Extraskeletal myxoid chondrosarcoma is a rare
locally aggressive low-grade soft-tissue sarcoma with a high
potential for metastasis, especially to the lungs. It tends
to metastasize more frequently than skeletal myxoid chondrosarcoma
but is biologically less
aggressive.
Age
-Extraskeletal myxoid
chondrosarcoma usually occurs in adults.
Site-
These are located in the deep tissue of the extremities ,
specially in the musculature and rarely on the trunk, neck,
mediastinum & retroperitoneum.
Gross-
Lobulated, well circumscribed mass.
Microscopic features-
Multinodular tumour
- Consists of cords and strands of small ovoid cells with
eosinophilic cytoplasm and round nuclei set in a myxoid matrix
(lace-like growth pattern).
- Hyaline rhabdoid inclusions may be present (some of these cells
are CAM5.2 & vimentin positive)
- Hypercellular areas are noted at the periphery.
- In some cases the entire tumour is diffusely cellular and the
cells are more spindle shaped.
- The tumour cells contain glycogen (PAS postive). Myxoid matrix
is alcian blue positive.
Immunohistochemistry-
S100 protein positive. Some cases are EMA positive.
The tumour cells are usually negative
for keratins. (Synaptophysin,
NSE, PGP9.5 may be positive in a few cases)
Differential
diagnosis-
Myxoid Tumours of Soft Tissue
The differential diagnoses
of EMC include skeletal myxoid chondrosarcoma, chordoma,
parachordoma, mixed myoepithelial tumor, and other myxoid soft
tissue lesions. Skeletal myxoid chondrosarcoma can closely
mimic EMC. Mixed
tumour of soft tissue shows epithelial differentiation
(keratin, actin and S100 protein-positive).
Chordoma
and parachordoma can be differentiated from EMC by the
presence of physaliferous cells and epithelial markers. EMC is
distinguished from other myxoid soft tissue lesions by its
location and distinctive morphologic features.
Cytogenetics-
The tumour shows
chromosomal translocation t(9:22)(q22:q12).
The least cellular and most myxoid tumours carry the best
prognosis.
Malignant
mesenchymal neoplasm that produces osteoid, bone or
chondroid material and is located in the soft
tissues without attachment to the skeleton. This is
an aggressive tumour with over 60% mortality rate.
Age:
The
tumour usually occurs in late adult life (6th and
8th decade of life).
Site:
Lower
extremities are most commonly affected , other sites
include retroperitoneum and muscles of the pelvic
and shoulder girdles.
Gross:
Macroscopically the tumour is a firm to stony hard
mass. Sectoning may reveal granular white with
yellow flecks and multiple foci of haemorrhage.
Radiologically,
extraskeletal
osteosarcoma manifests as a soft tissue mass with
spotty to massive calcification. There is no
evidence of bone involvement.
Microscopic features:
Like
osteosarcoma of the bone the histologic patterns
include osteoblastic, chondroblastic, fibroblastic,
MFH-like, telangiectatic and well differentiated
types. In soft tissue, MFH-like osteosarcoma is the
commonest variant.
Differential diagnosis:
Myositis
ossificans (presence of histological zoning and lack
of prominent atypical features). Soft tissue tumours
with metaplastic bone formation (Synovial sarcoma;
Malignant fibrous histiocytoma ; Fibrosarcoma)
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