Septal, reticular, nodular, reticulonodular, ground-glass, crazy paving, cystic, ground-glass with reticular, cystic with ground-glass, decreased and mosaic attenuation pattern characterise interstitial lung diseases on high-resolution computed tomography (HRCT). Occasionally different entities mimic each other, either because they share identical HRCT findings or because of superimposition of patterns. Idiopathic pulmonary fibrosis (IPF), fibrosis associated with connective tissue disease, asbestosis, end-stage sarcoidosis or chronic hypersensitivity pneumonitis (HP) may present with lower zone, subpleural reticular pattern associated with honeycombing. Lymphangiomyomatosis may be indistinguishable from histiocytosis or extensive emphysema. Both pulmonary oedema and lymphangitic carcinomatosis may be characterised by septal pattern resulting from thickened interlobular septa. Ill-defined centrilobular nodular pattern may be identically present in HP and respiratory bronchiolitis-associated with interstitial lung disease (RBILD). Sarcoidosis may mimic miliary tuberculosis or haematogenous metastases presenting with miliary pattern, while endobronchial spread of tuberculosis may be indistinguishable from panbronchiolitis, both presenting with tree-in-bud pattern. Atypical infection presenting with ground-glass mimics haemorrhage. Ground-glass pattern with minimal reticulation is seen in desquamative interstitial pneumonia (DIP), RBILD and non-specific interstitial pneumonia (NSIP). Obliterative bronchiolitis and panlobular emphysema may present with decreased attenuation pattern, while obliterative bronchiolitis, chronic pulmonary embolism and HP may manifest with mosaic attenuation pattern. Various mimics in interstitial lung diseases exist. Differential diagnosis is narrowed based on integration of predominant HRCT pattern and clinical history. Teaching Points • To learn about the different HRCT patterns, which are related to interstitial lung diseases. • To be familiar with the more "classical" entities presenting with each HRCT pattern. • To discuss possible overlap of different HRCT patterns and the more common mimics in each case. • To learn about some clues that help differentiate the various diagnostic mimics on HRCT.

The increasing use of chest CT imaging in medical practice rises the likelihood of the general practitioner to be confronted with cases of interstitial lung disease. Respiratory bronchiolitis (RB) and respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) are two smoking-related lung damages that may have important implications for the patient's management. The authors present in this paper a review of current knowledge of the epidemiology, clinical features, prognosis, and treatment options of RB and RB-ILD.

The idiopathic interstitial pneumonias are diffuse lung diseases characterized by interstitial inflammation and fibrosis. High resolution computed tomography (HRCT) is the best imaging technique for the study of interstitial disease. The general term "idiopathic interstitial pneumonia" includes usual interstitial pneumonia/idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis-associated interstitial lung disease, cryptogenic organizing pneumonia, acute interstitial pneumonia, and lymphocytic interstitial pneumonia. The radiologist's role consists of identifying the macroscopic morphological pattern and working together with clinicians and pathologists to generate an integrated clinical diagnosis. The objective of this article is to review the idiopathic interstitial pneumonias and to describe their different manifestations in HRCT.

Cigarette smoking is a recognized causative agent or precipitant of specific diffuse lung diseases characterized by bronchiolar and interstitial lung inflammation. Respiratory bronchiolitis-associated interstitial lung disease and pulmonary Langerhans cell histiocytosis are now considered smoking-induced diffuse lung diseases. Desquamative interstitial pneumonia is also recognized as a smoking-induced interstitial pneumonia in most cases. These disorders affect relatively young adult smokers and may be progressive. Although distinguishable by histopathological and radiographic features, significant overlap occurs in many cases with chest radiography and lung histology showing overlapping features of smoking-related bronchiolar and interstitial lung injury. Cigarette smoking is also recognized as an important precipitant of many acute eosinophilic pneumonia cases. Smokers are at higher risk of developing fibrotic interstitial lung diseases such as idiopathic pulmonary fibrosis and rheumatoid arthritis-associated interstitial lung disease. Certain smokers also develop combined emphysema and lung fibrosis. The avoidance of primary and second-hand cigarette smoke is a critical component of management for patients afflicted with these smoking-induced diffuse lung diseases. The role of corticosteroids and other immunosuppressive treatments in the management of smoking-related interstitial lung diseases remains poorly defined and should be reserved for individuals with progressive disease despite smoking cessation. Understanding mechanisms by which tobacco induces diffuse lung pathology is critical in the pursuit of novel therapeutic approaches for these diseases.

Common variable immunodeficiency is one of the most frequent immunity alterations. The most common clinical presentation occurs with recurrent respiratory infections, from pneumonia to otitis, and may be associated with other diseases such as bronchiectasis or interstitial lung diseases. We report the case of a 28-year-old patient with frequent respiratory infections and nodular pulmonary infiltrates, who was diagnosed with common variable immunodeficiency and follicular bronchiolitis. In some cases, follicular bronchiolitis is associated with immunodeficiencies and should be included in a differential diagnosis with lymphoid nodular hyperplasia, lymphocytic interstitial pneumonia and low-grade BALT lymphoma.

