Patient 1 is an asymptomatic 80-year-old man with a history of non-Hodgkin lymphoma who underwent [18F]FDG PET/CT after the end of immuno-chemotherapy in March 2020.
Compared with the previous PET/CT scan (Fig. 1.a), the current PET/CT (Fig. 1.b) showed resolution of mediastinal lymph node [18F]FDG uptake (black arrow). However, PET/CT and CT images (Fig. 1.c-l) revealed the appearance of multiple bilateral FDG-avid ground-glass opacities (GGOs, yellow arrows), with a predominantly peripheral distribution in the posterior segments of the inferior lung lobes. Moreover, new mildly increased uptake was seen in several mediastinal lymph nodes, without enlargement on CT images (Fig. 1.b, red arrow).
Ground glass opacities are the most common CT finding in COVID-19 pneumonia, particularly in the early phase of the disease, especially in asymptomatic patients [9]. The pattern is usually multifocal, bilateral and peripheral, with a posterior distribution, mainly in the lower lobes, while enlarged mediastinal or hilar lymph nodes are not typically observed [4, 10, 11].
FDG uptake has been described in COVID-19 pneumonia-related GGOs in both symptomatic and asymptomatic patients [5, 6, 12, 13], as well as in mediastinal lymph nodes [14].
Due to these findings, the patient was counseled, and isolation procedures and scanner sanitation measures were started. The gold standard for the diagnosis of COVID-19 infection, a reverse transcriptase-polymerase chain reaction (RT-PCR) test from pharyngeal swabs, was subsequently performed and confirmed the diagnosis of COVID-19 [1, 15].
Patient 2 is an asymptomatic 51-year-old man with a history of oral cavity squamous cell carcinoma, associated swallowing difficulties and repetitive aspiration pneumonia, previously treated by surgery, chemotherapy and immunotherapy, who underwent [18F]FDG PET/CT for restaging in March 2020.
Follow-up PET/CT (Fig. 2.b) showed a good partial metabolic response of the primary tumor (black arrows) compared with the baseline scan (Fig. 2.a). However, PET/CT showed the appearance of few bilateral GGOs (yellow arrows) in the posterior segments of the inferior lung lobes (Fig. 2.c-h) associated with hilar and mediastinal lymph nodes (Fig. 2.b, red arrow), both mildly FDG-avid.
Due to these findings suspicious for COVID-19, the patient was counseled, and isolation and sanitation measures were triggered. The patient was quarantined at home with adequate clinical monitoring. After two days, he developed fever > 38°C, which resolved spontaneously. RT-PCR for SARS-CoV-2 was negative in two consecutive tests.
In this patient, considering the clinical history, [18F]FDG PET/CT findings matched an aspiration pneumonia, mimicking COVID-19 infection [16, 17].