Accessory Mitral Valve Misdiagnosed as Vegetation: A Case Report

An accessory mitral valve (AMV) is a rare anomaly of the mitral valve (MV) that often causes left ventricular outflow tract (LVOT) obstruction. We describe a young woman presenting with infrequent palpitations to our outpatient clinic. She was evaluated for mid-systolic murmur at the left sternal border. At the initial transthoracic echocardiography, vegetation on the MV was suspected. The patient was referred to our advanced echocardiography lab, where transesophageal echocardiography revealed an AMV with mild LVOT obstruction. The findings, along with extensive laboratory tests, ruled out vegetation. Additionally, she had a bicuspid aortic valve. At follow-up after 1 year, the patient was asymptomatic regarding the AMV with LVOT obstruction, and the repeat echocardiography depicted no changes compared with the previous echocardiography. Distinguishing AMVs from other MV masses, including vegetation, sometimes poses a challenge and can lead to unnecessary diagnostic and therapeutic measures. This rare MV anomaly is associated with bicuspid aortic valves.