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76 Cards in this Set

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What is a tracheal bronchus?
What are they associated with?
-Tracheal bronchus or bronchus suis, so-called because it is the normal pattern of tracheal branching in pigs, consists of an accessory bronchus to all or a portion of the right upper lobe that arises from the right lateral tracheal wall within 2 cm of the tracheal carina
-It most often supplies the apical segment of the right upper lobe.
-While it is usually an incidental finding on chest CT in 0.5% to 1.0% of the population, there is an association with congenital tracheal stenosis and an aberrant left pulmonary artery.
-Most patients are asymptomatic
What are the most common entities to place mass effect on the trachea?
The most common causes of extrinsic mass effect on the trachea are an intrathoracic goiter and a large paratracheal lymph node mass.
What systemic diseases can cause tracheal narrowing?
-Saber-sheath trachea
-Amyloidosis
-Tracheobronchopathia osteochondroplastica
-Relapsing polychondritis
-Wegener granulomatosis
-Tracheal scleroma
What is scleroma?
-Scleroma is a rare chronic granulomatous disorder caused by infection with Klebsiella rhinoscleromatis.
-In its chronic phase, intense
granulation tissue and fibrosis lead to stenosis of the nasal cavity, pharyngeal, laryngeal, and upper trachea
-Radiographically, the upper trachea shows irregular nodular narrowing, which may extend to involve the length of the trachea.
-The diagnosis is made on biopsy
Describe manifestations of Wegener's granulomatosis affecting the trachea:
-Wegener granulomatosis can produce a necrotizing granulomatous inflammation of the trachea and central bronchi, leading to focal cervical tracheal narrowing or, in advanced disease, narrowing of the entire length of the trachea.
-The diagnosis of tracheal involvement by Wegener granulomatosis is made by the radiographic demonstration of tracheal narrowing in association with upper airway and renal involvement and characteristic findings on biopsy.
What systemic diseases can cause tracheal dilatation?
-Tracheobronchomegaly (Mounier-Kuhn
syndrome)
-Tracheomalacia
-Interstitial pulmonary fibrosis
What entities might cause focal tracheal dilatation?
-Focal tracheal dilatation is caused by congenital or acquired abnormalities of the elastic membrane or cartilaginous rings of the trachea.
-Localized tracheal dilatation may be seen with tracheoceles (tracheal diverticula), with acquired tracheomalacia related to prolonged endotracheal intubation, or as a result of tracheal traction from severe unilateral upper lobe parenchymal scarring.
Define saber-sheath trachea:
What does it look like on imaging?
What causes it?
-Saber-sheath trachea is a fixed deformity of the intrathoracic trachea in which the coronal diameter is diminished to less than two thirds of the sagittal diameter.
-The tracheal wall is uniformly thickened, and calcification of the cartilaginous rings is present in most cases.
-This entity exclusively affects older men with functional evidence of chronic obstructive pulmonary disease (COPD).
-The tracheal narrowing likely reflects the chronic transmission of increased intrapleural pressure seen in obstructive lung disease and tracheal injury from chronic cough.
How can amyloidosis affect the trachea?
What does this look like on imaging?
-Amyloidosis is characterized by the deposition of a fibrillar protein-polysaccharide complex in various organs.
-It may involve the airways as part of localized or systemic disease.
-Submucosal deposits in the tracheobronchial tree are more commonly a manifestation of localized disease and may be associated with nodular or alveolar septal deposits in the lungs.
-Masslike circumferential deposits that irregularly narrow the tracheal lumen are best demonstrated on CT and can result in recurrent atelectasis and pneumonia.
-Calcification of these deposits occurs in only 10% of cases.
-The diagnosis is made on biopsy
What is tracheobronchopathia osteochondroplastica?
How can you tell it apart from tracheal amyloidosis?
-Tracheobronchopathia osteochondroplastica is a rare disorder characterized by the presence of multiple submucosal osseous and cartilaginous deposits within the trachea and central bronchi of elderly men.
-The lesions arise as enchondromas from the tracheal and bronchial cartilage, and then project internally to produce nodular submucosal deposits that irregularly narrow the tracheal lumen and have a characteristic appearance and feel on bronchoscopy.
-The diagnosis is generally made on bronchoscopy and CT, where calcified plaques can be seen involving the anterior and lateral walls of the trachea.
-Sparing of the membranous posterior wall of the trachea, which lacks cartilage, is a helpful feature that distinguishes this entity from tracheobronchial amyloid.
-While usually asymptomatic, patients may have recurrent infection related to bronchial obstruction by the masses.
Which entities spare the posterior wall of the trachea?
Which entities do not spare the posterior wall?
-Tracheobronchopathia osteochondroplastica
-Relapsing polychondritis

