Cytology is an excellent screening tool for sampling easily accessible, raised lesions within the cutaneous or subcutaneous layers of the skin. Acquisition of adequately cellular, well-preserved, representative cytology samples is essential to obtaining meaningful information regarding the presence and characterization of underlying pathology.<\/p>\n
This article briefly reviews the broad categories of skin \u201clumps and bumps\u201d cytology, including features of hyperplastic, inflammatory, neoplastic, and cystic or fluid-filled masses, as well as the basics of slide evaluation. A simplified diagnostic algorithm is provided.<\/p>\n
Take-Home Points<\/strong><\/p>\n In small animal cytology, \u201clumps and bumps\u201d refer to lesions that manifest within the cutaneous and subcutaneous layers of the skin, resulting in raised, conspicuous masses. These masses may be neoplastic or nonneoplastic and generally fall into 1 or more recognized categories<\/span>1-3<\/sup>: <\/span><\/p>\n These lesions are ideal for cytologic sampling using fine needle aspiration (FNA), as they are accessed without advanced imaging (e.g., ultrasonography<\/a>), and sedation or anesthesia is typically not necessary; they require only minimal equipment for sample acquisition; and they are often of high diagnostic yield.1,3<\/sup><\/span><\/p>\n Although the overall incidence of skin tumors in dogs and cats is challenging to determine, skin is a common site for neoplasia in small animal species. In the presence of a mass, cytology can often accurately distinguish neoplastic from nonneoplastic lesions, determine general categories of neoplasia, and lead to a more specific diagnosis.4<\/sup> Multiple studies comparing cytologic with histologic diagnoses for neoplastic and nonneoplastic lesions have demonstrated the utility and reliability of cytology in veterinary medicine.2,5<\/sup><\/span><\/p>\n High concordance rates have been reported between cytology and histology in the evaluation of canine and feline cutaneous and subcutaneous lesions.2,5<\/sup> One retrospective study of 243 cytologic samples (198 from dogs and 45 from cats) agreed with histologic diagnoses on the presence or absence of neoplasia in 90.9% of cases when evaluated by clinical pathologists.2<\/sup> The same study reported a sensitivity of 89.3%, specificity of 97.9%, positive predictive value of 99.4%, and negative predictive value of 68.7% for the cytologic diagnosis of neoplasia.2<\/sup> An obvious advantage of achieving a cytologic diagnosis is avoiding additional diagnostics, thereby saving money for the client and enabling the prompt initiation of appropriate therapies.3<\/sup> However, clients should be aware that biopsy and histologic evaluation may still be required for a more specific diagnosis. It is important to consider the experience of the evaluator and the influence of inflammation, which may mask or mimic neoplasia.4<\/sup><\/span><\/p>\n Cytology, like all diagnostic tests, is not without limitations. The lack of tissue architecture restricts the amount of information cytology can provide, particularly when overlapping cytologic features (e.g., hyperplastic versus benign neoplastic lesions) exist. Acquiring a satisfactory sample also influences the usefulness of diagnostic cytology; inadequately cellular samples composed up to 16.8% of all cases in 1 study.2<\/sup> Therefore, appropriate sample acquisition, preparation technique, and screening for cellularity, along with resampling if needed, are recommended to avoid nonrepresentative or nondiagnostic samples.3<\/sup> Detailed descriptions of how to obtain cytologic samples via FNA<\/a> are provided elsewhere.6,7<\/sup><\/span><\/p>\n It is also important to remember that lesion type also affects the likelihood of a representative result.8<\/sup> Knowledge of accurate and detailed patient history and mass characteristics significantly influences the cytologic interpretation and is critical (<\/span>BOX 1<\/b><\/span>).8<\/sup> In many cases, histopathologic tissue evaluation should be pursued for a more definitive classification, with or without cytochemical, immunocytochemical, or immunohistochemical stains. Cytologic interpretation does not negate the need to submit a biopsy sample, as each yields essential information.<\/span><\/p>\n a<\/sup>When submitting slides to a pathologist, this information, at minimum, should also be included.<\/div><\/div>\n The first step in evaluating a cytologic sample from a skin mass is assessing the entire slide at low-power magnification (4\u00d7 to 10\u00d7 objective) for adequate cellularity, distribution, cellular preservation, and staining quality (<\/span>FIGURE 1<\/b><\/span>).3,9,11<\/sup> Inadequately cellular samples may reflect poor sampling technique. Other considerations include cystic or poorly exfoliative lesions, particularly if resampling produces similar results. In such cases, a tissue biopsy may be required. If only cellular debris or necrotic tissue is identified, sampling a different site or histopathology of the mass is recommended.<\/span><\/p>\n Once sample quality has been confirmed, the next step is to evaluate all slides to determine the predominant cell population. Slides should be first assessed at low magnification to identify specific cell patterns or structures, which may provide information about the process or tissue type present.11<\/sup> High-power magnification (40\u00d7, 50\u00d7, or 100\u00d7 objective) is then useful to scrutinize cellular morphology further, categorize the predominant cell type present (i.e., inflammatory or tissue cells), and identify criteria of malignancy or infectious agents.<\/span><\/p>\n Principal cell types determine classification, and evaluation for underlying causes (e.g., infectious or noninfectious etiologies) is warranted (<\/span>TABLE 1<\/b><\/span>). If only inflammatory cells are noted, inflammation would be suspected. An exclusively monomorphic tissue cell population with no significant inflammation suggests a hyperplastic or neoplastic population. Neoplasms are <\/span>grouped into 4 general categories to assist in interpreting or generating appropriate differentials based on cellular arrangements and cytomorphology (<\/span>TABLE 2<\/b><\/span>).<\/span><\/p>\n Although the 4 basic categories of skin masses (i.e., hyperplasia, cystic, inflammation, and neoplasia) are based on the overall underlying process, it is essential to remember that they are not mutually exclusive. The same lesion may fall into more than 1 category (e.g., cystic adenoma, inflammatory carcinoma), and sampling multiple areas may reveal additional diagnostically significant information.<\/span><\/p>\n While cytology is most effective in differentiating neoplastic from nonneoplastic lesions, concurrent inflammation can induce dysplastic epithelial changes and\/or reactive changes to fibrous tissue, mimicking neoplasia.2,5,8<\/sup> As such, extreme caution should be exercised in the presence of inflammation before diagnosing neoplasia, and consultation with a veterinary pathologist is advised. Overtly malignant neoplasms demonstrate specific structural changes that can be observed by light microscopy at high-power magnification (40\u00d7 to 100\u00d7 objective) as morphologic atypia, representing the basis of cytologic criteria of malignancy (<\/span>TABLE 3<\/b><\/span>).9,10,15<\/sup><\/span><\/p>\n\n
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Utility of Small Animal Cytology<\/h2>\n
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Approach to Sample Evaluation<\/h2>\n
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