What is the differential diagnosis for a flagellated, Eustachian valve-like object found in the free wall of the left atrium during a Transesophageal Echocardiogram (TEE) in a patient being evaluated for suspected infective endocarditis?

Differential Diagnosis of Flagellated Left Atrial Mass on TEE in Suspected Infective Endocarditis

The most likely diagnosis is a vegetation from infective endocarditis with atypical location (mural endocarditis), but you must also consider left atrial myxoma, thrombus, Lambl's excrescences, papillary fibroelastoma, and marantic endocarditis in your differential.

Primary Diagnostic Consideration

Mural Infective Endocarditis (Most Likely)

• Vegetations can occur on non-valvular endocardial surfaces, including the free wall of the left atrium, though this is uncommon 1, 2
• Giant vegetations attached to the posterior wall of the left atrium without mitral valve involvement have been documented in case reports 2
• The oscillating/flagellated appearance is characteristic of vegetations, which are defined as "oscillating or non-oscillating intracardiac mass on valve or other endocardial structures" 1
• This presentation can mimic left atrial myxoma on imaging 3, 2

Critical Differential Diagnoses

Left Atrial Myxoma

• Most common primary cardiac tumor and the most important alternative diagnosis to exclude 2
• Typically pedunculated and attached to the interatrial septum near the fossa ovalis (not the free wall) 2
• Can appear similar to large vegetations on echocardiography 3
• Key distinguishing feature: myxomas usually have a stalk attachment to the septum, whereas your case describes free wall attachment 2

Left Atrial Thrombus

• Can appear as a mobile mass in the left atrium 1
• More common in patients with atrial fibrillation, mitral stenosis, or left atrial enlargement 1
• Cannot be reliably distinguished from vegetation by echocardiography alone 1
• Clinical context (rhythm, anticoagulation status) helps differentiate 1

Lambl's Excrescences

• Small filamentous strands on valve closure lines that represent normal variants 1
• Can be indistinguishable from small vegetations on echocardiography 1
• Typically much smaller than what you're describing and located on valve edges, not atrial free wall 1

Papillary Fibroelastoma

• Small intracardiac tumor with characteristic frond-like appearance 1
• Can mimic vegetations but typically smaller and more uniform 1
• Most commonly found on valve surfaces rather than atrial free wall 1

Non-Infectious Endocarditis

• Marantic (non-bacterial thrombotic) endocarditis associated with advanced malignancy 1
• Libman-Sacks endocarditis in systemic lupus erythematosus 1
• Rheumatoid disease-associated valvular lesions 1
• Primary antiphospholipid syndrome 1

Diagnostic Algorithm

Step 1: Blood Culture Analysis

• Obtain at least 2 sets of blood cultures before antibiotics if not already done 1
• Blood cultures are positive in 90% of IE cases when properly obtained 1
• Positive cultures, especially Staphylococcus aureus, strongly support IE diagnosis 1

Step 2: Apply Modified Duke Criteria

• Use the Modified Duke Criteria to establish definite, possible, or rejected IE 1
• Your TEE finding represents a major criterion (oscillating intracardiac mass on endocardial structure) 1
• Combine with clinical and microbiological data 1

Step 3: Repeat TEE if Initial Diagnosis Uncertain

• If initial TEE is negative or equivocal but clinical suspicion remains high, repeat TEE within 7-10 days 1
• Earlier repeat imaging warranted for Staphylococcus aureus infection 1
• Small abscesses and early complications may not be visible initially 1

Step 4: Consider Advanced Imaging

• Cardiac CT is reasonable when anatomy cannot be clearly delineated by echocardiography 1
• CT particularly useful for assessing perivalvular extent of abscesses and pseudoaneurysms 1
• 18F-FDG PET/CT is reasonable for "possible IE" cases by Duke Criteria 1

Step 5: Multidisciplinary Heart Valve Team Consultation

• Mandatory consultation with infectious disease specialist, cardiologist, and cardiac surgeon 1
• Early surgical evaluation critical for atypical presentations 1

Key Clinical Pitfalls

False Positive Considerations

• Pre-existing severe valvular lesions (mitral valve prolapse, degenerative calcified lesions) can mimic vegetations 1
• Myxomatous valve disease may appear similar to vegetations 1
• Chordal rupture can create mobile structures 1

False Negative Considerations

• Very small vegetations (<2 mm) may not be visible even on TEE 1, 4
• Vegetations may have already embolized 1
• Non-vegetant IE exists 1

Temporal Evolution

• Perivalvular complications develop over time; negative early TEE does not exclude future development of abscesses, fistulae, or pseudoaneurysms 1
• Serial imaging may be necessary to capture evolving pathology 1

Prognostic Implications

• Intracardiac abscess is an independent predictor of in-hospital and 1-year mortality 5
• Large vegetations on initial echocardiogram indicate high risk for complications requiring close monitoring 1
• Atypical location (mural endocarditis) may have different embolic risk profile 2