Cutaneous and Subcutaneous Lesions

CHAPTER 5 Cutaneous and Subcutaneous Lesions



Evaluation of cutaneous and subcutaneous lesions is one of the more common uses of diagnostic cytology and can be an extremely useful clinical tool. Cutaneous and subcutaneous lesions are easily accessible and there are no significant contraindications to collecting samples from them. Tranquilization and/or anesthesia is seldom needed for sample collection. Often the specimen can be collected, prepared, stained, and microscopically evaluated in minutes—providing a diagnosis, prognosis, indication of appropriate therapy, and/or guidance as to the next diagnostic procedure.



COLLECTION TECHNIQUES


Samples may be collected as fine-needle biopsies (FNB) (using either an aspiration or nonaspiration technique), scrapings, imprints, and/or swabs, depending on the characteristics of the lesion and the tractability of the patient. FNBs by an aspiration or a nonaspiration technique (see Chapter 1) are the standard method of collection because they yield the most representative and diagnostic samples in most situations. There are times, however, when alternate techniques or combinations of techniques are warranted, as discussed subsequently.



Fine-Needle Biopsies


Fine-needle biopsy is described in Chapter 1.



Solid Masses


Most cutaneous or subcutaneous solid masses are well suited for both the aspiration and nonaspiration techniques; the primary determinant is the preference of the collector. Sometimes, it is wise to sample the lesion using both techniques, especially if the first method attempted appears to have obtained little material or resulted in marked blood contamination. If large enough, the mass should be sampled several times in different areas to increase the chance of obtaining diagnostic material. FNBs can be collected along with impression smears or swabs, if desired.





Imprints


Although impression smears are easy and are not painful for patients, they have limitations similar to those of swabs. Depending on the types of cells present, in the lesion may not yield enough cells for evaluation. Discrete cells, such as inflammatory cells and cells of round cell tumors, exfoliate well with imprints. Mesenchymal lesions generally do not exfoliate many cells; however, highly malignant mesenchymal tumors may yield very cellular specimens. The cells retrieved from imprints, as with swabs, may not be representative of the lesion. Impression smears of ulcerated neoplasms often yield only surface inflammation. Conversely, in inflammatory lesions, impression smears may yield surface epithelial cells that are dysplastic secondary to the inflammatory process present. Impression smears of exudative or ulcerative lesions are most useful for identifying the presence of infectious agents (e.g., fungal organisms).


Imprints can be made from ulcerated lesions or surgically removed tissue. Imprints of lesions are made by removing any scab that covers the lesion and then touching the dry surface of a clean, glass slide to the surface of the lesion. If a Dermatophilus congolensis infection is suspected, the underside of the scab is also imprinted. The lesion is then cleaned with a nonirritating antiseptic, blotted dry with a sterile gauze sponge or other clean absorbent material, and reimprinted. If the tissue is not blotted dry before impressions are made, the slides will usually contain only blood/tissue fluid.






EVALUATION OF AN INFLAMMATORY CELL POPULATION


Figure 5-2 provides an algorithm to aid in the evaluation of the inflammatory cell component of cutaneous and subcutaneous lesions, and Table 5-1 gives general considerations for some inflammatory responses. If most of the inflammatory cells are neutrophils (see Figure 5-7 later in the chapter), especially when degenerate neutrophils are present, but no bacteria are found, a covert infection may be present, or the neutrophilic inflammatory response may be due to one of the conditions listed in Table 5-1 under “Marked predominance of neutrophils.” The lesion can be cultured to identify a covert infection. If the culture reveals an infectious agent, appropriate therapy can be instituted. If the culture does not reveal an infectious agent or if therapy for the infectious agent identified by culture is not effective, cytology can be repeated or a biopsy can be submitted for histopathologic evaluation.



