The superficial layer is evaluated identifying different patterns:
1. Regular Honeycombed pattern
Typically is formed by 10 to 20 μm polygonal cells with dark nuclei and bright and thin cytoplasm (Fig. 1-3). This is the pattern of normal skin and corresponds to unaltered epidermis with small amount of melanin within keratinocytes.
2. Regular Cobblestone pattern
It consists of small polygonal cells with refractive cytoplasm separated by a less refractive border (Fig. 4-6). Cobblestone pattern is more frequently detected in pigmented melanocytic lesions, owing to the consistent amount of melanin within the keratinocyte cytoplasm.
3. Broadened Honeycombed pattern
Broadened honeycombed corresponds to a honeycombed pattern with bright enlarged and broadened intercellular spaces (Fig. 7). Although an exact histologic correlate was not found so far, this pattern is frequently observed in association with eosinophilic hyperkeratosis, frequently observable in nodular lesions, such as Nodular Melanomas and nodular non melanocytic skin cancers.
4. Irregularly Shaped Keratinocytes
The overall epidermal pattern is constituted by Irregular shaped keratinocytes when irregularity in size of the cells and thickness of the contour is present.
An overall honeycombed architecture characterized by atypical and irregular keratinocytes is observed in melanocytic (Fig. 8) and non melanocytic lesions (Fig. 9), such as Actinic Keratoses, Bowen's Disease, and Squamous Cell Carcinomas.
An overall cobblestone architecture showing irregular in size and/or refractivity keratinocytes may also define an «irregularly shaped keratinocytes» pattern (Fig. 10).
5. Disarranged pattern
It is characterized by disarray of the normal architecture of the superficial layers with unevenly distributed bright granular particles and cells, in the absence of honeycombed or cobblestone pattern (Fig. 11-13).
This pattern is more frequently observable in invasive Melanomas, usually associated with pagetoid cells, although other skin malignancy, such as Squamous Cell and, rarely, Basal Cell Carcinomas.
6. Undefined pattern
Superficial layers predominantly constituted by a more or less homogeneous reflectivity, not associated or pertaining to any cell type, dispersed throughout the image, giving rise to an aspect not referable to any of the previous ones (Fig. 14).
Presence of polarized elongated meshes
Some degree of keratinocytic atypia and architectural disarray within a generally honeycombed pattern, showing elongated cells with their nuclei oriented along the same principal axis, thus manifesting a polarized appearance (Fig. 15). The pattern is frequently observable in Basal Cell Carcinomas, although sometimes present in benign lesions, such as dermatofibromas.
Dark areas, usually with sharp borders and irregular contours, filled with amorphous substance and/or clotted bright small particles (Fig. 16).
Small erosions or ulcerated areas are frequently observable in non melanocytic skin tumors, such as Actinic Keratoses, Bowen's disease, Basal Cell and Squamous Cell Carcinomas, although sometimes present in melanocytic lesions too, such as ulcerated Melanomas or traumatized Nevi.
Presence and aspects of pagetoid cells
Pagetoid cells are considered when large nucleated cells, twice the size of keratinocytes, with a dark nucleus and bright cytoplasm, are observable within superficial layers (Fig. 17-22). Pagetoid cells, especially the «roundish» ones, represent the most accurate pattern for Melanoma diagnosis.
Melanomas are frequently characterized by numerous pagetoid cells, scattered throughout the lesions, usually roundish or pleomorphic in shape.
A small percentage of Clark nevi, as well as some Spitz/Reed nevi, shows pagetoid cells, usually few and localized in the center of the lesion.
Dendritic pagetoid cells have a lower diagnostic power, since they are sometimes observable in benign melanocytic lesions and in non melanocytic ones. They are referable to melanocytes spreading upword in a pagetoid fashion and/or to Langherans cells. Within Melanomas, Lentigo Maligna type may be characterized by the presence of dendritic pagetoid cells, frequently surrounding and infiltrating the hair follicles.
Concerning «Pagetoid Cells» some parameters will be considered:
1. Cell Type / Aspect
Aspect is evaluated, according to the predominant cell shape, as «roundish» or «dendritic». «Pleomorphism» is the variability of pagetoid cell morphology, characterized by the presence of both roundish and dendritic cells, and/or the presence of cells with bizarre shapes.
Numerosity corresponds to the density of pagetoid cells in the region where they are located. It is evaluated approximately per «square millimeter», corresponding to an area of 4 adjacent full resolution images (squares) in the mosaic. It is classified into three different levels, for the presence of less than 5 cells per square millimeter, «<5sqm», for 5 to 10 cells per square millimeter, «5-10sqm», and for more than 10 cells per square millimeter, «>10sqm», respectively.
Distribution takes into account the localization of pagetoid cells onto the lesion area. It is considered as «localized» when pagetoid spread is present and concentrated in a limited portion of the lesion, as «sparse» when it is possible to observe different, but not extended, foci of pagetoid infiltration, and as «widespread» when pagetoid cells are scattered throughout the whole lesion area.