Increased 18F-FDG Uptake in the Axillary Lymph Nodes of the Vaccinated Side Associated with COVID-19 Vaccination.

A 50-year-old female patient underwent (18fluorine-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) following modified radical mastectomy for cancer of the left breast. Ten days before the PET/CT, the coronavirus disease-2019 (COVID-19) vaccine was injected intramuscularly into the right deltoid muscle. Increased (18F-FDG uptake of maximum standardized uptake value (11.0) was observed in the lymph nodes of the right axilla, which had not been observed in the previous PET/CT. The size of the oval-shaped lymph nodes was up to approximately 11×9 mm; however, it was larger than that observed on the previous PET/CT. We contemplate that the increased (18F-FDG uptake was a reactive change in the lymph nodes associated with the COVID-19 vaccine.

Positron Emission Tomography with Computed Tomography in Evaluations of Classical Fever of Unknown Origin and Length of Hospitalization: A 10-Year Medical Record Review of a Tertiary Hospital

Background: Positron emission tomography with computed tomography (PET/CT) has proven its value for the differential diagnosis of fever of unknown origin (FUO). However, the extent to which PET/CT during FUO evaluation can shorten the length of hospital stay (LOS) remains unclear. Materials and Methods: A retrospective review of the medical records over a 10-year period from January 2009 to December 2018 of a tertiary university hospital was performed. The inclusion criteria were symptoms with fever persisting for >3 weeks before admission, as defined in classical FUO. Medical records in which PET/CT was performed after the final diagnosis, such as neoplastic causes, were excluded. Moreover, in the neoplasm category evaluated using PET/CT, only diagnostic PET/CT cases were enrolled;PET/CT cases for confirming metastasis or staging were excluded. Final diagnoses were categorized as infection, neoplasm, noninfectious non-neoplastic inflammatory disorder, miscellaneous, and uncategorizable. Each category was separated into evaluation with and without PET/CT for statistical analyses. Results: In total, 91 patients underwent evaluation for FUO and about one in three underwent PET/CT. Overall LOS was not different between the PET/CT and non-PET/CT groups;however, there were differences in LOS within the categories. For infectious causes, the mean LOS was 21.1 and 11.1 days in the PET/CT and non-PET/CT groups, respectively (P = 0.022). For neoplastic causes, the mean LOS was 11.4 and 36.0 days in the PET/CT and non-PET/CT Conclusion: Most patients with FUO were aged 50 - 60 years, and their family and work roles were crucial. A lower LOS may benefit both the patients' families and society at large. Interestingly, PET/CT may contribute to shortening the LOS during FUO evaluation when the causes are neoplastic, by approximately 24 days.

The Effects of CoronaVac (Sinovac) and BNT162b2 (BioNTech/Pfizer) Vaccination on Oncologic 18F-FDG PET/CT Studies.

Objectives: BioNTech (Pfizer) and CoronaVac (Sinovac) vaccines are two of the most administered coronavirus disease-2019 (COVID-19) vaccines worldwide. Vaccination against severe acute respiratory syndrome-coronavirus-2 has caused a diagnostic challenge in oncological 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) studies. The aim of our study was to evaluate the 18F-FDG PET/CT findings of the two most commonly administered vaccines worldwide. Methods: Patients over 18 years old who underwent 18F-FDG PET/CT for oncological purposes in our institution between January 13, 2021 and January 31, 2022, who received a single or second dose of the BioNTech or CoronaVac vaccines in the last two months, were included in the study. Descriptive analyses were presented as mean, standard deviation, frequency and ratio. Additionally, chi-square test was used to analyze categorical variables. Results: Ipsilateral deltoid muscle hypermetabolism was observed in 6.9% (n=15) and 14.3% (n=22) patients who received CoronaVac and BioNTech vaccines, respectively. Ipsilateral axillary lymph node hypermetabolism was observed in 11% (n=24) and 41.6% (n=64) patients who received CoronaVac and BioNTech vaccines, respectively. Synchronous deltoid muscle and axillary lymph node hypermetabolism was observed in 4.14% (n=9) and 12.33% (n=19) patients who received CoronaVac and BioNTech vaccines, respectively. Significant differences were detected between CoronaVac and BioNTech vaccines in terms of ipsilateral deltoid muscle hypermetabolism, ipsilateral axillary lymph node hypermetabolism and synchronous deltoid muscle and axillary lymph node hypermetabolism (p<0.05). Conclusion: COVID-19 vaccination may result in ipsilateral axillary lymph node hypermetabolism, ipsilateral deltoid muscle hypermetabolism, or synchronous deltoid muscle and axillary lymph node hypermetabolism with different frequencies depending on the type of vaccination. Although synchronous deltoid muscle and axillary lymph node hypermetabolism can reduce misinterpretation of 18F-FDG PET/CT, to avoid misinterpretation, it is important to question the vaccination history during ongoing COVID-19 vaccination process.

