Abstract
Bronchiolitis is injury to the bronchioles (small airways with a diameter of 2 mm or less) resulting in inflammation and/or fibrosis. Bronchioles can be involved in pathologic processes that involve predominantly the lung parenchyma or large airways, but, in some diseases, bronchioles are the main site of injury (“primary bronchiolitis”). Acute bronchiolitis caused by viruses is responsible for most cases of bronchiolitis in infants and children. In adults, however, there is a wide spectrum of bronchiolar disorders and most are chronic. Many forms of bronchiolitis have been described in the literature, and the terminology in this regard remains confusing. In clinical practice, a classification scheme based on the underlying histopathologic pattern (correlates with presenting radiologic abnormalities) facilitates the recognition of bronchiolitis and the search for the inciting cause of the lung injury. Respiratory bronchiolitis is the most common form of bronchiolitis in adults and is usually related to cigarette smoking. Currently, the diagnosis of respiratory bronchiolitis is generally achieved based on the clinical context (smoking history) and chest CT findings. Constrictive (obliterative) bronchiolitis is associated with airflow obstruction and is seen in various clinical contexts including environmental/occupational inhalation exposures, transplant recipients (bronchiolitis obliterans syndrome), and many others. Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) is increasingly recognized and can be associated with progressive airflow obstruction related to constrictive bronchiolitis (“DIPNECH syndrome”). Diffuse aspiration bronchiolitis is a form of aspiration-related lung disease that is often unsuspected and confused for interstitial lung disease. Novel forms of bronchiolitis have been described, including lymphocytic bronchiolitis and alveolar ductitis with emphysema recently described in employees at a manufacturing facility for industrial machines. Bronchiolitis is also a component of vaping-related lung injury encountered in the recent outbreak.
Highlights
Bronchiolitis is injury to the bronchioles resulting in inflammation and/or fibrosis
The forms of bronchiolitis described should not be confused with “bronchiolitis obliterans organizing pneumonia” or BOOP, which manifests as parenchymal lung disease rather than strictly bronchiolar disease
It should be noted that bronchiolitis can be encountered histopathologically or radiologically as a component of interstitial lung diseases, e.g. hypersensitivity pneumonitis, and large airway diseases such as bronchiectasis[1]
Summary
Faculty Reviews are written by members of the prestigious Faculty Opinions Faculty. They are commissioned and are peer reviewed before publication to ensure that the final, published version is comprehensive and accessible. It should be noted that bronchiolitis can be encountered histopathologically or radiologically as a component of interstitial lung diseases (involving predominantly the lung parenchyma), e.g. hypersensitivity pneumonitis, and large airway diseases such as bronchiectasis[1] This issue is exemplified by a disease entity formerly called BOOP, which was characterized by the histologic presence of organizing connective tissue in lumens of small airways, alveolar ducts, and alveoli[9]. It is generally associated with clinico-radiologic features of parenchymal lung disease including restrictive pulmonary impairment and parenchymal opacities. Perhaps the most useful framework in the clinical approach to patients with suspected bronchiolitis is a classification based on underlying histopathologic patterns (Table 1), which,
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