1924. Differentiation of FDG Positive COVID-19 Vaccine Associated Lymph Nodes and Metastatic Axillary Lymph Nodes on PET/CT in Oncology Patients
Authors * Denotes Presenting Author
  1. Praveen Polamraju *; Wake Forest University School of Medicine
  2. Sarpitha Rajamreddy; Wake Forest University School of Medicine
  3. Christopher Sheridan; Wake Forest University School of Medicine
  4. Janardhana Ponnatapura; Wake Forest University School of Medicine
The purpose of this study is to 1) assess characteristics of axillary lymph nodes (LNs) on PET/CT, that are deemed reactive secondary to COVID-19 vaccination in oncology patients and 2) compare characteristics of these LNs to metastatic LN on PET/CT with correlation to biopsy results if available.

Materials and Methods:
A sample of consenting patients with cancer receiving scans to investigate suspicious FDG PET positive axillary LNs ipsilateral to their COVID-19 vaccine injection site was identified via chart review of encounters taking place between February 2021 to February 2022 (n = 34, 24 women; nvaccine = 20, women 12; nmalignancy = 14, women = 12). Relevant information pertaining to demographics, COVID-19 vaccination history, FDG-PET/CT quantification of LN pathology, and disease course were extracted and deidentified. Bivariate statistics with corresponding measures of effect size were calculated for categorical and continuous PET/CT-derived measures of interest to assess for differences between groups. Variables that differed significantly between groups on bivariate analysis were incorporated into logistic regression models to assess their contribution to discrimination between the groups. The Shapiro-Wilk test was used to assess normality of continuous variables.

Bivariate analysis determined that nodes suspected to have been induced by COVID-19 vaccination were significantly more likely to have a preserved fatty hilum (Fisher’s exact p < 0.0001, OR = 0.01, 95% CI [0.0002 - 0.13]), to be <1 cm in size (Fisher’s exact p < 0.001, OR = 0.05, 95% CI [0.004 - 0.36]), and to display ovoid morphology (Fisher’s exact p = 0.04, OR = 0.2, 95% CI [0.03 - 1.01]). A logistic regression model of group as a function of preserved fatty hilum, nodule size <1 cm, and presence of ovoid morphology was statistically significant (p < 0.0001, McFadden R2 = 0.58) and correctly classified 92% (AUC=0.921, Delong’s 95% CI [0.847 - 0.996); the presence of a fatty hilum was the most important variable for discriminating COVID-19 vaccine-induced nodes from malignant nodes (OR = 0.015, 95% CI [0.0003 - 0.18]).

FDG PET/CT positive axillary LNs can be confidently distinguished between COVID-19 vaccination LNs and metastatic LNs by determining the characteristics on imaging. i.e., preserved fatty hilum, short axis <1 cm and ovoid morphology. This helps in reducing the morbidity by reducing the number of unnecessary biopsies and can be confidently followed by ultrasound in 6 weeks. This study advances the radiologist’s ability to confidently distinguish FDG positive LN related to COVID vaccination from metastatic LN, thus enabling clinicians to provide appropriate management for patients.