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Neural Tumours

Pathology of Malignant Peripheral Nerve Sheath Tumour

 Dr Sampurna Roy MD          

 

                                                                                                                      

 

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:

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).

Rarely there may be foci of glandular differentiation.  

Variants of Malignant Peripheral Nerve Sheath Tumour:

Myxoid Malignant peripheral nerve sheath tumour :  Myxoid Tumours of Soft Tissue

Epithelioid Malignant Peripheral Nerve Sheath Tumour:

       

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" Epithelioid malignant peripheral nerve sheath tumor (EMPNST) is rare and differs from conventional malignant peripheral nerve sheath tumor by showing diffuse S-100 protein positivity, infrequent association with NF1, and occasional origin in a schwannoma. Loss of INI1 expression is seen in a subset of tumors." Epithelioid malignant peripheral nerve sheath tumor: clinicopathologic analysis of 63 cases.

This variant consists of epithelioid cells with vesicular nuclei and prominent nucleoli.

Focal spindle areas are also present.

Immunohistochemistry: A strong cytoplasmic and nuclear staining with S 100 protein. Focal staining with Smooth Muscle Actin. Other stains are usually negative.

Differential diagnosis:  Amelanotic melanoma (HMB45 is negative in epithelioid MPNST)

Pigmented (Melanotic) Malignant Peripheral Nerve Sheath Tumour:

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:

Other sarcomas were ruled out mainly by immunochemistry.

The lack of expression of myogenic markers (desmin, caldesmon)   rules out leiomyosarcoma.

Malignant melanoma is ruled out on the basis of negatic melanocytic markers other than S100 protein (HMB45, Melan-A, MART1).

Congenital and childhood plexiform (multinodular) cellular schwannoma. (Congenital and childhood plexiform (multinodular) cellular schwannoma: a troublesome mimic of malignant peripheral nerve sheath tumor.  ). 

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.

 

Further reading:

Association between benign and malignant peripheral nerve sheath tumors in NF1.Neurology.

Malignant peripheral nerve sheath tumor: a comparison of grade, immunophenotype, and cell cycle/growth activation marker expression in sporadic and neurofibromatosis 1-related lesions.

Expanding the spectrum of malignant change in schwannomas: epithelioid malignant change, epithelioid malignant peripheral nerve sheath tumor, and epithelioid angiosarcoma: a study of 17 cases.

Malignant Peripheral Nerve Sheath Tumors Associated With Neurofibromatosis Type 1 A Clinicopathologic and Molecular Study of 17 Patients.

Subcutaneous malignant epithelioid schwannoma with cartilaginous differentiation.

Cutaneous epithelioid malignant nerve sheath tumor with rhabdoid features.

Cytologic features of malignant peripheral nerve sheath tumor

Malignant peripheral nerve sheath tumor with perineurial differentiation: 'malignant perineurioma'.

 

 

 

 


 

 

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