Quiz 29: What is your diagnosis?

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Diagnosis: Quiz 29

Quiz 29

Answer: Melanoma in situ  in association with a tiny intradermal congenital nevus, superficial and "deep"

Criteria for diagnosis clinically: An asymmetrical patch of shades of brown with a scalloped border is a melanoma, and the reddish brown papule off-center is a small congenital nevus.

Differential diagnosis clinically: There is none.

Criteria for diagnosis histopathologically: A broad proliferation of melanocytes within surface and infundibular epidermis that is characterized by predominance of melanocytes disposed as solitary units positioned not only at the dermoepidermal junction, but well above it, by incipient nests of melanocytes, those being seated mostly at the junction, and neither the solitary melanocytes being situated equidistant from one another nor the nests of them being equidistant from one another, computes to a diagnosis of melanoma in situ. In one discrete tiny locus in the upper part of the reticular dermis is a cluster of monomorphic melanocytes arrayed as strands, cords, and columns "splayed" between bundles of collagen, it being a congenital nevus of the superficial and "deep" type.

Differential diagnosis histopathologically: The small congenital nevus could be misinterpreted as being part of the primary melanoma, but it cannot be that because it is separated from the melanoma in situ by the entire papillary dermis and the uppermost part of the reticular dermis. Neither can it possibly be a metastasis of melanoma because the primary melanoma is housed entirely in situ, which precludes it from having metastasized.

Clinicopathologic correlation: The lesion is flat because the melanoma is wholly in situ, it is brown because of an increase in melanin in epidermal keratocytes and in neoplastic melanocytes, its hues of brown are the result of melanin in the epidermis being distributed unevenly, and its surface is smooth because the cornified layer is normal. The off-center dark red papule is made up largely of the congenital nevus situated in the upper part of the reticular dermis (the component of melanoma in situ being inconsequential to formation of it). 

Options for therapy predicated on knowledge of histopathologic findings: A melanoma in situ such as this one must be excised in the same manner as would a primary melanoma that extended deep in the dermis (or into the subcutaneous fat), namely, with just enough normal tissue around it to ensure that that desideratum has been achieved, as seems to have been the case in this instance.

1) In the most recent seventh edition of  Fitzpatrick's Dermatology in General Medicine  published in 2008, in a chapter titled "Atypical melanocytic nevi", Margaret A. Tucker writes under the heading "Complications," that "The major complication of DN [dysplastic nevus] is melanoma" and "These lesions [dysplastic nevi] are both risk markers for melanoma and precursor lesions for melanoma." Because nowhere in her chapter does she indicate that for 30 years what has been termed dysplastic nevus is not a single type of nevus but either a congenital nevus (superficial or superficial and "deep") or an acquired Clark's nevus, she is unable to appreciate the reality of Clark's nevus being uncommon in comparison to congenital nevi as an accompaniment of melanoma. The circumstance pictured here is illustrative of that phenomenon, namely, the tiny nevus in the upper part of the reticular dermis is congenital (superficial and "deep").

2) Although melanoma in Asians and Africans hardly ever occurs in association with a preexisting nevus, that is not the case for "Caucasians"; about 15% of all melanomas in "Caucasians" arise in association with a preexisting nevus. The majority of those nevi are congenital, either "superficial" or "superficial and 'deep'", the latter being the circumstance here.

3) Note that the findings architecturally and cytopathologically of this melanoma are the same in both surface epidermis and infundibular epidermis. In both locales, melanocytes disposed as solitary units predominate over nests and, in both places, the neoplastic melanocytes are situated at the dermoepidermal junction and above it. Nuclei of the neoplastic melanocytes in this melanoma are small and relatively monomorphic. In short, a diagnosis of melanoma cannot be made here on the basis of findings cytopathologic alone, but, as is the situation often, only on the basis of attributes architectural.

4) Although the aspects cytopathologic of the melanoma are not the very same as those of the tiny congenital nevus, the nuclear differences between the malignant and benign condition are not overt immediately. The congenital nevus is diagnosable correctly by virtue of wedding both the pattern architectural with the changes cytopathologic.

5) It is an article of faith among dermatologists that congenital nevi are large, the exemplars of that proposition being "giant hairy nevi" and "garment nevi." But a congenital nevus may be minuscule, as is the case here. Another notion dear to dermatologists is the role of ultraviolet radiation, sunlight in particular, in the induction of melanoma. Note the absence of solar elastosis in the dermis beneath this melanoma, an indication that this particular anatomic site was not subjected to excessive exposure to sunlight.

6) The congenital nevus cannot be coincidental for several reasons, among them being its location in the reticular dermis near the center of the overlying melanoma in situ and that the patient has few "moles" clinically.

7) No explanation has yet been provided for the phenomenon of melanoma developing in affiliation with a preexisting nevus, but if all nevi (acquired and congenital) and all melanomas are conditioned genetically (as I believe to be the case), then it could well be that that association also is programmed in utero.

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