Effect of Post-COVID-19 on Brain Volume and Glucose Metabolism: Influence of Time Since Infection and Fatigue Status.

Post-COVID-19 syndrome (PCS) fatigue is typically most severe <6 months post-infection. Combining magnetic resonance imaging (MRI) and positron emission tomography (PET) imaging with the glucose analog [18F]-Fluorodeoxyglucose (FDG) provides a comprehensive overview of the effects of PCS on regional brain volumes and metabolism, respectively. The primary purpose of this exploratory study was to investigate differences in MRI/PET outcomes between people < 6 months (N = 18, 11 female) and > 6 months (N = 15, 6 female) after COVID-19. The secondary purpose was to assess if any differences in MRI/PET outcomes were associated with fatigue symptoms. Subjects > 6 months showed smaller volumes in the putamen, pallidum, and thalamus compared to subjects < 6 months. In subjects > 6 months, fatigued subjects had smaller volumes in frontal areas compared to non-fatigued subjects. Moreover, worse fatigue was associated with smaller volumes in several frontal areas in subjects > 6 months. The results revealed no brain metabolism differences between subjects > 6 and < 6 months. However, both groups exhibited both regional hypo- and hypermetabolism compared to a normative database. These results suggest that PCS may alter regional brain volumes but not metabolism in people > 6 months, particularly those experiencing fatigue symptoms.

Longitudinal analyses using 18F-Fluorodeoxyglucose positron emission tomography with computed tomography as a measure of COVID-19 severity in the aged, young, and humanized ACE2 SARS-CoV-2 hamster models.

This study compared disease progression of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in three different models of golden hamsters: aged (≈60 weeks old) wild-type (WT), young (6 weeks old) WT, and adult (14-22 weeks old) hamsters expressing the human-angiotensin-converting enzyme 2 (hACE2) receptor. After intranasal (IN) exposure to the SARS-CoV-2 Washington isolate (WA01/2020), 2-deoxy-2-[fluorine-18]fluoro-D-glucose positron emission tomography with computed tomography (18F-FDG PET/CT) was used to monitor disease progression in near real time and animals were euthanized at pre-determined time points to directly compare imaging findings with other disease parameters associated with coronavirus disease 2019 (COVID-19). Consistent with histopathology, 18F-FDG-PET/CT demonstrated that aged WT hamsters exposed to 105 plaque forming units (PFU) developed more severe and protracted pneumonia than young WT hamsters exposed to the same (or lower) dose or hACE2 hamsters exposed to a uniformly lethal dose of virus. Specifically, aged WT hamsters presented with a severe interstitial pneumonia through 8 d post-exposure (PE), while pulmonary regeneration was observed in young WT hamsters at that time. hACE2 hamsters exposed to 100 or 10 PFU virus presented with a minimal to mild hemorrhagic pneumonia but succumbed to SARS-CoV-2-related meningoencephalitis by 6 d PE, suggesting that this model might allow assessment of SARS-CoV-2 infection on the central nervous system (CNS). Our group is the first to use (18F-FDG) PET/CT to differentiate respiratory disease severity ranging from mild to severe in three COVID-19 hamster models. The non-invasive, serial measure of disease progression provided by PET/CT makes it a valuable tool for animal model characterization.

