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| September 2008
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This is a distinctive benign fibrous soft tissue tumour that was first described by Evans in 1995. Clinical presentation: The lesion presents as a firm, well circumscribed, painless mass of long duration and are commonly located in the subcutaneous tissue or skeletal muscle in adults. The tumours range in size from 1 to 20 cm. Site: This entity has been reported in various locations, including the upper extremities, posterior neck, upper back, lower extremities, abdominal wall, and hip. Gross: Macroscopically, the lesion presents as an elongated, lobulated, or disc-shaped mass with a firm consistency and a homogeneous grayish-white colour. Microscopic features:
Image1 The tumour is relatively hypocellular. There is proliferation of bland spindle or stellate shaped cells embedded in a fibromyxoid to densely fibrotic collagenous stroma. The stroma may contain a large amount of mucin which is positive with alcian blue. Mitotic figures are very rare or absent, tumour necrosis is not seen, and vascularity is low. The tumour often focally infiltrate the surrounding skeletal muscle and adipose tissue. Immunohistochemistry: Diffusely positive for vimentin. In some cases there may be focal staining for smooth muscle actin. S-100, EMA , CD34, desmin and keratin are usually negative. Electron microscopy : Revealed features consistent with a fibroblastic or myofibroblastic lineage. Differential diagnosis:
Fibromatosis- Collagenous fibroma should be
differentiated from fibromatosis, which has a high risk of local
recurrence if simple local excision is done. Fibromatosis is more
cellular and shows short fascicular arrangements of tumour cells and
greater infiltration at the periphery than collagenous fibroma. The tumour did not recur after complete surgical excision.
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