Cytology is a relatively easy, relatively non-invasive, fast and inexpensive diagnostic technique. Sometimes you actually
get the diagnosis. Other times you don't get a specific diagnosis, but the cytologic findings can help you decide which diagnostic
technique might be indicated as a next step. Also some potential diagnoses often can be ruled out.
To perform a good cytologic evaluation you must have some knowledge including:
- The normal histological and cytological appearance of tissues in the area being sampled
- The histological and cytological appearance of potential lesions
- The types of pathologic abnormalities that might cause the lesion being sampled.
This knowledge may be relatively simple in some cases and pretty complicated in others. Many cases probably should be evaluated
by a specialist with advanced training in pathology. But some cases are straightforward in their cytologic appearance and
can be evaluated by interested practitioners. In addition, screening of a sample before submitting it to an outside laboratory
is useful in helping to assure its quality as well as being a learning tool if you compare your interpretation with the cytologist's
Frequently sampled tissues for cytology include blood, subcutaneous and cutaneous lesions, lymph nodes, prostate, bone marrow,
conjunctiva, ear exudates, vaginal and rectal mucosa, internal organs, urine, respiratory tract, and body cavity fluids.
General approach to the cytology slide
Start with a low power objective to see whether there are actually intact cells present, get an idea as to which cell types
are present, and find a suitable area to examine at higher magnification. Parasites and other large organisms are also usually
best found at low power.
Appropriate areas to examine have a monolayer of intact cells that are well stained. If cells are in a thick area, they are
difficult (if not impossible) to identify and morphologically examine. Avoid ruptured cells and areas where the stain is too
light or dark. Some highly cellular samples that stain poorly may have well-stained areas at the edge of the slide, or they
may require additional staining.
After finding a good area on low power, the slide should be examined with high power, or oil. At this magnification you can
positively identify various cell types, examine cellular detail, and search for small organisms.
In most cases, the most important distinction to make is whether a lesion is inflammatory or neoplastic/hyperplastic. Making
this determination can lead you to treat with such therapies as antibiotics and anti-inflammatories for inflammatory lesions
or to surgically excise or initiate chemotherapy for neoplastic lesions. Once you decide whether a lesion is inflammatory
or neoplastic, there are some other types of information that can be gained from a cytology sample that enhance your ability
to treat and give a reasonable prognosis.
Classification of inflammation
Inflammation is classified by the type of cells that predominate. Sometimes inflammation is considered to be mixed if there
are roughly equivalent numbers of different types of inflammatory cells. The degree of inflammation (mild, moderate or marked)
should be noted.
Suppurative (or purulent or neutrophilic) inflammation
- Usually ≥ 90% neutrophils.
- Septic, suppurative inflammation is the term used if bacteria are seen.
- You can't assume that something is non-septic just because bacteria are not seen cytologically. Culture is used to make the
- More than one type of inflammatory cell is present.
- Usually comprised predominantly of neutrophils with 10-50% macrophages and/or lymphocytes.
- Commonly seen with foreign body reaction or fungal infection.
- May be an indication of chronicity.
Mononuclear or granulomatous inflammation
- The majority of cells are macrophages and giant cells.
- Typical inflammatory process associated with mycobacterial agents and steatitis.
- If >15% of the cells are eosinophils an inflammatory reaction is usually considered to have a significant eosinophilic component.
- Commonly associated with allergic reactions or parasites.