Role of molecular imaging in the diagnosis of prosthetic aortic valve endocarditis by Bacillus licheniformis: a case report

Infective endocarditis is a challenging diagnosis that usually requires cardiovascular image confirmation as part of the approach. ¹⁸F-Fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT) is an imaging technique more sensible for the diagnosis of prosthetic valve endocarditis (PVE) when echocardiography is inconclusive.

We present the case of a 35-year-old man who had a previous Bentall–De Bono procedure 4 years prior that included biological, national institute of cardiology (INC)-type, locally manufactured aortic valve replacement and woven Dacron tube graft implantation in the ascending aorta. He was admitted because of dyspnoea, oedema, fever, and syncope. A complete auriculoventricular blockade was diagnosed, requiring cardiac pacing. Also, infective endocarditis (IE) was suspected. Blood cultures showed the isolation of Bacillus licheniformis. Transthoracic echocardiography, transoesophageal echocardiography, and CT angiography were inconclusive for IE. Treatment was initiated with intravenous (IV) antibiotic therapy, and an extensive protocol for IE, including molecular imaging modalities, was ordered. ^99mTc-Ubiquicidin scintigraphy was acquired without abnormal findings. Images of ¹⁸F-FDG-PET/CT revealed abnormally intense heterogeneous uptake in the prosthetic aortic annulus in a classic pattern. Applying the modified 2015 Duke criteria for PET/CT, PVE was confirmed.

Although the other imaging modalities were negative, the high clinical suspicion made it mandatory to continue the study protocol, remarking on the utility of ¹⁸F-FDG-PET/CT on patients categorized as having ‘possible’ endocarditis, as in our patient.