Chondroid Lipoma Dr. Gunnlaugur Petur Nielsen

Case History: A 46-year-old man presented with a 5.0 x 3.5 x 2.5 cm painless mass in his proximal thigh. At the time of surgery the mass was located between the gracilis and adductor muscles. Grossly it was encapsulated, lobulated, firm and bright yellow. Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Diagnosis: Chondroid Lipoma Meis and Enzinger were the first to recognize chondroid lipoma as a distinct entity when they reported a series of 20 cases in 1993. An identical tumor had, however, been reported in 1986 as an example of an "extraskeletal chondroma with lipoblast-like cells". Chondroid lipoma usually occurs in middle age patients and women are affected more frequently than men at a ratio of 4:1. They may be located subcutaneously or deep and are most commonly found on the proximal limb girdle, leg, trunk and head and neck. Chondroid lipomas are well-demarcated tumors. They range in size from 1.5-11 cm, but are usually around 4 cm. The cut surface is smooth and yellow. Microscopically chondroid lipomas are well defined or encapsulated and are composed of mature white adipocytes admixed with eosinophilic cells with granular to fibrillary cytoplasm containing small intracytoplasmic vacuoles which resemble lipoblasts and chondroblasts. These cells are arranged in cords and nests in a myxochondroid matrix. The nuclei have irregular contours and lack pleomorphism and mitotic activity. Occasional fibrous bands subcompartmentalize the tumor into lobules. Immunohistochemically the neoplastic cells stain for vimentin, S-100 and CD68 and some tumors may be keratin positive. Electron microscopy studies have shown the features of white adipocytes, or features of embryonal fat and embryonal cartilage. Cytogenetic studies have identified a t(11;16)(q13;p12-13) abnormality in these tumors. This is distinct from the 16p11 seen in myxoid and round cell liposarcoma but is similar to what has been seen in hibernomas. The cellularity of chondroid lipoma and the myxochondroid matrix have caused them to be histologically confused with myxoid liposarcoma, extraskeletal myxoid chondrosarcoma, mixed tumors and soft tissue chondroma. Myxoid liposarcoma may contain areas of mature fat and vacuolated and eosinophilic cells in a myxoid stroma similar to chondroid lipoma, however chondroid lipoma lacks the distinct delicate branching vascular pattern present in myxoid liposarcoma and is usually less cellular. Extraskeletal myxoid chondrosarcoma is composed of cords of eosinophilic cells that are smaller than those in chondroid lipoma and the cells do not demonstrate adipocytic differentiation. Mixed tumors of the dermis or deep soft tissue are composed of nests and cords of eosinophilic cells in a myxochondroid stroma, but they are not as vacuolated as the cells in chondroid lipoma, and do not demonstrate adipocytic differentiation. Epithelial differentiation manifested by glands and myoepithelial cells are also usually present in mixed tumors. Immunohistochemistry is helpful in distinguishing between chondroid lipoma and mixed tumor because in additional to S-100, mixed tumors may stain with keratin, epithelial membrane antigen, smooth muscle actin, muscle actin, and glial fibrillary acidic protein, and chondroid lipomas do not. Soft tissue chondroma usually has true hyaline cartilage, does not contain intracytoplasmic fat and arises in the soft tissues of the hand and feet. Chondroid lipomas are treated by excision and they have not been shown to recur or metastasize. References Ballaux F, Debiec-Rychter M, De Wever I, Sciot R. Chondroid lipoma is characterized by t(11;16)(q13;p12-13). Virchows Arch 444:208-210, 2004. Chan JK, Lee KC, Saw D. Extraskeletal chondroma with lipoblast-like cells. Hum Pathol 17:1285-1287, 1986. Green RA, Cannon SR, Flanagan AM. Chondroid lipoma: correlation of imaging findings and histopathology of an unusual benign lesion. Skeletal Radiol 33:670-673, 2004. Guillou L, Coindre JM. Newly described adipocytic lesions. Semin Diagn Pathol 18(4):238-249, 2001. Kindblom LG, Meis-Kindblom JM. Chondroid lipoma: An ultrastructural and immunohistochemical analysis with further observations regarding its differentiation. Hum Pathol 26:706-715, 1995. Meis JM, Enzinger FM. Chondroid lipoma. A unique tumor simulating liposarcoma and myxoid chondrosarcoma. Am J Surg Pathol 17(11)1103-1112, 1993. Nielsen GP, O'Connell JX, Dickerson GR. Chondroid lipoma, a tumor of white fat cells. A brief report of two cases with ultrastructural analysis. Am J Surg Pathol 19(11):1272-1276, 1995. Thomson TA, Horsman D, Bainbridge TC. Cytogenetic and cytologic features of chondroid lipoma of soft tissue. Mod Pathol 12(1):88-91, 1999.