Pulmonary Findings of [18F]FDG PET/CT Images on Asymptomatic COVID-19 Patients.

During the coronavirus disease 2019 (COVID-19) pandemic, several case studies demonstrated that many asymptomatic patients with COVID-19 underwent fluorine-18 fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) examination for various indications. However, there is a lack of literature to characterize the pattern of [18F]FDG PET/CT imaging on asymptomatic COVID-19 patients. Therefore, a systematic review to analyze the pulmonary findings of [18F]FDG PET/CT on asymptomatic COVID-19 patients was conducted. This systematic review was performed under the guidelines of PRISMA. PubMed, Medline, and Web of Science were used to search for articles for this review. Articles with the key words: "asymptomatic", "COVID-19", "[18F]FDG PET/CT", and "nuclear medicine" were searched for from 1 January 2020 to 20 May 2021. Thirty asymptomatic patients with COVID-19 were included in the eighteen articles. These patients had a mean age of 62.25 ± 14.85 years (male: 67.71 ± 12.00; female: 56.79 ± 15.81). [18F]FDG-avid lung lesions were found in 93.33% (28/30) of total patients. The major lesion was [18F]FDG-avid multiple ground-glass opacities (GGOs) in the peripheral or subpleural region in bilateral lungs, followed by the consolidation. The intensity of [18F]FDG uptake in multiple GGOs was 5.605 ± 2.914 (range from 2 to 12) for maximal standardized uptake value (SUVmax). [18F]FDG-avid thoracic lymph nodes (LN) were observed in 40% (12/40) of the patients. They mostly appeared in both mediastinal and hilar regions with an SUVmax of 5.8 ± 2.93 (range from 2.5 to 9.6). The [18F]FDG uptake was observed in multiple GGOs, as well as in the mediastinal and hilar LNs. These are common patterns in PET/CT of asymptomatic patients with COVID-19.

Polymyalgia Rheumatica (PMR) Lacking Shoulder Pain Following COVID-19 Vaccination.

This case highlights a 77-year-old woman with polymyalgia rheumatica (PMR) following coronavirus disease 2019 (COVID-19) vaccination without shoulder pain and its characteristic positron emission tomography-computed tomography (PET-CT) findings. Some cases of PMR following COVID-19 vaccination have been reported. However, patients without shoulder pain or PET-CT findings without uptake at the shoulders are not described. Our case suggests that PMR should be considered in the differential diagnosis of patients with neck pain following COVID-19 vaccination, even if they lack shoulder pain.

Axillary Lymph Node Uptake on 18F-FDG PET/CT after COVID-19 Vaccination: A Direct Comparison Study with Influenza Vaccination.

Objectives: To compare vaccinated-side axillary lymph node uptake on 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) after coronavirus disease-2019 (COVID-19) and influenza vaccination. Methods: We retrospectively analyzed 177 patients who underwent 18F-FDG PET/CT after COVID-19 or influenza vaccination. We compared the uptake of the vaccinated-side axillary lymph nodes of 109 COVID-19 vaccinated patients with those of a lot of influenza-vaccinated patients. We also compared the uptake between 66 patients who received the first COVID-19 vaccination with 43 who received the second COVID-19 vaccination. Results: 18F-FDG-avid axillary lymph nodes on the vaccinated side were significantly more frequently observed in the COVID-19 group (45%) than in the influenza group (19%) (p<0.001). When the interval between vaccination to PET/CT was within 7 days, there was no significant difference in the frequency of 18F-FDG-avid vaccinated-side axillary lymph nodes between the groups (COVID-19 group: 41% vs. influenza group: 45%, p=0.724). When the interval was over 7 days, 18F-FDG-avid lymph nodes were much more frequent in the COVID-19 group (47%) than in the influenza group (7%) (p<0.001). Comparing the first and second COVID-19 groups, 18F-FDG-avid lymph nodes were more frequent in the second vaccination group than in the first vaccination group, but the difference was not significant. Conclusion: 18F-FDG-avid vaccinated-side axillary lymph nodes were more frequently observed in the COVID-19 group than in the influenza group. In the case of the COVID-19 vaccine, a delay of 18F-FDG PET/CT examination is recommended by a longer interval from vaccination than in the influenza vaccine.

