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Problems in the Diagnosis of Melanocytic Neoplasms
The histologic diagnosis of melanocytic neoplasms often is difficult. If there were only “one melanoma” with “one” corresponding histologic pattern, our task would be greatly simplified. Unfortunately, the patterns are many, even when restricting the options to classic categories. Other variants include malignant blue nevus and melanoma of soft parts. There have been attempts to identify an intermediate category of melanocytic neoplasia. The concept of MDM is one example of an attempt to define an intermediate category. The category of nevoid melanoma is a play on words, if an attempt is made to clearly isolate it beyond the category of MDM and, in the process, discredit the concept of MDM. It is a more general definition of an intermediate category. In defense of such an intermediate category, some of the variant lesions rarely seem to produce progressive disease, even after documented nodal metastasis; as a consequence, it is easy to be lulled into a sense of security. It is then an easy matter to broaden one of the benign categories, and to classify the problematic lesions as variants of “nevi.” These variant problematic lesions possibly have biologic potentials which are neither those of the common nevi nor the common melanomas.
The possibility that there are variant melanomas of as many types as there variant “nevi” is difficult to document. The concept has been promoted but mostly has not received enthusiatic support. Part of the trouble has been a willingness, on the part of pathologists, to accept rather broad criteria for the diagnosis of common and variant nevi. We strive to avoid the over-diagnosis of melanoma, particularly in children and adolescents. The category of Spitz “nevus” has been broadened to include lesions which are cytologically atypical, and which show deviations in architecture. With increasing confidence, variants of Spitz “nevus” have been defined, and then promoted as representing a “benign lesion.” With increasing frequency during this same period, there has been a crescendo in the frequency of malpractice claims. Something seems to be lacking, or too much has been conceded in the definition of criteria for the diagnosis of Spitz “nevus.”
In this section, a small number of peculiar melanocytic neoplasms are presented as problems in histologic interpretation. Clincal histories and the nature of the clinical course for each lesion is not included. The photomicrographs are to be examined, and an interpretation is to be rendered without the biases which are introduced by having access to clinical information regarding the presentation of the lesion and the subsequent clinical course. Much of the histologic material was seen by me in consultation with other pathologists. The nature of my practice at the time of the diagnosis apparently has had an selective influence on the patterns encountered during histologic examinations; many of the lesions show uncommon histologic patterns. (CLICK to go to next chapter)
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