Soft Tissue Tumors - Well differentiated myxoid liposarcoma

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Soft Tissue Tumors

Adipose tissue-liposarcoma

Well differentiated myxoid liposarcoma

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 13 November 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

Definition
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● Low grade tumor with primitive non-lipogenic mesenchymal cells, signet ring lipoblasts and prominent myxoid stroma with branching vascular pattern

Terminology
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● Also called paucicellular myxoid liposarcoma

Epidemiology
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● Peaks in 30’s and 40’s
● May occur in children, very rarely in elderly

Sites
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● Usually thigh and lower extremity of young adults
● Retroperitoneal involvement is rare

Case reports
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● 71 year old man with supraclavicular fossa mass (Chest 2000;117:1518)
● Young men with multicentric tumors (World J Surg Oncol 2007;5:139)

Treatment and prognosis
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● Median survival 105 months (Ann Surg Oncol 2007;14:1507)
● Pure tumors (without round cells) have low grade behavior with only rare metastases
● Poorer prognosis if round or pleomorphic cells

Gross images
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Various images

Other images: well circumscribed white tumor; lobulated gray-white tumor within skeletal muscle

Micro description
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● Low grade and paucicellular with monomorphic, stellate or fusiform cells without atypia
● Prominent chicken wire vasculature (delicate thin walled arborizing and curving capillaries)
● Numerous signet ring lipoblasts, particularly at periphery of lobules, has mucoid matrix rich in hyaluronidase sensitive acid mucopolysaccharides, may have large mucoid pools
● Lymphangioma-like cystic degeneration is relatively specific
● Rarely metaplastic cartilage or cartilage with TLS-CHOP fusion gene (Appl Immunohistochem Mol Morphol 2007;15:477)
● No/rare mitotic figures

Micro images
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Histological sections of a myxoid liposarcoma showing sheets of multivacuolated lipoblasts with atypical nuclei (blue arrows) and interspersed arborising thin-walled vessels

Large (mature) and small fat cells

Resembles pulmonary edema due to large irregular cystic spaces, some with granular eosinophilic material

Hypocellular zones: left-small artery, middle-veins, right-transition between cellular and hypocellular areas

Cords of cells resembling myxoid chondrosarcoma

Hyalinized collagenous stroma (rare finding)

Lipoblasts, myxoid stroma and branched capillaries

Signet ring lipoblasts

Metastases

Other images: lipoblasts, myxoid stroma and branched capillaries #1; #2; #3; lipoblasts #1; #2; #3; #4

Cytology description
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● Myxoid material with arborizing blood vessels and lipoblasts (Acta Cytol 2007;51:456)

Positive stains
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● Vimentin, S100, CD36 (Am J Clin Pathol 1995;103:20)

Electron microscopy description
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● White adipose tissue, aggregates of 60-Angstrom intermediate filaments and large masses of glycogen (Am J Clin Pathol 1979;72:521)
● Cells have investing basal lamina, pinocytotic vesicles, cytoplasmic glycogen and cytoplasmic lipid (Am J Surg Pathol 1980;4:163)
● Resembles lipoblastoma

Differential diagnosis
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● Extraskeletal myxoid chondrosarcoma: malignant chondrocytes, no cytoplasmic fat vacuoles, no prominent vasculature
● Lipoblastoma: similar histology but age 5 years or less
● Myxofibrosarcoma: older adults, often superficial, infiltrative, no cytoplasmic fat vacuoles, more nuclear atypia, thicker curvilinear vessels, frequent mitotic figures
● Myxoma: extremely paucicellular, lacks a prominent vascular component

End of Soft Tissue Tumors > Adipose tissue-liposarcoma > Well differentiated myxoid liposarcoma

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