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                Well Differentiated

Represents 40-45% of all liposarcoma.

Commonly occurs in the retroperitoneum or the limbs and rarely in the spermatic cord and the mediastinum.

The alternative terms
'atypical lipoma' and  'atypical lipomatous tumour' have been suggested by different authors.

The behaviour of these lesions  is substantially different depending on the location of the tumour.

Tumour in somatic soft tissue may recur but is incapable of distant metastasis and there is no tumour related death.

Tumour in retroperitoneum have a high  incidence of recurrence.

The recurrent tumours may have 'dedifferentiated' appearance. Some of these patients die as a result.
 

Subtypes according to histopathological features:        

1. Adipocytic (lipoma like)
2. Sclerosing
3. Inflammatory
4. Spindle cell  

1.Adipocytic(Lipoma like )-

Large well cicumscribed and coarsely lobulated tumour.

Microscopically, there are  mature adipocytes showing  variation in cell size. Focally nuclear atypia is evident.

In areas individual nuclei are compressed to crescentic shape.

Some hyperchromatic stromal cells are present. Lipoblasts may or may not be present.

Note: Presence of lipoblasts is not diagnostic of liposarcoma.

Lipoblasts are noted in benign  adipocytic tumours, eg. chondroid lipoma, lipoblastoma,  pleomorphic lipoma .

2. Sclerosing-

These are relatively pale and firm lesions occur most frequently in the retroperitoneum and the paratesticular region.
Microscopically , there are scattered hyperchromatic stromal cells, multivacuolated lipoblasts set in a collagenous backround. Foci of atypical lipomatous elements are noted.

3.Inflammatory-


There is a dense chronic inflammatory infiltrate almost obscuring the lipogenic areas. Prominent aggregates of lymphoid cells and plasma cells are noted simulating inflammatory pseudotumour.

4. Spindle cell- 

There  is proliferation of bland spindle cells in a fibrous or myxoid backround together with atypical lipomatous component  including lipoblasts. The differential diagnosis include:  malignant peripheral nerve sheath tumour, spindle cell lipoma , neurofibroma (S100 positive), dermatofibrosarcoma protuberans (diffuse CD34 positive) ,  well differeniated sclerosing liposarcoma and low grade fibromyxoid sarcoma.

Cytogenetics-  Ring or long marker chromosome derived from q13-15 region of chromosome 12.

                       Pleomorphic
              

Rare form of liposarcoma (5% of liposarcomas) usually located in the limbs of older adults.

These are aggressive tumours showing distant metastasis and about 40% mortality rate.

Microscopic  appearances-

1) A high grade pleomorphic MFH-like sarcoma containing few, scattered  multivacuolated lipoblasts.

Careful sampling is necessary to identify these cells.

2) A cellular pleomorphic or spindle cell neoplasm containing sheets of large bizarre lipoblasts.

Numerous intracytoplasmic eosinophilic globules may be present.

3)Sometimes a heavy neutrophilic infiltrate is present.  This lesion may cause diagnostic confusion with well differentiated inflammatory liposarcoma.

4)A new variant of pleomorphic liposarcoma characterised by sheets of epithelioid cells and focal adipocytic differentiation.

Pleomorphic Liposarcoma: Clinicopathologic Analysis of 57 Cases. Am J Surg Pathol. 2004 Oct;28(10):1257-1267

Pleomorphic Liposarcoma: A Clinicopathologic Analysis Of 19 Cases. Modern  Pathology 2001 Mar;14(3):179-84

             Myxoid and Round Cell

 

Represents 30-35% of all liposarcomas.

Myxoid and round cell liposarcomas commonly occur in the limbs usually  between third and fifth decade.

Microscopic appearances-

Purely myxoid liposarcoma (low grade tumour) is characterised  by  hypocellular  bland spindle cells  in a myxoid  backround.

Univacuolated lipoblasts are noted around the vessels.

Multivacuolated lipoblasts are present in the peripheral subcapsular zone .

There are thin walled branching vessels arranged in a plexiform pattern ('crow's feet' or 'chicken wire pattern' )

Mitotic figures are extremely  scarce.

Myxoid/round cell liposarcoma is characterised by hypercellular areas with undifferentiated round cells.

These cells are larger with hyperchromatic and more rounded configuration, in contrast to the spindle cells in the myxoid variant . Mitotic figures are more frequent. 

These tumours  have an aggressive behaviour.

Transition to hypercellular (round cell) areas are noted in myxoid liposarcoma. 

Pure round cell liposarcoma is rare (more than 80% round cells). 

More than 10% round cell areas - increased potential for metastasis.

More than 25% round cell areas - High grade tumour.

Differential diagnosis-  

Myxoid Tumours of Soft Tissue


Myxoid liposarcoma - Differential diagnosis:  Intramuscular myxoma,  Myxofibrosarcoma (myxoid MFH) lipoblastoma, extraskeletal chondrosarcoma, myxolipoma, well differentiated liposarcoma.

Round cell liposarcoma - Differential diagnosis:  Metastatic carcinoma, lymphoma, melanoma, Ewing's sarcoma.

Immunohistochemistry-

Undifferentiated round cells and bland spindle cells in myxoid and round cells display cytoplasmic and nuclear positivity with S100 protein.

