Axillary and Neck Adenopathy in the Era of Mass COVID-19 Vaccination

Can you please raise your arm? A few enlarged and unilateral axillary lymph nodes come into view. The cortex is eccentrically or diffusely thickened, they are enlarged, and they are hypervascular. Spotting an abnormal lymph node is not often the challenge, but knowing what to do with the lymph nodes can certainly be. First, I have a confession to make. I am a breast radiologist by training, and I am also fortunate to work in the body division in our department. This opportunity puts me in a unique position to explore both of the worlds and allows for collaboration and the exchange of knowledge.

Any radiologist who performs or interprets ultrasound exams knows that the patient history is of paramount importance along with available previous imaging exams. For example, a recently diagnosed breast cancer, unilateral cellulitis, and lymphoma all influence the management of axillary adenopathy. Similarly, cervical adenopathy can be seen as a reactive finding with head and neck infection, as well as in the setting of known malignancy like head/neck and thyroid cancers, which are prone to metastasize to neck lymph nodes. Vaccination history is also important when considering unexplained adenopathy, and it becomes particularly important with the introduction of the COVID-19 vaccines, which is a mass vaccination undertaking.

The COVID-19 vaccination is administered in the deltoid muscle. As a result, the reactive locoregional adenopathy in the axilla and cervical region has been observed (1). Axillary and/or cervical adenopathy as unsolicited adverse events for the Pfizer-BioNTech vaccine were reported in up to 0.3% among vaccine recipients (as opposed to 0.1% in the placebo group) (2). This adenopathy had onset about 2 to 4 days after vaccination and lasted an average of about 10 days. In the Moderna trial, 1.1% of the vaccination group versus 0.6% of the placebo group reported axillary and/or cervical adenopathy within 2 to 4 days after vaccination (3). However, the median duration of adenopathy with the Moderna vaccine was reported to be 1 to 2 days. It is important to note that these trials did not pursue the incidence of adenopathy via imaging such as ultrasound or regular physical examinations by a practicing physician after vaccination. Therefore, true incidence of axillary or cervical adenopathy remains unknown and is likely much higher than reported.

A total of 0.02% to 0.04% of otherwise normal screening mammograms present with unilateral adenopathy (4-6). During the early months of 2021, it was surprising to encounter a higher frequency of screening mammograms demonstrating unilateral adenopathy, which subsequently required a screening callback for further evaluation. As word spread in the breast imaging community, the Patient Care and Delivery Committee of the Society of Breast Imaging (SBI) issued a set of management guidelines in January 2021 for axillary adenopathy following the COVID-19 vaccination (7).

The dilemma of unilateral adenopathy extended beyond just screening mammograms. Any exams covering the anatomical regions of the axilla and lower neck started to show enlarged lymph nodes. Some examples of these exams include soft tissue ultrasound in the setting of a palpable mass, screening ultrasound exams for indications such as thyroid cancers, and cross-sectional examinations including MRI shoulder exams, CT Chest, and PET-CT.

Locoregional adenopathy has been encountered in the setting of other vaccines like influenza and shingles. However, unlike other vaccines with documented adenopathy among adults, the COVID-19 vaccine is a mass-scale vaccination program and the incidence of adenopathy is expected to be very high in numbers. Furthermore, the vaccination history is not routinely available in the medical chart, at least in early 2021, presumably due to a lack of automated connection between state health departments and unique health center-based electronic medical records. Therefore, effort should be made to document vaccination history either at the time of scheduling or at the time of imaging. At our Institution, the COVID-19 vaccine history including the timing of dose(s) is now routinely reviewed and documented for all breast exams including mammography (both screening and diagnostic), ultrasound, and MRI exams as well as ultrasound exams evaluating the axillary and/or neck regions.

Cancer screening is an important and challenging responsibility. Early detection is important in order to improve mortality and reduce morbidity. The COVID-19 vaccination campaign continues, and the race to protect as many people as possible is more important than ever. As radiologists, it is imperative to follow the data and carefully evolve in order to appropriately diagnose vaccine-related reactive adenopathy while avoiding the unintentional consequence of missing a cancer diagnosis.

A 64-year-old female patient with a history of adenoid cystic carcinoma of the right tongue with prior multiple recurrences and treatments, now presents with a mass along the left thyroidectomy bed. During the initial CT imaging, left thyroidectomy bed mass was confirmed and enlarged left axillary lymph nodes (a) were also noted (largest measuring 10 mm in short axis). This was followed by the PET-CT exam to identify additional sites of metastatic disease. PET-CT was performed about 2 weeks after the initial CT, and the CT component of PET-CT (b) shows decreased size of left axillary node, now measuring 7 mm in short axis. Axial fused PET-CT image (c) shows FDG-avidity of this lymph node, with SUV measurement of 5.56. Ultrasound image (d) shows a round node with no discernible fatty hilum. It was noted that the patient recently received a COVID-19 vaccine prior to the first CT exam. Since biopsy of the thyroidectomy bed mass showed metastasis, biopsy of left axillary node was also pursued, which revealed no evidence of metastatic disease. The left axillary node enlargement was thought to be secondary to recent COVID-19 vaccination. 

