Histological Features of Delayed Foreign Body Granuloma With Epithelioid Histiocyte Aggregation and Eosinophilic Reaction due to Hyaluronic Acid Injection

Background: Dermal fillers such as hyaluronic acid (HA) have been widely used in recent years as a less surgically invasive cosmetic treatment. Although delayed foreign body granuloma may occur as a rare adverse reaction after the procedure, detailed histological reports are still limited. When occurring on the buccal mucosa of the oral cavity, the histopathology may resemble some lesions of minor salivary gland origin due to the material properties of HA. Here we report a delayed foreign body granuloma associated with HA showing eosinophilic infiltration of the buccal mucosa, with characteristic histological and immunohistological features. Case Presentation: A 61-year-old woman presented with swelling and a burning sensation in the right buccal mucosa. On initial examination, a 25 × 20-mm mass was palpated on the anterior margin of the right masseter muscle. Examination of a biopsy specimen revealed multiple pseudoduct-like structures containing mucoid substance within the mucosal lamina propria. The mucoid substance was positively stained with Alcian blue (AB) and surrounded by CD68-positive epithelioid cells and multinucleated giant cells. Many histiocytes had infiltrated into the surrounding area, and numerous eosinophilic infiltrates were also evident. After a review of the patient's history, a diagnosis of delayed foreign body granuloma associated with HA injection was made. Conclusion: We have reported a case of delayed foreign body granuloma with eosinophilic and histiocytic infiltration following injection of HA. It was suggested that the marked eosinophilic infiltration around macrophages was due to not only an allergic reaction, but also in part to increased macrophage aggregation.