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August 18, 2022 / molehunter

Lentigo maligna on forehead

Contrast this lesion with the harmless solar lentigo I posted earlier. Very different. The big difference is irregularity of colour and dermoscopic structures.

A very odd looking, large, pigmented lesion on the forehead which might have been reported earlier. I would certainly expect it to have been picked up on an annual skin check if this person had benefited from having one.

Lentigo malignas grow slowly and probably most of them won’t develop into invasive melanoma, but we know some certainly do, because we see them. We have to live with uncertainty, as a prospective trial of how many LM develop invasive malignancy is not possible. Most experts I have asked say ‘around 5-10%’ of LM lesions will develop malignancy over time, but I don’t think this is a reliable figure. You have to bear in mind that we generally excise them as soon as we suspect them so they don’t have time to develop.

Dermoscopy (of the most odd-looking part of this large lesion) shows many pale grey circles, also some very dark polygonal shapes (pseudonetwork) surrounding follicular openings. The lowest example of this, by the graticule lines, is dramatically angular. This handy and up to date article about lentigo maligna on dermoscopedia illustrates this point nicely, well worth studying.

I always advise learners at skin lesion recognition to study as many examples of harmless lesions as they can, and contrast them with lesions like this.

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