A Diagnostic Pitfall of Transthoracic Echocardiography: A Case of a Missed Large Mitral Valve Thrombus in the Setting of Suspected Nonbacterial Thrombotic Endocarditis.

Transthoracic echocardiography (TTE) is frequently utilized in the initial evaluation of cardioembolic stroke. However, the diagnostic utility of TTE is often operator-dependent, and in conjunction with anatomical limitations, there is a range of sensitivities reported in the literature specifically in the evaluation of nonbacterial thrombotic endocarditis (NBTE). Thus, relying on TTE findings to rule out NBTE in the setting of cardioembolic stroke evaluation can lead to misdiagnosis in the absence of confirmatory transesophageal echocardiography (TEE). We present a case of a 67-year-old female with a past medical history of hypertension, diabetes mellitus, human immunodeficiency virus (HIV), and recurrent ischemic strokes who was referred by her neurologist for TEE. Despite an initial TTE with a bubble study showing no evidence of intra-atrial septum, left ventricular thrombus, or any valvular pathology, there remained high suspicion of a cardioembolic source due to the bi-hemispheric presentation of the patient's previous strokes. Prior electrocardiography and cardiac event monitor showed normal sinus rhythm. Her TEE revealed a large, dense thrombus measuring 1.0 x 0.8 centimeters involving the anterior mitral valve leaflet with associated moderate mitral regurgitation. The patient was placed on systemic anticoagulation and discharged home with outpatient follow-up with cardiology. Our case highlights the diagnostic pitfalls of TTE use in the evaluation of cardioembolic stroke with a particular emphasis on NBTE in addition to discussing the rationale for follow-up TEE when TTE is otherwise unrevealing.