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Editor's Note. - RadioGraphics Update articles supplement or update information found in full-length articles previously published in RadioGraphics . These updates, written by at least one author of the previous article, provide a brief synopsis that emphasizes important new information such as technological advances, revised imaging protocols, new clinical guidelines involving imaging, or updated classification schemes.

The diaphragm serves as an anatomic border between the abdominal and thoracic cavities. Pathologic conditions traversing the diaphragm are often incompletely described and may be overlooked, resulting in diagnostic delays. Several routes allow abdominal contents or pathologic processes to spread into the thorax, including along normal transphrenic structures, through congenital defects in the diaphragm, through inherent areas of weakness between muscle groups, or by pathways created by tissue destruction, trauma, or iatrogenic injuries. A thorough knowledge of the anatomy of the diaphragm can inform an accurate differential diagnosis. Often, intraperitoneal pathologic conditions crossing the diaphragm may be overlooked if axial imaging is the only approach to this complex region because of the horizontal orientation of much of the diaphragm. Multiplanar capabilities of volumetric CT and MRI provide insight into the pathways where pathologic conditions may traverse this border. Knowledge of these characteristic routes and use of multiplanar imaging are critical for depiction of specific transdiaphragmatic pathologic conditions. © RSNA, 2020.

In response to the recommendation of the U.S. Preventive Services Task Force and the coverage decision by the Centers for Medicare and Medicaid Services for lung cancer screening (LCS) computed tomography (CT), the American College of Radiology introduced the Lung CT Screening Reporting and Data System (Lung-RADS) in 2014 to standardize the reporting and management of screening-detected lung nodules. As with many first-edition guidelines, questions arise when such reporting systems are used in daily practice. In this article, a collection of 15 LCS-related scenarios are presented that address situations in which the Lung-RADS guidelines are unclear or situations that are not currently addressed in the Lung-RADS guidelines. For these 15 scenarios, the authors of this article provide the reader with recommendations that are based on their collective experiences, with the hope that future versions of Lung-RADS will provide additional guidance, particularly as more data from widespread LCS are collected and analyzed. © RSNA, 2017.

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., ((©)RSNA, 2015.)

A variety of systemic disorders--infections, noninfectious inflammatory diseases, collagen vascular diseases, hereditary diseases, and acquired immune deficiency diseases--may affect both the skin and the lung. The findings in one organ system can help establish the diagnosis or limit the differential diagnosis. Cutaneous manifestations of many conditions (eg, Kaposi sarcoma) precede thoracic manifestations and sometimes have prognostic implications for respiratory disease; in other conditions (eg, organizing pneumonia in polymyositis and dermatomyositis), thoracic manifestations precede cutaneous ones. When skin and thoracic manifestations develop simultaneously, as occurs in the acute form of sarcoidosis known as Löfgren syndrome, the diagnosis is often readily established. Familiarity with the appearances of skin lesions that are commonly associated with systemic lung disease, especially those that are disease specific, may allow the radiologist to pinpoint a diagnosis even when thoracic imaging findings are nonspecific., (© RSNA, 2011.)

It is common to encounter pathologic processes of the lower cervical, thoracic, or upper lumbar spine in the course of routine computed tomography (CT) of the chest. Although magnetic resonance (MR) is the imaging modality of choice for evaluating known spinal disease, evaluation of the spine is an integral part of interpreting a chest CT study. Spinal diseases often have a characteristic CT appearance that allows the radiologist to make the diagnosis or provide a structured differential diagnosis. Pathologic conditions of the spine that can be identified at chest CT are categorized into benign or incidental findings, congenital anomalies, traumatic injuries, infectious spondylitis, primary or secondary neoplastic involvement, and associations with systemic disease. CT also provides information about bone mineralization and lesion calcification that complements the superior soft-tissue imaging capability of MR. In addition, chest CT data may be reformatted to create volumetric or multiplanar images of the spine to facilitate management decisions about spinal stabilization in symptomatic patients.

