Value of 18 F-FDG PET/CT to Identify Occult Infection in Presumed Aseptic Pseudarthrosis after Spinal Fusion: Correlation with Intraoperative Cultures.

Objective Fluorine-18 fluorodeoxyglucose ( 18 F-FDG) positron emission tomography/computed tomography (PET/CT) has gained attention as an emerging tool in case of suspicion of infection on spine, whether native or instrumented. However, the diagnostic performance of 18 F-FDG PET/CT in clinically occult low-grade surgical site infection (SSI) after spinal fusion, an important risk factor for pseudarthrosis, remains unknown. Methods We retrospectively identified all the presumed aseptic patients with pseudarthrosis confirmed by revision surgery who underwent preoperative 18 F-FDG PET/CT scans performed between April 2019 and November 2022. These patients were presumed aseptic because they did not have clinical signs or laboratory tests suggestive of SSI, preoperatively. The PET/CT images were analyzed in consensus by two nuclear medicine physicians blinded to the clinical, biological, and imaging information. Visual assessment of increased uptake around cage/intervertebral disk space (and/or hardware) higher than background recorded from the first normal adjacent vertebra was interpreted as positive. Image data were also quantitatively analyzed by the maximum standardized uptake value as an index of 18 F-FDG uptake, and the ratio between the uptake around cage/intervertebral disk space (and/or hardware) and background recorded from the first normal adjacent vertebra was calculated. The final diagnosis of infection was based on intraoperative cultures obtained during pseudarthrosis revision surgery. Results Thirty-six presumed aseptic patients with surgically confirmed pseudarthrosis after spinal fusion underwent preoperative 18 F-FDG PET/CT scans. Cultures of samples from revisions found that 20 patients (56%) were infected. The most frequent isolated bacterium was Cutibacterium acnes ( C. acnes ) in 15 patients (75%), followed by coagulase-negative staphylococci (CNS) in 7 patients (33%). Two patients had co-infections involving both C. acnes and CNS. Of the 36 PET/CT studied in this study, 12 scans were true-negative, 10 true-positive, 10 false-negative, and 4 false-positive. This resulted in sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 50%, 75%, 71%, 55%, and 61%, respectively. Conclusion In presumed aseptic pseudarthrosis after spinal fusion, 18 F-FDG PET/CT offers good specificity (75%) but low sensitivity (50%) to identify occult SSI. The high prevalence (56%) of SSI, mostly caused by C. acnes (75%), found in our presumed aseptic cohort of patients supports the utility of systematic intraoperative cultures in revision cases for pseudarthrosis.

18 F-NaF PET/CT in Presumed Aseptic Pseudarthrosis after Spinal Fusion: Correlation with Findings at Revision Surgery and Intraoperative Cultures.

Background Conventional imaging is useful to assess interbody fusion by showing complete trabecular bony bridging, but has a low positive predictive value for pseudarthrosis. Because alterations of bone metabolism may precede structural anatomical changes on computed tomography (CT), we aimed to investigate the ability of fluorine 18 sodium fluoride positron emission tomography/computed tomography ( 18 F-NaF PET/CT) to identify pseudarthrosis after spinal fusion using surgical revision as the reference standard. Methods We retrospectively reviewed 18 F-NaF PET/CT scans performed between February 2019 and September 2020 in patients experiencing pain after spinal fusion. We included the 18 patients who underwent revision surgery for suspicion of pseudarthrosis. Five consecutive patients who were clearly fused on CT served as the control group. Results In the revision surgery group ( n =18), visual assessment by 18 F-NaF PET/CT revealed that all 22 cages with an increased 18 F-NaF uptake around intercorporal fusion material had mobility at revision surgery, whereas none of the fused patients ( n =5) showed uptake around cage/intervertebral disk space. Among the 18 patients with presumed aseptic pseudarthrosis, intraoperative cultures revealed surgical site infection (SSI) caused by Cutibacterium acnes ( C. acnes ) in seven patients (38.9%). There was a statistically significant difference in standardized uptake values and uptake ratios between the revision surgery and control groups ( p =5.3× 10 -6 and p =0.0002, respectively). Conclusions 18 F-NaF PET/CT imaging appeared as a useful tool to identify pseudarthrosis following spinal fusion. The unexpectedly high prevalence (38.9%) of SSI caused by C. acnes found in presumed aseptic patients supports the utility of intraoperative cultures in revision cases for pseudarthrosis, even without preoperative clinical suspicion of SSI.

Hot-clot artifact in the lung parenchyma on 18F-fluorodeoxyglucose positron emission tomography/computed tomography mimicking malignancy with a homolateral non-small cell lung cancer.

18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (CT) is an important tool widely used in the oncology to stage and restage various malignancies. Intense focal FDG uptake in the lung parenchyma associated with the absence of anatomical lesion detected on CT can be explained by a lung microembolism, known as hot-clot artifact. We report, to the best of our knowledge, the first case describing a single hot-clot artifact located in the same lung as a histologically proven non-small cell lung cancer.

Diffuse 18F-FDG PET/CT Uptake of the Bilateral Atrial Walls in Atrioventricular Nodal Re-entrant Tachycardia.

ABSTRACT: An 84-year-old man was referred for the evaluation of a suspected gastrointestinal neoplasia. 18F-FDG PET/CT scan was performed showing, in addition to the physiological myocardial FDG uptake in the left ventricular wall, an unusual diffuse FDG uptake of the bilateral atrial walls. During his visit to the nuclear medicine unit, the patient became unwell, and an ECG was performed, suggestive of an atrioventricular nodal re-entrant tachycardia. Our case highlights the importance of including supraventricular arrhythmia such as atrioventricular nodal re-entrant tachycardia in the differential diagnosis of atrial FDG uptake.

18F-FDG PET/CT Detection of a Popliteal Mycotic Aneurysm Complicating Staphylococcus aureus Bacteremia.

ABSTRACT: A 75-year-old man presented with Staphylococcus aureus bacteremia, fever, and right posterior knee pain. Venous Doppler ultrasound of the lower extremity showed an isolated right calf muscle vein thrombosis, without any sign of deep vein thrombosis. 18F-FDG PET/CT revealed an intense focal uptake on the right popliteal artery, suggesting a mycotic aneurysm (MA). Lower limb CT angiography confirmed an MA of the right popliteal artery. The patient underwent surgical procedure with excision of the MA, whose cultures grew methicillin-sensitive S. aureus. Our case highlights the importance of including lower limbs in 18F-FDG PET/CT acquisition in case of suspicion of septic emboli.