Abstract

Desmoplastic fibromas are fibrous tissue tumors and can be called the bony analogs of the abdominal desmoid. They have been described as slow-growing, histologically benign tumors of fibroblastic origin with variable biologic behavior. Though relatively rare, they are known for their very high local recurrence rates. Amputation is not the first-line of treatment. Limb-sparing surgery is the treatment of choice; often repeated excisions may be necessary resulting in an amputation. We present herein a case of a boy who presented to us with such a tumor on his forearm and the course of his treatment and follow-up over a period of five years.

Introduction

Case History and Course of Treatment

The boy presented to us first in 1999 at eight years of age. He was right-handed and presented with a slow growing globular mass on the right lower forearm. There was no pain or tenderness over the mass, which was firm to hard in consistency. Tissues around the radius were involved but skin was free from the mass. Wrist joint had a free range of movement. Xray showed an osteolytic, loculated lesion with minimal periosteal reaction (Fig. 1a).

Magnetic resonance imaging (MRI) showed a fairly extensive soft tissue involvement around the radius. But, the surrounding neurovascular structures were not involved (Fig. 1b). Biopsy (open biopsy) revealed the mass to be a desmoplastic fibroma. A wide excision was done and a fibular autograft was placed to bridge the defect keeping the distal fibular physis intact (Fig. 1c).

The patient was lost to follow-up a few months after the surgery. He came back with fresh complaints, more than two years later, of a soft tissue mass at the distal ulnar aspect of the forearm (Fig. 2a), which was firm and adherent to bone but nontender. A similar mass was seen under the volar incision site (Fig. 2b). Wrist was in radial deviation and also had a flexion contracture of 50- 60°. No pronosupination was possible in the forearm (Fig. 2c and 3a). There were no local signs of malignancy. Hematology was also essentially normal with only a mildly raised alkaline phosphatase level. Open biopsy showed tumor recurrence both at the graft site and distal ulna. Bone scan showed an increased uptake at distal ulna and mid-forearm. A second surgery was done in which a wide excision was done again and the entire mass inclusive of most of the radius, ulna and fibular autograft was excised (Fig. 3b and d). Radial artery was retained along with median and ulnar nerves. A one-bone forearm was constructed using autogenous fibula (Fig. 3c). Few weeks later, there was severe infection at the wound site. Repeated debridements were done and different antibiotics given as per sensitivity. The wound healed at first but again over the next two years it proved to be a resistant infection with repeat wound breakdown and sinus formation (Fig. 4b). Repeat biopsy showed no tumor recurrence. Eventually, the ulnar strut started protruding from the ulnar aspect of the forearm. It eventually extruded out and the infection healed (Fig. 4a and c). Repeat MRI too showed no recurrence of tumor. The forearm was now viable, tumor-free and nonfunctional (Fig. 5). The patient, when he last reported, had undergone an above elbow amputation (Fig. 6).

Discussion

Desmoplastic fibroma constitutes 0.06% of all bony tumors and 0.3% of benign bony tumors.¹ It is primarily a fibrous tissue tumor analogous to the abdominal desmoid.² It is a benign tumor but may be histologically difficult to distinguish from low-grade fibrosarcomas. Grossly, it is a homogenous, grayish-white to tan-colored, firm resilient tissue. It consists of thin wavy fibroblasts in an abundant collagen matrix with occasional areas of hemorrhage surrounded by osteoclast type giant cells and hemosiderin-laden macrophages.³ Multiple osteoclasts have been found at the endosteal border of the lesion; the lesion appears to peel easily away from the endosteal surfaces, but tongues of tumor extend into the cortex and between the trabeculae in the medullary cavity.³ This may explain the high recurrence rate following intralesional excision. Fibrous dysplasia can appear similar to desmoplastic fibroma, but dysplastic bone is absent in the former except in areas of pathological fracture or near the periphery of the lesion. So, for accurate histologic diagnosis specimen must be taken from the central part of the tumor.⁴

These tumors are usually seen in the first three decades of life and generally involve metaphyses of long bones. They do not cross the physes. Lesions spread to adjacent bones. Gebhardt et al3 have reported a case of multicentric desmoplastic fibroma, where the tumor was present in the upper ends of both respective femurs. Soap-bubble appearance is suggestive of a slow-growing tumor. CT helps to delineate the extent of the tumor. In MRI, the specific feature described is low to intermediate intensity foci on T2 weighted images that do not correlate as calcifications on radiographs.⁵ The biology of desmoplastic fibroma differs in that it is locally very destructive, has a high morbidity and recurs after incomplete excision. Recurrence rates are very high.

It differs from low-grade fibrosarcoma in that it does not metastasize. Accurate diagnosis is essential as treatment of choice is simply excision, marginal or wide. Intralesional curettage has also been described for these tumors and that too with augmentation by cryosurgery and methylmethacrylate.⁴ A recurrence rate of 55-72% is known after nonresection procedures and 17% after resection procedures. Wider the resection, lesser is the recurrence rate. There is no time frame for recurrence; 25% cases end up with amputation; 12% have a pathological fracture and 48% have soft tissue infiltration.

Conclusion

Due to their semimalignant nature, it is important to treat these lesions with marginal or wide excision.⁶ Adjuvant radiotherapy has been tried but has not proven to be of any benefit. Sites like fibula and rib are suited for resection.

Where resection is not possible due to the eventuality of a major functional deficit, intralesional curettage with augmentation by various methods described and bone grafting is definitely warranted. Recurrent lesions can be treated with marginal or wide resection. Amputation should rarely be necessary. Overresection in cases of mistaken diagnosis can lead to unnecessary amputations and underresection,in cases such as this, can lead to severe morbidity.

References

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