Progress in imaging technology has improved the diagnostic performance in bronchiectasis, which is outlined by the continuing interest in recent years for this disease, previously considered as an orphan disease. The accessibility of diagnostic imaging tools has enhanced the diagnostic performance, both by identifying clues for the etiological diagnosis of bronchiectasis, as well as by highlighting imaging scores with a potential predictive role. The purpose of this review is to summarize diagnostic leads provided by main available imaging tools and to introduce imaging scores currently available for clinical practice and research in bronchiectasis patients.
Bronchiectasis has been a neglected disease for dec-ades. However, in the past years, a continuous interest for this area of respiratory medicine has been observed. This is partly due to a larger availability of noninvasive imaging tools required for bronchiectasis diagnosis. Imaging plays an essential role in the assessment of disease severity and the detection of bronchiectasis complications; it could even suggest the bronchiectasis etiology. Nevertheless, the role of imaging assessment for disease prognosis and follow-up is not clear yet. A significant input in this regard could be provided by bronchiectasis imaging scores; how-ever, their applicability in routine clinical practice has not been well established yet. The purpose of the review is to summarize diagnostic opportunities provided by main available imaging tools and to describe imaging scores currently proposed for clinical practice and research in patients with bronchiectasis. The images were sourced from the Pneumology/Allergology Clinic of the “Nicolae Testemiţanu” State University of Medicine and Pharmacy, Chişinău, Republic of Moldova. The patients’ consent was obtained.
Imaging for bronchiectasis diagnosis
Chest radiography is commonnly used as a first intention diagnostic tool for bronchiectasis. However, it misses sensitivity and does not detect mild or even moderate disease. In patients with chronic sputum pro-duction and bronchographically proven bronchiectasis, the overall sensitivity of chest radiography does not exceed 50%(1). A normal chest radiograph or one with nonspecific lesions is a common finding. So far, plain chest radiography is enough accurate only for the assess-ment of advanced lesions. That’s why the role of radiog-raphy in clinical management of bronchiectasis is currently reduced to ruling out some complications as intercurrent infections, progressive lobar collapse or cavitary disease in a patient with known disease.
Several radiological signs associated with bronchi-ectasis could be conventionally divided in direct and indirect ones.
Tram track sign is characterized by near-parallel lin-ear opacities, resembling a railway, reflecting luminal dilatation and variable wall thickening (Figure 1A).
Signet ring sign mirrors bronchial dilatation when the major axis of bronchiectasis runs parallel to the radia-tion beam. Signet ring and tram track signs essentially reflect the same anatomic abnormality but in two dif-ferent projections. In case of plentiful bronchial secre-tions, an air-fluid level could be seen within the ring (Figure 2A). Tubular opacities reflect the mucus filled bronchi.
Lung volume increasement is associated with bronchi-ectasis in patients with obstructive pulmonary disease (Figure 2B).
Asymmetric volume reduction with parenchymal opaci‑fication is due to segmental or lobar atelectasis and is accompanied by fissure displacement and/or obscura-tion of the diaphragm (Figure 2A).
Vascular lung structures may be more expressed due to fuzzy outlines caused by contiguous peribronchial inflammatory infiltrates and chronic fibrotic changes (Figure 3 A, B).
Thoracic computed tomography (CT) is more sensitive than radiography for bronchiectasis imaging. CT is consid-ered the gold standard for the assessment of the extension and type of structural changes of both bronchi and lung parenchyma. It allows to describe morphological types of bronchiectasis (cylindric, varicose, or cystic), many patients having a combination of the classical types described by Reid(2). The most common direct bronchiectasis signs revealed by CT are: increased broncho-arterial ratio (signet ring sign – Figures 1D and 4A), parallel linear opacities (tram track sign), lack of bronchial tapering, bronchi visible within 1 cm of subpleural parenchyma. All aforementioned CT signs are unspecific for bronchiectasis etiology. Small cylindrical bronchiectasis in a single pulmonary segment appears in a significant number of healthy adults; therefore, it should not be considered(3,4).
Other CT lesions associated in bronchiectasis are mucus plugging opacities, cysts, bullae and air trapping (caused by a vicious cycle of infection, inflammation and mucus deposition).
Mucus plugging is easily identified as complete or partial luminal filling (Figures 1B, 1D, 3A). Secondary changes in the adjacent lung parenchyma include volume loss, mosaic attenu-ation due to air trapping, fibrosis, and scarring. Collapsed lung areas secondary due to mucus plugging (Figure 5) can be iden-tified in more advanced and long-standing disease(5). The detection of patchy consolidations of adjacent lung parenchyma (Figure 3A), a more expressed peribronchial thickening, the presence of air-fluid levels, or centrilobular nodules are suggestive for superimposed infection.
