Case Report
A 22-year-old man with a fever was admitted as an emergency patient. At
presentation, his body
temperature was 40.3℃, and physical examination revealed no obvious
cardiac murmur.
However, there was evidence of splinter hemorrhages and Janeway lesions.
Although transthoracic echocardiography (TTE) revealed no obvious
vegetation or significant valvular disease (Figure 1A; Movie S1), blood
cultures grew gram-positive cocci in clusters, which were identified as
methicillin-sensitive Staphylococcus aureus . Therefore, we
performed transesophageal echocardiography (TEE), suspecting infective
endocarditis (IE). TEE revealed a mobile vegetation measuring 15 × 7 mm
on the surface of left ventricular muscle just below the anterolateral
commissure of the mitral valve (Figure 1B; Movie S2), but no significant
valve stenosis or regurgitation.IE was diagnosed according to the
modified Duke criteria. According to the American Heart Association
guidelines, early surgery is recommended for class Ⅱa in patients with
severe valve regurgitation and mobile vegetations > 10 mm
in size1. In our case, severe valve regurgitation was
not seen, but the > 10-mm mobile vegetation was thought to
involve a risk of embolism. Therefore, resection of the vegetation was
performed on the seventh day. Surgical findings revealed that a
vegetation existed on the surface of left ventricular muscle just below
the anterolateral commissure of the mitral valve, which partially
infiltrated subvalvular tissue (Figure 1C). A histological examination
of the vegetation revealed extensive inflammatory cell infiltration with
fibrin precipitation and necrotic tissue (Figure 1D).
Five days later, a new systolic cardiac murmur was ausculted. TTE and
TEE showed that moderate/severe mitral regurgitation owing to
anterolateral scallop flail leaflet. Chordal rupture supposedly occurred
due to infiltration of the vegetation; mitral valve plasty was performed
on the 19th day. Postoperatively, the patient remained
stable. Penicillin G, 24 million units, was infused continuously over 24
hours, and blood cultures were consistently negative for 6 weeks. On the
26th and 27th day, we performed
18-Fluorodeoxyglucose positron emission tomography
(18FDG-PET/CT) (Figure 1E) and gallium-67 scintigraphy
(Figure 1F). No abnormal accumulation in left ventricular muscle was
seen. The patient discharged on the 56th hospital day.
Although the normal endothelial lining of the heart is resistant to
bacterial adhesion, bacteria are able to adhere to abnormal or damaged
endothelium in the presence of regurgitation or shunt
jet2. A recent study revealed that vegetations exist
mostly on the valves or pacemaker leads; less than 3% of vegetations
occur at other sites3. We described a rare case of IE
that a vegetation on the surface of left ventricular muscle and
subvalvular tissue just below the anterolateral commissure of the mitral
valve without exposure to regurgitation or shunt jet. The results of18FDG-PET/CT and gallium-67 scintigraphy suggested
that vegetation did not exist on other lesions.
According to a previous review article, in patients with suspected
native valve endocarditis, TEE has a sensitivity of 90% to 100% and a
specificity of 90% for detection of vegetations, and it is superior to
TTE4. In the present case, IE could not be diagnosed
by TTE because of its unique location; however, TEE made it possible to
detect the vegetation. This case indicates the possibility that
vegetations may form without exposure to regurgitation or shunt jet.