Septic pulmonary embolisms and metastatic infections from methicillin-resistant Staphylococcus aureus endocarditis on FDG PET/CT

Pitfalls in interpretation of FDG PET/CT: Septic pulmonary emboli mimicking metastases in a case of gastric carcinoma

Inflammatory lesions may sometimes show intense tracer uptake and mimic neoplastic lesions on (18) F-fluoro-deoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT). We report one such false positive case on FDG PET/CT, where septic pulmonary emboli (SPE) mimicked pulmonary metastases. A 45-year-old man with stomach cancer had an indwelling central venous catheter (CVC) in situ while on neoadjuvant chemotherapy. He underwent FDG PET/CT scan for response assessment and the images revealed multiple, intensely FDG avid, peripheral, lung nodules with feeding vessels, which were suspicious for pulmonary metastases. A day later, the patient developed fever with chills and his blood culture showed bacterial growth (Enterobacter cloacae). A provisional diagnosis of SPE from an infected CVC was made. Chemotherapy was withheld, CVC removed, and the catheter tip was sent for bacterial culture. Following a 4-week course of antibiotic treatment, the patient became afebrile. Culture from the CVC tip grew the same organism, as was seen earlier in the patient's blood culture, thus pin-pointing the source of infection in our case. Diagnosis of SPE was clinched when follow-up CT chest done after completion of antibiotic course showed complete resolution of the lung lesions.

18F-FDG positron emission tomography/computed tomography in infective endocarditis

BACKGROUND

The diagnosis of infective endocarditis (IE), especially the diagnosis of prosthetic valve endocarditis (PVE) is challenging since echocardiographic findings are often scarce in the early phase of the disease. We studied the use of 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in IE.

METHODS

Sixteen patients with suspected PVE and 7 patients with NVE underwent visual evaluation of 18F-FDG-PET/CT. 18F-FDG uptake was measured also semiquantitatively as maximum standardized uptake value (SUVmax) and target-to-background ratio (TBR). The modified Duke criteria were used as a reference.

RESULTS

There was strong, focal 18F-FDG uptake in the area of the affected valve in all 6 cases of definite PVE, in 3 of 5 possible PVE cases, and in 2 of 5 rejected cases. In all patients with definite PVE, SUVmax of the affected valve was higher than 4 and TBR higher than 1.8. In contrast to PVE, only 1 of 7 patients with NVE had uptake of 18F-FDG by PET/CT in the valve area. Embolic infectious foci were detected in 58% of the patients with definite IE.

CONCLUSIONS

18F-FDG-PET/CT appears to be a sensitive method for the detection of paravalvular infection associated with PVE. Instead, the sensitivity of PET/CT is limited in NVE.

FDG-PET in cardiac infections

Cardiac infections include a group of conditions involving the heart muscle, the pericardium, or the endocardial surface of the heart. Infections can extend to prosthetic material or the leads in case of the implantation of devices. Despite their relative low incidence, these conditions that are associated with high morbidity and mortality involve a relevant burden of diagnostic workup. Early diagnosis is crucial for adequate management of patient, as early treatment improves the prognosis; unfortunately, the clinical manifestations are often nonspecific. Accurate and timely diagnosis typically requires the correlation of imaging findings with laboratory data. (18)F-FDG-PET is a well-established imaging modality for the diagnosis and management of malignancies, and evidence is also increasing regarding its value for assessing infectious and inflammatory diseases. This article summarizes published evidence on the usefulness of (18)F-FDG-PET for the diagnosis of cardiac infections, mainly focused on endocarditis and cardiovascular device infections. Nevertheless, the diagnostic potential of (18)F-FDG-PET in patients with pericarditis and myocarditis is also briefly reviewed, considering the most likely future advances and new perspectives that the use of PET/magnetic resonance would open in the diagnosis of such conditions.

A case of septic pulmonary embolism associated with renal abscess mimicking pulmonary metastases of renal malignancy

We report the case of a 46-year-old woman with acute febrile symptom who had multiple pulmonary nodules and a renal mass. She underwent (18)F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) to find a hidden malignancy and the cause of her fever. FDG PET/CT images demonstrated a renal mass and multiple lung nodules with intense FDG uptake, which was suspicious of a renal malignancy with multiple pulmonary metastatic lesions. CT-guided biopsies of the pulmonary and renal lesions only showed chronic inflammatory infiltrates without evidence of malignancy. She was diagnosed with septic pulmonary embolism from a renal abscess. One month after antibiotic treatment, the follow-up chest and abdomen CT showed improvement of the lung and renal lesions. This is the first case demonstrating the FDG PET/CT finding of septic pulmonary embolism associated with renal abscess in the published literature.

Cardiac imaging in infectious endocarditis

Infectious endocarditis remains both a diagnostic and a treatment challenge. A positive outcome depends on a rapid diagnosis, accurate risk stratification, and a thorough follow-up. Imaging plays a key role in each of these steps and echocardiography remains the cornerstone of the methods in use. The technique of both transthoracic echocardiography and transoesophageal echocardiography has been markedly improved across the last decades and most recently three-dimensional real-time echocardiography has been introduced in the management of endocarditis patients. Echocardiography depicts structural changes and abnormalities in the heart, but it does not uncover the underlying pathophysiological processes at the cellular or molecular level. This problem is addressed with introduction of new molecular imaging methods as (18)F-fluorodesoxyglucose ((18)F-FDG) PET-CT and single photon emission computed tomography fused with conventional CT (SPECT/CT). Of these methods, (18)F-FDG PET-CT carries the best promise for a future role in endocarditis. But there are distinct limitations with both SPECT/CT and (18)F-FDG PET-CT which should not be neglected. MRI and spiral CT are methods primarily used in the search for extra cardial infectious foci. A flowchart for the use of imaging in both left-sided and right-sided endocarditis is suggested.