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Review
. 2022 Jan;52(1):61-70.
doi: 10.1053/j.semnuclmed.2021.06.017. Epub 2021 Jun 22.

FDG-PET/CT of COVID-19 and Other Lung Infections

Liesl S Eibschutz  1 , Behnam Rabiee  2 , Shadi Asadollahi  3 , Amit Gupta  4 , Majid Assadi  5 , Abass Alavi  3 , Ali Gholamrezanezhad  6
Affiliations
Review

FDG-PET/CT of COVID-19 and Other Lung Infections

Liesl S Eibschutz et al. Semin Nucl Med. 2022 Jan.

Abstract

While not conventionally used as the first-line modality, [18F]-2-fluoro-2-deoxy-D-glucose (FDG) - positron emission tomography/computed tomography (PET/CT) can identify infection and inflammation both earlier and with higher sensitivity than anatomic imaging modalities [including chest X-ray (CXR), computed tomography (CT), and magnetic resonance imaging (MRI)]. The extent of inflammation and, conversely, recovery within the lungs, can be roughly quantified on FDG-PET/CT using maximum standardized uptake value (SUVmax) values. The Coronavirus disease 2019 (COVID-19) pandemic has highlighted the value of FDG-PET/CT in diagnosis, elucidation of acute pulmonary and extrapulmonary manifestations, and long-term follow up. Similarly, many other pulmonary infections such as previously documented coronaviruses, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, cryptococcosis, histoplasmosis, mucormycosis, and typical/atypical mycobacterial infections have all been identified and characterized using FDG-PET/CT imaging. The goal of this review is to summarize the actual and potential benefits of FDG-PET/CT in the imaging of COVID-19 and other lung infections. Further research is necessary to determine the best indications and clinical applications of FDG-PET/CT, improve its specificity, and ultimately ascertain how this modality can best be utilized in the diagnostic work up of infectious pathologies.

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Figures

Figure 1
Figure 1
A 53-year-old male with a history of colorectal cancer presented for restaging FDG-PET/CT. Axial low dose CT image (A) showing incidental peripheral ground-glass opacity involving the posterior right lower lobe lung (arrows), with borderline hypermetabolism (SUVmax of 2.2) on corresponding CT attenuation corrected PET image (arrows in B). Additionally, mild uptake (SUVmax of 2.6) was seen in the right hilar region likely representing reactive lymphadenopathy (white arrowhead in B). Given the morphology of lung opacities, equivocal FDG uptake, and clinical suspicion, patient underwent RT-PCR testing and was confirmed to have COVID-19.
Figure 2
Figure 2
(A) PET maximum intensity projection image shows a fluorine 18 fluorodeoxyglucose (FDG)–avid mass (arrow) with a maximum standardized uptake value of 4.9 in the right lung. Increased accumulation of FDG in the right paratracheal, right hilar lymph nodes (arrowheads), and bone marrow are also noted. (B) Low-dose axial CT scan and, (C) PET/CT fusion image show ground-glass opacities with areas of focal consolidation (black arrow) primarily in the right upper lobe and a focal opacity in the left upper and right middle lobes (white arrows). (D) Follow-up CT scan obtained 4 days later demonstrates progression of lesions in bilateral upper and right middle lobes (arrows) with newly developed focal opacities in the left upper and lower lobes (arrows). Figure 2 reproduced with permission from Zou S, Zhu X. FDG PET/CT of COVID-19. Radiology 2020;296: E118-E118.
Figure 3
Figure 3
FDG-PET/CT scan of a 27-year-old woman with persistent anosmia and positive PCR for SARS-CoV-2. Representative axial (A, B, D) and coronal (C) images are shown. There was decreased uptake in the left orbitofrontal cortex (arrows). The uptake of temporal lobes were symmetric and normal (arrows, D). Figure 3 reproduced with permission from Karimi-Galougahi M, Yousefi-Koma A, Bakhshayeshkaram M, Raad N, Haseli S. 18FDG PET/CT scan reveals hypoactive orbitofrontal cortex in anosmia of COVID-19. Academic radiology 2020; 27:1042-1043.
Figure 4
Figure 4
Grading of vaccine-associated hypermetabolic lymphadenopathy based on FDG-uptake intensity and nodal size: Grade 1, mild uptake intensity (SUVmax <2.2); Grade 2, moderate uptake intensity (2.2 ≤ SUVmax <4); Grade 3, high uptake intensity (SUVmax ≥4) in normal-size nodes; and grade 4, high FDG-uptake intensity (SUVmax ≥4) in enlarged nodes. Each row represents one patient. From left to right: CT, PET, and fusion PET-CT axial slices and a MIP image. HLN was identified in the axillary and supraclavicular lymph nodes (most likely due to recent vaccination, as annotated by black arrows) in each of the following patients: Patient A: colon cancer patient referred for staging imaged 9 days following the first vaccine dose (SUVmax of 1.97), Patient B: rectal cancer patient referred for follow-up, imaged 13 days following the second vaccine dose (SUVmax of 3.39), Patient C: prior history of breast cancer referred for follow-up study 10 days following the first vaccine dose (SUVmax of 10.10), and Patient D: right upper lobe lung cancer patient referred for staging 1 day following the booster vaccine dose (SUVmax of 14.34). Lymph node diameter of Patient D was noted to be 14 mm. Brown arrows indicate increased FDG uptake at the vaccine injection site on the MIP images. HLN, hypermetabolic lymphadenopathy; MIP, maximal intensity projection. Figure 4 adapted with permission from Cohen, D., Krauthammer, S. H., Wolf, I., & Even-Sapir, E. (2021). Hypermetabolic lymphadenopathy following administration of BNT162b2 mRNA Covid-19 vaccine: incidence assessed by (18)F-FDG PET-CT and relevance to study interpretation. Eur J Nucl Med Mol Imaging, 48(6), 1854-1863. https://doi.org/10.1007/s00259-021-05314-2. http://creativecommons.org/licenses/by/4.0/.
Figure 5
Figure 5
Fungal pneumonia in a 40-year-old man with AIDS and newly diagnosed anaplastic lymphoma. (A) Computed tomographic (CT) scan demonstrates a 6 × 3.5-cm thick- walled cavitary lesion in the posterior segment of the right lower lung. (B) FDG-PET scan demonstrates intense, heterogeneous accumulation of radiotracer in the posterior aspect of the right lower lung, a finding that corresponds to the abnormality identified at CT and that could indicate lymphomatous involvement of the pulmonary parenchyma. The final diagnosis, however, was fungal pneumonia. It was not possible to distinguish lymphoma from infection on the basis of the FDG-PET finding alone. Figure 5 reproduced with permission from Love, C., Tomas, M. B., Tronco, G. G., & Palestro, C. J. (2005). FDG PET of infection and inflammation. Radiographics, 25(5), 1357-1368. https://doi.org/10.1148/rg.255045122.
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