Desmoplastic fibroblastoma is usually a firm mobile slow-growing painless mass that is well-circumscribed, round to oval, or lobulated ⁹. Microscopically, it shows a hypocellular soft tissue mass that is mostly composed of abundant collagen fibers. Tumor cells are spindle or stellate-shaped with large nuclei that may contain eosinophilic nucleoli. In dense fibrotic areas, the cells do not have any mitotic activity or necrosis ². Binucleated cells and multinucleated giant cells may also be observed. Due to the surrounding collagenous stroma, few amounts of blood vessels were detected in this lesion. Inflammatory cells are usually absent ^1,2. By immunohistochemical staining, the cells show strongly positive immunoreactivity for vimentin and a variable immunoreactivity for smooth muscle actin ^10,11.

Herein we report a novel case of collagenous fibroma in the anterior part of maxilla and were unexpectedly presented as an intraosseous periapical lesion.

Click Here to Zoom

Figure 1: Periapical radiograph of the patient after root canal therapy: A well- defined radiolucent lesion mimicking periapical lesions.

Click Here to Zoom

Figure 2: Excisional biopsy of the mass.

Hematoxilyn& eosin stained sections showed a benign, wellcircumscribed mesenchymal tumor consisting of spindle and stellate-shaped fibroblasts in a collagen rich stroma. Some fibroblasts were binucleated and multinucleated with prominent nucleoli. A few blood vessels were detected. Inflammatory cells, areas of necrosis, calcification, and mitosis were absent (Figure 3A,B). Masson's trichrome staining revealed abundunt collagen bundles (Figure 4). Immunohistochemical (IHC) examination was positive for vimentin (Figure 5A), SMA, CD34 and S-100 were negative (Figure 5B). According to these findings, a diagnosis of desmoplastic fibroblastoma was established. The patient was examined after 1 year and there was no recurrence of the lesion.

Click Here to Zoom

Figure 3: A) Well-circumscribed paucicellular mesenchymal tumor (H&E; x40), B) Binucleated, stellate fibroblasts with prominent nucleoli (H&E; x400).

Figure 4: Stroma with abundant collagen bundles (Masson's trichrome; x200).

Click Here to Zoom

Figure 5: A) Spindle- and stellate-shaped cells positive for vimentin (IHC; x200), B) Negative for SMA (IHC; x200).

Seven cases have been reported in the oral cavity so far in the buccal mucosa, palate, parotid and gingiva. Our case is the first case that appeared to be intraosseous. After histopathological evaluation, a scar, desmoplastic fibroma, neurofibroma, chonromyxoid fibroma, lowgrade fibromyxoid sarcoma, calcifying fibrous- pseudo tumor and solitary fibrous tumor were considered in the differential diagnosis. There was no history of previous surgery or trauma that could cause a scar. Also there were no chondroid or myxoid area and no mitosis to prove chondromyxoid fibroma or fibromyxoid sarcoma. The lesion was hypocellular with no fascicular pattern so desmoplastic fibroma was ruled out and there was no calcification in the lesion for it to be a calcifying fibrous pseudo tumor. Neurofibroma has a myxoid stroma and spindle cells with wavy nuclei, which were not seen in our case. Negative S-100 protein and CD34 staining ruled out neurofibroma and solitary fibrous tumor.

Desmoplastic fibroblastoma is a tumor of soft tissue but Merriman et al. reported a case in which the tumor infiltrated and destructed the scapula ¹³.

This lesion is very rare in the oral cavity, Mesquita et al. has reported the first oral lesion in a 37-year-old woman. In their report, the histopathological features were similar to our case but clinically, in their case, the lesion was a solitary and firm 5 cm nodule in the palate and was not intraosseous. Histopathological sections showed stellate or spindle-shaped cells in a hypovascular fibrous stroma. Foci of fat were identified at the edges. Mitotic figures and tumor necrosis were absent. IHC staining was positive for vimentin, and a few cells were positive for alphasmooth muscle actin. Extracellular matrix of the tumor was immunopositive for type I and type III collagen and fibronectin ⁷.

Bhagalia et al. reported a 58-year-old female patient with the chief complaint of a firm, slow-growing, pedunculated lesion in the lingual gingival region in relation to the left 3rd molar that had appeared in three months without any pain or teeth mobility. The connective tissue demonstrated dense collagen bundles with distribution of spindle to stellate fibroblastic cells. Multinucleated giant cells were also observed. Blood vessels and inflammatory cells were few in number. Fat cells were seen in the center of the section. Masson's trichrome staining revealed areas positive for collagen and some areas positive for muscle ¹¹.

Immunohistochemical investigation can be for the definitive diagnosis and rule out other lesions in the differential diagnosis of desmoplastic fibroblastoma. We performed Masson's trichrome staining and immunohistochemical staining for vimentin, S-100 protein, SMA, and CD34. We found that collagen bundles were abundant by Masson's trichrome; the cells were strongly positive for vimentin and negative for S-100 protein, SMA and CD34. It is similar to the previous cases reported by Mesquita et al. ⁷.

De Sousa et al. in 2011 reported a 56-year-old man with a well-circumscribed, sessile, pink-colored mass in the left buccal mucosa. The mass was single, measuring 35 mm in diameter. Histopathologic features were similar to our case. Immunopositivity for vimentin and some positive cells with Factor XIIIa were seen ¹⁰.

