5-Minute Pathology Pearls: Inverted Follicular Keratosis (IFK)

Alright here is something else that looks
a little bit like a seborrheic keratosis and may in fact be related depending on your point
of view. This is a solitary lesion from the face and
it’s a shave biopsy. And you can see that it’s got that pink appearance
that’s kind of like a seborrheic keratosis, made of pink keratinocytes. You can see some areas that look like horns
pseudocysts that are filled with orthokeratin. But this lesion instead of having kind of
the flat bottom that most seborrheic keratoses have, it really pushes down. You can see that it’s kind of pushing down
with a kind of copper bowl shape. Here you can see it again, and pushed up and
above the epidermis but also is kind of bulging down into the dermis. And although the first part that we saw over
there was that was kind of cut across the bottom, you can actually see the base of the
lesion here on this a section. It looks like it’s got a smooth border and
no infiltrative growth, so that’s helpful. And when you look closer, some of the spaces
are artifacts unfortunately, but when you look at closer here what you find is this
really unusual pattern. The keratinocytes are making these little
tiny whirled balls. You can see that each individual keratinocyte
cluster, they’re kind of swirled together in these little balls or whirls and these
are called squamous eddies. And you can see these in irritated seborrheic
keratoses but when you see something that looks like a seb and it’s pushing down into
the dermis with kind of a cup shaped or bowl shaped kind of a high profile and then it
has lots of these squamous eddies, the other thing you can think of is what’s called an
inverted follicular keratosis. And the reason it’s called that is it tends
to be centered on hair follicles and I think that’s probably what we’re seeing right here
is a portion of the follicle that’s kind of been replaced by this tumor. Or maybe even here, maybe there’s kind of
more than one branch of the follicle that’s got this tumor growing. And these are benign tumors and the biggest
problem I think with them is that occasionally they can get some reactive atypia and oftentimes
on a shave biopsy they’re transected at the bottom, you can’t see the base. So in old sun damage person, I always worry
a little that could this maybe be a squamous carcinoma. And if I’m uncertain and I feel this kind
of some atypia there I might occasionally say, “Well keep an eye on the patient and
if it grows back, then you need to go biopsy yet again,” or if I’m really worried I’ll
tell him I just really can’t tell and please do a small reexcision. So that’s how I handle that issue. Everyone has their own way of addressing atypia
and uncertainty when we run into them in dermpath. But I try to be as definitive as I can but
sometimes we just can’t know if we can’t see the whole lesion. But these are really pretty. I really like these kind of squamous whirls
and eddies. And I think that’s a very very beautiful pattern
that you can see where the squamous cells come to swirl around. And they could get confused potentially I
guess with keratin pearls that you often see in squamous cell carcinoma. The biggest difference is that here these
little whirls and balls are in the middle of the tumor itself. They’re kind of up in the epidermis or in
the protrusion of the tumor from the epidermis whereas keratin pearls and squamous cell carcinoma
usually are kind of individual invading nests of keratinocytes down in the dermis, kind
of separate from the main tumor mass. But again look at that, you can just see each
one of these. Each one of these little discreet swirls or
whirls were eddies of keratinocytes. So again from low power kind of looks like
a seb but growing down often centered on a kind of a follicular opening here, and has
this little squamous eddies. Inverted follicular keratosis or IFK as we
often abbreviate it. We like to abbreviate names in dermpath.

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