Residents Corner
Looking at slides
When we start looking at slides as a
young resident we we find ourselves peering through the microscope looking
at fields of tissue one after the other with little more plan than to try
and tell what tissue we are looking at and to match what we are
seeing to one of the perfect examples of the entity in our texts. As we
gain more experience we have cases to reflect back on, the many variations
we have seen and those mistakes we have made or seen others make. I would
like to offer a more structured approach to examining slides which I have
found successful in helping me arrive at a correct diagnosis and avoid
embarrassment. First several observations:
| Observations on observation
1) You only see what you are looking for.
It is not uncommon to find myself self or others staring
into a field with an obvious diagnostic finding right under our nose. If
we do not look for it, often we will not see it. So if you want to be
sure you have not missed something, you better look for it.
2) You can only look for one thing at a time
carefully.
Example: Try screening carefully for microcalcifications
in a breast specimen and at the same time be comfortable that you
are not missing a microscopic focus of a near invisible invasive lobular
carcinoma. I cannot do it. I typically go over the slide twice or more. I
screen from 2 x which makes it go faster. If I am looking for involved
nerves and lymphatics I will take a third pass this time focusing
around neuro-vascular bundles.
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With every slide and specimen type I have a simple plan
for examining the tissue that starts with
"
What am I looking for and what don't I
want to miss?" For
example a simple gallbladder submitted for cholecystitis, I will look for
the cholecystitis on my first pass, then I will make sure I do not miss
the "invisible cancer" (small infiltrating tumor cells that can be very
easy to miss, particularly in an inflamed background); "blue epithelium" (dysplasia);
and other tiny things such as lymphatics with emboli ect. I will typically
make several passes of the slide under the scope.
In many tissues it is useful to examine all of the
histologic elements in an orderly fashion to compile the findings
into a diagnosis. Liver, bone marrow, kidney biopsies and colitis
biopsies are good examples of this.
In a biopsy for colitis I will first look at the
glandular archetecture at 2x. Then move to 4x or higher and
systematically look at the surface epithelium, basement membrane,
glandular epithelium, inflammatory cells within the lamina propria and
epithelium, look at the vasculature, look for granulomata, look at the
secretions for organisms, and again come back to the lamina propria to
make sure I have not missed an occult metastasis to a lymphatics or a few
sneaky signet rings or a rare parasitic organism. By looking at all of the
histologic elements this way I am reducing my chances to miss a diagnostic
clue. It may seem like a lot of passes through the tissue but it really
goes quite quickly as you are quite focused on what you are looking at.
Learning to read at 2x
It also helps to be able to recognize as many of these
features as possible at 2x. You can learn to recognize even single cells
at 2x simply by looking at them at higher powers and then go to scanning
powers and look to see if you can recognize it. Finding Reed Sternberg
cells, CMV inclusions and even a rare tumor cell in a lymph node is
possible at 4x and sometimes 2x if you are looking specifically for a very
tiny but recognizable structure. The better you get at seeing things at
scanning power, the faster you will be able to work and the multiple
passes of the slide will go quickly.
I have found that taking this organized approach to
reviewing slides leaves me feeling more comfortable that I have not missed
anything critical.
Struggling with the tough ones
You can only make a diagnosis if
you think of it!
You can be the most well read
encyclopedic mind in our field but if you are handed a slide that takes a
little thought you will not make a diagnosis if you do not think of it. I
teach my residents from day one to learn the broad classifications of
diseases by classification and organ system. Try throwing up an imaginary
chest film with a few vague findings and ask a group of young residents
what is there differential diagnosis. Typically someone will say tumor or
pneumonia and not much more. Now open the table of contents of Robbins and
read the chapter titles. By mentioning diseases of immunity, congenital
diseases, vascular diseases, occupational diseases ect. out will pop
numerous possibilities that nobody thought of. They all heard of Wegoner's
granulomatosis, silicosis, pulmonary emboli and numerous others but unless
stimulated, you do not always think of it. If you think
about the pneumonias by class then out will pop, bacteria, mycobacteria,
fungi and parasites. If you think about the tumor classes numerous
possibilities will come into your head not just the common ones. If all
one knows is the classification and a few points about each disease, you
will be stimulated to look deeper into the possibilities when confronted
with the tough case.
Always start by reading the table of
contents. It is the broadest outline of the disease class. Knowing
only this will give you an important first step to learning and feeling
comfortable with the subject.
I ask my residents at the beginning to "Label the files
in there head." As they see cases they will add to these files with
experience. But even as a neophyte, if for example you know the
classification of salivary gland tumors and are confronted with an example
you have not seen before, if you are familiar with the classification, you
can go through the files in your head, cross out the ones you are sure do
not fit and read on the ones that are possibilities. You will have a
familiarity with the subject that leaves you with the comfort that you
thought of most of the possibilities. Compare this to reading the same
slide and only knowing the names of four of the twenty or more
possibilities. You will feel quite insecure.
As a resident, I kept a list of
"Things to think about when your stuck". I encourage my residents to
keep a similar list and add to it. Of course on the top of this list is
the the king of the monkeys, malignant melanoma. Melanomas can show up
anywhere and mimic just about anything. It is an easy diagnosis to
make.....if you think about it! On this list should also be
diagnoses you will never make without thinking about it. Good examples of
these are histiocytosis, mastocytosis and hairy cell leukemia in the
marrow, demyelinating pseudotumor in the CNS, amyloidosis and many many
more. On this list should be germ cell tumors, myeloma, renal cell
carcinoma, granulocytic sarcoma, thymoma, mesothelioma, sarcomatoid
carcinomas and, epithelioid sarcomas, all things that you can miss if seen
outside their element as an occult met or mass.
There are many types of "tough ones"
Probably the most common example is a miserable crushed, burned or
fragmented example of something that would be easy if you had a good
sample. This can be something as simple as a colon polyp or as tough as
calling dysplasia in a Barretts. Here the best we can do is cut a
bunch of levels and get the opinion of a colleague. The more
exiting "tough ones" are the good examples of things we have never
seen before. This may be a rare tumor type or disease state, or more
commonly an uncommon variation of something more familiar to us. Be aware
that many tumors can have numerous variations that overlap with different
entities. Just think of the variety of patterns that can be seen in
mesothelioma, menengioma, and melanoma. If we at least think of the
possiblities we can use our immuno stains to help sort it out.
When faced with very high grade anaplastic tumors often if we look hard enough these tumors will tell us
secrets in the form of subtle differentiation. A little melanin, bile,
lipoblasts, osteoid, mucin, a rare gland ect. The point is if we think
about it and look for it patiently we are sometimes rewarded.
Study the obvious examples to learn
the subtleties
If you want to learn to recognize
gastric dysplasia look at the premalignant changes adjacent to the obvious
cancers. There will often be beautiful examples of these early changes
which will offer a wealth of learning material. Say to your self, what
would I call this on a biopsy. You will see things that are clearly
dysplastic and subtle things that you would hedge on in a biopsy but are
sure is dysplasia in the context of this large display. Look at the
neighboring glands in a endocervical adenocarcinoma. You will see things
you would only call atypia in a biopsy but seeing in in context will
convince you that it is extremely early dysplastic change. Look at the
ducts in a pancreatic cancer you will see a spectrum of early
changes. These big resection specimens are often full of examples of
early neoplasia which are more valuable learning material than recognizing
the obvious cancer. And when faced with that miserable biopsy you will
have good examples of what is and is not tucked away in the files in you
mind.
To be continued.......