Neurogenic Tumours of the Lung

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:

IMAGE LINKS(ESCOP): click1  2  3  4  5  6  7  8

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  3  4  5

Rarely there may be foci of glandular differentiation.  IMAGE LINKS (ESCOP): click1  2  3  4

Variants of Malignant peripheral nerve sheath tumour:

Myxoid MPNST:  Myxoid Tumours of Soft Tissue

Epithelioid:  IMAGE LINKS(ESCOP): click1  2  3  4

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 LINKS(ESCOP):  click1  2  3  4

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.