Covid-19 vaccine related uptake in Ga-68 DOTATATE scan

A 43-year-old woman with a pancreatic neuroendocrine tumour (NET) history was scheduled for a routine surveillance Gallium-68-DOTATATE PET/CT scan. The patient reported recent immunisation for Covid (Pfizer BioN-Tech) in their left arm two weeks prior to the examination.

This study was performed on a Siemens Biograph mCT. A contrast-enhanced CT scan from the vertex to the mid-thigh was acquired, with an intravenous administration of 65 ml of Omnipaque 350g/ml iodine-based contrast medium. The PET study was performed approximately 45 minutes post-administration of 220 MBq of Gallium-68-Dotatate .

The PET-CT imaging demonstrated stable uptake at the patient’s previously demonstrated pancreatic NET. In addition, there was new moderate uptake (Krenning 2) at asymmetric left axillary lymph nodes, with a short-axis diameter ranging to 13mm. There is a noted artefact from tracer retention within the left antecubital fossa injection site and left arm venous activity. Low grade asymmetric left inguinal node activity was also noted, unchanged from previous Gallium-68 Dotatate PET-CT and previously felt to be due to low-grade reactive adenopathy.

Molecular imaging interpretation requires an understanding of the physiologic distribution of the tracer and the appearance of incidental processes that may exhibit tracer avidity.

Because of its high sensitivity and specificity, 68Gallium-Dotatate PET-CT is the most frequently used imaging modality for staging and follow-up neuroendocrine tumours and prior to PRRT [1].

The patient had no recent history of left-arm inflammation or injury to suggest other causes of reactive adenopathy. Given the site of the uptake and the indolent behaviour of the known oligometastatic NET, new lymph node metastasis was excluded as a cause. A new SSTR expressing neoplastic process is also extremely unlikely. There is some tracer retention within the injection tube and activity within the left arm veins. However, late lymphatic drainage of tracer extravasation at the injection site was excluded on review of the workstation images. In this case, unexpected left axillary Gallium-68 Dotatate uptake was unlikely to be due to isolated lymph node metastasis. Although there is a differential for this appearance, the most likely cause was felt to be the recent vaccination, with the distribution very similar to post-vaccination FDG uptake also seen in several cases in our practice.

Uptake of FDG by reactive nodes has been previously documented following vaccination against Covid-19 [2]. However, in this case, unexpected 68Galllium-Dotatate uptake was unlikely to be due to isolated lymph node metastasis and most likely related to recent vaccination.

It has been previously recognised that 68Gallium-Dotatate may show benign lymph node uptake, typically at reactive nodes [3] or in sarcoid [4]. In this case, uptake is likely reactive following Covid-19 immunisation.

Unexpected axillary lymph node uptake at 68Gallium-Dotatate PET should prompt review for any history of recent Covid-19 vaccination.

Written informed patient consent for publication has been obtained.