Pathology of Ancient Melanocytic Nevus

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Dermpath-India

Ancient Melanocytic Nevus:

A pigmented benign skin tumour which should not be confused with melanoma.

Dr Sampurna Roy MD 2023

Ancient melanocytic nevus may mimic malignant melanoma.

The name 'ancient' is used because it shares numerous features with 'ancient schwannoma'.

Site: Found most commonly on the face of older persons.

Gross: The neoplasm is usually a dome-shaped, skin-colored or reddish brown papule.

Microscopic features:

Exo-endophytic, mostly intradermal proliferations of two populations of melanocytes .

(i) Large melanocytes with pleomorphic nuclei.

These may resemble those of the epithelioid-type of Spitz nevus.

(ii) Small monomorphous melanocytes.

A few mitotic figures may be present in a particular section.

Epidermis is usually uninvolved. Sometimes there may be a junctional component.

If the mitotic figures are in the base of the lesion, atypical or numerous,the diagnosis is almost certainly that of melanoma.

The lesion may be associated with areas of hemorrhage, perivascular sclerosis, thrombi formation, stromal fibrosis and mucin.

Other important findings :

Degenerative changes that include thrombi, zones of hemorrhage, pseudo- angiomatous changes, thick rims of sclerosis around dilated venules, fibrosis, and mucin.

Ancient nevi are often misdiagnosed as melanoma arising in an intra-dermal nevus.