Journal of Clinical and Diagnostic Research. 2018 Feb, Vol-12(2): ED06-ED08 6 6 DOI: 10.7860/JCDR/2018/32613.11207 Case Report Pathology Section Intraosseous Collagenous Fibroma (Desmoplastic Fibroblastoma) Involving Maxillary Bone CASE REPORT A 43-year-old woman who was using a removable partial prosthesis came with a request for placement of dental implants. During anamnesis, the patient reported agenesis of left maxillary lateral incisor and extraction of impacted maxillary left canine a few years ago. There was no pain and no history of trauma in that region. The radiographic records of the patient showed well-circumscribed radiolucency involving maxillary edentulous area corresponding to 22 and 23 [Table/Fig-1a]. The radiographic hypothesis was odontogenic cyst or tumour. On intraoral examination, the edentulous ridge was covered by normal oral mucosa [Table/Fig-1b]. The patient underwent an excisional biopsy and, during the trans-surgical procedure, we detected that the lesion was solid mass and firmly adhered to the oral mucosa. In addition, the vestibular and palatine bone between 21 and 24 teeth were absent. On gross examination we observed two fragments of smooth brown tissue measuring 2.0 x 1.5 x 0.5 cm, which were sent for histopathological analysis [Table/Fig-1c]. The diagnostic hypothesis was odontogenic lesion. Microscopically the tumour was composed of spindle to stellate shaped cells scattered within a myxocollagenous stroma with invasion of the skeletal muscle [Table/Fig-2a,b]. Neither cellular atypia nor mitotic figures were observed. Some areas of the tumour had collagen bands showing strong positivity for Masson’s trichrome [Table/Fig-2c]. The immunohistochemical staining was negative for S-100 [Table/ Fig-2d], CD34 [Table/Fig-2e] and Ki-67 [Table/Fig-2f]. A focal positivity was observed for HHF-35 [Table/Fig-2g] and smooth muscle actin [Table/Fig-2h]. The diagnosis was collagenous fibroma according to both clinical and histopathological patterns. The patient was followed up for six months and there was no sign of recurrence. NATÁLIA GALVÃO GARCIA 1 , SILAS ANTONIO JUVENCIO DE FREITAS FILHO 2 , CLÉVERSON TEIXEIRA SOARES 3 , CAIO MÁRCIO FIGUEIREDO 4 , DENISE TOSTES OLIVEIRA 5 Keywords: Benign tumour, Intraosseous lesion, Oral cavity ABSTRACT The collagenous fibroma (desmoplastic fibroblastoma) is a rare benign soft tissue tumour that can occur in the oral mucosa; intraosseous lesion is uncommon. A 43-year-old woman showed a well-circumscribed intraosseous radiolucency involving the maxillary edentulous area corresponding to 22 and 23 teeth. On intraoral examination, the edentulous ridge was covered by normal oral mucosa. The patient underwent an excisional biopsy and histopathological analysis revealed a tumour composed of spindle to stellate shaped cells scattered within a myxocollagenous stroma with invasion of skeletal muscle. The collagen bands showed strong positivity for Masson’s trichrome and the tumour cells showed focal positivity for HHF-35 and α-smooth muscle actin. The diagnosis was intraosseous collagenous fibroma according to both clinical and histopathological patterns. The patient was followed up for six months and there were no signs of recurrences. We report the second case of oral intraosseous collagenous fibroma and a critical review of English literature of the tumour in oral cavity. [Table/Fig-1]: Radiographic and clinical manifestations: a) Radiographic features of the intraosseous desmoplastic fibroma involving the maxillary bone (arrow); b) Clinical characteristics of the alveolar ridge covered by normal oral mucosa in the lesion area; c) Surgical specimen of the lesion. [Table/Fig-2]: a) Dense collagenous matrix in oral collagenous fibroma (H&E, 5X); b) Hypocellularity in dense fibrous area (H&E, 20X); c) Dense collagenous stroma (blue) and some positive areas for muscle (red) (Masson's Trichrome, 20X); d) S-100 protein negative in neoplastic cells and positive in neural fascicles (Immunohistochemistry: S100, 10X); e) Negative for CD34 in neoplastic cells and positive in blood vessels (Immunohistochemistry: CD34, 10X); f) Negative for Ki-67 (Immunohistochemistry: Ki-67, 40X); g) Focal immunoexpression of HHF-35 in tumour cells and muscle fibers (Immunohistochemistry: HHF-35, 20X); h) Immunoreactivity for α-smooth muscle actin in few cells and in the blood vessels (Immunohistochemistry: smooth muscle actin, 10X).