Cigarette smoke consists of several chemical compounds with a variety of effects in many organs. In the lung, apart being the main cause of chronic obstructive pulmonary disease, carcinoma and idiopathic spontaneous pneumothorax, tobacco smoke is associated with interstitial lung diseases (ILDs), including respiratory bronchiolitis-associated ILD (RB-ILD), desquamative interstitial pneumonia (DIP), pulmonary Langerhans' cell histiocytosis (PLCH), idiopathic pulmonary fibrosis, acute eosinophilic pneumonia, ILD in rheumatoid arthritis and pulmonary haemorrhage in Goodpasture syndrome. This review will focus on the diseases with a stronger epidemiological association with tobacco smoke, namely RB-ILD, DIP and PLCH. Although the exact pathogenetic evidence linking smoking with these disorders is still not completely understood, there is growing evidence that tobacco smoke targets the terminal or respiratory bronchioles in these diseases, and the differences are reflective of the degree of severity of small airway and parenchymal reaction to the smoke exposure. Despite considerable clinical, radiological and histological overlap between RB-ILD, DIP and PLCH, it is useful to retain the separate classifications for prognostic and therapeutic implications.

Bronchiolar disorders are generally difficult to diagnose. A detailed clinical history may point toward a specific diagnosis. Pertinent clinical questions include history of smoking, collagen vascular disease, inhalation injury, medication use and organ transplantation. It is important also to evaluate possible systemic and pulmonary signs of infection, evidence of air trapping, and high-pitched expiratory wheezing, which may suggest small airways involvement. Pulmonary function tests and plain chest radiography may demonstrate abnormalities; however, they rarely prove sufficiently specific to obviate bronchoscopic or surgical biopsy. High-resolution CT (HRCT) scanning of the chest is often an important diagnostic tool to guide diagnosis in these difficult cases, because different subtypes of bronchiolar disorders may present with characteristic image findings. Some histopathologic patterns of bronchiolar disease may be relatively unique to a specific clinical context but others are nonspecific with respect to either etiology or pathogenesis. Primary bronchiolar disorders include acute bronchiolitis, respiratory bronchiolitis, follicular bronchiolitis, mineral dust airway disease, constrictive bronchiolitis, diffuse panbronchiolitis, and other rare variants. Prominent bronchiolar involvement may be seen in several interstitial lung diseases, including hypersensitivity pneumonitis, collagen vascular disease, respiratory bronchiolitis-associated interstitial lung disease, cryptogenic organizing pneumonia, and pulmonary Langerhans' cell histiocytosis. Large airway diseases that commonly involve bronchioles include bronchiectasis, asthma, and chronic obstructive pulmonary disease. The clinical and prognostic significance of a bronchiolar lesion is best determined by identifying the etiology, underlying histopathologic pattern and assessing the correlative clinic-physiologic-radiologic context.

A 37-year-old man was referred to our hospital with a cough. His blood test result and chest radiography findings were normal. High resolution chest computed tomography (HRCT) showed diffuse ground glass attenuation (GGA) with centrilobular distribution in the bilateral upper lung fields. As diagnosis could not be made using transbronchial lung biopsy and bronchoalveolar lavage, video-assisted lung biopsy was performed. The histological findings were a thickening of the alveolar walls with infiltration of lymphocyte-dominant inflammatory cells, and exudation of pigmented macrophages in the air spaces of the respiratory bronchioles and alveolis. We diagnosed his illness as respiratory bronchiolitis-associated interstitial lung disease. Six months after stopping smoking, his symptoms, and the GGA on chest HRCT improved.

Breathing disorders in Rett Syndrome (RS) have been generally attributed to severe autonomic and/or brain stem dysfunction, and, to our knowledge, no information regarding lung morphologic characteristics exists to date. The aim of the present study was to determine if there are RS-associated pulmonary abnormalities.A total of 27 female subjects (age, M +/- SD: 12.6 +/- 5.9 y; age range: 3-32 y) with gene-encoding, methyl-CpG-binding-protein-2-mutation-confirmed RS underwent high-resolution CT (HRCT) scans of the thorax. A volumetric acquisition was used, and isotropic data sets were acquired with thin collimation (< 1-mm slice), scanning through the lungs and processing on a high-spatial-resolution kernel (bony algorithm).Abnormal HRCT scan findings were observed in 15 of 27 (55.5%) cases, consisting of centrilobular nodules (10/15, 66.7%), thickening of the bronchial walls (8/15, 53.33%), and patchy ground-glass opacities (4/15, 26.7%), with upper lobe predominance. In addition, bronchiolectasis were found in nine of 15 (60%) patients.Pulmonary lesions, respiratory bronchiolitis-associated interstitial lung disease-like lesions, are present on imaging studies in about half of typical patients with RS. Further research is needed to clarify the epidemiologic characteristics and the pathogenesis of these previously unrecognized pulmonary abnormalities.

Clubbing is very uncommon in respiratory bronchiolitis-associated interstitial lung disease, and primarily raises the suspicion of idiopathic pulmonary fibrosis in a patient presenting with diffuse parenchymal lung disease. If idiopathic pulmonary fibrosis can be excluded, clubbing should raise the suspicion of an occult tumour.We describe a heavy smoker presenting with dyspnea and severe clubbing. Surgical lung biopsy revealed the histologic diagnosis of respiratory bronchiolitis-associated interstitial lung disease. Respiratory bronchiolitis-associated interstitial lung disease is a distinct clinicopathologic entity within idiopathic interstitial pneumonia patients described almost exclusively in cigarette smokers. The disease is associated with a good prognosis and mild symptoms but not with clubbing. After smoking cessation the radiologic findings of interstitial lung disease improved in parallel with improvement in lung function and gas exchange. However, a central squamous cell carcinoma was detected in the follow-up.In this case, clubbing was most probably caused by the occult tumor rather than by respiratory bronchiolitis-associated interstitial lung disease.