Abstract

Diffuse interstitial lung diseases (DILDs) comprise a huge number of diseases which diffusely involve the lung parenchyma. The DILDs have been subcategorized into (a) DILDs that have a known etiology, (b) the idiopathic interstitial pneumonias, (c) the granulomatous DILDs, and (d) a group of diffuse lung diseases that include Langerhans cell histiocytosis and lymphangioleiomyomatosis. HRCT plays a central role in the differential diagnosis of interstitial lung diseases. The differential diagnosis of HRCTs is based on the analysis of the predominant CT pattern, the ancillary CT findings, and the distribution of the findings. The final diagnosis of DILDs requires a combination of radiological, clinical, and sometimes pathological information, which is best accomplished in an interdisciplinary discussion.

Highlights

  • There is little doubt that imaging tests have a central role in the investigation of patients with suspected and established diffuse interstitial lung diseases (DILD)

  • This was elegantly demonstrated in the very early days of high-resolution computed tomography (HRCT) by Müller and colleagues who showed that morphologic features in patients with idiopathic pulmonary fibrosis—at that time still known by the moniker “cryptogenic fibrosing alveolitis”—reflected the histopathological changes [37]

  • It is important to recognize that findings of Respiratory bronchiolitis (RB), Desquamative interstitial pneumonia (DIP), pulmonary Langerhans cell histiocytosis (LCH), and the non-specific interstitial pneumonia (NSIP) pattern of fibrosis commonly coexist in biopsies of dyspneic smokers

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Summary

The HRCT Technique

In the era of multi-detector row CT machines, a brief reminder of the HRCT technique is pertinent. The two technical features that differentiate HRCT imaging from conventional CT are, first, the narrow x-ray beam collimation that significantly improves spatial resolution and, second, the use of a dedicated reconstruction algorithm [35]. The “high-­ frequency” algorithm effectively exaggerates the naturally high-contrast milieu of the lungs (i.e., aerated lung versus more solid elements) [35]. The conspicuity of vessels, small bronchi, and interlobular septa is increased compared to conventional (thick-section) CT images [38]. An important downside of high-frequency algorithms is the increased visibility of image noise, in practice, this generally does not hamper radiological interpretation

HRCT in Diffuse Interstitial Lung Disease
An Approach to HRCT Diagnoses
Is There a “Real” Abnormality?
If There Is An Abnormality, What Is/Are the Predominant HRCT Pattern(s)?
Are There Any Ancillary Findings?
What Is the Likely Pathology?
What Is the Clinical Background?
Usual Interstitial Pneumonia/Idiopathic Pulmonary Fibrosis
Non-specific Interstitial Pneumonia
Smoking-Related Lung Diseases
Sarcoidosis
Hypersensitivity Pneumonitis
Concluding Remarks
Full Text
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