[18F]FDG-PET/CT in mechanically ventilated critically ill patients with COVID-19 ARDS and persistent inflammation.

Purpose: We report the findings of four critically ill patients who underwent an [18F]FDG-PET/CT because of persistent inflammation during the late phase of their COVID-19. Methods: Four mechanically ventilated patients with COVID-19 were retrospectively discussed in a research group to evaluate the added value of [18F]FDG-PET/CT. Results: Although pulmonary PET/CT findings differed, bilateral lung anomalies could explain the increased CRP and leukocytes in all patients. This underscores the limited ability of the routine laboratory to discriminate inflammation from secondary infections. Based on PET/CT findings, a secondary infection/inflammatory focus was suspected in two patients (pancreatitis and gastritis). Lymphadenopathy was present in patients with a detectable SARS-CoV-2 viral load. Muscle uptake around the hips or shoulders was observed in all patients, possibly due to the process of heterotopic ossification. Conclusion: This case series illustrates the diagnostic potential of [18F]FDG-PET/CT imaging in critically ill patients with persistent COVID-19 for the identification of other causes of inflammation and demonstrates that this technique can be performed safely in mechanically ventilated critically ill patients.

Myocardial Inflammation on FDG PET/MRI and Clinical Outcomes in Symptomatic and Asymptomatic Participants after COVID-19 Vaccination.

Purpose: To evaluate potential cardiac sequelae of COVID-19 vaccination at 2-month follow-up and relate cardiac symptoms to myocardial tissue changes on fluorodeoxyglucose (FDG) PET/MRI, blood biomarkers, health-related quality of life, and adverse outcomes. Materials and Methods: In this prospective study (ClinicalTrials.gov: NCT04967807), a convenience sample of individuals aged ≥17 years were enrolled after COVID-19 vaccination and were categorized as symptomatic myocarditis (new cardiac symptoms within 14 days of vaccination and met diagnostic criteria for acute myocarditis), symptomatic no myocarditis (new cardiac symptoms but did not meet criteria for myocarditis), and asymptomatic (no new cardiac symptoms). Standardized evaluation was performed 2 months after vaccination, including cardiac fluorine 18 FDG PET/MRI, blood biomarkers, and health-related quality of life. Statistical analysis included Kruskal-Wallis and Fisher exact tests. Results: Fifty-four participants were evaluated a median of 72 days (IQR: 42, 91) after COVID-19 vaccination, 17 symptomatic with myocarditis (36±[SD]15 years, 13 males), 17 symptomatic without myocarditis (42±12 years, 7 males), and 20 asymptomatic (45±14 years, 9 males). No participants in the symptomatic without myocarditis or asymptomatic groups had focal FDG-uptake, myocardial edema or impaired ventricular function. Two participants with symptomatic myocarditis had focal FDG-uptake, and three had high T2 on MRI. Health-related quality of life was lower in the symptomatic myocarditis group than the asymptomatic group. There were no adverse cardiac events beyond myocarditis in any participant. Conclusions: At two-month follow-up, FDG PET/MRI showed evidence of myocardial inflammation in 2/17 participants diagnosed with acute myocarditis early after COVID-19 vaccination, but not in symptomatic and asymptomatic participants without acute myocarditis.Keywords: Myocarditis, Vaccination, COVID-19, PET/MRI, Cardiac MRI, FDG-PET.

