• Gregory R Toci, Christa L LiBrizzi, Jarred A Bressner, Adam Scott Levin, and Carol D Morris.
• The Johns Hopkins University School of Medicine, Baltimore, MD.
• Medicine (Baltimore). 2022 Apr 22; 101 (16): e28942e28942.

RationaleSoft tissue masses are common within the general population with a minority diagnosed as soft tissue neoplasms. Differing between benign and malignant soft tissue processes can be a challenge given the overlapping clinical and imaging characteristics. We present the case of a 69-year-old female referred to the Orthopaedic Oncology Service for evaluation of a suspected soft tissue sarcoma in the upper arm.Patient ConcernsShe reported a mass localized over the deltoid with associated tenderness 1 month after influenza vaccination.DiagnosisAfter thorough consideration of the patient's clinical course, history, advanced imaging, and physical examination, the diagnosis of injection granuloma associated with recent influenza vaccination was considered.InterventionsBiopsy was deferred and close interval follow-up with clinical and imaging evaluation revealed a resolving process.OutcomesThe patient was followed until complete resolution of all symptoms, which occurred 5 months after initial presentation.LessonsIt was hypothesized that due the patient's body habitus, the injection contents intended for intramuscular administration remained in the subcutaneous tissues and elicited a granulomatous reaction. This case highlights several important factors for physicians to consider in the work up of suspicious masses for which injection granuloma is on the differential diagnosis.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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