Teaching Case

A 14-year-old male patient was referred to the unit of Oral and Maxillofacial Surgery for a swelling in the vestibular aspect of the left mandible. The patient did not experience any symptoms related to the mass. On clinical examination a hard tumefaction on the vestibular aspect of LL6 was detected.

OPG showed a partially defined lytic lesion on the mesial root of LL6, without clear margins. CBCT examination was performed with the following parameters: 90 kV, 6 mA, 12 seconds, 8 cm FOV. CBCT revealed the presence of a unilocular radiolucent lesion of the vestibular cortical bone with internal pseudo-trabeculations. The overall appearance of the lesion was of a soap bubble appearance, with focal interruption of the vestibular cortical bone. The lesion dimensions were 0.86 x 1.59 cm, with the major axis parallel to the mandible margin.

Desmoplastic fibroma is a rare benign bone tumour which originates from connective tissue with characteristics of local aggression and a high recurrence rate. It is a fibrous tumour of the bone, histologically appearing similar to soft tissue desmoid tumour. It is characterised by the presence of mesenchymal cells, mainly fibroblasts, in an abundant collagenous stroma [1]. Historically desmoplastic fibroma is an intraosseous fibrous lesion of the metaphysis of long bones, first described by Jaffe in 1958 [2]. Involvement of the jaw bones was first reported by Griffith and Irby in 1965. Desmoplastic fibroma accounts for 0.06% of all tumours of the bone, affecting mostly the mandible (22-27%), other sites are long bones (femur, radius and tibia) and the pelvis. It affects mainly adolescents and young adults, the mean age at presentation is 15-25 years [3]. Clinically there are no pathognomonic symptoms, except for a painless swelling, trismus and lymphadenopathy [4]. On radiographic investigations, desmoplastic fibroma appears as a unilocular radiolucent bone lesion with a narrow zone of transition and non-sclerotic margin; in some cases it can present with a ‘soap bubble’ appearance. The differential diagnosis of these radiological findings is broad, making the diagnosis quite difficult, however, desmoplastic fibroma should be considered in case of an aggressive radiolucent lesion in children [5]. Histological examination is fundamental to diagnosis. The surgical management of desmoplastic fibroma includes curettage to complete resection. Curettage has been associated to higher recurrence rates, this is thought to be due to the absence of a capsule which may hinder the identification of the margins of the lesion; therefore in case of soft tissue invasion, a wider resection margin is recommended. Radiotherapy and chemotherapy, even if not as a first choice, have been used to support surgical treatment [6]. In terms of investigation, CBCT can be a useful means for the investigation of the osseous extent of the lesion, although multi-slice CT and especially MR are more effective in the evaluation of soft tissue involvement.

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