Cytology and stroma reaction
The aspect of cells in basal layer and upper dermis is considered. Cells are morphologically described considering cytological atypia throughout the lesion.
No atypical cells
It corresponds to the lack of cellular atypia in basal layer and upper dermis. Cells are morphologically described considering cytological atypia throughout the lesion. Typical cells correspond to mono-morphous small cells (Fig. 76,77), observable in benign melanocytic and non melanocytic lesions.
The presence of cellular atypia in basal layer and/or upper dermis is considered. Atypical cells correspond to irregular in size, shape and reflectivity, round to oval or stellate, cells, occasionally with branching dendritic-like structures (Fig. 78-82). They show a bright cytoplasm with clearly outlined borders and sharply contrasted dark nucleus inside.
Atypical cells are usually observed in melanocytic lesions. Rarely present in Clark nevi, they are frequently observed in Melanomas. Few atypical cells, with no marked pleomorphism are also present in atypical/dysplastic nevi. It is possible to detect atypical cells within tumour islands and cords of pigmented Basal Cell Carcinoma and in pigmented Bowen's Disease, due to the activation of melanocytes within the tumour masses.
Concerning «Atypical Cells», some parameters will be considered:
Predominant aspect and distribution:
Aspect is evaluated, according to the predominant cell shape, as «roundish-polygonal» or «dendritic-spindled». «Pleomorphism» is the variability of atypical 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 atypical 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 atypical 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.
Atypical cell organization:
Organization of atypical cells at the DEJ and upper dermis is taken into account.
1. In single cells at DEJ
Presence of single, not clustered, atypical cells in basal layers (Fig. 83).
2. In nests (at least 4 cells)
Atypical cells within junctional and/or dermal nests, or small clusters of atypical cells at the DEJ (Fig. 84).
Atypical cells infiltrating dermal papillae
Presence of single, not clustered, atypical cells infiltrating dermal papillae.
Nucleated cells correspond to round to oval non aggregated cells with well-demarcated refractive cytoplasm and well-demarcated dark nucleus infiltrating dermal papilla. These cells are clearly separated in between (Fig. 85,86).
Pagetoid / Atypical cells surrounding hair follicles
Presence of pagetoid cells and/or atypical cells surrounding and infiltrating the hair follicle. This pattern is frequently observed in Lentigo Maligna (Fig. 87).
Plump bright cells / small bright particles in papillae
Plump bright cells are described as plump irregularly shaped bright cells with ill-defined borders and usually no visible nucleus. Sometimes they are crowded within the papilla (Fig. 88,89).
Bright Spots and small bright particles are small cells with very bright hyper-reflecting cytoplasm, sometimes visible nuclei, corresponding to leukocyte infiltration (Fig. 90).
Since the presence of small bright particles is almost constantly detectable in skin tumours, as well as few plump bright cells, the parameter has to be considered only in case of clearly visible and extended infiltration.
Coarse collagen structures
Coarse collagen structures appear as an amorphous fibrillary material which distribution could be reticulated, forming coarse web-like structures in the dermis, or in boundles, gathered into large fasciae (Fig. 91,92).
In the upper dermis it is possible to identify vessels. The blood flow within the vessels is clearly detectable during in vivo imaging, also in normal skin, whereas on still images only elongated and/or enlarged vessels can be evaluated. Presence of canalicular structures within dermal papillae, as sometimes observable in normal skin, has not to be reported.
Considering the aspects of vessels observable on still images, three main categories are defined:
Perpendicular vessels correspond to enlarged vessels forming a loop in dermal papillae. They are visible in case of inflammation, such as in irritated or traumatized nevi or, within non melanocytic skin lesions, in irritated Seborrhoeic Keratoses and Actinic Keratoses. Rarely, enlarged comma-like vessels are observable within tumoral masses in nodular malignancies (Fig. 93).
Elongated vessels distributed parallel to the skin surface. Sometimes they are enlarged and each other anastomoized, forming a retiform connection. They are predominantly observable in Basal Cell Carcinomasimmediately below the DEJ (Fig. 94,95).
Irregular and convoluted vessels show up as tortuos glomerular structures. Usually they are visible within the nodular component of melanocytic and non melanocytic malignancies (Fig. 93).