Papillary synovial metaplasia–like change in oral mucoceles: a rare and previously undescribed histopathologic variant of a common oral lesion

The development of synovial membrane–like structures has been described previously only in association with breast implants, the bone-cement interface of hip prostheses, tendon implants, testicular implants, and traumatized skin. Previous investigators have theorized that this phenomenon—referred to as “synovial metaplasia”—develops in response to gliding trauma. In some cases, these lesions can exhibit a papillary growth pattern. We report 2 unusual cases of oral mucoceles exhibiting papillary synovial metaplasia–like change: the first arising in the lower lip of an 11-year old African-American boy and the second in the lower lip of a 12-year-old European-American girl. We propose that these cases represent a rare and previously undescribed histopathologic variant of the oral mucocele. These lesions should be distinguished from other oral lesions that may exhibit a papillary cystic growth pattern.