Regression structures / Blue white structures
On histopathology fully evolved regression shows fibrosis and melanosis (infiltrate of melanophages), and sparse lymphocytic infiltrates. The normal undulating DEJ pattern formed by rete ridges and dermal papillae is attenuated to completely Flattened. Regression structures consisting of both scar like depigmentation and peppering (granularity) should raise suspicion for melanoma. Regression structures consisting of only peppering can be seen in melanoma, lichen planus like keratosis and nevi. In lichen planus like keratosis the granularity tends to be coarse and diffusely distributed. In melanocytic lesions the granularity tends to be finer and focally distributed.
These areas should not be chosen for sectioning when grossing a suspected melanoma as they may reveal non-diagnostic features or underestimate the Breslow thickness.
corresponds to a white discoloration of the lesion, which is lighter than the surrounding normal skin. On histopathology, this dermoscopic structure correlates with fibrosis.
Granularity / Peppering
Granularity (also known as “peppering”) is defined as accumulation of multiple very small (<0.1 mm), nondescript, blue-grey dots. If a large area shows dense, confluent granularity, it is difficult to distinguish from blue-white veil, however, clinically, granularity often is seen in macular portions of the lesion, while blue-white veil is seen in palpable areas. Histopathologically, granularity correlates with melanin in the superficial dermis, either as fine melanin particles in melanophages or extracellular “dust-like” particles. When granularity is encountered in nevi it tends to encompass less than 10% of the lesion’s surface area. In contrast, in melanoma the granularity often encompasses more than 50% of the lesion’s surface area.
Blue whitish veil
Blue-white veil is confluent blue pigmentation with an overlying white “ground-glass” haze. In melanoma, the bluewhite veil does not occupy the entire surface area of the lesion, but rather is present as a focal, ill-defined area. Histopathologically, this dermoscopic structure corresponds to an aggregation of heavily pigmented cells (melanocytes and/or melanophages) or melanin in the dermis (blue color) in combination with compact orthokeratosis  . At times, it is difficult to distinguish between regression structures (namely melanosis) and blue-white veil by dermoscopy because both structures display blue-white color. However, examining the lesion without dermoscopy can help differentiate between blue-white color due to regression versus due to deep melanocytes. In regression the surface contour will be flat (macular) and in blue-white veil the surface will be raised and palpable. In melanoma the blue-white veil is nonuniform in color and is present focally within the lesion. In contrast, the blue-white veil has a uniform steel-blue color in blue nevi and it occupies the entire surface area of the lesion.
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