A 29-year-old female subject underwent US examination 3 days after receiving the second dose of Pfizer-BioNTech vaccine, due to the rapid occurrence of a palpable lump at the level of the left axilla (same site of vaccine injection), along with fatigue. Multiple, round, hypoechoic axillary lymph nodes (maximum diameter 11 × 10 mm) with no fatty hilum and mild hilar vascularization. Shear-wave elastography revealed a soft consistence (mean values between 6 and 19 kPa). Follow-up US examination performed 5 weeks after the second dose only showed a reduction in lymph node size (maximum diameter 9 × 6 mm) (Fig. ). No pathological lymph nodes were found in both ipsilateral and contralateral supra/subclavicular and cervical stations as well as in the contralateral axilla.
A 28-year-old woman, who experienced headache and left axillary pain after the second vaccine dose, performed a US examination 2 days after that revealed the presence of enlarged (26 × 7 mm) axillary lymph nodes with preserved fatty hilum, thickened cortex (5 mm) and increased vascularization at color-Doppler. A pathological ipsilateral sub-clavicular lymph node (33 × 11 mm) was also found with no visible fatty hilum and increased vascular signal (Fig. ). In both nodes, shear-wave elastography showed a soft texture (mean values between 13 and 18 kPa). No pathological lymph nodes were found in lymph node stations contralateral to the site of vaccine injection. The patient had previously undergone a breast US for a routine control after receiving the first vaccine dose, that did not show any significant abnormalities.