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Soft Tissue Tumors
Lipoblastoma / lipoblastomatosis
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Reviewer: David Lucas, M.D., University of Michigan Health Systems (January 2009)
Revised: 26 June 2009, last major update June 2009
Definition
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● Lobulated tumor, either localized (lipoblastoma) or diffuse (lipoblastomatosis), resembling fetal adipose tissue
Terminology
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● Lipoblastoma: also called fetal/embryonal lipoblastoma; well circumscribed and subcutaneous
● Lipoblastomatosis: deep-seated and ill-defined
Epidemiology
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● Rare; infants and young children age 3 years or less (rarely ages 14-24 years), 80% are boys
Sites
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● Extremities, trunk, head and neck
● Occasionally mediastinum, retroperitoneum or inguinal region
Clinical
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● Usually presents as painless superficial soft tissue mass, 75% on left side
● If not removed, matures into lipoma but with prominent fibrous septa
● FISH is helpful to confirm diagnosis (Histopathology 2008;52:294)
Case reports
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● 10 month old girl with 17 cm omental tumor (J Pediatr Surg 2007;42:1149)
● 1 year old boy with cervical mass (Case of Week #123)
● 1 year old boy with scrotal tumor and complex karyotype (Archives 2004;128:797)
● Buttock lesions (J Pediatr Orthop B 2006;15:356)
Treatment and prognosis
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● Complete excision, but with sparing of neurovascular bundle in large tumors (J Pediatr Surg 2008;43:1295)
● 14% recur due to incomplete removal (particularly lipoblastomatosis, AJSP 1997;21:1131)
● Does not metastasize
● Follow up for 3+ years is recommended (Pediatr Surg Int 2005;21:809)
Gross description
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● Soft, lobulated; usually 2-5 cm, mucoid cut surface
Gross images
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Mucoid cut surface
Micro description
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● Hypocellular lobules of adipocytes in various stages of differentiation including preadipocytes (spindle or stellate shaped), uni- or multi-vacuolated lipoblasts and mature adipocytes in central lobule
● Separated by prominent fibrous septa that may be cellular
● Has plexiform vascular pattern and abundant myxoid stroma
● May have prominent extracellular mucinous pools
● Resembles fetal fat and myxoid liposarcoma
● Lipoblastomatosis: less lobulation; infiltrates skeletal muscle
Micro images
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Lobular architecture with Plexiform vascular pattern Resembles lipoma with
prominent fibrous septa with myxoid matrix and minimal myxoid stroma
small fat cells
1 year old boy with neck mass
Lobulated tumor with prominent fibrous septa Resembles myxoid
liposarcoma
Various images Patterns
Other images: scapula tumor #1; #2; #3; #4
Cytology description
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● Moderate to poorly cellular; clusters of lipocytes, lipoblasts, spindle cells
● Background of myxoid material and naked oval nuclei (Diagn Cytopathol 2005;33:195)
Cytology images
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1 year old boy with neck mass
Electron microscopy
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● Cells have investing basal lamina, pinocytotic vesicles, Golgi membranes, round/oval mitochondria, cytoplasmic glycogen and cytoplasmic lipid (AJSP 1980;4:163)
● Resembles myxoid liposarcoma and normal developing fat
Electron microscopy images
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Intracytoplasmic lipid
Molecular / cytogenetics
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● Rearrangement of 8q11 approximately q13 region in 82% (Cancer Genet Cytogenet 2008;183:60), includes PLAG1 gene (Am J Pathol 2001;159:955)
● Produces HAS2-PLAG1 and COL1A2-PLAG1 hybrid genes (Atlas of Genetics and Cytogenetics)
● Also polysomy for chromosome #8
Differential diagnosis
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● Infantile fibromatosis - fibrous tissue only but may entrap mature fat cells, no myxoid stroma, no plexiform vascular pattern
● Myxoid liposarcoma - rare in children, no distinct lobulation, usually more cellular with giant cells containing pleomorphic nuclei, different molecular abnormalities
● Well differentiated liposarcoma - rare in children, has mature fat but no lipoblasts, has spindle cells with large, deep-staining nuclei and marked nuclear enlargement or pleomorphism; low cellularity, MDM2 and CDK4 immunostains are sensitive and specific (AJSP 2005;29:1340)
Additional references
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End of Soft Tissue Tumors > Lipoblastoma / lipoblastomatosis
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