CT-Pathology Correlations

Case 23--Continued

Section 3

Gross Appearance

This slice of lung shows extensive, peripheral honeycombing (architectural distortion) in upper and lower lobes. The cystic spaces, which vary from 2 mm to 2 cm, represent traction bronchiectasis or bronchiolectasis. The dark brown areas in the upper lung represent normal lung parenchyma. This disease has a patchy distribution even at the end-stage.

The homogeneous, pale regions represent partially fibrotic lung parenchyma, some of which might show ground-glass opacity on HRCT. Note that the arterial walls are thickened as a result of the inflammation. Pulmonary hypertension may result.

In this closer view, find 2 areas of normal lung.

Find two examples of traction bronchiectasis.

Find an area of traction bronchiolectasis.

Find 2 thick-walled arteries.

Find an example of partly fibrotic lung parenchyma.

Section 4: Histologic Findings

Early lesion: Here, a respiratory bronchiole is accompanied by its artery. An adjacent alveolus shows alveolitis, which consists of a thickened, edematous wall with chronic inflammatory cells, type II cell hyperplasia, and a collection of alveolar macrophages. This lesion progresses to alveolar collapse and fibrosis. It does not resolve.

Find the respiratory bronchiole.

Find the artery.

Find the alveolus with alveolitis.

Fibroblast focus: A characteristic feature of the fibrosing stage is the presence of recent bluish granulation tissue next to an area of old pink scar, indicating temporal heterogeneity of the disease. Note that the granulation tissue (fibroblast focus) has already been epithelialized and incorporated into the interstitium. A few chronic inflammatory cells are present.

Find the granulation tissue (fibroblast focus).

Find the area of old scar.

Progression: As fibrosis proceeds, alveoli collapse and cause traction on small airways to eventually form honeycombed spaces with thickened walls. Note that normal alveoli are still present.

Find a dilated terminal bronchiole.

Find a dilated respiratory bronchiole.

Find a dilated alveolar duct.

Find a subpleural area of alveolar collapse and fibrosis.

End stage, architectural distortion: This bronchiole has adjacent honeycombed spaces, some of which are filled with edema fluid. Some of the spaces are lined by bronchiolar epithelium (bronchiolization). Some of the interstitium is pink indicating fibrosis, but other parts still show fibroblast foci. Inflammatory cells are sparse. These changes constitute architectural distortion.

Find the bronchiole.

Find 2 honeycombed spaces with fibrotic walls.

Find a fibroblast focus.

Differential diagnosis of architectural distortion with honeycombing and traction bronchiectasis on HRCT: Idiopathic pulmonary fibrosis, collagen vascular disease (especially scleroderma), asbestosis, drug- or radiation-related fibrosis, sarcoidosis, and chronic hypersensitivity pneumonia

Histologic differential diagnosis: Usual interstitial pneumonia or end-stage disease caused by drug reaction, asbestosis, radiation, collagen vascular diseases, aspiration, or hypersensitivity pneumonia

Diagnosis: Advanced, irreversible pulmonary fibrosis consistent with usual interstitial pneumonia

Diagnostic features of usual interstitial pneumonia on HRCT

Subpleural reticular opacities at the lung bases, early
Associated cystic air spaces, 2 to 20 mm in diameter (honeycombing)
Traction bronchiectasis
Patchy ground-glass opacities
Architectural distortion in relation to normal lung
Basal, subpleural predominance

See Case Study 27 for another example of usual interstitial pneumonia.

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