Time-related aortic inflammatory response, as assessed with 18F-FDG PET/CT, in patients hospitalized with severely or critical COVID-19: the COVAIR study.

AIM: Arterial involvement has been implicated in the coronavirus disease of 2019 (COVID-19). Fluorine 18-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) imaging is a valuable tool for the assessment of aortic inflammation and is a predictor of outcome. We sought to prospectively assess the presence of aortic inflammation and its time-dependent trend in patients with COVID-19. METHODS: Between November 2020 and May 2021, in this pilot, case-control study, we recruited 20 patients with severe or critical COVID-19 (mean age of 59 ± 12 years), while 10 age and sex-matched individuals served as the control group. Aortic inflammation was assessed by measuring 18F-FDG uptake in PET/CT performed 20-120 days post-admission. Global aortic target to background ratio (GLA-TBR) was calculated as the sum of TBRs of ascending and descending aorta, aortic arch, and abdominal aorta divided by 4. Index aortic segment TBR (IAS-TBR) was designated as the aortic segment with the highest TBR. RESULTS: There was no significant difference in aortic 18F-FDG PET/CT uptake between patients and controls (GLA-TBR: 1.46 [1.40-1.57] vs. 1.43 [1.32-1.70], respectively, P = 0.422 and IAS-TBR: 1.60 [1.50-1.67] vs. 1.50 [1.42-1.61], respectively, P = 0.155). There was a moderate correlation between aortic TBR values (both GLA and IAS) and time distance from admission to 18F-FDG PET-CT scan (Spearman's rho = - 0.528, P = 0.017 and Spearman's rho = - 0.480, p = 0.032, respectively). Patients who were scanned less than or equal to 60 days from admission (n = 11) had significantly higher GLA-TBR values compared to patients that were examined more than 60 days post-admission (GLA-TBR: 1.53 [1.42-1.60] vs. 1.40 [1.33-1.45], respectively, P = 0.016 and IAS-TBR: 1.64 [1.51-1.74] vs. 1.52 [1.46-1.60], respectively, P = 0.038). There was a significant difference in IAS- TBR between patients scanned ≤ 60 days and controls (1.64 [1.51-1.74] vs. 1.50 [1.41-1.61], P = 0.036). CONCLUSION: This is the first study suggesting that aortic inflammation, as assessed by 18F-FDG PET/CT imaging, is increased in the early post COVID phase in patients with severe or critical COVID-19 and largely resolves over time. Our findings may have important implications for the understanding of the course of the disease and for improving our preventive and therapeutic strategies.

Brain 18F-FDG PET imaging in outpatients with post-COVID-19 conditions: findings and associations with clinical characteristics.

BACKGROUND: Brain 18F-FDG PET imaging has the potential to provide an objective assessment of brain involvement in post-COVID-19 conditions but previous studies of heterogeneous patient series yield inconsistent results. The current study aimed to investigate brain 18F-FDG PET findings in a homogeneous series of outpatients with post-COVID-19 conditions and to identify associations with clinical patient characteristics. METHODS: We retrospectively included 28 consecutive outpatients who presented with post-COVID-19 conditions between September 2020 and May 2022 and who satisfied the WHO definition, and had a brain 18F-FDG PET for suspected brain involvement but had not been hospitalized for COVID-19. A voxel-based group comparison with 28 age- and sex-matched healthy controls was performed (p-voxel at 0.005 uncorrected, p-cluster at 0.05 FWE corrected) and identified clusters were correlated with clinical characteristics. RESULTS: Outpatients with post-COVID-19 conditions exhibited diffuse hypometabolism predominantly involving right frontal and temporal lobes including the orbito-frontal cortex and internal temporal areas. Metabolism in these clusters was inversely correlated with the number of symptoms during the initial infection (r = - 0.44, p = 0.02) and with the duration of symptoms (r = - 0.39, p = 0.04). Asthenia and cardiovascular, digestive, and neurological disorders during the acute phase and asthenia and language disorders during the chronic phase (p ≤ 0.04) were associated with these hypometabolic clusters. CONCLUSION: Outpatients with post-COVID-19 conditions exhibited extensive hypometabolic right fronto-temporal clusters. Patients with more numerous symptoms during the initial phase and with a longer duration of symptoms were at higher risk of persistent brain involvement.

