Veterinarians often rely heavily on the results of various diagnostic tests, including hematologic, biochemical, cytologic
and immunologic tests to confirm or rule-out the presence of disease and to monitor response to therapy. Of those techniques,
cytologic examination of tissues, masses and fluids is often the least expensive, the easiest to perform, and also provides
However, it should also be noted that cytology might not provide a definitive diagnosis. This article will present guidelines
for evaluating cytological samples obtained from various sources for avian patients.
Cytology of the conjunctiva and cornea
Cytology samples may be collected from the conjunctiva and cornea using a swab moistened with saline or carefully scraping
lesions with a metal or plastic spatula. Local ophthalmic anesthetic agents should be used judiciously when collecting these
samples as they are toxic to the cells and may affect the results. Individual epithelial cells or sheets of cells with brown-black
pigmented cytoplasmic granules is characteristic of normal conjunctival cytology. These granules should not be confused with
bacteria since normal cytology of the conjunctiva may contain a few extracellular bacteria. Inflammatory responses can indicate
a bacterial, parasitic, protozoan or mycotic conjunctivitis. Chronic, non-healing corneal lesions should be evaluated for
the presence of inflammatory or infectious etiologies and foreign bodies.
Cytology of the skin and subcutaneous tissues
Conventional methods of scraping, tape tests, aspiration, biopsy or tissue imprints may be used to evaluate lesions of the
skin and subcutaneous tissues. Skin diseases include, but are not limited to, cutaneous xanthomatosis, feather cysts, neoplasia,
inflammation, infections (bacterial, viral, fungal and parasitic diseases) and foreign bodies.
Normal cytology of the skin consists of anucleated cornified squamous epithelial cells, nucleated partially cornified squamous
cells, a variable amount of background debris and extracellular bacteria. Mixed-cell populations may indicate an inflammatory
or neoplastic condition with secondary infection.
The presence of numerous heterophils and extracellular bacteria is indicative of bacterial infections. Gram's stains are commonly
used in avian practice. However, some bacterial pathogens may require special stains other than Gram stains to clearly identify
them. Fungal infections are characterized by mixed-cell (macrophages, lymphocytes, plasma cells and giant cells) inflammation
with fungal organisms present in the sample. Cutaneous or subcutaneous foreign body lesions often produce mixed inflammatory
cell populations consisting of macrophages, multinucleated giant cells and heterophils (See suggested reading). Parasitic
infections, such as Knemidocoptic mange, usually are identified by hyperkeratosis of the skin around the cere, feet, legs,
eyes or vent and the presence of the mites on skin scrapings. Viral infections, such as avian poxvirus, produce lesions on unfeathered areas of skin around the eyes, cere and feet, as
well as lesions in the oropharynx or cornea. Diagnosis of poxvirus infections may be accomplished by scraping the raised lesions
and examining them for the presence of large cytoplasmic vacuoles (Bollinger bodies), which contain smaller, round eosinophilic
inclusions (Borell) on Wright's stain.
Dermatologic conditions, such as lipomas, xanthomas, lymphoid neoplasia, carcinomas or sarcomas may also be identified by
cell type and presence or absence of inflammatory cells. Lipomas often are identified easily following aspiration by the presence
of fat droplets and fat cells. Cytology of xanthomas should show macrophagic inflammation with multinucleated giant cells
and cholesterol clefts.
Round-cell neoplasms, such as lymphosarcoma, usually yield few individual round cells when aspirated. Carcinomas or neoplasms
of epithelial cell origin often yield sheets or clumps of cells of varying size, and nuclear/cytoplasmic ratio characteristic
of the type of neoplasia. Neoplasias of mesenchymal cell origin (spindle-cell tumors) also tend to yield few cells that are
found as individuals in contrast to epithelial or round-cell tumor types.
Cytology of the digestive tract
Differential diagnoses for plaques, nodules and ulcers in the oropharynx include candidiasis, trichomoniasis, bacterial abscesses,
squamous metaplasia due to hypovitaminosis A, papilloma, neoplasia, poxvirus, herpesvirus or physical trauma. These lesions
may be assessed by scrapings, swabs, aspiration or imprints of excised tissue. Cytology samples of the esophagus and ingluvies
may be obtained using saline-moistened swabs, flushes or washes.