The short version of the post is that hemosiderin-laden macrophages are cells derived from monocytes (part of your white blood cells responsible for immunity) that have taken residence in the tissue and took up extracellular hemoglobin into their system to break it down for recycling(freeing up iron for hemoglobin production and producing biliverdin waste product).
These are still the same cells that can efficiently kill large number of pathogens and them turning into hemosiderin-laden macrophages is one of the functions they can do. Sometimes you'll read about foamy macrophages (still the same cells but they took up more lipids into their system).
I mentioned previously how these dark brown pigments taken up by these cells could make them look malignant in cases where you suspect melanoma especially when surrounded by existing hemorrhage. Hemosiderin-laden macrophages are present where there is hemorrhage especially if it's been there for a long time. Melanoma lesions are prone to bleeding due to being fragile upon manipulation.
Red circles show the hemosiderin-laden macrophages, the green ones are plasma cells (another group of cells that are present for chronic conditions), and you can vaguely see some neutrophils in the background.
This was taken from a fistula tract specimen. I didn't took the high power views for this but you're not missing out if you check this closer view of hemosiderin-laden macrophages.
A distinguishing feature is checking the nuclear details of the cells if it's atypical and then if there is hemorrhage present. I never had any difficulty determining which is which despite encountering melanoma rarely as seeing hemosiderin-laden macrophages often gave me an idea these pigmented cells don't look like normal macrophages.
Here's a comparison of what neoplastic cells of Melanoma looks like from my old post.
It's a fun trivia I used to do with the rotating post graduate interns trying to study for their board exams in our department. I'd ask them what hemosiderin laden macrophages look like and they would describe it and then show them a slide of the melanoma case to see if they can tell as a test.
If you're dealing with a granulation tissue (tissue in the process of healing) you'll expect to see hemosiderin-laden macrophages and this is a good clue that the diagnosis is something that is chronic in nature.
If you made it this far reading, thank you for your time.
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