A middle-aged female presents with a history of dyspnoea on exertion and when lying down. Echocardiography reveals a left atrial mass. What is the most likely diagnosis?
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Left Atrial Myxoma = Most common primary heart tumor, arises from the interatrial septum, presents with positional syncope/dyspnea, early diastolic "tumor plop," and can cause systemic embolization (strokes).
Concept:
A middle-aged patient presents with positional dyspnea, and an echocardiogram identifies a solid mass residing within the left atrium.
The clinician must integrate the epidemiology of cardiac masses with the highly characteristic positional symptom profile to deduce the most statistically likely diagnosis. Explanation: • When a mass is identified inside the heart, the differential primarily includes tumors, thrombi, and vegetations.
• Atrial Myxoma is by far the most common primary cardiac tumor found in adults, accounting for over $50\%$ of all primary cardiac neoplasms.
• Approximately $80\%$ of myxomas arise specifically in the Left Atrium, classically originating from a stalk attached to the interatrial septum, right at the border of the fossa ovalis.
• Because these tumors are typically pedunculated (attached by a stalk) and gelatinous, they are mobile within the atrial cavity. During diastole, as the patient changes positions (e.g., sitting up or lying down), gravity causes the tumor to drop or prolapse into the mitral valve orifice.
• This prolapse mimics a ball-valve mechanism, intermittently obstructing left ventricular filling and perfectly simulating the hemodynamics of severe mitral stenosis. This sudden obstruction causes the classic positional dyspnea on exertion or positional syncope described in the vignette.
• Auscultation classically reveals an early diastolic "tumor plop" sound as the mass abruptly impacts the mitral valve ring.
• While an atrial thrombus (Option B) is also found in the left atrium (often in the appendage, especially in atrial fibrillation), it does not typically present as a large mobile mass causing severe positional obstructive symptoms. Metastatic tumors (Option D) usually involve the pericardium or myocardium rather than forming a solitary intracavitary atrial mass. Final Answer:
The combination of a left atrial mass and positional dyspnea is the textbook clinical presentation for a Left Atrial Myxoma.