Although most lesions that occur in the chest have a nonspecific soft-tissue appearance, fat-containing lesions are occasionally encountered at cross-sectional computed tomography (CT) or magnetic resonance imaging. The various fat-containing lesions of the chest include parenchymal and endobronchial lesions such as hamartoma, lipoid pneumonia, and lipoma. Endobronchial hamartoma usually appears at CT as a lesion with a smooth edge, focal collections of fat, or fat collections that alternate with foci of calcification. Mediastinal fat-containing lesions include germ cell neoplasms, thymolipomas, lipomas, and liposarcomas. The most frequent CT manifestation of the germ cell neoplasm teratoma is a heterogeneous mass with soft-tissue, fluid, fat, and calcium attenuation. Cardiac lesions with fat content include lipomatous hypertrophy of the interatrial septum and arrhythmogenic right ventricular dysplasia. Diagnosis of the former is made with CT when a smooth, nonenhancing, well-marginated fat-containing lesion is identified in the interatrial septum. Finally, fat may herniate into the chest at several characteristic locations. When such a lesion is identified, the time required for differential diagnosis is significantly reduced, often allowing a definitive radiologic diagnosis. Sagittal and coronal reformatted images can add valuable information by showing diaphragmatic defects and hernia contents.

Hepatopulmonary syndrome is the most widely recognized of the processes associated with end-stage liver disease. Chronic liver dysfunction is associated with pulmonary manifestations due to alterations in the production or clearance of circulating cytokines and other mediators. Hepatopulmonary syndrome results in hypoxemia due to pulmonary vasodilatation with significant arteriovenous shunting and ventilation-perfusion mismatch. Hepatic hydrothorax may develop in patients with cirrhosis and ascites. Rarely, pulmonary hypertension occurs in the setting of portal hypertension. A second group of disorders may primarily affect the lungs and liver (the hepatopulmonary axis). Among these are the congenital conditions alpha(1)-antitrypsin deficiency and cystic fibrosis. Autoimmune liver disease may be associated with lymphocytic interstitial pneumonitis, fibrosing alveolitis, intrapulmonary granulomas, and bronchiolitis obliterans with organizing pneumonia. Sarcoidosis affects the lung and liver in up to 70% of patients. Medications such as amiodarone can result in a characteristic radiologic appearance of pulmonary and hepatic toxic effects. Knowledge of these associations will assist the radiologist in forming a meaningful differential diagnosis and may influence treatment decisions.

Cartilaginous disorders of the thorax can arise in the parenchyma, airways, chest wall, and axial skeleton. At radiography, pulmonary hamartoma is characterized by "popcorn" calcification or fat density, either of which is diagnostic. Bronchiectasis is best demonstrated at high-resolution computed tomography (CT) and has a "tramline" or "signet ring" appearance. Tracheopathia osteochondroplastica appears at CT as multiple sessile submucosal nodules with or without calcification along the cartilaginous portion of the trachea. In relapsing polychondritis, the trachea and mainstem bronchi have diffuse or focal thickening with luminal narrowing at radiography. Costochondritis of the chest wall has become more prevalent with increased intravenous drug abuse and may be demonstrated at CT as soft-tissue swelling along with underlying cartilaginous fragmentation and bone destruction. Enchondromas are expansile and may display a calcified cartilaginous matrix at radiography. In osteochondroma, the thickness of the cartilaginous cap determines the likelihood of malignant degeneration. At radiography, chondroblastomas have a round contour, sharp margins, and cortical scalloping, whereas chondrosarcomas are large masses with indistinct margins, cortical breakthrough, and soft-tissue extension. By identifying either a process affecting a cartilage-containing structure or a cartilaginous matrix within a lesion, the chest radiologist may be able to narrow the list of differential diagnostic possibilities substantially.

The authors review the radiologic spectrum of fat-containing soft-tissue masses of the extremities, with emphasis on computed tomography, magnetic resonance imaging, and pathologic correlation. These masses include both common and uncommon, benign and malignant lesions, such as lipoma, intramuscular and intermuscular lipoma, neural fibrolipoma, lipoblastoma, lipomatosis, hibernoma, hemangioma, elastofibroma, and liposarcoma, as well as lesions that may mimic fat-containing soft-tissue masses. Imaging studies of fat-containing lesions will often allow a specific presumptive diagnosis. When a specific diagnosis is not possible, however, knowledge of the spectrum of fat-containing lesions will allow a suitably ordered differential diagnosis.