Subcutaneous lymphoid follicular hyperplasia secondary to vaccination: correlation of ultrasound findings with clinical and histological findings.

In recent years, the use of vaccines has been standardized within vaccination programs. Adverse effects at the puncture site are usually mild and transient. Nevertheless, in some cases, persistence subcutaneous nodules can develop; these are often underdiagnosed because they are so rare and because of the long time that can transpire between the vaccination and their appearance. Histologically, they consist of a lymphoid follicular hyperplasia that occurs as a reaction to the aluminum particles usually used as an adjuvant in some vaccines. We were unable to find any reference in the radiological literature to these soft-tissue nodules secondary to vaccination. We report the characteristic ultrasound findings that will enable radiologists to identify or strongly suspect these lesions and thereby avoid unnecessary imaging tests that might lead to confusion and inadequate management of these patients.