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The virtual images of the parcels for the interpretation of Spitz nevus, if they are to accommodate the real images of our problem case, would require considerable molding and modification. As an alternative,
parcels for the interpretation of halo nevus-like lesions have also been evaluated.
We have briefly examined the virtual images of the parcel for the interpretation of classic halo nevus but here again molding and modifications would be required. There are other relevant parcels for the
interpretation of variations in the halo nevus-like category but they are not without their critics; they are to be found in the concept of MDM.
In the parcels associated with the concept of minimal deviation melanoma, peculiar variations of melanocytic neoplasia, in which halo nevus-like phenomena are histologically evident, have been characterized
as minimal deviation melanoma of halo nevus-like type. As in all categories of minimal deviation melanoma, patterns of typical vertical growth in association with cytologic disparities are basic and most definitive.
There are intermediate stages between classic halo nevus and MDM of halo nevus-like type; they might be characterized as dysplastic, epithelioid melanocytoma of halo nevus-like type.
In the category of MDM of halo nevus-like type, it has been proposed that there are two separate pathways, either of which might terminate in vertical growth patterns in association with halo nevus-like phenomena.
Perhaps the more significant of the two is expressed in the lentiginous and junctional patterns of a peculiar, premalignant melanocytic dysplasia. This neoplastic process is usually manifested in the epidermis over
a dermal component that shows the features of a variant of halo “nevus.” This combination, in the absence of a typical vertical growth component, qualifies as ATYPICAL
HALO NEVUS (P4-1); this designation should be restricted to lesions measuring less than 1 mm in greatest vertical dimensions. The related neoplasm
evolves in sequential steps at the dermal-epidermal interface; in a sequence, nests of atypical cells are delivered (“drop into”) to the dermis. In evaluating atypical halo nevus, the tools for the interpretation of
the common premalignant dysplasias have application for the interpretation of the patterns and the degree of dysplasia. Similarly, the criteria for the recognition of patterns of variant and typical vertical growth
have utility in making a distinction between atypical halo nevus and minimal deviation melanoma (see MDMHALO and the WHITHERS). The atypical halo nevus is usually expressed in spindle cell patterns and as such, this lesion is likely to be dismissed as a Spitz nevus-like variant. In some
examples, the cytologic features of the junctional component is remarkably Spitz nevus-like but more often the cells are not plump and nuclei are smaller than those of the cells of a Spitz nevus.
NEAR-NEOPLASIA
Of the varying patterns in halo nevus variants, the changes in a dermal component (if such is represented) are most characteristic. In the dermal component of
classic halo nevus the cells of a melanocytic hamartoma (“nevus”) are intermixed with the cells of a lymphoid infiltrate.
In conceptualizations, halo nevus-like phenomena have taken on the qualities of auto-immunity. The cells of the host destroy those of the hamartoma. One approach
to the problem would be to propose that the nevus cells have become antigenically distinct from those of most common nevi. If we take this approach, the reach is short to the notion that halo nevus phenomena are
associated with a neoplastic progression, and that the dermal “nevus cells,” although morphologically little changed, are representative of a new growth in which the halo nevus-like phenomena are secondary (the
lesion in essence has become, in part, a dysplastic melanocytoma (a new growth). For most examples, the basic pattern of a “nevus” is maintained early on; it would be difficult to histologically examine such a
lesion and identify cytologic or architectural changes that would correlate with morphologically well-defined neoplastic progressions. Two features are common: 1.) the nuclei of the small, dermal nevus cells tend to
be densely chromatic, and 2.) the nevus-like cells of many of the dermal clusters are pigmented (pigmented at a structural level that would be unusual in a common nevus) (P2-1, P4-4). The halo nevus-like phenomena would appear to be an immune response destined
to destroy part, or all, of the affected “nevus” (i.e., new growth in nevus-like patterns) (see P1a-3).
In some halo nevi, distinctive epithelioid cells (P4-2) make an appearance among the more common “dermal nevus cells.” Initially, the cells are few
in number and individually isolated among the “common nevus cells.” With time, more and more of the cells make an appearance, often near, or within, lytic defects. Eventually, in some examples, these distinctive
cells cluster to form small aggregates. These cells might be cited as the earliest, histologically recognizable marker of a neoplastic progression. An otherwise typical, halo nevus-like lesion containing these
cells, in isolation or in small clusters, might be cited as an example of NEAR-NEOPLASIA. The
epithelioid cells are the first distinctive, marker providing morphologic evidence for a neoplastic progression in a dermal population of cells. The degree of cytologic atypia is variable in lesions of
near-neoplasia of halo nevus-like type; in the problem case, it is only moderate and remarkably uniform.
In the parcels of virtual images for the interpretation of Spitz nevi (i.e., a special variant of epithelioid melanocytoma), there is no provision for the
emergence of neoplastic cells from, and among, a dermal population of common “nevus cells” arranged in common “nevus-like” patterns. It is most uncommon for the fascicles of spindle cells of a Spitz nevus to be
associated with a remnant of a common nevus (i.e., combined nevus of Spitz nevus-like type). When lesions, that might be characterized as such, are encountered, almost invariably they also manifest halo nevus-like
phenomena; they may only incidentally resemble classic Spitz nevus. From this perspective, there is an intermediate neoplastic category in which cells are plump (epithelioid), and round, or spindle shaped. These
lesions in different guises are spindle cell, or round cell, epithelioid melanocytomas. They should be additionally and precisely characterized as Spitz “nevus” (melanocytoma) only when the virtual images of the
relevant parcel for the interpretation of classic Spitz nevus can be closely matched with the real images of a problematic lesion. From this perspective, the lesion of near-neoplasia of halo nevus-like type is a
dermal epithelioid melanocytoma of halo nevus-like type. It is a melanocytic lesion of indeterminate malignant potential. Its cells may resemble the cells in the reticular dermis of a Spitz nevus but the
kinetics of the manner in which the cells develop can be remarkably different in halo nevus-like variants. In addition, it should be noted that the “maturation” of a Spitz nevus is a quality mostly restricted to
individual cells isolated among collagen bundles of the reticular dermis (near the advancing deep margin of the lesion). In our problem lesion, the dermal component often is confined to a widened papillary dermis (P1-2a, P2-1). There is no component in the reticular dermis; in fact, the deep margin of
the lesion is outlined by inflamed, vascularized fibrous tissue, much like a similar barrier in common melanomas confined to level III. These characteristics, as well as the fascicular patterns that more closely
resemble those of a common nevus than a classic Spitz variant, deserve strong consideration when searching for a parcel of relevant virtual images.
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