Alveolar Damage and Pneumocystis Pneumonia

Alveolar damage (AD) with hyaline membranes is an infrequent pattern seen in pneumocystis pneumonia, occurring in both AIDS and non-AIDS patients [1]. It probably results from a superimposed cause of AD, such as oxygen toxicity. Sometimes intraalveolar foamy material can also be found. In cases where hyaline membranes predominate or are the sole feature of disease, a GMS stain for organisms is the only way to confirm the diagnosis, histologically.

Figure 1. Alveolar Damage

Here, an alveolar duct and two alveolar spaces are lined by dense, pink hyaline membranes. Type II cells are hypertrophic, and some alveoli contain a few inflammatory cells. There is one prominent focus of foamy alveolar exudate to the left of center.

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Find the focus of foamy exudate.

Find hyaline membranes in 2 alveoli and around the alveolar duct. (Not all parts are marked.)

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Figure 2. Silver Stain

A Gomori methenamine silver stain shows clusters of pneumocystis spore cases in the hyaline membranes.

Find 2 clumps of spore cases.

This slice of lung is from a 44-year-old man with AIDS who was admitted to the hospital for 3 to 4 weeks of progressive dyspnea, dry cough, fever, and night sweats. Despite therapy for pneumocystis, he developed respiratory failure requiring 100% oxygen and 15 cm of PEEP. Terminally, multiple pneumothoraces developed, and he died one month after admission.

Figure 3. Chronic Pneumocystis Pneumonia

This slice of lung shows consolidation of most of the upper lobe with areas of fine and coarse honeycombing. Rupture of the subpleural honeycombed cysts was the cause of the terminal pneumothoraces. Note that disease is mostly confined to the upper lobe.

Histologically, scattered areas of pneumocystis organisms were found along with cytomegalovirus infection.

Figure 4. Honeycombing

A closer view shows the fine honeycombing in the upper lobe. Some larger spaces are present at the lower left.

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Figure 5. Early Histologic Honeycombing

A section from another patient with early honeycombing shows dilation of respiratory bronchioles and alveolar ducts produced by collapse of intervening alveolar spaces. The alveolar walls show slight thickening by fibrous tissue, which progresses with time to interstitial fibrosis. A few hyaline membranes and alveolar hemorrhage persist.

Find an area with hyaline membranes and blood in an air space .

Reference

1. Watts J, Chandler F. Evolving concepts of infection by Pneumocystis carinii. Pathol Annu 1991; 26:93-138.

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Foamy exudate of pneumocystis

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Hyaline membranes in alveolus

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Hyaline membranes in alveolar duct

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Clump of pneumocystis spore cases

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Hyaline membranes and blood in air space

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