COVID-19-Associated Erythema Nodosum Detected on FDG PET/CT.

We report the case of a 69-year-old woman who underwent 18F-FDG PET/CT due to prolonged fever. One month before, the patient was diagnosed with COVID-19 infection. The 18F-FDG PET/CT showed several subcutaneous nodules with 18F-FDG uptake on the thorax and upper extremities and bilateral lung infiltrates due to organizing pneumonitis. Clinical examination revealed multiple tender nodules on thorax, arms, and legs, consistent with erythema nodosum (EN) induced by COVID-19 infection. The woman was treated with prednisone with a good effect on EN. To our knowledge, this is the first report on EN secondary to COVID-19 infection diagnosed on 18F-FDG PET/CT.

An Exceptional Cause of Increased 18F-Fluorodeoxyglucose Uptake on PET/CT in a Thyroid Nodule.

A 41-year-old female underwent a cervical spine CT for the workup of posterior neck pain irradiating to the shoulders for several months. An incidental thyroid nodule was found and classified as Bethesda III on the Fine-needle aspiration cytology (FNAC) results. Three months later, the patient developed mild shortness of breath, dry cough, and fever. Chest X-ray revealed a mild enlargement in the bilateral hilar regions. CT showed mediastinal and bilateral hilar enlarged lymph nodes and pulmonary micronodules. The workup was further completed with a 18F-FDG PET/CT, showing intense FDG uptake in the mediastinal and bilateral hilar lymph nodes and increased uptake in the thyroid nodule. Endobronchial Ultrasound-guided Transbronchial needle aspiration (EBUS-TBNA) of a left hilar lymph node showed epithelioid non-necrotizing granulomas. Because of the FNAC results, size of the nodule and tracheal shift, thyroid lobectomy was performed one month later. Histopathological results also revealed multiple non-necrotizing epithelioid granulomas, suggesting systemic sarcoidosis with involvement of the thyroid. To our knowledge, this is the first report of thyroid sarcoidosis detected on 18F-FDG PET/CT. Although an increased FDG uptake in a thyroid nodule is usually suggestive of thyroid malignancy, toxic nodule, or follicular hyperplasia, our case report shows that it could also suggest thyroid sarcoidosis.

Change in cancer diagnosis during the COVID-19 pandemic: Trends estimated from FDG-PET/CT.

