Hypersensitivity pneumonitis was the most common new-onset ILD in India, followed by CTD-ILD and idiopathic pulmonary fibrosis; diagnoses varied between site investigators and CILD experts, emphasizing the value of MDD in ILD diagnosis. Prompted case report forms including environmental exposures in prospective registries will likely provide further insight into the etiology and management of ILD worldwide.

Sarcoidosis is a multisystem disease characterized by the formation of noncaseating granulomas. Lung and intrathoracic lymph nodes are classic sites of involvement; however, sarcoidosis can affect any site in the body. The clinical course is extremely variable, and the imaging features are diverse and dependent on the affected site, degree of inflammation, and treatment the patient receives. Atypical manifestations and imaging findings can make diagnosis and/or management challenging. In addition, assessment of treatment response can be difficult in the setting of chronic disease. Fluorine 18 fluorodeoxyglucose (FDG) PET/CT is sensitive for assessment of the inflammatory activity of sarcoidosis in any organ. Although FDG PET/CT is not included in the standard workup for sarcoidosis, there has been growing evidence that supports the value of this examination in guiding diagnosis and management. FDG PET/CT may be especially useful for assessing reversible granuloma, treatment response, disease extent, occult disease, and cardiac or osseous sarcoidosis, and determining the most suitable biopsy site. Capability to image the entire body during a single examination is advantageous in cases of systemic disease such as sarcoidosis. The authors review the use of FDG PET/CT, providing up-to-date evidence and describing various cases of sarcoidosis in which FDG PET/CT has an important role in diagnosis and/or management. They also discuss the usefulness of FDG PET/CT in cases of selective manifestations of sarcoidosis. RSNA, 2018.

Histiocytic disorders of the chest comprise a broad spectrum of diseases. The lungs may be involved in isolation or as part of systemic disease. Some of these disorders are primary and have unknown etiology, and others result from a histiocytic response to a known cause. Among primary histiocytic disorders, pulmonary Langerhans cell histiocytosis (PLCH) is the most common; others include Erdheim-Chester disease and Rosai-Dorfman disease. Adult PLCH occurs almost exclusively in adults aged 20-40 years who smoke. Pediatric PLCH is extremely rare and typically occurs as part of multisystemic disease. Erdheim-Chester disease affects middle-aged and older adults; thoracic involvement usually occurs as part of systemic disease. Rosai-Dorfman disease affects children and young adults and manifests as painless cervical lymphadenopathy. Examples of secondary histiocytic disorders are storage diseases such as Gaucher disease, Niemann-Pick disease, and Fabry disease; pneumoconiosis such as silicosis and coal workers' pneumoconiosis; and infections such as Whipple disease and malakoplakia. These disorders are characterized at histopathologic examination on the basis of infiltration of alveoli or the pulmonary interstitium by histiocytes, which are a group of cells that includes macrophages and dendritic cells. Dendritic cells are a heterogeneous group of nonphagocytic antigen-presenting immune cells. Immunohistochemical markers help to distinguish among various primary histiocytic disorders. Characteristic radiologic findings in the appropriate clinical context may obviate biopsy to establish a correct diagnosis. However, in the absence of these findings, integration of clinical, pathologic, and radiologic features is required to establish a diagnosis.

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