Despite its high sensitivity, even CT imaging sometimes does not provide straightforward answers regarding bron-chiectasis diagnosis. So far, cystic bronchiectasis could appear as a group of clustered air-filled “cysts-like” struc-tures that require differential diagnosis with true paren-chymal cysts. The presence of accompanying pulmonary artery branch (the signet ring sign) or scrolling through the adjacent scan slices figuring out the tubular nature of the “cyst-like” structure allow the differentiation between two entities (Figure 4C, D).
Additionally, the eventual presence of the air-fluid levels and patchy distribution argue in favor of bronchiectasis. Cystic lung diseases (lymphangiomyomatosis or Langerhans histiocytosis) often have a bilateral diffuse spreading.
Volumetric and multiplanar reconstruction could be helpful in the differential diagnosis between bronchiectasis and a range of cystic abnormalities, in particular honeycombing.
CT scan is not recommended for bronchiectasis fol-low-up, especially in case of young and female patients. That is mainly due to significant radiation risk without any clinical benefits(4,6).
IMAGING CLUES TOWARDS ETIOLOGY
The wide list of differential diagnosis in bronchiectasis can be substantially narrowed by considering their ana-tomic location and distribution(7). Some CT features of bronchiectasis may provide important clues regarding the etiology (Table 1)(8-10). Thus, severe bronchiectases are often seen in the context of congenital disorders such as cystic fibrosis, congenital immunodeficiency, or abnor-malities of cartilage development (Figures 6-9).
The predominant involvement of the subsegmental bronchial branches is suggestive for Williams-Campbell syndrome (Figure 6) – a rare form of congenital bronchi-ectasis characterized by deficiency of cartilage in subseg-mental bronchi, usually diagnosed in childhood or sometimes in adult age(11).
Marked dilatation of the trachea and main bronchi is definitory for Mounier-Kuhn syndrome (Figure 7) caused by primary atrophy of the musculo-elastic tissue. With a
higher incidence in males, idiopathic tracheobroncho-megaly is usually diagnosed in the 3rd or 4th decade of life. The clinical presentation varies from minimal disease with well-preserved pulmonary function to severe bron-chiectasis with emphysema and pulmonary fibrosis lead-ing to respiratory failure and death.
Bronchiectasis in cystic fibrosis (CF) usually has a bilateral, proximal, perihilar and upper lobe predomi-nance. CT images show extensive cystic and cylindrical
bronchiectasis (typically, more extensive than in non-CF cases), thick bronchial wall and peribronchial intersti-tial thickening (Figure 8). Upper lobe predominance is commonly seen, but it is not mandatory. A mosaic pat-tern of attenuation secondary to air-trapping, tree-in-bud nodules and diffuse distribution of bronchiectasis are also common findings(9).
Due to genetically determined abnormal chloride transportation, CF bronchiectases are associated with reproductive tract and digestive system abnormalities. The classic diagnostic triad in patients with CF includes an abnormal sweat chloride test and signs of pulmonary and pancreatic disease.
A finding of predominantly middle and basal distrib-uted bronchiectasis is suggestive for primary ciliary dys-kinesia (PCD), also known as immotile cilia syndrome(12,13). It is a genetic abnormality of the dynein arms of epithelial cilia that causes an impaired muco-ciliary clearance, resulting in chronic oto-sino-pulmonary disease. Bronchiectasis is a consistent finding in all adults with PCD. A subset of PCD patients could present with a triad of bronchiectasis, situs inversus, and either chronic sinusi-tis, or nasal polyps, which is known as Kartagener syndrome (Figure 9). PCD is considered the most common congenital cause for non-CF fibrosis bronchiectasis.
Bilateral centrally distributed bronchiectasis is a com-mon feature of bronchial lesions in patients with allergic bronchopulmonary aspergillosis (ABPA). About 75-95% of ABPA patients have CT identifiable bronchiectasis(14,15). High-attenuating (>70 to 100 HU) bronchial content is reported in 18-28% of patients with ABPA (Figure 10). That usually represents fungal debris containing iron and man-ganese and is considered a characteristic ABPA feature(16,17). Bronchiectasis in ABPA is a consequence of chronic airway inflammation, damage and remodeling resulting from a reaction to the presence of endobronchial Aspergillus species in asthma and cystic fibrosis patients. The diagnostic cri-teria for ABPA include symptoms of bronchial asthma, immediate skin test reactivity to Aspergillus fumigatus, elevated serum immunoglobulin E levels, pulmonary infil-trates, central bronchiectasis, peripheral blood eosinophilia and the presence of serum precipitins against Aspergillus antigen(9,18). ABPA should be always suspected in patients with recurrent asthma exacerbations, expectoration of dark mucus plugs, hemoptysis and/or systemic symptoms such as fever and malaise.