Table 5-1 Some Conditions Suggested by Certain Proportions of Inflammatory Cells







































Inflammatory cell population First considerations Second considerations
Marked predominance (85%) of neutrophils
Many neutrophils are degenerate Gram-negative bacteria
Gram-positive bacteria
Abscess secondary to neoplasia, foreign bodies, etc.
A few neutrophils are degenerate Gram-positive bacteria
Gram-negative bacteria
Higher bacteria (nocardia, Actinomyces, etc.)
Fungi
Protozoa
Foreign body
Immune-mediated chemical or traumatic injury
No neutrophils are degenerate Gram-positive bacteria
Higher bacteria (nocardia, Actinomyces, etc.)
Chemical or traumatic injury Panniculitis
Abscess secondary to neoplasia
Gram-negative bacteria
Fungi
Foreign body
Abscess secondary to neoplasia
Admixture of inflammatory cells
15% to 40% macrophages Higher bacteria (Nocardia, Actinomyces, etc.)
Fungi
Protozoa
Neoplasia
Foreign body
Panniculitis
Any resolving inflammatory lesion
Nonfilamentous gram-positive bacteria
Parasites, chronic allergic inflammation and eosinophilic granuloma if eosinophil numbers are increased
>40% macrophages Fungi
Foreign body
Protozoa
Neoplasia
Panniculitis
Any resolving inflammatory lesion
Parasites, chronic allergic inflammation, and eosinophilic granuloma if eosinophil numbers are increased
Inflammatory giant cell present Fungi
Foreign body
Protozoa
Collagen necrosis
Panniculitis
Parasites (if eosinophils are present)
>10% eosinophils Allergic inflammation
Parasites
Eosinophilic granuloma
Collagen necrosis
Mast cell tumor
Neoplasia
Foreign body
Hyphating fungi

When >15% of the inflammatory cells present are macrophages (Figure 5-3, A), and/or inflammatory giant cells are present (Figure 5-3, B), fungal infection, infection with Actinomyces or Nocardia spp., foreign-body granuloma, or other causes of granulomatous inflammation (e.g., lick granuloma) should be considered. The slide should be carefully studied for organisms (Figure 5-3, C) or signs of a foreign body, such as refractile debris (Figure 5-4). Also, historical information about the possible introduction of foreign material should be sought. If no organisms are found and no historical information indicates the introduction of a foreign substance into the area, the tissue can be cultured, or a biopsy can be submitted for histopathologic examination.




If the proportion of eosinophils exceeds 10% (Figure 5-5), an allergic, parasitic, or foreign-body reaction or an eosinophilic granuloma complex lesion should be considered. The slide should again be carefully searched for organisms or signs of foreign material. If no organisms or signs are found, the lesion can be cultured (including fungal cultures), or a biopsy can be submitted for histopathologic evaluation. If the lesion is cultured, but not biopsied, and the culture fails to yield an organism, the lesion may be treated as an eosinophilic granuloma if the historical and clinical evidence is indicative of an eosinophilic granuloma complex lesion. In this situation, the lesion should be watched carefully. If the response to therapy is not appropriate, a biopsy of the lesion should be submitted for histopathologic evaluation.



When tissue cells showing criteria of malignancy are accompanied by inflammatory cells (Figure 5-6), the sample should be interpreted cautiously. Dysplasia occurring in tissue adjacent to inflammatory reactions can alter tissue cell morphology. As a result, tissue cells undergoing dysplasia in response to a local inflammatory process can be erroneously classified as neoplastic cells. As the intensity of the inflammatory reaction increases, the assurance with which a diagnosis of neoplasia can be made decreases.




INFECTIOUS AGENTS


See Chapter 3 for more photographs of infectious agents. Infectious agents invariably cause lesions characterized by the presence of inflammatory cells. Bacterial agents usually produce lesions characterized by being composed of more than 85% neutrophils (Figure 5-7)—many of which may be degenerate. When bacteria are pathogenic, some can usually be found phagocytized within neutrophils in addition to those that may be present extracellularly. Mycotic agents produce lesions that tend to have more macrophages present than do bacterial lesions. However, neutrophils may still be the predominant cell type, and eosinophils may be plentiful with certain hyphating fungi. Cytologic evaluation often reveals the type of infectious agent (e.g., bacteria, yeast, protozoa) and in some cases yields a definitive diagnosis (e.g., histoplasmosis, cryptococcosis). Size, shape, staining characteristics, and internal structures are helpful in classifying the type of organism and in some cases, specific identification of the organism.




