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The problem lesion displays a variety of histologic patterns. In mobilizing parcels of relevant virtual images for the interpretation of the histologic patterns, an observer, by his choice of a parcel, may come
away pleased with both his selection and his interpretation only to discover that another observer, having selected an entirely different parcel, has arrived at a different interpretation and is equally pleased with
himself.
For those who endorse the approach of Harvell, et al (1), the patterns at the dermal-epidermal interface of this problem lesion could be characterized as “Spitz nevus-like.” The cells of the junctional component
are pigmented but are spindle shaped, and are moderately plump (they are epithelioid spindle cells) (P3-1, P3-4). In some of the nests, the spindle cells are loosely attached to their neighbors; this is a Spitz nevus-like quality (NOTE 1). The spindle cells form
vertically oriented fascicles at the dermal-epidermal interface, also a Spitz nevus-like quality (at least at the verbal level, if not at the level of the real images). In the dermal component, the cells are rounded
and plump (P4-3&4) (a quality commonly characterized as epithelioid, and certainly a feature of the dermal component of most classic Spitz nevi at
the deep, advancing margin). Elson Helwig characterized Spitz nevi as spindle and epithelioid nevi, and Jules Kernen and Lauren Ackerman endorsed this characterization. As a consequence, many observers, upon
identifying spindle and epithelioid cells in a lesion, have little trouble in molding a wide variety of real images so that they can be accommodated in the category of spindle and epithelioid cell nevus (hence,
Spitz nevus); the words alone can come to be equated with “Spitz nevus.”. It would seem that this is the approach of Harvell, et al (1); in their approach, spindle cells and fascicular patterns have been
accommodated in a category of “Spitz nevus with halo nevus phenomena.” In their approach to this category of problem lesions, even lesions with typical vertical growth-like patterns also can be
accommodated in the category of “Spitz nevus with halo nevus phenomena;” although, such patterns were not, and are not, basic to the definition of classic Spitz nevus. In their approach, the parcel of virtual images
for the interpretation of Spitz nevus has been significantly altered to provide accommodations for vertical growth components in the category of “Spitz nevus with halo nevus phenomena.”
There is an alternate approach to the patterns in this lesion. If emphasis is placed primarily on halo nevus-like phenomena, the parcels for the interpretation of halo nevi and halo nevus-like lesions have some
relevance to the patterns in the case at hand.
The halo nevus parcel includes the following virtual images:
1. diffuse lymphoid infiltrates generally in association with dermal nests of nevus-like cells (P1-1b) (see also a more characteristic example: P1a-1)
2. intermingling of lymphocytes among nevus-like cells in the dermal nests (P4-2)-
3. progressive loss of a population of dermal nevus-like cells, either focally or diffusely (P4-2); the cytolysis of halo nevus-like phenomena (NOTE 2: see also an example with focal regression: P1a-3)
4. senescence in sclerosing patterns; fibrous inlays of lytic defects, comparable to the fibrous inlays of lytic defects in lichen planus-like reactions (P4-3) (NOTE 3: see lichen
planus-like senescence in drawing (P1a-4) and photomicrographs (P1a-5 & 6)
The depigmented, peripheral halo which is clinically so distinctive for a halo nevus is associated with epidermal hypomelanosis; it shows features of a spotty lichenoid reaction at the dermal-epidermal interface.
In fact, even the reaction in the dermal component of nevus cells in a halo nevus is a modified lichenoid reaction (cell-mediated immune response) in which the target cell is a melanocytic cell rather than a
keratinocyte. By extending the analogy, halo nevus phenomena are manifestations of a cell-mediated, immune response with melanocytes as target cells, and with cytolysis as the chief expression of the cytopathy. As a
consequence in halo nevi, we should anticipate lytic defects in the domain of the nevus as an expression of the cellular response; halo nevus-like phenomena are cytolytic but the effects are masked by the dense
lymphoid infiltrates; they must be searched for (P4-3). Halo nevus-like phenomena are not restricted to classic halo nevi; they also affect melanocytic
neoplasms of a higher order than halo nevus.
Other corollaries for a cell-mediated, immune response include histiocytes in the lymphoid infiltrates, sometimes in the form of epithelioid granulomas. Eosinophils are occasionally a feature of the dermal
inflammatory infiltrates of a halo nevus-like reaction. Junctional components often are found in the epidermis of a halo nevus. Not uncommonly, the lymphoid infiltrates extend into the junctional nests and the
resulting phenomena include cytolysis of melanocytic cells; the resulting patterns have a lichenoid quality. Such a lesion late in its evolution may be mistaken as a common lichenoid reaction, if most of the target
melanocytic cells have undergone cytolysis and are not easily identifiable.
Most of the above features of halo nevus and the respective parcels have application to the patterns in the problem case but should they be given precedence over the parcel of Spitz nevus-like features?
Reference
1. Harvell, JD, Meehan, SA, LeBoit, PE: Spitz’s nevi with halo reactions: a histopathologic study of 17 cases. J Cutan Pathol 1997;24:611-619.
2. Kernen, JA, Ackerman, LV: Spindle cell nevi and epithelioid cell nevi (so-called juvenile melanomas) in children and adults: A clinicopathological study of 27 cases. Cancer 1960;13;612-625.
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