Pathology and radiology correlation of idiopathic interstitial pneumonias

Highlights

• Multidisciplinary clinical, radiology, and pathology correlation is fundamental in the diagnosis of idiopathic interstitial pneumonia (IIP).

• The article emphasizes the key diagnostic features for radiologic and pathologic diagnosis of IIP.

• Recognized IIP categories by the ATS and ERS are described along with other important entities.

• New IIP variants are being recognized and deserve a mention in this manuscript.

Summary

By nature, idiopathic interstitial pneumonias have been diagnosed in a multidisciplinary manner. As classifications have been subject to significant refinement over the last decade, the importance of correlating clinical, radiologic, and pathologic information to arrive at a diagnosis, which will predict prognosis in any given patient, has become increasingly recognized. In 2013, the American Thoracic Society and European Respiratory Society updated the idiopathic interstitial pneumonias classification scheme, addressing the most recent updates in the field. The purpose of this review is to highlight the correlations between radiologic and pathologic findings in idiopathic interstitial pneumonias while using updated classification schemes and naming conventions.

Introduction

Among the major revisions to the American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/Latin American Thoracic Association (ATS/ERS/JRS/ALAT) classification of idiopathic interstitial pneumonias (IIPs) is a reorganization of the categories, which, in our opinion, serves to better clarify and organize these often-confusing entities. The new classifications, summarized from the 2013 revision, are in Table 1 [1]. An important update is the grouping of these entities into major, rare, and unclassifiable categories.

The major IIP category is further subgrouped into 3 types: chronic fibrosing IIP, which includes idiopathic pulmonary fibrosis (IPF) and nonspecific interstitial pneumonia (NSIP); smoking-related IIP, which includes respiratory bronchiolitis–interstitial lung disease (RB-ILD) and desquamative interstitial pneumonia (DIP); and acute/subacute IIP, which includes cryptogenic organizing pneumonia (COP) and acute interstitial pneumonia (AIP) [1]. The second group, rare IIP, is composed of idiopathic lymphoid interstitial pneumonia (ILIP) and idiopathic pleuroparenchymal fibroelastosis (IPPFE). The final group, unclassifiable IIP, is characterized by cases where, despite often-lengthy multidisciplinary discussions, a definitive diagnosis cannot be reached. Unclassifiable IIP include either cases with inadequate clinical, radiologic, or pathologic data or cases with major discordance between clinical, radiologic, or pathologic findings. Examples include evaluations of cases after previous therapy, new unrecognized entities, or unusual variants of recognized entities. This group represents a significant number of patients and in 1 interstitial lung disease cohort represented 10% of the total [2]. We will also briefly review important differential diagnoses and, when appropriate, will make reference to our own experience and prior published articles.

Thoracic high-resolution computed tomography (HRCT) has been shown to alter the clinical diagnosis, investigation, and management plans in patients with interstitial lung disease [3]. In the following review, we will summarize the radiologic and pathologic features of these entities with additional emphasis on radiologic/pathologic correlation. Although the current classification is an improvement over previous classifications, there continues to be areas that require clarification by evidence-based consensus. For instance, infrequent histologic patterns of IIP, such as acute fibrinous organizing pneumonias and a group of bronchiolocentric patterns, are currently unrecognized as distinct IIP by the ATS or ERS. It remains uncertain if these are variants of existing IIP or exist only in association with other known etiologies such as hypersensitivity pneumonitis (HP) or collagen vascular diseases (CVDs) [1].