Clinical and histologic features of 26 canine peripheral giant cell granulomas (formerly giant cell epulis)

Clinical and histologic features of 26 cases of canine peripheral giant cell granuloma (formerly giant cell epulis) are reported. Two main histologic categories were evident: (1) "classic" peripheral giant cell granuloma, characterized by variable numbers of multinucleated giant cells (MNGCs) admixed with densely cellular mononuclear spindle-shaped cells in variable amounts of collagenous matrix, and (2) the "collision" peripheral giant cell granuloma, with features of both a peripheral giant cell granuloma and a fibromatous epulis of periodontal ligament origin. In the 16 dogs for which the outcome was known, 2 peripheral giant cell granulomas recurred after excision. No age or sex predilection was evident; however, lesions were more common in maxillary than in mandibular gingiva. In contrast to cats, peripheral giant cell granulomas in dogs behave like fibromatous epulides of periodontal ligament origin and seldom recur after excision. Positive staining with TRAP (tartrate-resistant acid phosphatase) of the MNGCs and a fraction of the mononuclear cell population is consistent with osteoclastic origin.