Myxoinflammatory Fibroblastic Sarcoma

Myxoinflammatory fibroblastic sarcoma is a low-grade sarcoma with myxoid stroma and a mixed acute and chronic inflammatory infiltrate. Three main types of neoplastic cells are seen: spindled cells, large polygonal and bizarre ganglion-like cells, and variably sized multivacuolated lipoblast-like cells. All three types also have features of fibroblasts. The lesion predominantly affects the extremities, usually the hands and feet.

MRI findings are variable. The lesions can be well-defined or poorly defined. The signal characteristics are also variable. They can be low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, mimicking a cyst on unenhanced imaging. Post-contrast imaging reveals these to be solid lesions with avid enhancement ranging from mildly heterogeneous to homogeneous.

Differential considerations include much more common entities, such as ganglion cyst (in cases of predominantly myxoid lesions), giant cell tumor of the tendon sheath (in cases of well-defined heterogeneous lesions near tendon sheaths), and tenosynovitis (in cases of poorly defined lesions near tendon sheaths), nodular fasciitis (for lesions occurring in the subcutaneous tissues), and other soft tissue sarcomas.

The case above is from a 50-year-old woman who palpated a nodule in her right knee. The images reveal a heterogeneous, poorly defined lesion in the subcutaneous tissues abutting the vastus medialis muscle. The lesion is predominantly T1- and T2- hypointense with central areas of T2 hyperintensity and a peripheral T2-hyperintense rim. Post-contrast imaging was not performed.

References

• Kindblom LG and Meis-Kindblom JM. Myxoinflammatory fibroblastic sarcoma. in Pathology and Genetics of Tumours of Soft Tissue and Bone. Fletcher CDM, Unni KK, Mertens F (eds). IARCPress Lyon, 2002. pp 96-97.
• Narváez JA, Martinez S, Dodd LG, Brigman BE. Acral myxoinflammatory fibroblastic sarcomas: MRI findings in four cases. AJR Am J Roentgenol. 2007 May;188(5):1302-5.
• Tateishi U, Hasegawa T, Onaya H, Satake M, Arai Y, Moriyama N. Myxoinflammatory Fibroblastic Sarcoma: MR Appearance and Pathologic Correlation. AJR Am J Roentgenol. 2005 Jun;184(6):1749-53.