Periosteal desmoid tumour: a rare finding in the oral cavity.

A 55-year-old female patient reported with an intraoral well-localised asymptomatic swelling on the right side of the mandible in relation to the right mandibular first molar along with a history of trauma 6 months back. Panoramic radiograph revealed normal trabecular bone pattern in relation to the lesion. The lesion was excised along with the associated buccal cortical plate and tooth. The microscopic examination revealed a well-circumscribed lesion consisting of spindle cells arranged in storiform pattern associated with the buccal cortical plate. The key feature to note was presence of reactive periosteum, which was in continuum with the lesion. Immunohistochemistry (IHC) revealed faint nuclear positivity for β-catenin. The above findings led to our diagnosis of periosteal desmoid, which is rarely reported in the head-and-neck region. The major challenge in the diagnosis of such lesions is good clinicopathological correlation as the differential diagnosis of spindle-cell lesions is vast and needs IHC confirmation.