Tumefactive foreign body giant cell reaction following high‐pressure paint injection injury: A case report and review of literature

High‐pressure paint injection injury is an uncommon but well‐described injury. The histologic features of long‐term paint injection injury with retained material are less recognized. A 46‐year‐old male presented clinically as “recurrent giant cell tumor of tendon sheath.” The right index finger demonstrated fusiform enlargement by a pigmented mass with diffuse infiltration into the soft tissue of the hand. Histologically the tumor showed multiple giant cells in a fibrotic stroma extending into the dermis. There were multiple types of foreign material including diffuse brown black pigment, weakly optically polarizing foreign material and white inclusions with a “train track” appearance. The cells were positive for CD68 and negative for S100 antigen. Further investigation revealed that the patient had a history of high‐pressure paint injection injury to his digit 6 years prior. Foreign material injected under high pressure into tissues may result in a pseudo‐neoplastic foreign body granulomatous reaction that can mimic giant cell tumor of tendon sheath. Our case demonstrates that this reaction can be florid and can have slow growth over years. A high index of suspicion, a good clinical history and careful examination can distinguish these 2 entities.