-Wegener's
-Tracheal amyloidosis
What is relapsing polychondritis?
What does it look like on imaging?
-Relapsing polychondritis is a systemic autoimmune disorder that commonly affects the cartilage of the earlobes, nose, larynx, tracheobronchial tree, joints, and large elastic arteries.
-Early in the disease, tracheal wall inflammation associated with cartilage destruction leads to an abnormally compliant and dilated trachea.
-Later in the disease, fibrosis leads to diffuse fixed narrowing of the tracheal lumen.
-Respiratory complications secondary to involvement of the upper airway cartilage accounts for nearly 50% of all deaths from this condition.
-The diagnosis is made by noting recurrent inflammation at two or more cartilaginous sites, most commonly the pinnae of the ear (producing cauliflower ears) and the bridge of the nose (producing a saddlenose deformity).
-Radiographs and CT show diffuse smooth thickening of the wall of the trachea and central bronchi with narrowing of the lumen.
-Posterior wall of the trachea is spared
What is the syndrome of congenitally large trachea and central airways?
Tracheobronchomegaly (Mounier-Kuhn syndrome)
What is tracheobronchomegaly (Mounier-Kuhn syndrome)?
What does it look like on imaging?
-Tracheobronchomegaly (Mounier-Kuhn syndrome) is a congenital disorder of the elastic and smooth muscle components of the tracheal wall.
-Associated with Ehlers-Danlos syndrome and cutis laxa, a congenital defect in elastic tissue
-The disease is found almost exclusively in men under the age of 50.
-Abnormal compliance of the trachea and central bronchi leads to central bronchial collapse during coughing.
-The airways obstruction impairs mucociliary clearance, predisposing the patient to recurrent episodes of pneumonia and bronchiectasis.
-Symptoms are indistinguishable from those associated with chronic bronchitis and bronchiectasis.
-On frontal radiographs, the trachea and central bronchi measure greater than 3.0 cm and 2.5 cm, respectively, in coronal diameter.
-The trachea has a corrugated appearance caused by herniation of tracheal mucosa and submucosa between the tracheal cartilages.
-The lungs are typically hyperinflated and may demonstrate bullae.
What are the most common causes of tracheobronchomalacia?
-The most common causes of acquired tracheomalacia are COPD, chronic bronchitis, cystic fibrosis, and relapsing polychondritis
-In some patients with long-standing interstitial pulmonary fibrosis, diffuse tracheal dilatation may be seen.
-The etiology of the tracheal dilatation may relate to long-standing elevation in transpulmonary pressures caused by diminished lung compliance or to chronic coughing.
How does tracheal/central bronchial injury most often occur?
What does it look like on imaging?
-The mechanism of injury is forceful compression of the central tracheobronchial tree against the thoracic spine during impact.
-The fractures generally involve the proximal main bronchi (80%) or distal trachea (15%) within 2 cm of the tracheal carina; the peripheral bronchi are involved in 5% of cases.
-Horizontal laceration or transection parallel to the tracheobronchial cartilage is the most common form of injury.
-The diagnosis of tracheobronchial injury is often first suggested on early posttrauma chest radiographs by the presence of pneumothorax and pneumomediastinum, particularly in a patient not receiving mechanical ventilation
-Typically, the pneumothorax fails to respond to chest tube drainage owing to a large air leak at the site of airway interruption.
-The subtended lung remains collapsed against the lateral chest wall (“fallen lung” sign)
-An aberrant endotracheal tube or overdistended balloon cuff are further clues to the presence of an unsuspected tracheobronchial disruption.
-As many as one third of tracheobronchial injuries have a delayed diagnosis; these patients may present with a collapsed lung or pneumonia secondary to bronchial stenosis.
What causes broncholiths?
How do these patients present clinically?
-Broncholithiasis, the presence of calcified material within the tracheobronchial tree, develops from erosion of a calcified peribronchial lymph node into the bronchial lumen
-Most calcified lymph nodes result from granulomatous lymph node inflammation caused by histoplasmosis or TB.
-Broncholiths may occlude the airway and lead to bronchiectasis, obstructive atelectasis, or pneumonia.
-Patients are often asymptomatic but may have cough productive of stones or calcified material (lithoptysis).
-Hemoptysis may develop from erosion of the broncholith into a bronchial vessel.
Define Asthma:
What does uncomplicated asthma look like on imaging?
-Asthma is an airways disorder characterized by the rapid onset of bronchial narrowing with spontaneous resolution or improvement as a result of therapy.

