So the first case that we have here this is a seborrheic keratosis.
These are kind of benign keratinocyte proliferations that usually occur in older people and have
this kind of stuck on appearance.
Usually they’re dark in color.
And microscopically there's a variety of different patterns you can see.
This was kind of an acanthotic pattern.
The epidermis is really thick.
Look here's the normal epidermis.
You can see the thickness of it right there.
And then here's the lesion, look at how thick and how elongated the rete ridges are there,
really thick and fat and filled with cells.
And the rete ridges all kind of interconnect together as they come down.
Let’s find our arrow here.
See they come down, kind of interconnect and kind of spread along merging with each other.
And what is left behind are these cystic spaces that are filled with usually with loose orthokeratin.
So this is dead keratin like you would have up here in the corneal layer.
It's the same stuff that you have it's accumulating down here.
And these are not really cysts, these are pseudocysts because if you cut deep but of
what will happen is these cysts actually connect up to the surface.
So this is kind of a funny artifact of the way we cut through and section the tissue.
So these are called horn pseudocysts.
So you get a thickening of the epidermis and it's made of these kind of small some people
say basaloid, I don't really like that term personally because I think these look a quite
a bit different basal cells, but they're kind of small keratinocytes, they're usually very
uniform and monotonous.
And they often have pigment in them, and that's why these lesions look dark brown clinically.
You can see that pigment there, that's melanin pigment.
Now remember that melanocytes make melanin and then kind of feed it to their neighboring
keratinocytes.
So just because he's a brown and it doesn't mean that they're actually melanocytes, it's
actually keratinocytes.
And you can see this little halo that they have.
If you have a little halo with the naked nucleus in the middle, that's a good sign that you're
probably done the keratinocyte not a melanocyte.
Alright, so this is a seborrheic keratosis.
And these are benign sometimes they can clinically look like melanoma or other melanocytic lesions.
Here's another cut from the same lesion, look, again there's a thickening of the epidermis
and these horn pseudocysts that are filled with that orthokeratin.
Now if you start seeing a bunch of dense pink keratin with retain nuclei, parakeratosis,
in the middle of these pseudocysts, then you have to stop and think about up the possibility
of a subtle squamous cell carcinoma.
Because squamous cells they tend to make little keratin pearls but instead of it being loose
orthokeratin like this, it usually has parakeratosis in the middle.
When seborrheic keratoses get inflamed or irritated they can also make parakeratin down
in those horn pseudocysts.
So you don't want to use that as a hard and fast rule, but it is a thing that's worth
considering.
And another thing I think is useful about seborrheic keratosis, let me get in focus
here, is that they usually kind of grow up from the surface of the skin.
They kind of push up.
And that actually if you can kind of draw a straight line across the bottom of the lesion,
most the time.
See if we go to the top piece, it gives you the same thing.
The lesion looks like it's growing down, but it's actually not.
It's actually pushed up like a little dome above the skin.
And you can draw a straight line across the bottom.
So seborrheic keratosis usually do not infiltrate down the skin, they kind of push up.
See again the same thing on the third piece here, you can draw a straight line underneath.
So thickening, a thickened lesion that's kind of a rising for the epidermis, made of bland
small keratinocytes, often with melanin pigment and then horn pseudocysts.
That's a seborrheic keratosis.
Let’s do the next case.
We'll make it right side up.
This lesion is so big that we can't actually even put the whole thing underneath the microscope,
but let's look and see if we can figure out what this says.
It's a lot bigger than the previous case and all that bright red stuff, that's keratin,
just like the last case.
It’s just a little more dense, that's why it looks so red and also I think this slide
I may have just picked up some more of the eosin stain.
But look if you see the epidermis is thickened, the rete ridges are really elongated and fusing
together, and what you're left with are these horn pseudocysts again.
These kind of pseudocystic areas in between.
And look, when you get a certain cut here, you can see those cysts aren’t really cysts
at all.
They open up to the surface, that's why we call them pseudo cysts.
And here it almost looks a little bit warty.
So you can sometimes think about a verruca or a wart with this lesion.
But look right here, you get kind of a straight line across the bottom.
I think this is another example of seborrheic keratosis.
This one is very irritated and inflamed.
It's got an area over here that you can see is really thick.
And has got a lot of lymphocytes, a lot of inflammation.
So sometimes these lesions get really inflamed over time and when they do they can sometimes
mimic squamous carcinoma clinically.
And look at all that pigment there, this is why they look so dark.
Not only is the pigment in the keratinocytes, which you can see up here, there's pigment
in keratinocytes, but there's also these little branchy thin dendritic cells.
Dendritic means as little branches arms.
Sorry just let me adjust the light a little bit.
And those are actually melanocytes, those are pigmented melanocytes that are kind of
dendritic, you can tell because of their little branching processes.
So melanocytes usually aren’t very darkly pigmented, but sometimes they are.
So there's always exceptions to every rule in dermatopathology, and sometimes dendritic
melanocytes get caught up in the middle of a seborrheic keratosis, and they further contribute
to the dark color.
And also when seborrheic keratosis s get inflamed, they often will do this, they will drop melanin
pigment out of the epidermis and into the dermis, and then macrophages come and eat
that up.
And so those are called melanophages.
So if you see real dark cells in the dermis, usually they’re going to be melanophages,
which are pigmented macrophages that are eating up the melanin.
Usually they’re not melanocytes.
Again, exceptions exist for all these rules, but that's kind of a good rule of thumb if
you see real dark cells in the dermis, most the time they're melanophages.
So go back to lower power here again, even in this area that's more inflamed, you can
see it's a thickened lesion arising from the epidermis.
You got horn pseudocysts which are really useful clue for low power.
And again, when they look kind of darker blue or purple, sometimes squamous cell carcinomas
can have the same kind of pattern.
So go a little closer and look, but I still think of the cells here are very uniform and
monotonous looking.
And I think that's good.
And sometimes they can get a little bit of atypia and some mitotic activity when a seborrheic
keratosis is gets really inflamed.
And you see when you get irritation or inflammation in a seborrheic keratosis, sometimes the horn
pseudocysts do begin to produce parakeratin.
And so again I always look a little closer when I see that just to make sure I'm not
missing a squamous cell carcinoma, but in this case I think what we have is just a very
big robustly irritated and inflamed seborrheic keratosis.
This is a very large one.
And I can imagine that if I had that on my skin, I would want it to be removed as well.
Probably very uncomfortable.