Low-grade fibromyxoid sarcoma
Low-grade fibromyxoid sarcomas are malignant fibroblastic soft tissue neoplasms characterized by alternating fibrous and myxoid elements and a propensity to late recurrence and metastasis.
Terminology
An alternative term for low-grade fibromyxoid sarcoma is Evans tumor. The term hyalinizing spindle cell tumor with giant rosettes is now discouraged.
Epidemiology
The incidence of low-grade fibromyxoid sarcomas might have been underestimated due to their propensity of mimicking other soft tissue tumors but is generally considered as relatively rare. They can occur in a wide age range but occur most frequently in younger adults and about one-fifth of tumors are seen in adolescents. Men are slightly more commonly affected .
Clinical presentation
Typical manifestation is a painless slow-growing mass sometimes present over years .
Pathology
Low-grade fibromyxoid sarcomas are malignant tumors with alternating collagenous and myxoid components with bland spindle cells arranged in a fascicular or whorling growth pattern .
Etiology
The cause of low-grade fibromyxoid sarcomas is unknown.
Location
In adults, low-grade fibromyxoid sarcomas usually arise from the subfascial soft tissues of the proximal extremities and the trunk. Less common sites of involvement are the abdominal cavity, the retroperitoneum or mediastinum. In children, the superficial soft tissues of the head and neck region are often involved .
Macroscopic appearance
The macroscopic appearance of low-grade fibromyxoid sarcomas is characterized by a firm well-demarcated fibrous tumor with mucoid areas .
Microscopic appearance
Microscopic characteristics of low-grade fibromyxoid sarcomas include the following :
- an admixture of collagenous with few cells and more cellular myxoid zones
- abrupt transitions between the two patterns
- bland spindle cells growing in a fascicular whorling or storiform pattern
- arcades of small vessels with occasional staghorn pattern of vascularity
- giant hyaline collagen rosettes surrounded by epithelioid tumor cells in a number of cases
- sometimes sclerosing epithelioid fibrosarcoma-like patterns
Immunohistochemistry
Immunohistochemistry stains express MUC4 in a very high number of cases, which is highly sensitive and specific for low low-grade fibromyxoid sarcomas and sclerosing epithelioid fibrosarcoma. Other expressions include CD99, BCL2, EMA and vimentin in many cases as well as smooth muscle actin in a low number .
Genetics
Low-grade fibromyxoid sarcomas regularly show either FUS-CREB3L2 or FUS-CREB3L1 gene fusions.
Radiographic features
Imaging features of the tumor have been described as multinodular, heterogeneous, gyriform often with complex solid cystic components and mostly well-defined tumor margins .
Ultrasound
Ultrasound findings of low-grade fibromyxoid sarcomas are described as solid soft tissue tumors with heterogeneous echogenicity .
CT
Low-grade fibromyxoid sarcomas show the following imaging features :
- hypodense compared to skeletal muscle in most cases
- calcifications are uncommon
MRI
MR imaging findings have been described as tumors with a striated appearance or gyriform patterns of signal intensity and contrast enhancement . A substantial number of cases have been reported showing peritumoral edema and/or a split fat sign.
Signal characteristics were described as follows :
- T1
- mostly hypo- to isointense to muscle
- fibrous components: hypointense
- myxoid components: hypointense
- T2
- heterogeneous high-signal intensity
- fibrous components: hypointense
- myxoid components: hyperintense
- T2FS/PDFS: iso- to hyperintense
- DWI: diffusion restriction
- T1 C+ (Gd): inhomogeneous or alternating or gyriform patterns of enhancement
Radiology report
The radiological report should include a description of the following features:
- form, location and size
- tumor margins
- relation to adjacent bones and the muscular fascia
- relationship to local nerves and vessels
- relationship to other organs
Treatment and prognosis
Recurrences and metastasis are low within the first five years after excision but much higher in the long term with overall recurrence rates higher than 60% and a fatality rate of over 40%. Metastases have been observed even more than 40 years after primary resection. The most common sites for metastasis are lung, pleura, bone and liver .
History and etymology
Low-grade fibromyxoid sarcoma was first described by an American pathologist Harry L Evans in 1987, hence its alternate name of Evans tumor .
Differential diagnosis
Conditions which can mimic the appearance of low-grade fibromyxoid sarcomas include :
