Myxoinflammatory fibroblastic sarcoma is a distinct soft tissue tumour of low-grade malignancy.

Acral myxoinflammatory fibroblastic sarcoma was first described by Meis-Kindblom and Kindblom in 1998.

It was also named 'inflammatory myxohyaline tumor' of distal extremities with virocyte or Reed-Sternberg cells by Montgomery et al.

This tumour can recur locally and on rare occasions can metastasize.

Clinical presentation:  Clinically, the patients usually has a long history of a painless mass. The lesions are suspected to be ganglion cysts, tenosynovitis, or giant cell tumours of tendon sheath.

Age:  Peak incidence in mid-adult life.

Site:  Mostly located in the distal extremities (hands, feet, ankles, and the wrists). Proximal sites include forearm, arm, and thigh. The lesion may rarely present as a subcutaneous neck mass.

Gross: Poorly circumscribed mass. The lesion is often yellow-tan in colour with focal myxomatous areas. The size varies between 1.5 to 18 cm in diameter . 

Microscopic features:  Image1  ; Image2

Histologically, the lesions are multinodular, poorly delineated, with infiltrative margins.

The tumour is characterized by myxoid and fibrotic zones with hyalinized areas, moderately pleomorphic cells and an inflammatory infiltrate. There are solid nests of oval, spindle and epithelioid neoplastic cells.

The numerous inflammatory cells  include polymorphonuclear leukocytes, eosinophils, lymphocytes, and plasma cells. Focally aggregated inflammatory cells are present.

The large, bizarre tumour cells are characterized by large, lobulated, or multiple nuclei, prominent inclusion-like nucleoli and abundant eosinophilic cytoplasm, which is homogeneous to vacuolated and often contain intracytoplasmic inflammatory cells. Some of these cells resemble Reed-Sternberg cells, lipoblasts, and ganglion cells.

Immunohistochemistry:  The tumour cells are uniformly positive for vimentin; some cells are also positive for CD68 and CD34.  There is variable immunoreactivity for cytokeratin, and smooth-muscle actin.

Differential diagnosis:  

Reactive and neoplastic processes including:

Superficial acral fibromyxoma: Superficial acral fibromyxoma: a clinicopathologic and immunohistochemical analysis of 37 cases of a distinctive soft tissue tumor with a predilection for the fingers and toes.Hum Pathol. 2001;32(7):704-14.

Myxoid malignant fibrous histiocytoma (myxofibrosarcoma) ;

Epithelioid sarcoma ;   Liposarcoma ;   Hodgkin's disease.

The tumour has a relatively good prognosis with a long life expectancy despite frequent local recurrence.