The aim of this study is to clarify changes in the circumstances of cancer diagnoses during the COVID-19 pandemic in Tokyo, Japan, estimated from [18F]-2-fluoro-2-deoxy-D-glucose (FDG) -positron emission tomography/ computed tomography (PET/CT) for cancer patients. Cancer diagnosis in pandemic status (PANS) was evaluated by retrospective review of the findings of FDG-PET/CT examinations performed between 11 March 2020 and 28 December 2021 for initial staging and restaging for malignancy. Evaluation of cancer diagnosis in pre-pandemic status (pPANS) was conducted similarly in FDG-PET/CT examinations performed between 4 January 2018 and 10 March 2020. Of these, patients with malignant lymphoma (ML), lung cancer, esophageal cancer, and colorectal cancer who had a pathologically proven diagnosis or clinical diagnosis following therapy of the disease were selected for analysis. Initial cancer staging was determined by the diagnostic report of FDG-PET/CT. Change in cancer stage and in the number of FDG-PET/CT examinations performed was evaluated between pPANS and PANS, and according to term of the pandemic and vaccination status. The COVID-19 epidemic influenced the number of cancer patients who underwent FDG-PET/CT. There was a marked decrease in the number of cancer patients receiving FDG-PET/CT in Terms 1-3 (March 2020 to February 2021), but it recovered in Terms 4-6 (March 2021 to December 2021). There was no significant difference between PANS and pPANS in terms of the initial stage of cancer, but Stage IV ML and Stage II esophageal cancer were more frequent in PANS. Initial staging of ML, lung cancer, and esophageal cancer revealed more advanced cancer stages in Terms 4-6 compared with Terms 1-3. The number of patients receiving FDG-PET/CT in Tokyo was influenced by the COVID-19 epidemic. Staging based on FDG-PET/CT shifted to more advanced cancer stage during the pandemic compared with pre-pandemic.

Comparison between viral vector and mRNA based COVID-19 vaccination in prevalence and severity of regional immune reactions, and 18F-FDG PET/CT features.

Objectives: The coronavirus pandemic caused by SARS-CoV-2 commenced in late 2019, and global wide vaccination appears to be the only reasonable solution to fight this dreadful virus. There are two main types of COVID-19 immunization using viral vector and mRNA-based vaccines. However, the impact of each of type on 18F-FDG PET/CT needs to be accurately assessed. This study aimed to compare the 18F-FDG PET/CT features of these two types of COVID-19 vaccines. Methods: A total of 188 patients referred for 18F-FDG PET/CT with a recent history of either BioNTech/Pfizer or AstraZeneca COVID-19 vaccination, and a control group of 40 patients with no history of any type of recent vaccination, were included in the study. 18F-FDG PET/CT studies of vaccinated patients assessed for injection site uptake and regional nodal and systemic reactions post vaccination. The data were compared to the control group and to the contralateral side for each patient. The findings were compared between patients who received Pfizer and AstraZeneca vaccines. Results: 18F-FDG PET/CT was semiquantitatively positive in 50.5% of the studied population for vaccine-related features. The ipsilateral axillary and infra- and supraclavicular lymph nodes were significantly larger in size and exhibited higher metabolic activity compared to the contralateral lymph nodes after both types of vaccination. The prevalence of regional nodal reactions post Pfizer and AstraZeneca vaccination was 39% and 17.9% on visual, and 61% and 47.6% on semiquantitative assessments, respectively. Patients receiving the Pfizer vaccine exhibited higher metabolic activity in the ipsilateral regional lymph nodes (p<0.05). No significant difference in the intensity of regional nodal reaction post vaccination was noted between the first four weeks. Conclusion: Significant local and regional nodal reactions are observed after both viral vector and mRNA COVID-19 vaccination with a tendency to extend toward the infra- and supraclavicular nodal stations but not to the pulmonary hilum. The greater intensity and extension of the nodal reaction after Pfizer vaccination suggests a higher possibility of false-positive results on 18F-FDG PET/CT studies using mRNA vaccination technology.

COVID-19-Related Incidental Pancreatitis Detected on FDG-PET Scan.

Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)/coronavirus disease 2019 (COVID-19) infection predominantly affects the respiratory system, it has also been found to be responsible for several gastrointestinal effects due to its capability to attack angiotensin-converting enzyme (ACE) type 2 cells in various parts of the body. Several cases of radiologically confirmed thyroiditis, axillary lymphangitis, and acute pancreatitis related to COVID-19 infection have been reported, which seem to arise from a direct cytotoxic effect of the virus itself. This case report presents an incidental 18-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) computed tomography (CT) finding of mild pancreatic inflammation/pancreatitis in an otherwise asymptomatic patient undergoing routine imaging as part of the staging process following stem cell transplant, who had recently recovered from a severe form of COVID infection. This case highlights the fact that COVID can trigger insidious inflammatory processes in a variety of organs often remaining clinically undetectable until resultant end-organ damage causes incipient clinical symptoms.