-The radiographic findings in uncomplicated asthma are primarily the result of diffuse airways narrowing.
-Hyperinflation producing increased lung volume, flattening or inversion of the diaphragm, attenuation of the peripheral vascular markings, and prominence of the retrosternal airspace is the result of expiratory air trapping
-Bronchial wall inflammation and thickening appear radiographically as peribronchial cuffing and “tram tracking.”
-In some patients, the hila are prominent from transient pulmonary arterial hypertension caused by hypoxic vasoconstriction
Why is it a good idea to get a chest x-ray on an asthma exacerbation patient?
-There are several reasons to obtain a chest radiograph in patients with asthma.
-Tracheal and central bronchial narrowing from extrinsic or intrinsic lesions may produce dyspnea and wheezing and be mistaken for asthma.
-Bacterial pneumonia may induce airway hyperreactivity and present as an acute asthmatic attack.

-Complications of asthma may be detected on chest radiographs obtained during and following the asthmatic episode.
-Mucus plugs can cause bronchial obstruction and resorptive atelectasis; pneumonia can develop in these collapsed regions.
-Expiratory airflow obstruction with resultant alveolar rupture and dissection of air medially may produce pneumomediastinum.
-If the extra-alveolar air dissects peripherally to the subpleural space to form subpleural blebs, pneumothorax may result.
-Both pneumomediastinum and pneumothorax may be exacerbated in ventilated patients receiving high-positive-pressure ventilation.
Describe possible complications of an asthma attack:
-Complications of asthma may be detected on chest radiographs obtained during and following the asthmatic episode.
-Mucus plugs can cause bronchial obstruction and resorptive atelectasis; pneumonia can develop in these collapsed regions.
-Expiratory airflow obstruction with resultant alveolar rupture and dissection of air medially may produce pneumomediastinum.
-If the extra-alveolar air dissects peripherally to the subpleural space to form subpleural blebs, pneumothorax may result.
-Both pneumomediastinum and pneumothorax may be exacerbated in ventilated patients receiving high-positive-pressure ventilation.
Define chronic bronchitis:
-Chronic bronchitis is a clinical and not a radiographic diagnosis.
-It is defined as the excess production and expectoration of sputum that occurs on most days for at least 3 consecutive months in at least 2 consecutive years.
-The majority of individuals with chronic bronchitis are cigarette smokers.
What does chronic bronchitis look like on imaging?
-Fifty percent of patients with a history of chronic bronchitis have normal chest films
-Some patients show peribronchial cuffing or tram tracks when the thick-walled and mildly dilated bronchi are viewed end on or in length, respectively.
-Other patients have a “dirty chest,” in which the peripheral lung markings are accentuated.
-This radiographic appearance has no definite pathologic correlate but may represent small airways disease or prominent pulmonary arteries from pulmonary arterial hypertension complicating associated centrilobular emphysema.
-CT in patients with chronic bronchitis may show bronchial wall thickening
-Morphologically, the lower lobe bronchi are most often affected, with thickening of their walls from mucous gland hyperplasia.
Describe the different types of bronchiectasis:
-Morphologically, bronchiectasis is divided into three groups: cylindric, varicose, and saccular (cystic).

-Cylindric bronchiectasis is characterized by mild diffuse dilatation of the bronchi.
-Varicose bronchiectasis is cystic bronchial dilatation interrupted by focal areas of narrowing, an appearance that has been likened to a string of pearls.
-Cystic bronchiectasis is seen as clusters of bronchi with marked localized saccular dilatation.
What does bronchiectasis look like on chest x-ray?
-The chest radiographic findings of bronchiectasis are typically nonspecific.
-Scarring, volume loss, and loss of the sharp definition of the normal bronchovascular markings are present in the affected regions.
-Parallel linear shadows representing the walls of cylindrically dilated bronchi seen in length may be visualized.
-Cystic bronchiectasis has a characteristic appearance of multiple peripheral thin-walled cysts, with or without air–fluid levels, that tend to cluster together in the distribution of a bronchovascular bundle.
-The findings tend to be peripheral in most cases of localized bronchiectasis; central bronchiectasis is seen only in allergic bronchopulmonary aspergillosis, cystic fibrosis, bronchial atresia, or acquired central bronchial obstruction.
Bronchiectasis is usually peripheral. Which diseases are associated with central bronchiectasis?
Central bronchiectasis is seen only in allergic bronchopulmonary aspergillosis, cystic fibrosis, bronchial atresia, or acquired central bronchial obstruction.
List some caues of focal bronchiectasis:
-Tuberculous scarring, upper lobes (postprimary disease)
-Bronchial disease
Extrinsic compression
Enlarged hilar nodes
Bronchial stenosis/occlusion
Bronchial atresia
Tuberculosis
Sarcoidosis
Prior bronchial injury
Endobronchial mass
Carcinoid tumor
Bronchogenic carcinoma
-Foreign body
List some caues of diffuse bronchiectasis:
-Cystic fibrosis
-Dysmotile cilia syndrome
-Congenital immunodeficiency
-Postinfectious
Adenovirus (Swyer-James syndrome)
Measles
Pertussis
-Chronic aspiration
-Allergic bronchopulmonary aspergillosis
-Interstitial pulmonary fibrosis (traction bronchiectasis)
Define cystic fibrosis:
What does it look like on imaging?
-Cystic fibrosis is a hereditary disease of young Caucasians characterized in the lung by the production of abnormally thick, tenacious mucus.
-The thick mucus plugs the small airways and leads to bronchial obstruction and infection.
-A vicious cycle of recurrent infection, most often with Pseudomonas aeruginosa or Staphylococcus aureus, eventually causes severe bronchiectasis.
-The bronchiectasis is associated with functional airways obstruction and dyspnea.
-Hemoptysis, sometimes massive, may complicate the bronchiectasis and may require treatment by transcatheter bronchial artery embolization.

