Quiz 30: What is your diagnosis?

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Diagnosis: Quiz 30

Quiz 30

Answer: Melanoma in situ

Criteria for diagnosis clinically: An asymmetrical plaque made up of shades of brown, mostly ones dark, and with a scalloped and notched border is a melanoma.

Differential diagnosis clinically: There is none

Criteria for diagnosis histopathologically: Abnormal melanocytes disposed as solitary units mostly, but in loci also in incipient nests, the latter having become confluent in foci, and distributed throughout the entire thickness of the epidermis, including the cornified layer, are those of melanoma.

Differential diagnosis histopathologically: There is none

Clinicopathologic correlation: The lesion is slightly elevated at its periphery because the epidermis there is thickened not only by a marked increase in number of melanocytes, but also of keratocytes, and the papillary dermis is widened by fibroplasia and by patchy infiltrates of lymphocytes and melanophages. The brown hue is contributed by the abundant melanin in melanocytes and keratocytes of the epidermis and by melanin in macrophages in the papillary dermis. The surface of the lesion is smooth because the stratum corneum (apart from its housing abnormal melanocytes) is normal for skin of the ankle.

Options for therapy predicated on knowledge of histopathologic findings: This melanoma, like all melanomas, should be excised completely with enough normal skin around it to accomplish that aim.

1) This melanoma can be judged to be in situ because the neoplastic melanocytes involve only the epidermis and eccrine ducts. In the widened papillary dermis repose numerous melanophages, but no neoplastic melanocytes.

2) As so often is the case for melanoma, many of the constituents of it in a particular section of tissue are distributed in fashion uneven. That is the case here for neoplastic melanocytes in the epidermis and in eccrine ducts and for lymphocytes and melanophages in the upper part of the dermis. There is a striking tendency to confluence of neoplastic melanocytes in the lower half of the epidermis, both those arrayed as solitary units and those in incipient aggregations. Had this lesion not been removed, it was merely a matter of time before ill-formed aggregations of melanocytes in the epidermis came to be well-formed and to predominate over melanocytes disposed as solitary units.

3) In a melanoma on or near volar skin, such as this one, it is common to behold scatter of abnormal melanocytes in the cornified layer. That also happens, not uncommonly, in various types of nevi on volar skin, they ranging from the conventional acral nevus to Spitz's nevus. In brief, scatter of melanocytes throughout the entire width of the epidermis is a circumstance expected for both nevi and melanomas that appear on or near volar skin. Also note well that melanocytes in the stratum corneum are separated from adjacent corneocytes by an encircling cleft, whereas corneocytes themselves pigmented greatly by melanin are cohesive, i.e., unaffiliated with a cleft.

4) Curiously, it is not common to observe a mitotic figure in a neoplastic melanocyte of melanoma lodged within the epidermis. One such mitotic figure is apparent here. As can be intuited, it is even less common to encounter a mitotic figure in a melanocyte in the epidermis of a nevus. That, too, however, can be met with in various situations, from Clark's nevus to Spitz's nevus. Practically never, however, is more than a single mitotic figure noted in the epidermis of a Clark's nevus.

5) Solar elastosis is missing from the dermis beneath this melanoma, which tells that "sun exposure" has not been plentiful over the course of many years.

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