Bronchiectasis Revisited: Imaging-Based Pattern Approach to Diagnosis

Authors: AnuradhaSinghMBBS, MDAshu SeithBhallaMBBS, MDManishaJanaMBBS, MD


Background
Bronchiectasis is one of the causes of non-resolving, persistent or recurrent pulmonary infection which, if uncorrected may have deleterious consequences on the lung parenchyma and pulmonary circulation. High-resolution computed tomography (HRCT) is needed for the confirmation, localization and directing management accordingly.

Contents
Bronchiectasis is one of the major cause of morbidity worldwide. Chest radiograph is done at the initial suspicion which is supplemented by HRCT to confirm the diagnosis. Imaging diagnosis supplemented by the recognition of the pattern of involvement is essential to outline the differential diagnosis, map the complications and, hence, guiding the further management. Identification of the causative aetiology may not only prevent its further progression but obviate recurrent insults to the lung parenchyma as well. This article focuses on an algorithmic approach to bronchiectasis based on the distribution on imaging

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Introduction
Bronchiectasis refers to the permanent irreversible dilatation of cartilage containing airways. Although its exact etiopathogenesis is not known, it is believed to be the end result of multiple factors including recurrent infection or inflammation, impaired mucociliary clearance and attrition of the bronchial wall occurring in concurrence leading to the subsequent bronchial dilatation.1, 2 It remains a disease of international concern with high prevalence worldwide, although the etiology differs. Clinically, there may be hypoxia, dyspnea, or hemoptysis depending upon the severity of affliction and superimposed infection. Milder disease presents with occasional cough and dyspnea. With chronicity and increasing severity, there is worsening of symptoms. Abnormalities in pulmonary function tests ensue with an obstructive pattern of abnormality.

Diagnosis of bronchiectasis is essentially based on imaging which morphologically defines airway enlargement. Imaging may also help in determining the etiology in certain cases, guiding management (surgical vs medical) and to rule out secondary complications. In children, it is essential to diagnose bronchiectasis early to prevent irrevocable damage to the developing airways and lung parenchyma, besides prognostication and genetic counseling in certain causes.2

This article discusses the criteria for diagnosing bronchiectasis, evaluation of complications and then proposes an imaging-based algorithmic approach toward an etiologic diagnosis.

Criteria for Diagnosing Bronchiectasis on HRCT
The foremost step in managing bronchiectasis is ascertaining its presence on HRCT, which is the most sensitive imaging modality to establish its diagnosis. With the available multidetector row CT scanners, it is possible to visualize airways as small as 2 mm in diameter with a wall thickness of up to 0.2 mm. In general, there should not be any visible airways within 1 cm of the costal pleura, although this criterion does not hold true for mediastinal pleura; which may show airways within 1 cm. Further, the internal diameter of the bronchus is equal to the accompanying pulmonary artery at the same branching level. This is referred as broncho-arterial ratio. Special CT reconstructions like minimum intensity projection are very useful in providing an overview of involvement and may identify subtle abnormalities in certain cases.1, 3, 4, 5