1. McGraw, Mark

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A task force assembled by the Society of Nuclear Medicine & Molecular Imaging (SNMMI) has found that the Omicron variant of COVID-19 seems to cause an unusual imaging pattern on fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) scans done on cancer patients. The findings are noteworthy, as FDG PET/CT has become a key modality for imaging patients with cancer. The scans are typically done to detect metabolically active malignant lesions, including lung cancer, colorectal cancer, brain cancer, and multiple myeloma. FDG-PET scans can also be used to stage and monitor patients' response to therapy of malignant disease.

FDG PETCT Scans. FDG... - Click to enlarge in new windowFDG PET/CT Scans. FDG PET/CT Scans

Throughout the last 18 months, the SNMMI Task Force has met on a biweekly basis to "monitor, support, educate, and provide guidance to the nuclear medicine and molecular imaging community" in the midst of the coronavirus pandemic, according to an SNMMI statement announcing the task force's most recent observation regarding FDG PET/CT scans.


Unlike the FDG PET/CT pattern seen with infections from previous COVID-19 strains, with principal involvement of the lungs, "this new array of findings is primarily centered in the upper aerodigestive tract and cervical lymph nodes," the task force noted. More specifically, the group has observed what it describes as "prominent, symmetric FDG update throughout the nasopharynx, oropharynx, and tonsils with or without associated FDG-avid cervical lymphadenopathy, particularly in the suprahyoid neck."


"Normally, there is very low-grade uptake in the tonsils and minimal to no uptake in the oropharynx and nasopharynx," explained Munir Ghesani, MD, FACNM, FACR, Chief of Nuclear Medicine and Molecular Imaging at Mount Sinai Health in New York, and Chair of SNMMI's COVID-19 Task Force. "In patients with COVID-19 infection, there is moderate- to high-grade uptake in all three sites."


Based on what is currently known about the Omicron variant, "it is conceivable" that this pattern, whenever correlated with COVID-19 infection, is a result of the presently dominant Omicron strain, according to SNMMI.


In terms of how FDG PET/CT scans are performed, the task force's observations "will not change anything," stated Ghesani, "as the process is fairly standardized."


With regard to interpretating the scans, the SNMMI Task Force recommends the pattern they've witnessed "be taken into consideration at the time of FDG PET/CT interpretations and the possibility of infection with Omicron variant of COVID-19 should be entertained in the differential diagnosis." As the pattern can "by no means" be diagnostic of COVID-19 infection, the task force makes a series of recommendations:


* Check the patient records to see if there is a recent positive COVID-19 test.


* Determine if the patient is at higher risk of COVID-19 infection based on current symptoms or due to recent exposure or travel. If so, a recommendation can be made to test for COVID-19 in the appropriate setting.


* Compare with prior FDG PET/CT examinations and the patient's history to determine if this represents chronic inflammatory/reactive process or stable malignancy such as lymphoma.


* Various differential diagnostic possibilities should be considered if this pattern is new or if there is interval progression including, but not limited to, infection with COVID-19, other viruses such as Epstein-Barr virus, malignancy, and bacterial infections.


* This pattern may also be seen in children and younger adults, but should be interpreted cautiously in view of normal increased activity that can be physiologic. Correlation with history and symptoms and comparison to prior examinations are recommended.



In addition, the organization advises comparing with previous FDG PET/CT examinations and patient histories to identify whether this signifies chronic inflammatory/reactive process or stable malignancy such as lymphoma.


SNMMI also recommends considering a number of differential diagnostic possibilities in the event the Omicron pattern is new or if there is interval progression, including but not limited to infection with viruses such as Epstein-Barr and bacterial infections, for example. Finally, the association cautions that this pattern may be seen in children and young adults, but urges that images be interpreted cautiously in light of normal increased activity that can be physiologic.


Mark McGraw is a contributing writer.


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