Reflected light microscopy, brown/black dot against blue-grey background

Reflected light microscopic phenomenon caused by punctiform accumulations of melanin pigment in the stratum corneum (black) or in the upper epidermis (brown), measuring about 0.05-0.15 mm in horizontal diameter. The pigment is found both within melanocytes and extracellularly.

Reflected light microscopy: Dark brown or black round, oval or polygonal disc-shaped pigment densities are distributed irregularly in the epidermis either solitarily or multiple times. The spots are located in front of a blue, blue-grey or grey background (melanophagus agglomerates or deep melanocyte nests).

If the pigment dots or spots are located in front of a more or less bluish coloured background, the specificity for malignant melanomas within the group of pigment cell tumours is above 80% (sensitivity 47%). An irregular distribution of dots in the tumor periphery is also an indication of the presence of a malignant melanoma or a dysplastic nevus. In other melanocytic nevi, such as spindle cell nevi, congenital nevi or junctional nevi, the dots are usually evenly distributed over the lesion and the background pigment rarely assumes a bluish colour.

Histologically, superimposed melanin pigment can be detected. In the stratum corneum melanin appears black, in keratinocytes, epidermal naevocytes or melanocytes it is black to dark brown, in the basal cell layer and junctional zone it is reddish brown, brown or light brown, in the upper stratum papillary and the papilla tips grey, grey-brown or grey-blue, in the deep stratum papillary, at the border to the stratum reticulare, steel blue to turquoise. Melanin pigment incorporated by corial melanophages appears grey, grey-blue, grey-violet or steel-grey, depending on the depth of localisation.