4. Cryptococcus neoformans- The presentation of these samples is variable in that there can be a marked inflammatory response
or almost none. Inflammation can be suppurative, granulomatous or eosinophilic. The organism itself can range in size from
2-20 micrometers; however the thick, non-staining (with traditional polychromatic stains) capsule can reach nearly 200 micrometers
5. Coccidioides immitis- Pyogranulomatous inflammation is common with this organism. The yeast ranges in size from 20 - 200
micrometers in diameter. They have a double refractile wall and can contain myriad endospores. These endospores are similar
morphologically to Histoplasma sp. they are 2 - 5 micrometers in diameter
Figure 2. Cryptococcus neoformans with suppurative inflammation, 40x, Modified Wright's
1. Benign cutaneous histiocytoma- Not to be confused with malignant tumors bearing a similar sounding name, these lesions
is dogs are readily diagnosable via cytology. Grossly, these lesions are commonly seen around the head, neck and limbs. These
samples are heavily cellular and consist of large numbers of discrete, round cells that have a round nucleus set in a moderate
amount of pale blue cytoplasm set in a background of finely granular protein. Occasionally, the cytoplasm is light enough
that it appears as a negatively staining halo around the intact nucleus. The cells themselves are monotonous and rather non-descript.
If a large population of small lymphocytes is also present, spontaneous regression is taking place.
2. Mast cell tumors- As they can present clinically as just about anything, it is always worth aspirating every skin mass
that is seen. Early detection of mast cell tumors (MCT) can improve prognosis and increase the number of treatment options
available. The main feature of this sample is large numbers of mast cells. These discrete round cells have a round nucleus
set in a moderate to large amount of light blue cytoplasm that is variably filled with dark purple granules. Eosinophils,
reactive fibroblasts and occasional flecks of collagen are also often present. Described based on their level of differentiation,
not grade. On occasion, some stains may not reveal the granules as readily as others. If a round cell tumor is diagnosed,
yet the cytomorphology does not fit any of the others, consider the use of another stain or special stains such as Giemsa
or toluidine blue.
Figure 3. Mast Cell Tumor, 100x, Modified Wright's
1. Sialocele- These samples are variable in appearance. Initially, they are low cellularity samples that are made up of foamy
salivary epithelial cells that are nearly always seen as singlets in a background of erythrocytes and small globs of mucus.
Windrowing is often very prominent. Occasional signs of hemorrhage are also present, with erythrophagia, hematoidin or less
frequently hemosiderin. If the lesion is compromised, secondary suppurative inflammation can be present and the windrowing
2. "Benign skin lesion". This is a blanket cytologic interpretation for a host of skin lesions, all of which are benign. These
lesions produce smears that are often very busy. They generally contain a large amount of keratin, which presents in many
forms (flakes, bars and particles) in a heavy background of assorted debris. Occasional small, tight clusters of basal-type
epithelial cells are seen. In the more cyst-like lesions, cholesterol crystals are frequently noted. Inflammation is generally
absent unless the lesion ruptures, exposing keratin to the subcutis, which leads to sterile granulomatous inflammation. Differential
diagnoses include: epidermal inclusion cyst, epidermoid cysts, follicular cysts, cornifying epitheliomas, keratinizing acanthomas,
dermoid cyst, intracutaneous cornifying epitheliomas and any one of a number of follicular tumors. Differentiation requires
biopsy with histologic evaluation; however, biologically, these entities behave similarly.
3. Lipoma- Extremely common cytologic diagnosis that is made easily and rapidly. Grossly, the smears often appear as lipid
or water droplets that do not dry after an appropriate length of time. Microscopically, the smears are usually sparsely cellular
and consist of several aggregates of adipocytes in a clear to light background of blood and cell-free lipid. Adipocytes have
abundant, clear cytoplasm with thin cell margins. Occasionally, clumps of cells aggregate with capillaries associated with
Figure 4. Lipoma, 20x, Modified Wright's. Not the capillaries running through the clumps of adipocytes
4. Sebaceous adenoma- Aspiration of these wart-like lesions typically results in a highly cellular sample. Epithelial cells
are generally seen in cohesive clusters, which are rarely arranged in acinar structures, as well as singlets, often in a light
background of blood. The bulk of the epithelial cells are large cells that have abundant foamy cytoplasm. The vacuoles are
fine and similar in size. These cells are monomorphic and sometimes accompanied by small cells that have dark blue cytoplasm
and have high N:C ratios. These cells represent reserve cells. Occasionally, necrotic material can be found in the center
of the lesions. Cytologic differentiation between a sebaceous adenoma and sebaceous hyperplasia is impossible.
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Cowell RL Ed. Cytology I. Veterinary Clinics of North America: Small Animal Practice. 32(6). November 2002.
Cowell RL Ed. Cytology II. Veterinary Clinics of North America: Small Animal Practice. 33(1). January 2003.
Cowell RL, Tyler RD. Diagnostic Cytology and Hematology of the Horse. 2nd Edition. St. Louis. Mosby. 2002.
Raskin RE, Meyer DJ. Atlas of Canine and Feline Cytology. W.B. Saunders. Philadelphia. 2001.
Thrall MA. Cytologic Examination of Cutaneous and Subcutaneous Lumps and Lesions. \Veterinary Medicine. 95(3): 224-241. 2000.