The desmoid tumor is an invasively proliferating fibrous lesion of soft tissue origin. It commonly arises in abdominal musculature and has been rarely observed in oral tissues. The present paper reports a case of desmoid tumor of the mandibular region.
A fifty one year old man was admitted complaining of gingiva swelling of the left lower first molar region, which he noticed approximately 10 days prior to admission. His history comprised appendectomy 20 years previously and extraction of the left lower first molar 10 years previously. He had no history of any facial trauma.
The intraoral examination revealed a 25 × 19 mm tough and rubbery mass on the gingiva of the left lower first molar area extending to the second premolar medially and the second molar distally. The radiological examination revealed a radiolucent area exteding from the alveolar ridge to the mandibular body, where a few nonradiolucent bone traveculae were observed. Some parts of border of the radiolucent area were indistinct and the other were thickened.
A provisional diagnosis made from clinical findings was a malignant tumor. However, the examination of biopsy specimens taken twice from the lesion revealed the characteristic of desmoid tumor.
Partial resection of the left mandible including some radiologically normal bone and gingiva was performed under general anesthesia. The postoperative course was uneventful and there was no evidence of recurrence approximately 3 years after the operation.
Macroscopically the lesion was whitish-gray in cdor, tough and rubbery. The lesion border was irregular and partially indistinct without the capsule.
Microscopically the lesion consisted of abundant, mature collagen fibers which ran parallelly, swirly and radiately in all directions. In fibrous stroma were spindle-shaped fibroblasts showing neither atypicality nor mitosis. Cellularity varied depending on area.
The elctron microscopic findings showed that cytoplasm contained considerably developed the rough endoplasmic reticulum. Collagen fibers were dense not only around cells but also in cytoplasm.
The lesion was consequently diagnosed as a desmoid tumor possibly originating from the connective tissue under the gingiva.
