5 July 2006 – Case of the Week #52
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We thank Dr. Sungmi Jung, Mayo Clinic, Rochester, Minnesota (USA) for contributing this case. We invite you to contribute a Case of the Week by sending an email to NPernick@PathologyOutlines.com with microscopic images (any size, we will shrink if necessary) in JPG or GIF format, a short clinical history, your diagnosis and any other images (gross, immunostains, EM, etc.) that may be helpful or interesting. We will write the discussion (unless you want to), list you as the contributor, and send you a check for $35 (US) for your time after we send out the case. Please only send cases with a definitive diagnosis.
Case of the Week #52
A 33 year old man had an asymptomatic hand mass, which was excised.
Gross images: image1
Microscopic images: low power - image2
Cytogenetics: image9 - t(11;16)(q13;p12-13)
What is your diagnosis?
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Chondroid lipoma is a rare, benign soft tissue tumor first described as a distinct entity in 1993 (Am J Surg Path 1993;17:1103). They are slow growing, painless masses of subcutaneous or deep soft tissue. Eighty percent occur in females, and age varies from 14 to 70 years. They typically occur in the extremities and limb girdles, but may be incidental findings at hip replacement surgery (J Surg Orthop Adv 2004;13:42). They may also occur within the oral cavity (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:331), trunk (Skeletal Radiol 2004;33:666) and at other sites.
Grossly, these tumors range up to 11 cm, are encapsulated and yellow-white. Microscopically, they contain nests and cords of multivacuolated cells resembling lipoblasts within a prominent chondromyxoid matrix, with variable mature fat. Fine needle aspiration shows mixtures of mature lipocytes and lipoblast-like cells within a chondromyxoid matrix (Arch Path Lab Med 2001;125:1224). There is usually prominent vasculature with variable wall thickness. There is no pleomorphism, no atypia and no/rare mitotic activity. The tumor cells are immunoreactive for S100 and vimentin, with variable staining for CD68 and keratin (Hum Path 1995;26:706). They are negative for EMA, HMB45 and smooth muscle actin. Cytogenetics shows a t(11;16) translocation, which is also found in hibernomas (Am J Surg Path 1999;23:1300, Mod Path 1999;12:88). Electron microscopy shows abundant intracytoplasmic lipid and glycogen and numerous pinocytotic vesicles, characteristic of white adipocytes, which suggests that there is no true cartilaginous differentiation (Am J Surg Pathol 1995;19:1272).
Excision is curative. These tumors do not recur, metastasize or transform.
The differential diagnosis includes myxoid liposarcoma and extraskeletal myxoid chondrosarcoma. Myxoid liposarcoma contains a delicate, plexiform capillary matrix and true lipoblasts. Extraskeletal myxoid chondrosarcoma has fibrous septa, and the chondroblasts typically lack intracytoplasmic vacuoles. It frequently contains mitotic figures and necrosis.
Nat Pernick, M.D.
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