Bacteria




Bacterial Cocci


Pathogenic bacterial cocci (Figure 5-8) are usually gram positive and of the genera Staphylococcus or Streptococcus. Staphylococci usually occur in clusters of 4 to 12 bacteria, but Streptococcus spp. tend to occur in short or long chains of organisms. When cocci are identified in cytologic preparations, aerobic and anaerobic cultures and sensitivity tests should be performed to identify the organism and the optimum antibiotic therapy. Because most cocci are gram positive, antibiotic therapy effective against gram-positive organisms should be used when it is necessary to start therapy before culture and sensitivity results are received.



D. congolensis replicates by transverse and longitudinal division, producing long chains of coccoid bacterial doublets that resemble small, blue railroad tracks. It infects the superficial epidermis, causing crusty lesions. Cytologic preparations from the undersurface of scabs from these crusty lesions are most rewarding in demonstrating organisms. The preparations usually contain mature epithelial cells, keratin bars, debris, and organisms (Figure 5-9). A few neutrophils may also be found.





Filamentous Rods


Pathogenic filamentous rods that cause cutaneous or subcutaneous lesions are usually Nocardia or Actinomyces spp. Some other anaerobes, such as Fusobacterium and Mycobacterium spp. may be filamentous, but rarely are. Nocardia and Actinomyces spp. are characterized by long, slender (filamentous) strands that stain pale blue and have intermittent, small, pink or purple areas (Figure 5-11; see Figure 5-3). This morphology is characteristic of both Nocardia and Actinomyces spp. and the filamentous form of Fusobacterium spp. When these features are recognized cytologically, cultures should be performed specifically for Nocardia and Actinomyces spp. and for other anaerobes.



On the other hand, Mycobacterium spp. often do not stain with Romanowsky-type stains. As a result, negative images (Figure 5-12, A) may be observed in the cytoplasm of macrophages and/or inflammatory giant cells. When epithelioid macrophages and/or inflammatory giant cells are encountered in cytologic preparations that do not contain any obvious organisms, a careful search for negative images of Mycobacterium spp. should be made. Mycobacterium spp. stain with acid-fast stains; therefore when negative images are encountered, or when the character of the lesion suggests that Mycobacterium spp. be considered, an acid-fast stain can be performed to show the organism (Figure 5-12, B) and/or cultures for Mycobacterium spp. can be performed for identification.



Because these organisms are often refractory to common antibiotic therapy, and reliable culture has special requirements, cytology is very useful in indicating to the practitioner that special cultures are needed.




Yeast, Dermatophytes, Hyphating Fungi, and Algae









Fungi That Form Hyphae in Cutaneous and Subcutaneous Tissues


Many fungi can infect the cutaneous and subcutaneous tissue and form hyphae (Figure 5-22). These fungi usually cause small to large raised, proliferative lesions that often ulcerate. They also induce a granulomatous, inflammatory response that is characterized by epithelioid macrophages and inflammatory giant cells (see Figure 5-3). The number of neutrophils, lymphocytes, plasma cells, and eosinophils varies. Some hyphating fungi do not stain well with hematologic-type stains and are recognized as negative images (Figure 5-23). The organisms that cause the disease phycomycosis typically do not stain with hematologic stains and induce an eosinophilic, granulomatous response in the infected tissue (Figure 5-24). A fungal culture or histopathology with special immunohistochemical stains may be used to definitively classify the organism involved.






Prototheca zopfii and P. wickerhamii


Prototheca spp. are colorless algae that are ubiquitous in the southern regions of America, but only rarely cause disease (i.e., protothecosis). In dogs, the disease is often disseminated, but only cutaneous protothecosis has been reported in cats.14 Cytologic preparations reveal an inflammatory response characteristic of pyogranulomatous or granulomatous inflammation and organisms ranging in number from a few to many. The organisms (Figure 5-19) are round to oval and are from 1 to 14 microns wide and 1 to 16 microns long. When stained with Romanowsky-type stains, they have granular basophilic cytoplasm and a clear cell wall about 0.5 micron thick. The organisms, except those that are small and immature, contain a small nucleus that stains pink to deep purple. A single organism may consist of two or four or more endospores. Most organisms are extracellular, but small forms may be found in macrophages and neutrophils.

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Aug 31, 2016 | Posted by in GENERAL | Comments Off on Cutaneous and Subcutaneous Lesions
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