A hypothetical correlation between hyaluronic acid gel and development of cutaneous metaplastic synovial cyst

Thousands of patients receive hyaluronic acid filler injections, and the effects are generally considered acceptable. The acid rarely causes cutaneous reactions, which are only occasionally reported in the literature. The aim of the present work is to analyze a clinical case that has never been reported in the literature to our knowledge. This case is of a 26-year-old woman who presented with a cyst in the infrazygomatic region that was injected with non-animal stabilized hyaluronic acid at another centre a few months ago. Consequently, we made an external incision to remove the neoplasm: histological examination of the capsule revealed it to be a cutaneous metaplastic synovial cyst.