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The term 'Malignant peripheral
nerve sheath tumour' (MPNST) is used by most authors (previously called
neurosarcoma, neurogenic sarcoma, neurofibrosarcoma and malignant
schwannoma).
This name indicates the possibility that the tumour may have diverse
origins, some arising from Schwann cells, others from perineurial cells
and still others from fibroblasts of the nerve sheath.
Individuals with internal plexiform
neurofibromas are 20 times more likely to have MPNSTs than individuals
without internal plexiform neurofibromas.
Age: Usually
occurs in young and middle aged adults.
Site: Commonly
occurs in deep soft tissues of the proximal extremities.
Clinical presentation:
i)Sporadic cases ii) 50% cases associated with Neurofibromatosis iii)
10% cases radiation induced
Gross features:
These are large tumours, more than 5 cms in diameter.The tumour arises as
large fusifom mass within a major nerve. It has a fleshy, white tan
surface. Focal areas of hemorrhage and necrosis may be present. Most
cases are deeply situated, however some cases may develop in superficial
neurofibroma.
Histopathological features:
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The tumour is composed of spindle cells arranged in sweeping fascicles.
Dense cellular areas alternate with hypocellular, myxoid zones.
Geographic areas of necrosis with tumour cells palisading at the edges.
The spindle cells in some areas show nodular or whorled appearance.
There is perivascular accentuation and proliferation of tumour cells
within the subepithelium of blood vessels.
Grade of the tumour depends on the cellularity and mitosis
Foci of osteogenic sarcoma, chondrosarcoma, angiosarcoma or
rhabdomyosarcoma is present in about 15% cases (Malignant
Triton tumour). IMAGE LINKS(ESCOP):click1 2
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Rarely there may be foci of
glandular differentiation.
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Variants of Malignant peripheral
nerve sheath tumour:
Myxoid MPNST:
Myxoid Tumours of Soft Tissue
Epithelioid: IMAGE
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This variant consists of epithelioid cells with vesicular nuclei and
prominent nucleoli. Focal spindle areas are also present.
D/D Amelanotic melanoma (HMB45 is negative in epithelioid MPNST)
Pigmented (Melanotic): IMAGE
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The tumour
displays epithelioid cells with vesicular nuclei and grooved nuclei,
abundant melanin pigment and numerous mitotic figures.
Immunohistochemistry:
S100 protein- Positive (only 50% cases)
Neuron-specific enolase, GFAP and neurofilament-Positive
Leu7 and myelin basic protein- weakly positive (not very reliable)
In the perineurial variant- S100 protein- Negative and EMA- Positive
In the epithelioid variant the number of S100 protein positive cells are
much higher.
Heterologous elements show positivity with relevant immunostains.
Differential diagnosis:
Congenital and childhood plexiform (multinodular) cellular
schwannoma. (Congenital and childhood plexiform (multinodular) cellular schwannoma: a troublesome mimic of
malignant peripheral nerve sheath tumor.
Am J Surg Pathol. 2003 Oct;27(10):1321-9).
Cellular neurofibromas and
neurilemmoma in Neurofibromatosis
Synovial sarcoma shows positivity with
cytokeratin 7 and 19 unlike malignant peripheral nerve sheath tumour.
Intramuscular myxoma(S100
protein negative) should be distinguished from low grade peripheral nerve
sheath tumour.
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