Quiz 46: What is your diagnosis?

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Diagnosis: Quiz 46

Quiz 46

Answer: Melanoma

Criteria for diagnosis clinically: A black, somewhat oblong papule at one pole of a peculiarly-shaped plaque that displays hues of brown and pink is a melanoma.

Differential diagnosis clinically: There is none.

Criteria for diagnosis histopathologically: An asymmetrical proliferation with an uneven base consisting of strikingly abnormal melanocytes disposed as solitary units and in nests at all levels of the epidermis, including the cornified layer, and in crowded aggregations variable in size and shape in the upper part of the dermis is a melanoma.

Differential diagnosis histopathologically: There is none.

Clinicopathologic correlation: The black papule is made up of dense aggregations of neoplastic melanocytes in the upper part of the dermis and in the epidermis; it is black because so much melanin is present in neoplastic melanocytes and keratocytes in the epidermis, including corneocytes, as well as in neoplastic melanocytes and macrophages in the dermis; and the surface is smooth because the cornified layer is mostly normal. The surrounding plaque is formed by the proliferation of melanocytes in the epidermis and to a much lesser extent by the infiltrate of lymphocytes in the upper part of the dermis, and it is mostly brown because melanin is increased in amount in an epidermis peppered by abnormal melanocytes of melanoma.

Options for therapy predicated on knowledge of histopathologic findings: A malignant neoplasm such as this one must be excised in its entirety with a margin of normal skin sufficient to assure that that purpose has been accomplished.

1) The component of this melanoma that still is  in situ involves strikingly both surface epidermis and infundibular epidermis, the neoplastic melanocytes in the latter extending as solitary units especially, but also in tiny nests, to the level of a sebaceous duct.

2) The cleft that formed artifactually in a locus just beneath the epidermis is a phenomenon expected in some melanomas as a consequence of extraordinary confluence of neoplastic melanocytes at the dermoepidermal junction. A band of neoplastic melanocytes there compromises the normal adhesion between epidermis and dermis, and during the process of preparing a specimen for sectioning the fault becomes accentuated and resultant failure to remain fast becomes evident in the form of a subepidermal cleft. Note that some neoplastic melanocytes are present above, as well as below, the artificial cleft.

3) At the periphery of this lesion, small nests of monomorphic melanocytes seated at the dermoepidermal junction could be misread as those of a Clark's nevus. In reality, they are part of the melanoma. They do not, however, extend to lateral margins of this section of tissue.

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