.
CT
- May show a well-defined, round or oval mass in the left atrium.
- Stalk-like connection to interatrial septum may be visualised.
- Calcification is seen in 50% of right atrial myxomas, but rarely seen in left atrial myxomas.
- Can show variable enhancement, depending on its size and vascularity.
- May demonstrate cystic change
MRI
- T1: Majority of the lesion will be hypointense relative to myocardium.
- T2: Markedly hyperintense on T2-weighted images relative to myocardium. Heterogenous signal else reflects varying amounts of myxomatous tissue, fibrous tissue, blood products and tumour necrosis.
- Gd+: Heterogeneous low-grade late enhancement.
- CINE GRE: Prolapses through the mitral valve may be seen with a four-chambered long axis view
Differential Diagnosis
- Cardiac Lipoma: Benign tumours composed of mature fat cells. Unlike myxomas, they are typically located in the myocardium or pericardium rather than in the atrial chamber. Typically homogeneous and show signal intensity similar to fat on all MRI sequences.
- Papillary Fibroelastoma: Benign cardiac tumours that are most commonly found on the valvular surfaces, in contrast to myxomas which are most commonly found in the atrial chambers. May cause similar embolic symptoms as myxomas but are typically much smaller in size. On echocardiography, they appear as small, mobile masses with a characteristic frond-like appearance.
- Cardiac Sarcoma: Malignant tumours and can arise from any part of the heart, often appearing more invasive and irregular compared to myxomas. They often present at a younger age and have a much poorer prognosis. On imaging, sarcomas are often heterogeneous with areas of necrosis or haemorrhage.
- Thrombus: Can mimic myxomas on imaging, but they usually occur in the setting of risk factors for thrombus formation such as atrial fibrillation or post-myocardial infarction. Typically non-mobile and may exhibit different characteristics on MRI and CT imaging such as lack of enhancement. Can be treated medically, whereas a myxoma requires surgical intervention.
Management
- Management of atrial myxoma typically involves surgical resection of the tumour.
- Regular follow-up is required due to the risk of recurrence, especially in cases associated with Carney Complex.
- The surgical approach is typically through a median sternotomy and using cardiopulmonary bypass.
- After removal, the prognosis for patients with atrial myxoma is generally good. However, it can be affected by factors such as the size of the tumour, the presence of symptoms, and any complications related to embolisation or obstruction.