The lipoblasts stain positively with S100 protein.

Plexiform vascular areas may be  demonstrated by CD31 and CD34 immuno- stains.

Cytogenetics-  t(12;16) (q13;p11) with rearrangement of the CHOP gene.

                       Dedifferentiated

    
Dedifferentiated liposarcoma is characterised by abrupt transition from low grade to high grade non lipogenic morphology within a well differentiated liposarcoma.

The transition is usually abrupt in nature.

90% cases occur  in primary tumour.

10% cases occur in recurrent tumour.
       
 

Microscopic appearances-

- Dedifferentiated areas are characterised by spindle and pleomorphic cells resembling  storiform-pleomorphic MFH or myxofibrosarcoma.

-May exhibit heterologous differentiation (myogenic, osteochondrosarcomatous or angiosarcomatous).

-New variant has been described exhibiting neural-like or meningothelial-like whorls of spindle cells.

Rarely paraganglioma-like histologic pattern has been observed.

-Sometimes the tumour exhibits fascicles of bland spindle cells these are described    as low-grade areas.

-Spindle cell liposarcoma which represents lipogenic lesion,must be distinguished  from low grade dedifferentiated liposarcoma  which is non lipogenic in nature and has a relatively better prognosis.

-High grade dedifferentiated liposarcoma (non lipogenic) must be differentiated  from pleomorphic liposarcoma.

-There is no difference in biological  behaviour of low and high grade dedifferentiated liposarcomas.

These are associated with 20-25% metastasis.

Recurrence rate is usually high.

                                                  

Abstracts:

Distant metastasis in retroperitoneal dedifferentiated liposarcoma is rare and rapidly fatal: a clinicopathological study with emphasis on the low-grade myxofibrosarcoma-like pattern as an early sign of dedifferentiation.Mod Pathol. 2005 Jul;18(7):976-84.

Dedifferentiated liposarcoma with a paraganglioma-like histologic pattern: a case report and review of the literature.Arch Pathol Lab Med. 2004 Jul;128(7):788-91

Pleomorphic Liposarcoma: Clinicopathologic, Immunohistochemical, and Follow-up Analysis of 63 Cases. Am J Surg Pathol 2002 May;26(5):601-16

Lipoleiomyosarcoma (well-differentiated liposarcoma with leiomyosarcomatous differentiation): a clinicopathologic study of nine cases including one with dedifferentiation.Am J Surg Pathol 2002 Jun;26(6):742-9

Liposarcoma with meningothelial-like whorls: a study of 17 cases of a distinctive histological pattern associated with dedifferentiated liposarcoma.Histopathology. 1998 Nov;33(5):414-24

Retroperitoneal liposarcoma with combined well-differentiated and myxoid malignant fibrous histiocytoma-like myxoid areas.Am J Surg Pathol 1999 Dec;23(12):1480-92

Liposarcoma: new entities and evolving concepts.Ann Diagn Pathol. 2000 Aug;4(4):252-66

Atypical and malignant neoplasms showing lipomatous differentiation. A study of 111 cases.Am J Surg Pathol. 1987 Mar;11(3):161-83

Leptin and Leptin Receptor mRNA are Widely Expressed in Tumors of Adipocytic Differentiation .Mod Pathol 2001;14:549-555

Lipomatous tumours of soft tissues: an update.Virchows Arch. 1995;427(4):353-63

Soft tissue liposarcoma: histological subtypes, MRI and CT findings.Radiol Med (Torino). 2002 Sep;104(3):140-9.

Primary liposarcoma of the skin: a rare neoplasm with unusual high grade features.Am J Dermatopathol. 1998 Aug;20(4):332-8

Well-differentiated inflammatory liposarcoma: an uncommon and easily overlooked variant of a common sarcoma.Am J Surg Pathol. 1997 May;21(5):518-27.

Lymphocyte-rich well-differentiated liposarcoma: report of nine cases. Am J Surg Pathol. 1997 Aug;21(8):884-95

Spindle cell liposarcoma, a hitherto unrecognized variant of liposarcoma. Analysis of six cases.Am J Surg Pathol. 1994 Sep;18(9):913-21.

Combined morphologic and karyotypic study of 28 myxoid liposarcomas. Implications for a revised morphologic typing, (a report from the CHAMP Group).Am J Surg Pathol.1996 ;20(9):1047-55

Cytologic features of round cell liposarcoma: a report on five patients.Cancer. 2003 :25;99(1):28-32

Dedifferentiated liposarcoma. Clinicopathologic analysis of 32 cases suggesting a better prognostic subgroup among pleomorphic sarcomas.Am J Surg Pathol. 1994 Dec;18(12):1213-23

Dedifferentiated liposarcoma: a clinicopathological analysis of 155 cases with a proposal for an expanded definition of dedifferentiation.Am J Surg Pathol. 1997 Mar;21(3):271-81

Dedifferentiated myxoid liposarcoma: a clinicopathological study suggesting a closer relationship between myxoid and well-differentiated liposarcoma.Histopathology. 1997 May;30(5):457-63

Epithelioid variant of pleomorphic liposarcoma: a comparative immunohistochemical and ultrastructural analysis of six cases with emphasis on overlapping features with epithelial malignancies.Ultrastruct Pathol. 2002 Sep-Oct;26(5):299-308


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