In 2014, another case of oral cavity involvement has been reported in an 8-year-old boy with the complaint of a swelling in the left buccal mucosa in 6 months. In periapical radiography, there was no evidence of any periapical or other osteolytic lesions. Van Gieson special staining was positive for thick bundles of collagen ¹².

Shimoyama et al. reported a case of desmoplastic fibroblastoma in a 49-year-old woman with a painless slowlygrowing polypoid palatal mass. Her medical history was significant for rheumatoid arthritis and she had taken prednisolone for 4 years. There was no evidence of root resorption or bone destruction in the radiography. Histopathologic features were similar to other reported cases. Thick collagenized desmoid-like areas were also seen focally. IHC was diffusely positive for vimentin and there were some positive cells for SMA ¹⁴. All of the cases mentioned above were excised with no recurrence during follow-up. The case discussed in our report is a 58-year-old woman, although epidemiologic features of the previous studies point out to male predominance in the fifth to seventh decades of life ². However, case reports in the oral cavity revealed female predominance. Most of the cases were found in sixth decades of life, and palate was the most common site of involvement. Buccal mucosa, gingiva and alveolar ridge have also been reported with less frequency.

The exact cause of this lesion is still unclear but some studies stated that it might develop due to a chromosomal rearrangement (11q12) that could also occur in the fibroma of the tendon sheath ¹⁵. Some authors considered this lesion as a neoplasm, which does not have a preceding traumatic or inciting factor ^1,16. The treatment of choice for this lesion is total surgical excision and the prognosis is excellent with no recurrence ⁷.

ACKNOWLEDGMENT
The authors thank the Vice-Chancellery of Shiraz University of Medical Science for supporting this research. The authors would like to thank Dr. Sh. Hamedani (DDS, MSc) from the Dental Research Development Centre for helping with the English and editorial assistance in the manuscript.

1) Evans HL. Desmoplastic fibroblastoma. A report of seven cases. Am J Surg Pathol. 1995;19:1077-81.

2) Miettinen M, Fetsch JF. Collagenous fibroma (desmoplastic fibroblastoma): A clinicopathologic analysis of 63 cases of a distinctive soft tissue lesion with stellate-shaped fibroblasts. Hum Pathol. 1998;29:676-82.

3) Stacy RC, Jakobiec FA, Fay A. Collagenous fibroma (desmoplastic fibroblastoma) of the orbital rim. Ophthal Plast Reconstr Surg. 2013;29:e101-4.

4) Park JS, Bae KH, Oh HK, Park JB, Park DH. Genital desmoplastic fibroblastoma (collagenous fibroma). Urol J. 2014;11:1849-51.

5) Kawaguchi Y, Fujita T, Hanaoka J. Invasive desmoplastic fibroblastoma in the chest wall. Ann Thorac Surg. 2015;99:e85-6.

6) Cazal C, Etges A, Almeida FC, de Souza SC, Nunes FD, de Araujo VC. Collagenous fibroma (desmoplastic fibroblastoma) of alveolar bone: A case report. J Br Pathol Med Lab 2005;41:185-8.

7) Mesquita RA, Okuda E, Jorge WA, de Araujo VC. Collagenous fibroma (desmoplastic fibroblastoma) of the palate: A case report. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2001;91: 80-4.

8) Wilson C, Summerall J, Lubin J, Mesko TW. Collagenous fibroma (desmoplastic fibroblastoma): A unique presentation as a goiter in an 88-year-old man. Ann Diag Pathol. 2000;4:165-9.

9) Jham BC, De Mesquita Netto AC, Resende RG, Ribeiro DC, Mesquita RA . Pedunculated desmoplastic fibroblastoma (collagenous fibroma) of the oral cavity: A previously unreported clinical presentation. Int J Oral Maxillofac Pathol. 2013;4:21-6.

10) de Sousa SF, Caldeira PC, Grossmann Sde M, de Aguiar MC, Mesquita RA. Desmoplastic fibroblastoma (collagenous fibroma): A case identified in the buccal mucosa. Head Neck Pathol. 2011;5:175-9.

11) Bhagalia S, Jain M, Pardhe N, Sireesha SK. Collagenous fibroma (desmoplastic fibroblastoma) of the oral cavity. J Oral Maxillofac Pathol. 2012;16:277-9.

12) Varghese T, Pillai KS, Sarojini SB, Khosla E. Desmoplastic fibroblastoma (collagenous fibroma) in the oral cavity. J Indian Soc Pedo Prev Dent. 2014;32:238-41.

13) Merriman DJ, Deavers MT, Czerniak BA, Lin PP. Massive desmoplastic fibroblastoma with scapular invasion. Orthopedics. 2010;33.

14) Shimoyama T, Horie N, Ide F. Collagenous fibroma (desmoplastic fibroblastoma): A new case originating in the palate. Dentomaxillofac Radiol. 2005;34:117-9.

15) Sciot R, Samson I, van den Berghe H, Van Damme B, Dal Cin P. Collagenous fibroma (desmoplastic fibroblastoma): Genetic link with fibroma of tendon sheath? Mod Pathol. 1999;12:565-8.

16) Nielsen GP, O’Connell JX, Dickersin GR, Rosenberg AE. Collagenous fibroma (desmoplastic fibroblastoma): A report of seven cases. Mod Pathol. 1996;9:781-5.