Definition

Increase in transradiancy of a lung field.

Etiology, pathophysiology, pathogenesis

One of several causes may be involved: Primary congenital pulmonary artery hypoplasia MacLeod/Swyer-James syndrome, i.e., hypoplasia of pulmonary parenchyma including the territory of the pulmonary artery secondary to viral infection in the first 8 years of life prior to complete maturation of the lung Perfusion defect from reflex vasoconstriction where a central bronchial obstruction (central bronchial carcinoma, bronchial adenoma, or endobronchial foreign body) creates a ventilation defect.

Imaging Signs

Modality of choice

CT.

Radiographic findings

Hypertransradiant hemithorax with hypoperfusion Signs of hyperinflation in the presence of a central bronchial obstruction.

CT findings

Depend on the cause Pulmonary artery hypoplasia: Hypoplastic pulmonary arterial system with otherwise normal parenchymal texture MacLeod/Swyer–James syndrome: Mixed picture with hyperinflated and normally inflated areas, bronchiectatic tissue remodeling with thickened bronchi in collapsed, scarred lung segments Central bronchial carcinoma with bronchial and/or pulmonary artery obstruction Endobronchial obstruction due to tumor or foreign body.

Pathognomonic findings

Depend on the cause.

Clinical Aspects

Typical presentation

Asymptomatic incidental finding in MacLeod/Swyer–James syndrome and in pulmonary artery hypoplasia Symptomatic in tumor cases.

Therapeutic options

Depend on the cause and/or underlying disorder.

Course and prognosis

Depend on the cause and/or underlying disorder.

What does the clinician want to know?

Determine the cause and specifically exclude a tumor.

Tips and Pitfalls

Can be confused with off-center grid, post-mastectomy, and unilateral atrophy of the pectoralis muscles.

Selected References

Lucaya J et al. Spectrum of manifestations of Swyer-James-MacLeods syndrome. J Comput Assist Tomogr 1998; 22: 592–597

Fig. 2.1 Hypertrans-radiant hemithorax (MacLeod/Swyer–James syndrome) in an 18-year-old woman. The plain chest radiograph (a) shows increased transradiancy of the left lung with significantly diminished vascularity. The coronal slices (b – d) clearly demonstrate diminished vascularity (b, MIP), shrinkage (c), and bilateral bronchi-ectasis (d).

Irreversible dilation of a bronchus or bronchi, especially large and small subsegmental bronchi Reid classification differentiates cylindrical, varicose, and cystic dilation.

Etiology, pathophysiology, pathogenesis

Congenital (Kartagener syndrome, mucociliary dysfunction, cystic fibrosis, etc.) Infectious (allergic bronchopulmonary aspergillosis, measles, whooping cough, tuberculosis, etc.) Bronchial obstruction or compression (tumor, foreign body, etc.) Pulmonary fibrosis (traction bronchiectasis) and/or thickening and inflammation of the bronchial wall Destruction of the bronchial wall Peribronchial fibrosis.

Imaging Signs

Modality of choice

CT.

Radiographic findings

Nonspecific findings Pronounced striped pattern Parallel stripes (“railroad track” sign) Ring shadows.

CT findings

“Signet ring” sign (bronchial diameter exceeds the diameter of the accompanying artery) Bronchi fail to taper peripherally Bronchi can be differentiated up to a subpleural depth of 1 cm Changes in bronchial contour (cylindrical bronchi appear as tracklike parallel lines, varicose bronchi as intermittent widening of the bronchial lumina or “strings of pearls,” and cystic bronchi as bunched “clusters of grapes,” because of shrinkage Nonspecific findings include bronchial thickening, fluid or mucus-filled bronchi, loss of volume, air trapping, and nodular bronchial dilation (“tree-in-bud” sign).

Pathognomonic findings

Predilection for the posterobasal segments of the lung “Signet ring” sign and “railroad track” sign (see above) Ring shadow.

Clinical Aspects

Typical presentation

Recurrent bronchopneumonia Voluminous expectorations Hemoptysis Dyspnea.

Therapeutic options

Surgery (segmental resection or lobectomy) Pulmonary toilet Bronchospasmolytic Specific antibiotic therapy Active immunization against influenza and pneumococcus.

Course and prognosis

Severity correlates with the diameter of the abnormal bronchi (cylindrical bronchiectasis has the best prognosis, cystic bronchiectasis the worst).

Fig. 2.2 Bronchiectasis in an 18-year-old man with immunodeficiency.

a The plain chest radiograph shows thickening of the bronchovascular bundles in the right paracardiac and left retrocardiac areas. Isolated, sharply demarcated, fine nodular densities are visible in the right lower lung field.

b On CT these changes primarily correlate with tubular bronchiectasis, occasionally concentrated, and with significant thickening of the bronchial wall and focal mucus retention.

Diagnosis of bronchiectasis Is resection of localized bronchiectatic areas indicated? Comorbidities detected (scarring, emphysema, abscess, empyema, broncholiths, pyemia).

Differential Diagnosis

Tips and Pitfalls

Motion artefacts on the CT due to breathing can be misinterpreted as a “railroad track” sign Reactive bronchial dilation (“reversible bronchiectasis”) occurs in the presence of atelectasis.

