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  Dr Sampurna Roy MD

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Mesothelioma of Atrioventricular Node

Clinical presentation:

Clinically, the lesions are usually found on the head and neck region and present as bulky firm fibrous masses of tumour or indurated plaques. These are usually amelanotic lesions.

Most desmoplastic melanomas are variants of lentigo maligna melanoma.

Microscopic features: Image Link1 ; Image Link2 ; Image Link3 ; Image Link4 ; Image Link5

Poorly demarcated, infiltrating intradermal tumours often with sparse cellularity.

The tumour consists of elongated spindle-shaped (fibroblast like) cells surrounded by mature collagen bundles. 

A few scattered cells display hyperchromatic, atypical nuclei.  Occasional mutinucleate cells may be present.

The tumour displays haphazard, fascicular or storiform growth pattern.

The stromal component varies in different tumours.  In spindle cell melanoma there is less desmoplasia. 

In desmoplastic melanoma there are scattered collection of lymphocytes and plasma cells.

Small foci of neural transformation and neurotropism may be present.  The presence of neurotropism correlates with a tendency to local recurrence.

Desmoplastic melanoma is often associated with a lentigo maligna epidermal component overlying or towards one edge of the lesion.

It is often difficult to find melanin in usual H&E sections.

Mitotic figures are usually present.

The tumour infiltrates deep and it may be difficult to estimate the full extent of the tumour.

   IMAGE LINKS:  Image1 ; Image2 ;  Image3 ;

        Image 4 ; Image5 ; Image6 ;Image7; DermAtlas

Immunohistochemistry:

The tumour cells are positive for vimentin in all cases and for S100 protein and neuron specific enolase in about 95% of cases.

HMB45 is usually  negative in desmoplastic melanoma.

In spindle cell melanoma about 50% of cases show some HMB45  positivity (these cases have aggressive behaviour)

Melan A is negative in desmoplastic melanoma. It has been reported  that some cases of metastatic desmoplastic melanoma are CD34 positive.

Actin is also expressed in some cases.

Occasionally, the spindle cells of desmoplastic melanoma  can be negative for S100 , making distinction from other spindle cell lesions difficult.

Differential Diagnosis:

Desmoplastic melanoma should be distinguished  from other spindle cell lesions such as sclerosing melanocytic nevi, nodular fasciitis,  atypical fibroxanthoma,  dermatofibrosarcoma protruberance and spindle cell squamous carcinoma and scar tissue.

Unlike immature scar tissue, in desmoplastic melanoma there is neurotropism, epidermal proliferation of melanocytes, and S100 and/ or HMB45 positivity. (Histologic differentiation of desmoplastic melanoma from cicatrices. Am J Dermatopathol. 1998;20(2):128-34)

The sclerotic/desmoplastic and hypopigmented blue naevi are uniformly positive for Melan-A, while desmoplastic melanoma is negative in the spindle cell compartment.

The nuclei in desmoplastic melanoma have a haphazard pattern and in scar tissue the nuclei have a  parallel arrangement.

Spitzoid melanoma (cells are more plump) should also be excluded from spindle cell melanoma (cells are longer and thinner, less aggressive clinical behaviour).

Neurotropic melanoma:

The neurotropic melanoma is characterized by spindle shaped cells showing neuroma- like pattern.

These tumour cells  infiltrate around nerve bundles in the deep dermis and subcutaneous tissue. Hence the lesion is  called neurotropic melanoma. Often a combined desmoplastic and neurotropic patterns are present. 

Differential diagnosis : Neural and melanocytic lesions (desmoplastic melanocytic nevus , neurofibroma and malignant schwannoma).