66Figure 4.1a — Tuberculosis, Fine Needle Aspiration [H&E Stain; High Power]. This fine needle aspiration came from a right apical cavitary mass in a woman with a positive PPD and exposure to tuberculosis through family members. The field contains necrosis and macrophages. The presence of necrosis with granulomatous inflammation should raise concern for infectious organisms, in particular mycobacteria and yeast, and staining for these organisms should be performed.

Figure 4.1b — Tuberculosis, Fine Needle Aspiration [Ziehl–Neelsen Special Stain; High Power]. The Ziehl–Neelsen stain is an acid-fast stain useful for the detection of mycobacteria and other acid-fast organisms. Because the sensitivity for detection on tissue sections is low, cultures should also be taken at the time of biopsy and patients with suspected tuberculosis infection should not be dismissed due to negative staining. In this case, the stain highlights the organism in a hot pink color. The organisms “cord” together, forming small rope-like structures.

Figure 4.2 — Nocardia, Bronchoalveolar Lavage [Gomori Methenamine Silver Special Stain; High Power]. Pulmonary nocardiosis is caused by infection with Nocardia asteroids or Nocardia brasiliensis and is most common in patients with weakened immune systems. The organism is typically found in soil and may be inhaled with dust in the air. Nocardia are gram positive and weakly acid-fast bacteria with a branching, rod-shaped growth. Here, the organisms are demonstrated on a Gomori methenamine silver stain.

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Figure 4.3a — Rhodococcus equi, Bronchoalveolar Lavage [H&E Stain; High Power]. Rhodococcus equi infection may cause malakoplakia, as demonstrated in this image. There is a diffuse dispersion of histiocytes with abundant pink granular-appearing cytoplasm and Michaelis-Gutmann bodies (round, lamellated intracytoplasmic inclusions) seen most prominently in the center of the field. Other bacterial infections (Escherichia coli, Proteus) may also cause malakoplakia.

Figure 4.3b — Rhodococcus equi, Bronchoalveolar Lavage [Pap Stain; High Power]. On Pap-stained aspirates, Michaelis-Gutmann bodies are more readily appreciated as a lamellar intracytoplasmic inclusion in the center of the large, granular histiocyte. The Michaelis-Gutmann bodies are composed of intracellular accumulations of calcium and iron, and are thought to be a response to organisms.

Figure 4.3c — Rhodococcus equi, Bronchoalveolar Lavage [Diff-Quik Stain; High Power]. Rhodocococcus equi is a gram-positive, partially acid-fast bacterium that can be found within histiocyte cytoplasm and may mimic true acid-fast bacilli. The infection was first described in livestock and particularly foals, but the bacterium can also be a human pathogen, particularly in immunocompromised individuals. The name Rhodococcus derives from the red pigment produced in cultures.

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Figure 4.4a — Aspergillus, Bronchial Washing [Diff-Quik Stain; High Power]. This high power image from a bronchial wash shows the classic form of Aspergillus spp. mold—thin, septate hyphae with acute angle branching, and a background of inflammatory cells. Pulmonary aspergillosis takes many forms; ranging from a colonizer of a preexisting cavitary lesion (“fungus ball”) or airway (“bronchocentric granulomatosis”) to allergic disease to the potentially fatal angioinvasive disease.

Figure 4.4b — Aspergillus, Bronchial Washing [Gram-Weigert Stain; High Power]. This image from another bronchial wash shows again the morphology associated with Aspergillus: acute angle branching and thin, septate hyphae. The diagnosis of Aspergillus species can be suggested by morphology, but definitive diagnosis should be made based on microbiologic studies, as other fungal species may have similar morphology.

Figure 4.4c — Aspergillus, Bronchoalveolar Lavage [Pap Stain; High Power]. This bronchoalveolar lavage specimen is remarkable for the thin, arching fungal hyphae seen surrounded by necrotic debris, neutrophils, and abundant intra-alveolar macrophages. A possible fruiting body, resembling a broom-head, with spore formation is present at the center of the field. Aspergillus may be an airway contaminant, but the presence of hyphae with associated inflammatory reaction and necrosis supports the diagnosis of infection.

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Figure 4.4d — Aspergillus, Bronchoalveolar Lavage [Pap Stain; High Power]. This image highlights the delicate, septate, 45-degree angle branching hyphae of Aspergillus, intimately associated with neutrophils and pulmonary alveolar macrophages. Invasive aspergillus is most commonly associated with decreased T cell immunity, particularly vulnerable are organ transplant recipients and leukemia patients receiving chemotherapy.

Figure 4.5a — Aspergillus, Bronchoalveolar Lavage [Pap Stain; High Power]. The hyphae of Aspergillus on high power examination reveal the thin septations and clear acute angle branching of the growing hyphae. This image also has associated pulmonary alveolar macrophages and chronic inflammatory cells. Invasive aspergillosis is usually angiocentric and the classic findings in histologic sections include thrombosed vessels with walls invaded by hyphae.

Figure 4.5b — Aspergillus, Bronchoalveolar Lavage [Diff-Quik Stain; High Power]. A tangled assortment of fungal hyphae dominate in this high power image of a Diff-Quik stained bronchoalveolar lavage fluid. The hyphae are thin and septate, with acute angle branching evident, best appreciated at the top of the image. The background cells are primarily pulmonary alveolar macrophages with associated inflammatory cells and proteinaceous fluid. This constellation of findings is most suggestive of pathologic involvement by Aspergillus spp. Allergic bronchopulmonary aspergillosis can be seen in patients with underlying asthma and an IgE-mediated reaction to the fungus, and may or may not evolve to chronic inflammation with granuloma formation.

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Figure 4.5c — Aspergillus Fruiting Body, Bronchial Washing Pap Stain; High Power]. While in most cytologic preparations Aspergillus spp. are seen as hyphal forms, fruiting bodies can occasionally be seen in specimens taken from cavities or airways. In this case, the conidiophore ends in a flask-shaped vesicle around which phialids and conidia are arranged. While the subspeciation of Aspergillus on cytologic preparations is usually unnecessary and challenging, the morphology seen here strongly suggests Aspergillus spp.; in the absence of a vesicle, the 45-degree angles formed by branching, septate hyphae are nonspecific for Aspergillus spp. and may be seen in other fungi, even if Aspergillus spp. is the usual culprit in immunocompromised patients.

Figure 4.6a — Mucor, Bronchoalveolar Lavage [Pap Stain; High Power]. An aggregate of rust-colored, aseptate, “ribbon-like” hyphae stream across the center of this field of view from a bronchoalveolar lavage specimen. These hyphae also exhibit 90-degree angle branching. In the background there are scattered alveolar macrophages, neutrophils, and red blood cells. These observations all point to a diagnosis of infection by fungi of class Zygomycetes, a type of angioinvasive fungal disease usually targeting patients with decreased cellular immunity or diabetes and which may be rapidly fatal. Pulmonary infections are acquired through inhalation of environmental spores, and present as a hemorrhagic pneumonia.