Bronchiectasis of apical and posterior upper lobe segments is highly suggestive for tuberculous origin, particularly in patients from high TB burden countries. The bronchiectasis could be the expression of post-pri-mary active tuberculosis (30-60% of TB patients), as well as scarring due to prior infection (71-86% of TB cured patients)(19). Post-tuberculous bronchiectasis is rarely gross, usually asymmetric with upper lobe pre-dominance. In previously treated TB patients bronchi-ectasis can remain stable for years. Lung volume loss, calcified lymph nodes and parenchymal calcifications are frequently found as accompanying features (Figures 11 and 12). Tree-in-bud pattern and cavities could sug-gest the reactivation of TB infection.
Focal bronchiectasis is usually caused by airway obstruction by a variety of causes. The differential diag-nosis includes tumors, endobronchial foreign body, extrinsic compression or post-infectious broncholithi-asis. Bronchial compression could be caused by lymphad-enopathy usually from previous granulomatous infection, sarcoidosis, hilar mass or metastatic lymphad-enopathy. Broncholithiasis describes calcified material within the bronchial lumen secondary to granulomatous infections such as tuberculosis or non-tuberculous mycobacteria. Diagnostic work-up in bronchiectasis sec-ondary to airway obstruction usually implies bronchoscopy(7,10,20).
Beside the site of bronchus obstruction, patient’s age may be helpful in predicting the bronchiectasis origin. Intraluminal occlusion in adults is more frequent due to neoplasms, of which carcinoid is the commonest cause of long-standing occlusion. Foreign body is a typical intra-luminal cause of bronchiectasis in children. In the major-ity of the cases, foreign body aspiration involves the right mainstem bronchus followed by left mainstem bronchus due to their alignment in line with the trachea. In patients without acute symptoms, the aspirated foreign bodies may remain undetected for months or even years and are often misdiagnosed (Figure 13). Undiagnosed and retained aspi-rated foreign bodies may cause recurrent infections, leading to bronchiectasis. Inorganic foreign bodies are known to cause fewer secondary infections compared to those of organic origin(21).
IMAGING SCORING SYSTEM
Structural lung changes seen on CT scans in bron-chiectasis patients could be expressed by several scoring systems. These can be used in adjunction to clinical parameters to assess severity and predict disease evolu-tion(22-24). Currently proposed scores try to quantify the extension and imaging severity of bronchiectasis. For disease extension, the assessment usually considers either the number of the affected segments, or the per-centage of each lung lobe involvement(25).
The Bhalla score (Table 2), based on thin section CT appearances of CF bronchiectasis, was published in 1991(25). However, currently it is used for the assessment of bronchiectasis of any etiology(24). The Bhalla score is a quite complex one, assessing nine CT features by three categories of severity. That makes it quite laborious for routine application. The Reiff score (Table 3) is a simpler one, and similarly to the Bhalla score, it is focused on the assessment of imaging lesions extension(24). A sig-nificant limitation of both Bhalla and Reiff systems is that quantity and extension of imaging lesions do not always reflect the rate of airway damage, namely, the disease activity. So far, a patient can have a similar score either due to a severe localized disease, or as result of a widespread mild disease. Additionally, the scores do not consider the diverse etiologies of bronchiectases, which could have different middle- and long-term prognosis.
An alternative simplified CT score is BRICS (Bronchiectasis Radiologically Indexed CT Score) based on the degree of bronchial dilatation and the number of bronchopulmonary segments with emphysema, in patients with idiopathic and post-infective bronchiec-tasis with limited smoking history. The BRICS was pro-posed to be used to follow-up patients longitudinally, being a potentially useful tool for future researches(22).
Recently, a couple of multidimensional scores which combine clinical and imaging variables have been proposed: BSI (Bronchiectasis Severity Index) and FACED (F – FEV1; A – Age; C – Chronic colonization;
E – Extension; D – Dyspnea). These scores are using several clinical parameters and counting the number of lobes affected by bronchiectasis on CT scan. They seem to be more accurate in assessing severity and prognosis of the disease(23,26).
Bronchiectasis is an irreversible disease of various eti-ologies. HRCT is indispensable for bronchiectasis detection, assesses its morphology, distribution and disease activity. New insights into bronchiectasis management by combin-ing clinical data, functional and imaging features are still required. Accurate multimodal tools aiming to provide a personalized approach for clinical care of bronchiectasis patients should be developed.
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- Dettmer S, Ringshausen F, Vogel-Claussen J et al. Computed tomography in adult patients with primary ciliary dyskinesia: Typical imaging findings. PloS one. 2018; 13(2):e0191457.
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- Bedi P, Chalmers JD, Goeminne PC et al. The BRICS (Bronchiectasis Radiologically Indexed CT Score): A Multicenter Study Score for Use in Idiopathic and Postinfective Bronchiectasis. Chest. 2017.
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