Description: A lentiginous melanoma in situ on the lower leg of a 69 year old female. Not all large polygons are obvious and defined by darker lines (as in Images 479 and 480), but careful inspection reveals the presence of paler large complete and partial polygonal shapes bounded by slightly darker lesional pigment. Again, the background pigment pattern of this lesion is that which is described for solar lentigo, but lacks the typical border of solar lentigo

History:

Large Polygons - a dermoscopic feature of Lentiginous Melanoma

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21/27 non-facial lentiginous melanomas detected over a 2 year period had these structures.

These polygonal shapes may be obvious and complete or subtle and incomplete. They are defined by darker grey or brown relatively straight lines, or by darker (sometimes only barely so) surrounding lesional pigment or a combination of the two. They are much larger than the rhomboidal structures seen in facial lentigo maligna and may be rhomboidal, pentagonal, or hexagonal. In some cases the large polygons do appear to be centred on follicular openings, as in lentigo maligna of the face, but this is not a constant.

I have termed these shapes “large polygons”, in contrast to the smaller rhomboidal structures seen in facial lentigo maligna.

Large polygons usually occurred within a pigmented lesion that had lentigo-like pigment patterns, but lacking the sharply defined scalloped edge usually seen with solar lentigo.