Desmoplastic fibroma

Clinical History

We report a seven-year-old boy with a history of right ulnar and radial fractures three years ago, now presenting with a large right forearm mass.

Imaging Findings

Initial AP and lateral radiographs of his right forearm demonstrated an expansile and lytic lesion with cortical breakthrough involving the proximal ulna just distal to the elbow joint (Fig. 1). Subsequent Computed Tomography (CT) shows multiloculated lytic bone lesion with a large soft tissue mass (Fig. 2). An MRI was performed and showed a well-circumscribed 20 x 6 x 5 cm soft tissue mass with extensive erosive destruction of the proximal right ulna (Fig. 3).

Discussion

Desmoplastic fibromas are exceedingly rare tumours that represent approximately 0.1 percent of all bone tumours. Incidence peaks in the first three decades of life with equal gender distribution [1]. The most frequent clinical presentation is an enlarging firm soft tissue mass. Originally described by Jaffe in 1958, desmoplastic fibromas histologically resemble locally aggressive soft tissue desmoid tumours [2] and are considered by some to be the bony counterpart of these tumours [3]. Although benign, desmoplastic fibromas are locally aggressive which often results in extensive deformity and morbidity.

Radiographically, they can have a geographic mostly lytic pattern or extensive bone destruction with ‘moth-eaten’ appearance (Fig. 1a). The osteolytic lesion characteristically lacks matrix calcification or sclerotic margins and often shows internal pseudotrabeculation [4]. Cross section imaging such as MRI is useful in further defining the soft tissue extent and neurovascular involvement, which aids in preoperative planning. Since recurrence rates after curettage exceeds 70%, the preferred management is resection with wide surgical margins [5], which frequently means amputation when the tumour involves the extremities. The patient initially underwent an incisional biopsy which showed interlacing bundles of uniform spindle cells with abundant collagen compatible with desmoplastic fibroma. Due to the significant deformity of the right forearm and to decrease the chance of recurrence, an above the elbow amputation was performed.

In conclusion, a slowly growing and locally aggressive bone tumour with a large soft tissue component but with a benign clinical course should raise the possibility of desmoplastic fibroma.

Differential Diagnosis List

Final Diagnosis

Desmoplastic fibroma

URL:	https://www.eurorad.org/case/13058
DOI:	10.1594/EURORAD/CASE.13058
ISSN:	1563-4086