Pneumatoceles and Honeycombing

Figure 1. HRCT: Typical PCP and Pneumatoceles

HRCT scan through the apices shows bilateral, thin-walled cysts with surrounding ground-glass opacity. Pneumothoraces are present, right >> left.

Figure 2. Extensive Pneumatocele Formation with PCP

Frontal chest radiograph shows bilateral reticulation with preserved lung volumes. If one looks closely, the reticulation can be seen to represent the walls of numerous bilateral cysts.

Figure 3. HRCT: Extensive PCP Pneumatoceles

HRCT of patient in Figure 2 shows extensive, bilateral, cystic lesions with somewhat bizarre shapes, resembling Langerhans' cell histiocytosis. These lesions subsequently resolved following therapy for PCP.

This slice of lung from an AIDS patient with pneumocystis pneumonia shows a consolidated, yellowish upper lobe with several subpleural, thin-walled cysts and many parenchymal cysts, in addition to honeycombing. Note that the diffuse honeycombed cysts and traction bronchiectasis overlap in appearance with the cysts of necrotizing pneumocystis pneumonia. The lower lobe is largely spared.

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Figure 4. Lung with Cystic PCP and Honeycombing

Some larger parenchymal cysts show remnants of necrotic material on their walls; others have smooth walls without exudate.

Find 2 parenchymal cysts with remnants of necrotic material.

The subpleural cysts have walls without exudate. One connects to an interlobular septum that leads to a parenchymal cyst, suggesting that the subpleural cyst may represent a focus of interstitial emphysema distal to the parenchyma cyst.

Find a subpleural cyst connected to an interlobular septum.

 

 

 

Much of the rest of the upper lobe parenchyma is replaced by honeycombing, indicating chronic disease. Focally, interlobular septa are prominent, probably due to edema.

Pathogenesis of cysts and pneumothorax in acute pneumocystis pneumonia: The presence of cysts is strongly associated with pneumothorax [1]. Parenchymal cysts arise from necrotic foci that develop early in disease, and may initially have irregular shapes and thick walls. Over time, exudate disappears, and walls thin. In one report, one such cyst showed a connection to a subpleural cyst with a fibrous wall without organisms, suggesting dissection of air (interstitial emphysema) as mechanism for development of some subpleural cysts [2]. Both subpleural and parenchymal cysts usually resolve with therapy [1].

Differential diagnosis of cysts: While cysts suggest pneumocystis pneumonia in AIDS patients, subpleural bullae also occur with intravenous drug abuse. The latter are usually thin-walled, apical, regular in shape, and not usually accompanied by ground-glass opacities. Intrapulmonary cysts with thicker walls must be distinguished from those of mycobacteria, fungi, nocardia, and septic emboli [3].

References: To return to reference section after viewing abstract, click here before clicking on "abstract".

1. Chow C, Templeton P, White C. Lung cysts associated with Pneumocystis carinii pneumonia: Radiographic characteristics, natural history, and complications. AJR 1993: 161:527-531. Abstract

2. Feuerstein I, Archer A, Pluda J, Francis P, Falloon J, Masur H, Pass H, Travis W. Thin-walled cavities, cysts, and pneumothorax in Pneumocystis carinii pneumonia: further observations with histolopathologic correlation. Radiology 1990:174:697-702. Abstract

3. Boiselle P, Crans Jr C, Kaplan M. The changing face of Pneumocystis carinii pneumonia in AIDS patients. AJR 1999; 172:1301-1309. Abstract

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Parenchymal cyst with mural exudate

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Subpleural cyst connected to interlobular septum

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