In our case, COVID-19 was suspected at the time of interpretation of the PET/CT images, without the knowledge of a positive RT-PCR test, but rather based on the rapid development of extensive pulmonary infiltrates in a relatively short interval since the unremarkable baseline CT, and the patient’s risk profile. The findings were significant but certainly unexpected given the clinical question of characterisation of a potential lung malignancy, which in this case was proven to be a red herring and possibly secondary to an intrapulmonary haematoma related to bleeding diathesis. A number of key issues emerge from this case.
Firstly, assessment for COVID-19 was not the primary objective and resulted in unnecessary exposure of the staff in the PET/CT department to the virus during the transfer and preparation of the patient, which ideally should have been postponed pending a negative test result. This case highlights the potential role of nuclear medicine departments in the current pandemic in the detection of unexpected COVID-19 in patients scanned for other indications. Importantly, as for our case, the majority of PET/CT studies are performed for oncology patients, often on immunosuppressive therapy, and therefore requiring urgent medical attention and contact tracing within oncology units (Albano et al. 2020). It also reinforces the importance of close patient movement monitoring throughout the hospital during the time interval between testing suspected cases and laboratory results (Albano et al. 2020; Lu et al. 2020).
Next, the imaging findings on the CT component of the study were in line with the other case reports available in the literature and included a crazy-paving pattern with areas of ground-glass infiltration and consolidation in a subpleural distribution (Zu et al. 2020). Furthermore, the extent and intensity of FDG uptake in the lungs, concordant with the areas of CT abnormality, were thought to be indicative of active COVID-19 infection (Zu et al. 2020). Having since imaged a number of other confirmed or suspected cases with less pronounced FDG activity on PET/CT, and particularly since “casual FDG uptake” has been shown to be a feature of COVID-19 infection in a small case series of asymptomatic patients in a recent publication, the possibility of a more aggressive strain of the virus, and patient’s immunosuppression may have been the contributing factors (Setti et al. 2020). Based on our findings and limited available evidence from other investigators, there may be a role in the future for PET/CT in the management of patients during the endemic phase to assist in the differential diagnosis, differentiating active from non-active disease and assessment of the response to treatment (Deng et al. 2020). Critically, the location of the intensely FDG-positive normal size upper mediastinal lymph node, demonstrated in our case study, was discordant with the distribution of the pulmonary parenchymal involvement. This may suggest that lymphadenopathy could be an independent imaging biomarker of the disease, similar to what demonstrated for other infections (Chadburn et al. 1989). Indeed, based on limited data, lymphadenopathy has been suggested as a prognostic marker of COVID-19 infection severity (Valette et al. 2020) and a predictor of a worse outcome (Sardanelli et al. 2020). In view of the grave clinical outcome of our patient, there may be an argument in support of a further prognostic role of higher SUVmax values of FDG positive nodal disease, as a biomarker which could herald a more severe case of the infection with the virus.
Finally, the presence of nodal uptake, in a more suggestive setting of malignancy such as lymphoma or lung tumour, could have erroneously resulted in over-staging of the nodal disease (Zanoni et al. n.d.).