Pigmented Epithelioid Melanocytoma (“Animal-Type Melanoma”)

 Medium-sized epithelioid cells, large epithelioid cells, and spindled cells



• Spindled blue nevus-like cells

• Large epithelioid cells

• Does not exhibit brisk dermal mitotic activity




Ancillary Tests




• Loss of expression for protein kinase A regulatory subunit 1-α


Top Differential Diagnoses




• Malignant blue nevus

• Atypical cellular blue nevus

• Cellular blue nevus

• Common blue nevus

image
Extensive Pigmentation in PEM
A punch biopsy from an 11-year-old girl, right posterior auricular, shows a heavily pigmented compound melanocytic tumor with overlying epidermal hyperplasia and squamous proliferation image. Typically, pigmented epithelioid melanocytoma (PEM) is over pigmented out of proportion to the tumor.


image
Intraepidermal Melanophages in PEM
Among the epidermal psoriasiform hyperplasia image, there lies intraepidermal melanophages image. The squamous eddies image are reactive and not neoplastic. Large epithelioid dermal cells are evident image.

image
High Magnification of Large Epithelioid Cytology
High magnification shows large epithelioid cells image with open chromatin and cherry-red macronucleoli. The melanophages are packed with chunky clusters of melanin image, masking the nuclei. The tumor cells condense around the blood vessels and lymphatics but do not invade vascular spaces image.

image
Nodal Metastasis in PEM
A sentinel lymph node biopsy from the 11-year-old girl diagnosed with PEM shows melanophages image and large epithelioid tumor cells image, seen in multiple foci throughout the lymph node.


TERMINOLOGY


Abbreviations




• Pigmented epithelioid melanocytoma (PEM)


Synonyms




• Older terms, not recommended
image Animal-type melanoma

image Equine-type melanoma


Definitions




• Heavily pigmented, deeply invasive melanocytic proliferation with low-grade malignant potential

• Very controversial entity, not universally accepted (especially inclusion of some epithelioid blue nevi in this category)


ETIOLOGY/PATHOGENESIS


Genetic Syndrome




• May occur sporadically or in association with Carney complex


CLINICAL ISSUES


Site




• Extremities, trunk, and head and neck are most commonly affected sites


Presentation




• Heavily pigmented, dome-shaped, or verrucous nodule ≥ 1.0 cm in diameter

• Often of long duration


Treatment




• Surgical approaches
image Complete excision necessary

image Most experts recommend sentinel lymph node biopsy

image Systemic therapy may not be indicated, given lower malignant potential of PEM


Prognosis




• Has capacity to metastasize to lymph nodes but with less frequent systemic spread

• Short-term follow-up suggests better prognosis for PEM than for conventional metastatic melanoma


MICROSCOPIC


Histologic Features




• Extends into deep reticular tissue and subcutaneous fat along adnexal structures or neurovascular bundles
• More cellular in center and shows infiltrative growth pattern at periphery

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Pigmented Epithelioid Melanocytoma (“Animal-Type Melanoma”)

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