So, where do we go from here now that we know adenopathy has been reported with both the Moderna and Pfizer vaccines? Initial consensus statement from a multidisciplinary panel specifically highlights the benefit of prioritizing COVID vaccination among patients with known cancer history, as the protection offered by the vaccine outweighs the unintended side effect of adenopathy (1).

Here, we would like to discuss possible solutions highlighted by the Society of Breast Imaging (SBI) and multi-institutional cancer imaging specialists, along with solutions based on our anecdotal institutional experience, that might be of benefit when faced with the dilemma of adenopathy in your clinical practice following COVID-vaccination.

  • Collaborate with your colleagues in other divisions and departments. Coordinate and establish a consistent algorithm to assist with the management of unexpected adenopathy in the context of recent COVID-19 vaccination.
  • Document COVID-19 vaccination history. This could consist of three phases: 1) The collected information could possibly include date of vaccine doses, laterality of the arm receiving the vaccine, and the brand of the vaccine) prior to a screening exam, particularly when it involves a head/neck or axillary evaluation. 2) Once set up, this strategy of vaccination documentation could then be expanded to all modalities including cross-sectional imaging exams, either at the time of scheduling or at the time of patient’s intake on the day of the exam. 3) The final phase would consist of documentation across your entire hospital system at the time of scheduling of various appointments or using online secured tools to encourage patients to document the same on a voluntary basis. Inter-connection between different systems already existing on many Electronic Medical Record (EMR) systems would be a powerful tool in this regard. Organized COVID vaccination history in a standard location within the EMR could improve accessibility for all healthcare providers.
  • Consider the timing of a routine screening exam. If the screening exam is non-urgent, consider scheduling the exam at a minimum of 4–6 weeks following the second dose of the COVID vaccine (SBI). However, a longer interval of 6 weeks has also been advised in this setting given preliminary evidence of adenopathy persisting at 4 weeks (1). The patient’s existing risk factors and anxiety should also be considered while pursuing delaying the exam.
  • Keep your patients informed. Discuss the known reports of adenopathy following vaccination. Review short-term follow-up as a reasonable initial option in this situation and when biopsy may be indicated.
  • Know when tissue diagnosis may be indicated. According to SBI, in the absence of any other suspicious mammographic finding or contributing history beyond the vaccine, short-term follow-up in 4–12 weeks following the second vaccine dose can be considered. If axillary adenopathy persists after that period of time, tissue diagnosis is warranted to exclude breast and non-breast malignancy. However, for patients with a newly diagnosed breast cancer, it may be more appropriate to rule out metastasis with a biopsy instead of short-interval imaging follow-up.
  • Identify clearly abnormal lymph nodes. Reactive lymph nodes typically present as diffuse enlargement while maintaining their reniform shape. Fatty hilum is present, although could be thinned out. Ultrasound exams might show tiny hypoechoic (not anechoic) areas, indicative of prominent germinal centers. On PET-CT exams, the standardized uptake values (SUVs) of >7.0 have been reported within the lymph nodes as opposed to the typical scenario of reactive lymph nodes in the neck showing SUVs between 2 and 3. However, heterogeneous distribution of SUVs within lymph nodes, clearly necrotic or cystic areas within lymph nodes across all modalities, calcifications on CT and echogenic foci on ultrasound would indicate clearly abnormal lymph nodes, and tissue sampling in these cases will be indicated irrespective of COVID vaccine administration.  

It is important to keep in mind that new knowledge and data continue to contribute to evolving guidelines and that current recommendations may change as we learn more.

Dr. Noelle Hoven is an Assistant Professor in the breast imaging division and Dr. Anil Chauhan is an Associate Professor in the thoracoabdominal division in the diagnostic radiology department at the University of Minnesota.


  1. Becker AS, Perez-Johnston R, Chikarmane SA, et. al. Multidisciplinary Recommendations Regarding Post-Vaccine Adenopathy and Radiologic Imaging: Radiology Scientific Expert Panel. [published online ahead of print February 24, 2021] Radiology. doi: 10.1148/radiol.2021210436.
  1. Polack FP, Thomas SJ, Kitchin N, et al. Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine. N Engl J Med. 2020; 383(27):2603–2615.
  1. Baden LR, El Sahly HM, Essink B, et al. Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine. N Engl J Med. 2021; 384(5):403–416.
  1. Patel T, Given-Wilson RM, Thomas V. The clinical importance of axillary lymphadenopathy detected on screening mammography: revisited. Clin Radiol. 2005; 60:64–71.
  1. Lim ET, O’Doherty A, Hill AD, Quinn CM. Pathological axillary lymph nodes detected at mammographic screening. Clin Radiol. 2004; 59:86–91.
  1. Chetlen A, Nicholson B, Patrie JT, Harvey JA. Is screening detected bilateral axillary adenopathy on mammography clinically significant? Breast J. 2012; 18:582–587.
  1. SBI Recommendations for the Management of Axillary Adenopathy in Patients with Recent COVID-19 Vaccination. Society of Breast Imaging Patient Care and Delivery Committee.

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