Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma



Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma


Thomas Mentzel, MD









Gross pathology photograph shows a well-circumscribed neoplasm of deep soft tissues with indurated, yellow-white cut surfaces.






Hematoxylin & eosin shows striking variations in size and shape of lipogenic cells, as well as scattered enlarged cells with enlarged hyperchromatic nuclei.


TERMINOLOGY


Abbreviations



  • Atypical lipomatous tumor (ALT)


Synonyms



  • Well-differentiated liposarcoma (WDLS)


Definitions



  • Intermediate (locally aggressive, nonmetastasizing) lipogenic neoplasm composed of atypical adipocytes


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Accounts for 40-45% of all liposarcomas


    • Most frequently in deep soft tissues



      • Retroperitoneum, abdominal cavity, paratesticular region, mediastinum


      • Limbs


    • May also arise in subcutaneous tissue and very rarely in skin


  • Age



    • Middle-aged to elderly adults


    • Extremely rare in childhood


  • Gender



    • M = F


Presentation



  • Deep-seated, painless, and slowly enlarging tumor mass


Treatment



  • Complete surgical excision


Prognosis



  • In surgically amenable site



    • Recur only rarely after complete excision


  • Intraabdominal, retroperitoneal, mediastinal, or paratesticular lesions



    • Often recur locally and may be fatal


  • Variable risk of dedifferentiation in extremities (< 2%) and in retroperitoneum (> 20%)


IMAGE FINDINGS


General Features



  • Best diagnostic clue



    • Circumscribed lobular mass


  • Location



    • Deep soft tissues


  • Size



    • Variable


    • Usually > 5 cm


  • Morphology



    • Circumscribed lipomatous lesion


MACROSCOPIC FEATURES


General Features



  • Well-circumscribed lobular neoplasms


  • Color varies from yellow to white


  • Fat necrosis may be seen in large lesions


Sections to Be Submitted



  • Sample margins and representative sections of tumor


  • Look for indurated, firm areas


Size



  • May attain very large size


MICROSCOPIC PATHOLOGY


Histologic Features



  • Lipoma-like subtype



    • Adipocytes show significant variation in size and shape



    • Enlarged hyperchromatic nuclei


    • Hyperchromatic and multinucleated stromal cells


    • Lipoblasts may be seen but are not essential for diagnosis


    • Involvement of large vessel walls by atypical tumor cells


    • Prominent myxoid stromal changes may be present


    • Rare chondroid stromal changes


  • Sclerosing subtype



    • Scattered bizarre stromal cells with hyperchromatic nuclei


    • Rare atypical lipogenic cells and multivacuolated lipoblasts


    • Fibrillary, collagenous stroma


  • Inflammatory subtype



    • Prominent inflammatory infiltrate (lymphocytes, plasma cells)


    • Scattered atypical lipogenic cells/lipoblasts


    • Often edematous stroma


  • Spindle cell subtype



    • Atypical lipogenic cells


    • Slightly atypical neuroid spindle cells


    • Fibrous, fibromyxoid stroma


  • Heterologous differentiation rarely seen



    • Smooth or striated muscle


    • Cartilage, bone


Predominant Pattern/Injury Type



  • Circumscribed


Predominant Cell/Compartment Type



  • Adipose



    • Atypical adipocytes, atypical stromal cells, lipoblasts


Grade



  • Intermediate (locally aggressive but nonmetastasizing) malignant mesenchymal tumor

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma
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