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Bronchiectasis is permanent irreversible dilatation of the airways and occurs in a variety of pathologic processes. Recurrent infection and inflammation and the resulting chemical and cellular cascade lead to permanent architectural changes in the airways. Bronchiectasis can confer substantial potential morbidity, usually secondary to recurrent infection. In severe cases of bronchiectasis, massive hemoptysis can lead to death. Thin-section computed tomography is the most sensitive imaging modality for the detection of bronchiectasis; findings include bronchial diameter exceeding that of the adjacent pulmonary artery and lack of normal tapering of terminal bronchioles as they course toward the lung periphery. The authors will review various causes of bronchiectasis, including common causes, such as recurrent infection or aspiration, and uncommon causes, such as congenital immunodeficiencies and disorders of cartilage development. The authors will also present an approach emphasizing the distribution (apical versus basal and central versus peripheral) and concomitant findings, such as nodules, cavities, and/or lymphadenopathy, that can assist in narrowing the differential diagnosis. Although an adequate understanding of these underlying causes in conjunction with their specific imaging appearances will allow radiologists to more confidently determine the process causing this common radiologic finding, clinical history and patient demographic characteristics play an integral role in determining a pertinent and concise differential diagnosis. Online supplemental material is available for this article.
支气管扩张：相关常见及不常见疾病的机制及影像特征
支气管扩张是气道永久性不可逆的扩张，可发生于一系列病理情况下。反复感染、炎症和其导致的一系列化学、细胞改变可导致气道永久性的结构改变。支气管扩张可引起大量潜在的疾病发生，通常继发于反复感染。严重的支气管扩张可引起大量咯血导致死亡。薄层CT是发现支气管扩张最为敏感的影像学手段，其发现包括支气管直径超过伴行肺动脉直径、终末细支气管在向肺外带走形时没有逐渐变细的正常表现。作者将回顾支气管扩张的各种原因，包括常见病因，如反复感染或误吸，不常见的病因，如先天性免疫缺陷、软骨发育异常等。此外，作者将会展现强调分布（如肺尖&肺底和中央&外周）和伴发的表现，如结节、空洞，和/或淋巴结肿大的方法，有助于缩小鉴别诊断范围。尽管熟悉了解这些潜在的病因和其特定的影像学表现能让放射科医生更有信心判定引起这一常见影像学表现的疾病过程，但临床病史及病人的个人基本信息在确定恰当的简明的鉴别诊断起着不可或缺的作用。
TEACHING POINTS
■■ Spatial distribution, morphologic features, and associated airway or parenchymal findings can guide the radiologist in formulating a rational differential diagnosis from a large number of potential causes. In some cases, a pathognomonic appearance can lead to a confident diagnosis of a particular disorder.
■■ Spirometry often reveals an obstructive physiologic condition that worsens over time.
■■ According to Cole’s generally accepted “vicious cycle” hypothesis, airway damage and infection play reinforcing roles in the development of bronchiectasis. A primary insult to the airways leads to damage of ciliated epithelium and mucosal glands, impairing the mucociliary clearance system and thus increasing the frequency and severity of pulmonary infections and perpetuating this vicious cycle. Host factors, such as impaired glandular secretion (as in cystic fibrosis), impaired ciliary function (ciliary dyskinesia), or systemic immune dysfunction, can predispose to infection and, thus, to development of bronchiectasis.
■■ Bronchial wall thickening and mucous plugging are common in most diseases causing bronchiectasis and are signs of chronic airway inflammation. Other findings are more common in certain diseases and can help narrow the differential diagnosis. The distribution and morphologic features of bronchiectasis, architectural distortion and other findings of fibrosis, mosaic attenuation, and the presence and pattern of diffuse nodular lung disease can provide clues to the diagnosis.
■■ Pathologic conditions affecting primarily the upper lung zones include cystic fibrosis, sarcoidosis, silicosis and other pneumoconioses, allergic bronchopulmonary aspergillosis, and tuberculosis. Lymphatic clearance is thought to be less effective in the upper zones than in the lower lobes. This finding may account for the upper lobe predominance of certain inhalational- and perilymphatic-predominant diseases and may be attributable to the typical gravitational gradient of blood flow and lower respiratory excursion in the upper lobes.
教学要点
l 发病部位，形态学特征，相关的气道或肺实质表现可以引导放射科医师从大量的可能原因中做出合理的鉴别诊断。在一些病例中，根据特异性征象可以确诊一些特殊病症。
l 肺活量测定常显示阻塞性通气功能障碍，并逐渐恶化。
l 根据被普遍接受的科尔的“恶性循环”假设，气道损伤和感染强化了支气管扩张的进展。对气道最初的损伤导致纤毛上皮和粘膜腺体损伤，粘液纤毛清除系统受损加剧了肺部感染的频率和严重程度，并恶性循环下去。宿主因素，如腺体分泌受损（如囊性纤维化），纤毛功能受损（纤毛运动障碍），或全身免疫功能障碍，使宿主易患感染，因此发展为支气管扩张。
l 支气管壁增厚和黏液栓塞在多数导致支气管扩张的疾病中很常见，是气道慢性炎症的征象。在某些疾病更常见的一些表现可以帮助缩窄鉴别诊断范围。如支气管扩张的分布和形态学特征，结构扭曲和其他纤维化发现，马赛克征，以及弥漫结节性肺疾病的存在和分型可以为诊断提供线索。
l 主要影响上肺区的病理因素包括囊性纤维化，结节病，矽肺及其他尘肺，过敏性支气管肺曲菌病和结核病。有观点认为肺上叶的淋巴清除力比下叶低。这一发现可以解释某些吸入和淋巴周分布为主疾病以上叶分布为主，可能归因于典型的血流量重力梯度分布和上叶的呼吸活动度较下叶小。
1. 识别有助于支气管扩张诊断的影像学关键征象。
2. 描述支气管扩张的病生理学特征。
3. 根据病变影像学特征和分布，给出引起支气管扩张的简明的鉴别诊断。
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