Hypermetabolic Ipsilateral Supraclavicular and Axillary Lymphadenopathy: Optimal Time Point for Performing an 18F-FDG PET/CT after COVID-19 Vaccination.

Background: We aimed to evaluate the incidence of severe acute respiratory syndrome coronavirus type-2 (SARS-CoV2) vaccine-related hypermetabolic lymphadenopathy (HLA) and evaluate which time point produces the least number of false-positive findings in an 18F-2-Fluor-2-desoxy-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT). Methods: For this retrospective, multi-center imaging study, patients with any form of SARS-CoV2 vaccination prior to an 18F-FDG-PET/CT were included between January 2021 and December 2021. Patients were divided into six groups according to the time point of vaccination prior to their 18F-FDG-PET/CT imaging, e.g., group one (0−6 days) and group six (35−80 days). As the reference standards, the SUVmax of the mediastinal blood pool (MBP) and the SUVmax contralateral reference lymph node (RL) were determined. (A) The absolute SUVmax of HLA, (B) the ratio of SUVmaxHLA/SUVmax mediastinal blood pool (rHLA/MBP), (C) the ratio SUVmax HLA vs. SUVmax contralateral reference lymph node (rHLA/RL), (D) and the incidence of HLA defined as rHLA/MBP > 1.5 were assessed. Results: Group one (days 0−6) showed the highest incidence of HLA 16/23 (70%) and rHLA/MBP (2.58 ± 2.1). All three parameters for HLA reduced statistically significantly in the comparison of Groups 1−3 (days 0−20) versus Groups 4−6 (days 21−80) (p-values < 0.001). Conclusions: If feasible, an FDG PET should be postponed by at least 3 weeks after SARS-CoV2 vaccination, especially if an accurate evaluation of axillary status is required.

[18F]FDG PET/CT in Patients Affected by SARS-CoV-2 and Lymphoproliferative Disorders and Treated with Tocilizumab.

OBJECTIVES: Interstitial pneumonia is a severe complication induced by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Several treatments have been proposed alone or, more often, in combination, depending, also, on the presence of other organ disfunction. The most frequently related, well-described, and associated phenomenon is pan-lymphopenia with circulating, high levels of cytokines. We report, here, on two patients with COVID-19 and lymphoproliferative disorders treated with Tocilizumab (a humanized monoclonal antibody against the interleukin-6 receptor) and followed by an [18F]FDG PET/CT to early evaluate the therapy's efficacy. METHODS: One patient with angioimmunoblastic T-lymphoma (A), one with Hodgkin lymphoma (A), and both with positive RT-PCR for SARS-CoV-2 and with similar clinical findings of interstitial pneumonia at the CT scan, were imaged by [18F]FDG PET/CT before and 14 days after a single dose of Tocilizumab. RESULTS: In both patients, the basal [18F]FDG PET/CT showed a diffused lung parenchyma uptake, corresponding to the hyperdense areas at the CT scan. After 2 weeks of a Tocilizumab infusion, patient B had an improvement of symptoms, with normalization of the [18F]FDG uptake. By contrast, patient A, who was still symptomatic, showed a persisting and abnormal distribution of [18F]FDG. Interestingly, both patients showed a low bone marrow uptake of [18F]FDG at the diagnosis and after 15 days, while the spleen uptake was low only in lymphopenic patient A; both are indirect signs of an immune deficiency. CONCLUSIONS: In conclusion, in these two patients, interstitial pneumonia was efficiently treated with Tocilizumab, as demonstrated by the [18F]FDG PET/CT. Our results confirm that interleukin-6 (IL6) has a role in the COVID-19 disease and that anti-cytokine treatment can also be performed in patients with lymphoproliferative disorders.