Selected References

Cartier Y et al. Bronchiectasis: Accuracy of high resolution CT in the differentiation of specific diseases. AJR Am J Roentgenol 1999; 173: 47–52

King P, Song X, Rockwood K. Bronchiectasis. Intern Med J 2006; 36: 729–737

Definition

Epidemiology

Inflammation of the peripheral respiratory bronchioles (diameter < 2 mm).

Etiology, pathophysiology, pathogenesis

Acutely infectious (viruses, Mycoplasma, chlamydia, aspergillosis) Chronic inflammatory (asthma, chronic bronchitis) Panbronchiolitis Respiratory bronchiolitis (nicotine).

Imaging Signs

Modality of choice

CT.

Radiographic findings

Usually normal Reticulonodular shadowing Pneumonic infiltrate may be present Dystelectasis.

CT findings

Centrilobular and peribronchovascular nodules “Tree-in-bud” sign (usually peripheral) Ground-glass opacities Bronchial wall thickening Air trapping.

Pathognomonic findings

None Findings such as a mosaic pattern, “tree-in-bud” sign, or centrilobular nodules are nonspecific.

Clinical Aspects

Typical presentation

Dyspnea Nonproductive cough (productive cough occurs in diffuse panbronchiolitis) Fever.

Therapeutic options

Elimination of the noxious agent Steroids (inhalational or systemic) Bronchoalveolar lavage.

Course and prognosis

Prognosis is good in infections Course is more rapid in patients with bone marrow or stem cell transplantation In severe cases respiratory insufficiency andpulmonary fibrosis may develop Prognosis is poor in diffuse panbronchiolitis.

Differential Diagnosis

Fig. 2.3 Bronchiolitis in a 62-year-old man.

a The plain chest radiograph shows increased finely nodular shadowing, especially in the left upper field and slightly more prominent bronchial walls.

b Findings on CT are localized to the peribronchovascular region. Note the significant focal wall thickening in the small bronchi (arrowhead).

False-negative diagnosis due to overlooking discrete changes.

Selected References

Hartmann TE et al. CT of bronchial and bronchiolar diseases. Radiographics 1994; 14: 991–1003

Howling SJ et al. Follicular bronchiolitis: thin-section CT and histologic findings. Radiology 1999; 212: 637–642

Müller NL, Miller RR. Diseases of the bronchioles: CT and histopathologic findings. Radiology 1995; 196: 3–12

Definition

Epidemiology

Depends on the etiology. Every second lung transplant recipient develops a bronchiolitis obliterans syndrome within 5 years of transplantation.

Etiology, pathophysiology, pathogenesis

Rarely idiopathic, usually secondary to infection (mycoplasmal, viral, in children especially respiratory syncytial virus), secondary to inhalation of noxious agents, as a hypersensitivity reaction (collagen diseases), secondary to transplantation (lung, heart, bone marrow), in the setting of chronic obstructive pulmonary disease Inflammation of the respiratory bronchioles Proliferation of submucosal and peribronchial tissue leading to concentric constriction of the respiratory bronchioles.

Imaging Signs

Modality of choice

CT on inspiration and expiration (to detect air trapping).

Radiographic findings

Signs of pulmonary hyperinflation of variable severity with diminished vascularity.

CT findings

Increased transparency of the pulmonary parenchyma with narrowed vessels and signs of air trapping On expiration the density of the affected areas fails to increase Affected areas show increased transparency as on inspiration Mosaic perfusion Peribronchiolar fibrosis (rare) In postinfectious bronchiolitis there is bronchial wall thickening and bronchiectasis “Tree-in-bud” sign is rare.

Pathognomonic findings

Increased transparency of the pulmonary parenchyma with narrowed vessels Severe air trapping Mosaic perfusion.

Clinical Aspects

Typical presentation

Cough Dyspnea Fever, resembles chronic obstructive pulmonary disease but with subacute course Primarily restrictive ventilation defect due to early complete occlusion.

Therapeutic options

Steroids Immunosuppression after lung transplant.

Course and prognosis

Prognosis is good with steroid therapy.

What does the clinician want to know?

Confirmation of tentative diagnosis in at-risk patients (post bone marrow, peripheral blood stem cell, or lung transplantation).

Fig. 2.4 Bronchiolitis obliterans in a 24-year-old man (graft-versus-host disease following bone marrow transplantation).

a The plain chest radiograph shows significant hyperinflation of both lungs (left more than right) with slightly more prominent bronchial walls in the perihilar region.

b CT confirms the findings and shows diminished vascularity, especially on the left side and in the right lower lobe. There was no increase in density on expiration, which is consistent with air trapping.

Tips and Pitfalls

Generalized air trapping can escape detection, as can air trapping in an uncooperative patient (recognizable by the absence of impression of the membranous part of the trachea).

Selected References

Bankier AA et al. Bronchiolitis obliterans syndrome in heart-lung transplant recipients: diagnosis with expiratory CT. Radiology 2001; 218: 533–539

Choi YW et al. Bronchiolitis obliterans syndrome in lung transplant recipients: correlation of CT findings with bronchiolitis obliterans syndrome stage. J Thorac Imaging 2003; 18: 72–79

Hansell DM et al. Obliterative bronchiolitis: individual CT signs of small airway disease and functional correlation. Radiology 1997; 203: 721–726

Definition

Pulmonary disorder characterized by increased resistance to airflow FEV₁/FVC <70%.