Image Gallery: Transtracheal Wash Cytology

Figure 1 Oropharyngeal contamination resulting from improper sampling technique is a common problem with transtracheal wash cytology. The presence of uniform squamous epithelial cells (black arrow) alongside oral bacterial flora, such as Simonsiella spp as pictured here (red arrow), indicates oropharyngeal contamination. Simonsiella spp can be recognized by their pathognomonic morphology that resembles a pill capsule with internal striations (ie, “stacked coin” appearance). Modified Wright’s; 600x total magnification

Figure 2 Normal transtracheal wash fluid predominately consists of alveolar macrophages, which usually comprise up to 90% of the total nucleated cells. Alveolar macrophages (white arrows) are large mononuclear cells with an eccentrically placed nucleus and a moderate amount of foamy, basophilic cytoplasm. Neutrophils typically make up less than 5%-10% of the nucleated cells found in these samples. Other cell types that may be seen include small lymphocytes (5%-14%), eosinophils (typically up to 5% in dogs and up to 25% in cats), and mast cells (<2%).^1-4 Modified Wright’s; 600x total magnification

Figure 3A Other cells typically found in transtracheal wash fluid include ciliated columnar respiratory epithelial cells (A) and goblet cells (B). The presence of ciliated columnar epithelial cells (A, black arrow) is usually indicative of adequate fluid retrieval. Low numbers of goblet cells (B, black arrow) or goblet cell granules can be normal, whereas high numbers may point toward goblet cell hyperplasia, an indicator of chronic inflammation. Modified Wright’s; 1000x total magnification

figure 3B Other cells typically found in transtracheal wash fluid include ciliated columnar respiratory epithelial cells (A) and goblet cells (B). The presence of ciliated columnar epithelial cells (A, black arrow) is usually indicative of adequate fluid retrieval. Low numbers of goblet cells (B, black arrow) or goblet cell granules can be normal, whereas high numbers may point toward goblet cell hyperplasia, an indicator of chronic inflammation. Modified Wright’s; 1000x total magnification

Figure 4 Mucus is commonly found in both normal and abnormal transtracheal wash specimens and may be seen as fluffy pink material in the background or as dark purple to blue, spiral-shaped material when inspissated. The latter, known as Curschmann’s spirals (black arrows), indicate small airway disease. Modified Wright’s; 1000x total magnification

Figure 5 A predominance of neutrophils (black arrows) can indicate either acute or chronic inflammation. When there is an increased percentage of neutrophils, the fluid should be thoroughly examined for infectious agents (both bacterial and fungal), especially if the neutrophils are degenerate in appearance. Noninfectious causes of suppurative inflammation include foreign body pneumonia and neoplasia. Modified Wright’s; 600x total magnification

Figure 6 Eosinophils (black arrow) are a type of WBC named for their cytoplasmic granules that readily stain with eosin. They are usually rare in transtracheal wash fluids, typically comprising only 5% of nucleated cells in dogs. Eosinophil percentage is extremely variable in cats, with reported values of up to 25%. In either case, when they comprise greater than 10% of the total nucleated cell count, causes of eosinophilic inflammation should be considered and correlated with clinical information. Causes of eosinophilic inflammation include allergic/hypersensitivity reactions, eosinophilic pneumonitis/pulmonary infiltration with eosinophilia (PIE), parasitism, aspergillosis, or paraneoplastic syndrome. In rare instances, bacterial pneumonia can cause eosinophilic inflammation. Modified Wright’s; 600x total magnification

Figure 7 Of all cell types found in transtracheal wash fluid, degenerate neutrophils are most commonly associated with bacterial pneumonia. Diagnosis of bacterial pneumonia requires demonstration of intracellular organisms (black arrow). The organisms may also be present in the background, but this may merely indicate contamination and extracellular bacteria should be interpreted with caution when viewed in the absence of intracellular bacteria. Bacterial pneumonia typically consists of a monomorphic population; however, with aspiration pneumonia, a mixed population may be identified. Transtracheal wash samples should be transported to the laboratory as soon as possible to prevent bacterial overgrowth. Bacterial proliferation rarely occurs in samples stored at 4°C, even over 24 hours; however, unrefrigerated samples are at risk for rapid bacterial overgrowth with either pathogenic or contaminant organisms, which can confound cytologic interpretation. At least one direct or concentrated smear should be made for cytology as soon as possible after sample collection; this smear can serve as a reference point for the pathologist with regards to cellular morphology and bacterial populations at the time of sampling. Smears should be submitted to the laboratory along with the collected fluid. Modified Wright’s; 1000x total magnification

Figure 8 Although suppurative inflammation characterizes the majority of bacterial pneumonias, Mycobacterium spp constitute an exception. Granulomatous or pyogranulomatous inflammation is most commonly seen with this type of infection. Macrophages often predominate; in the macrophagic population, multinucleated giant cells and epithelioid macrophages are common. Mycobacteria spp are recognized as nonstaining rods (black arrows) in cytologic specimens. Acid-fast staining can confirm their presence. Modified Wright’s; 1000x total magnification

Figure 9A Although more commonly seen in lung aspirates, systemic fungal organisms can sometimes be identified from airway washes. Blastomyces dermatitidis (white arrows) is a dimorphic fungus that frequently infects the lungs, and sometimes other organs, of dogs. Cats are infrequently infected. Blastomyces spp are most often identified in yeast form in transtracheal fluids, though hyphal elements may be seen in rare instances. Modified Wright’s; 600x total magnification

Figure 9B B dermatitidis yeasts (white arrow) are round, dark blue, and 5-20 μm in diameter, with a thick wall and broad-based budding (ie, the “neck” connecting the budding yeast organisms is wide as compared with the narrow-based budding associated with Cryptococcus spp). B dermatitidis is typically associated with pyogranulomatous inflammation. Modified Wright’s; 1000x total magnification

Figure 10 Like other dimorphic fungi that infect both dogs and cats, Histoplasma capsulatum (white arrow) typically induces pyogranulomatous inflammation. The yeast forms are much smaller than B dermatitidis (1-4 μm diameter) and are characterized by their purple nucleus, lightly basophilic cytoplasm, and thin halo. They are commonly found within macrophages as well as scattered throughout the background. In this image, the majority of nucleated cells depicted alongside the organisms are lysed, as evidenced by the purple nuclear streaming material scattered throughout. Modified Wright’s; 600x total magnification

Figure 11 Neoplastic disease can also be identified via transtracheal wash cytology. Both primary and metastatic cancers can be diagnosed with this method. The most commonly seen neoplasm in transtracheal wash specimens, as pictured here, is carcinoma. Carcinoma often appears as sheets or clusters of pleomorphic cells with clear cell–cell junctions and multiple criteria of malignancy, including prominent nucleoli and marked anisocytosis and anisokaryosis. In fluid samples, including tracheal washes, carcinoma cells dissociate and appear rounded and more individualized. These cells are typically quite large (>20 μm diameter) and have a high nuclear:cytoplasmic ratio with deeply basophilic cytoplasm and a large round nucleus with several nuclear characteristics of malignancy. Modified Wright’s; 600x total magnification