Importance of chest HRCT in the diagnostic evaluation of fibrosing interstitial lung diseases

Abstract

Many conditions result in chronic interstitial lung disease (ILD), being classified as fibrosing ILDs, including idiopathic pulmonary fibrosis, connective tissue diseases, sarcoidosis, and fibrotic hypersensitivity pneumonitis. HRCT plays an important role in the clinical evaluation of fibrosing ILDs. Current treatment perspectives are encouraging and reinforce the need for HRCT scans of adequate technical quality for early detection of fibrosing ILD. Despite efforts in this regard, the significance and management of imaging findings of early interstitial lung abnormalities have yet to be clarified. After identification of CT findings consistent with fibrosing ILD, radiologists must be able to identify characteristic morphological patterns and, in some cases, features of specific clinical entities. In cases in which HRCT features are not sufficiently specific for a definitive diagnosis, HRCT can aid in selecting the best site for surgical lung biopsy. CT follow-up is useful for identifying progressive fibrosing ILDs and detecting complications unrelated to the underlying disease, including infections, acute exacerbations, and neoplasms. Automated quantification tools have clinical applicability and are likely to be available for use in imaging analysis in the near future. In addition, incorporation of CT evaluation into scoring systems based on clinical and functional parameters for staging fibrosing disease is likely to become valuable in determining prognosis. Knowledge of the clinical applications of CT evaluation is essential for specialists managing patients with fibrosing ILD and can have a positive impact on the clinical course of the disease.

Figure 1. Axial HRCT scans with lung window settings. Note diffuse peripheral lower lobe reticular opacities (arrows in A) that are also seen on prone CT images (arrows in B), characterizing incipient interstitial lung disease.

Figure 2. Axial HRCT scans with lung window settings, showing fibrosing interstitial lung disease in different patients. In A, typical honeycombing, presenting as multiple layers of cysts. In B, traction bronchiectasis in an oblique coronal plane. Note the usefulness of multiplanar reconstruction in differentiating between traction bronchiectasis and honeycombing. In C, early honeycombing, presenting as a single layer of cysts. In D, note the difficulty in differentiating between honeycombing and paraseptal emphysema.

Figure 3. Axial HRCT scans with lung window settings, showing fibrosing interstitial lung disease in patients suspected of having idiopathic pulmonary fibrosis and presenting with different HRCT features of the usual interstitial pneumonia (UIP) pattern. In A, UIP pattern, with extensive honeycombing (arrows), peripheral distribution, and basal predominance. In B, probable UIP pattern, with peripheral reticular opacities and traction bronchiolectasis (open arrows), without honeycombing. In C, indeterminate-for-UIP pattern, with diffuse axial distribution and central involvement (arrowheads), as well as areas of ground-glass opacity, together with reticular opacities. In D, a pattern suggestive of an alternative diagnosis, with extensive areas of ground-glass opacity and a mosaic pattern of lung attenuation (open arrowheads).

Figure 4. Axial HRCT scans of the chest showing features related to different fibrosing diseases. In A, features suggestive of nonspecific interstitial pneumonia, with a predominance of ground-glass opacities. In B, features of pleuroparenchymal fibroelastosis confirmed by histopathology showing predominantly apical fibrosing disease with upper lobe volume loss and upward hilar retraction. In C, scan of a patient with sarcoidosis, showing fibrosing disease with an upper-lobe predominance. In D and E, scans of a patient with fibrosing lung disease caused by exposure to asbestos. Note the presence of pleural plaques (arrows in E).

Figure 5. Axial HRCT scans with lung window settings (in A, D, and G), coronal reconstructions (in B, E, and H), and coronal minimum intensity projection reformatted images (in C, F, and I) for three patients with fibrotic hypersensitivity pneumonitis (HP). In A, B, and C, a typical HP pattern, with diffuse interstitial fibrosis axially and relatively spared lower lung zones, as well as marked mosaic attenuation in a predominantly caudal distribution, indicating small airway disease (in C). In D, E, and F, a compatible-with-HP pattern, with predominantly peripheral, basal interstitial fibrosis and extensive honeycombing (characteristic of usual interstitial pneumonia), as well as scattered areas of mosaic attenuation, constituting evidence of small airway disease (in F). In G, H, and I, an indeterminate-for-HP pattern, with areas of ground-glass opacity, reticular opacities, and traction bronchiectasis in a diffuse axial/craniocaudal distribution, as well as no evidence of small airway disease.

Figure 6. Specific CT signs of fibrosis in connective tissue disease-associated fibrosing interstitial lung disease. In A and B, the “anterior upper lobe” sign (arrows) in a patient with rheumatoid arthritis. In C, the “four corners” sign (open arrows)-fibrosis focally involving the bilateral anterolateral upper lobes and posterosuperior lower lobes-in a patient with systemic sclerosis. In D, the “straight-edge” sign (arrowheads)-isolation of fibrosis to the lung bases with sharp demarcation in the craniocaudal plane. In E, the “exuberant honeycombing” sign-extensive honeycombing constituting most of the fibrotic portions of lung.

Figure 7. Axial HRCT scans. Initial CT scan (in A) and follow-up CT scans at six years (in B) and six and a half years (in C) in a patient with systemic sclerosis-related fibrosing interstitial lung disease. Although the follow-up scans apparently show no changes in disease progression, a comparison between the initial and follow-up scans reveals a progressive disease phenotype, underscoring the importance of comparing follow-up CT findings with initial CT findings.

Figure 8. Coronal reconstructions of HRCT scans showing complications of fibrosing interstitial lung disease in two patients. In A and B, scans of a patient with progressive idiopathic pulmonary fibrosis. Initial CT scan (in A) and follow-up CT scan at seven years and 10 months (in B), showing disease progression and an irregular subpleural expansile neoplastic lesion in the right lower lobe, diagnosed as adenocarcinoma (arrow in B). In C and D, scans of a patient with progressive idiopathic pulmonary fibrosis. Initial CT scan (in C) and follow-up CT scan at 15 months (in D), showing disease progression and new bilateral ground-glass opacities, characterizing acute exacerbation of idiopathic pulmonary fibrosis.