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Soft Tissue Tumors

Adipose tissue

Lipoblastoma / lipoblastomatosis


Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 11 November 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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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, thigh, parotid region, scrotum, intrathoracic region

Clinical features
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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 boys with cervical mass (Case of the Week #123), scrotal tumor (Arch Pathol Lab Med 2004;128:797), thigh mass (J Cancer Res Ther 2012;8:157), thoracic cavity / mediastinal tumor (Rare Tumors 2011;3:e51)
● 18 month old boy with intraabdominal mass (Afr J Paediatr Surg 2011;8:320)
● 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, Am J Surg Pathol 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

Clinical images
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Lobulated and encapsulated tumor

Gross images
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Various images

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 prominent fibrous septa


Plexiform vascular pattern with myxoid matrix and small fat cells


Resembles lipoma with minimal myxoid stroma


Various images


1 year old boy with neck mass


Scrotal tumor

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 description
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● Cells have investing basal lamina, pinocytotic vesicles, Golgi membranes, round/oval mitochondria, cytoplasmic glycogen and cytoplasmic lipid (Am J Surg Pathol 1980;4:163)
● Resembles myxoid liposarcoma and normal developing fat

Electron microscopy images
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Primitive lipoblast has high nuclear-cytoplasmic ratio, intracytoplasmic lipid droplets, few organelles

Molecular/cytogenetics description
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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
● t(3;8)(p13;q21.1) also described (Pediatr Surg Int 2012;28:737)

Molecular/cytogenetics images
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FISH / CISH of PLAG1 gene

Differential diagnosis
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Lipofibromatosis / 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 (Am J Surg Pathol 2005;29:1340)

Additional references
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Stanford University

End of Soft Tissue Tumors > Adipose tissue > Lipoblastoma / lipoblastomatosis


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