http://www.histopathology-india.MelanocyticTumours.htm

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:

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

 i) large melanocytes with pleomorphic; may resemble those of the epithelioid type of Spitz's 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, are atypical, or numerous, the diagnosis is almost certainly that of melanoma.

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.

Ancient melanocytic nevus. Semin Diagn Pathol. 1998 Aug;15(3):210-5.

Ancient melanocytic nevus is an example of a simulator of malignant melanoma, designated ancient because it shares numerous features with ancient schwannoma. Knowledge of the histopathologic characteristics of this benign melanocytic neoplasm should enable pathologists to avoid overdiagnosis of it as melanoma arising in the intradermal portion of a nevus. Ancient nevi are found most commonly on the face of older persons. The neoplasm is usually a dome-shaped, skin-colored or reddish brown papule, usually with features of a Miescher's nevus. Histopathologically, ancient nevi are exoendophytic, mostly intradermal proliferations of two populations of melanocytes: one with large pleomorphic nuclei and the other with small monomorphous ones. The large melanocytes may resemble those of the epithelioid type of Spitz's nevus. A few mitotic figures may be present in a particular section. The epidermis usually is uninvolved, but sometimes there may be a junctional component. Other important findings are degenerative changes that include thrombi, zones of hemorrhage, pseudoangiomatous changes, thick rims of sclerosis around dilated venules, fibrosis, and mucin. Ancient nevi frequently are misdiagnosed as melanoma arising in an intradermal nevus.