EU Radiology: H1N1 vaccination increases FDG uptake in the lymph nodes
PET/CT with 18F-FDG needs to be accurately interpreted since higher FDG uptake is seen in axillary lymph nodes after vaccination against pandemic swine-origin influenza A (H1N1), according to a study published online Feb. 26 in European Radiology.

Emmanouil Panagiotidis, MD, and colleagues from PET/CT unit at Evangelismos General Hospital in Athens, analyzed the FDG uptake in 10 patients who had been referred for PET/CT between  Nov. 23, 2009  and Dec. 11, 2009 and had undergone recent H1N1 vaccination.

According to Panagiotidis and colleagues, all studies showed FDG uptake in the draining axillary lymph nodes close to the vaccination site, while low-dose CT revealed lymph nodes between 0.5 cm and 1.2 cm at the same site.

None of the patients had a high likelihood of their disease occurring with axillary lymph node involvement, ipsilaterally to the vaccination site, except for one patient with melanoma, noted the authors.

“The range of mean maximal standardized uptake values (SUVmax) of axillary lymph nodes was 1.3 to 3.4. In four patients SUVmax was higher than that of large vessels of the mediastinum, while the other six patients had mild uptake,” wrote Panagiotidis and colleagues.

Patients who were vaccinated five–12 days before examination had the highest uptake of FDG in the lymph nodes and this potential pitfall in PET/CT should be borne in mind during current vaccination programs, concluded the authors.