-Chest radiographs in affected adults show hyperinflation with predominantly upper lobe bronchiectasis and mucus plugging.
-Distal atelectasis and obstructive pneumonitis are common findings.
-The pulmonary hila may be prominent from enlarged lymph nodes caused by chronic infection or from vascular dilatation associated with pulmonary arterial hypertension.
Is cystic fibrosis a predominantly upper or lower lobe process?
Upper lobe
What is dysmotile cilia syndrome?
What is Kartagener's syndrome?
-Dysmotile cilia syndrome is a disorder in which the epithelial cilial motion is abnormal and ineffective.
-The abnormality may result in rhinitis, sinusitis, bronchiectasis, dysmotile spermatozoa and sterility, situs inversus, and dextrocardia.
-The triad of sinusitis, situs inversus, and bronchiectasis is known as Kartagener syndrome.
Describe Swyer-James syndrome:
-Severe childhood pneumonia, usually a sequela of infection with adenovirus, measles, or pertussis, may cause severe bronchial damage and recurrent infection with resultant bronchiectasis
-In some patients, childhood bronchitis and bronchiolitis are associated with obstructive airways disease and an underdeveloped lung, the latter known as Swyer-James syndrome
What syndrome is ABPA associated with?
cystic fibrosis
Describe allergic bronchopulmonary aspergillosis:
What does it look like on imaging?
-Allergic bronchopulmonary aspergillosis represents a hypersensitivity reaction to Aspergillus and is characterized clinically by asthma, blood eosinophilia, bronchiectasis with mucus plugging, and circulating antibodies to Aspergillus antigen.
-An immediate (type 1) hypersensitivity reaction to Aspergillus antigen accounts for acute episodes of wheezing and dyspnea, while an immune complex–mediated (type 3) hypersensitivity within the lobar bronchi leads to bronchial wall inflammation and proximal bronchiectasis.
-Affected patients invariably have an allergic history, and it is often associated with cystic fibrosis.
-Patients with this disorder have recurrent episodes of cough, wheezing, and expectoration of mucus plugs.

-The chest radiograph is diagnostic and shows proximal, predominantly upper lobe bronchiectasis.
-The dilated bronchi may be seen as dilated air-filled tubules or as broadly branching opacities characteristic of mucoid impaction within the dilated bronchi.
-CT and HRCT are helpful in characterizing the opacities as dilated bronchi
Describe causes of bronchial obstruction that can lead to formation of bronchiectasis:
-Bronchiectasis can develop distal to an endobronchial obstruction caused by neoplasm, atresia, or stenosis.
-Slow-growing central bronchogenic neoplasms that have a large endoluminal component (e.g., carcinoid tumor) may obstruct the distal bronchi and produce bronchiectasis with mucus plugging (mucoceles)
-Similarly, bronchial atresia or bronchostenosis from trauma or chronic bronchial infection (i.e., endobronchial TB) can lead to distal bronchial dilatation.
What is a mucocele?
bronchiectasis with mucus plugging
Describe traction bronchiectasis:
What are two common settings in which traction bronchiectasis occurs?
-Traction bronchiectasis is a term used to describe the effect of severe pulmonary fibrosis on the peripheral airways.
-Airways that traverse regions of parenchymal fibrosis and honeycombing often become irregularly dilated as their walls are retracted by the fibrotic process.
-This occurs most commonly in the upper lobes in patients with long-standing TB and in the subpleural regions of the lower lobes in patients with end-stage idiopathic pulmonary fibrosis.
Define Emphysema:
Emphysema is a pathologic diagnosis that is defined as an abnormal, permanent enlargement of the airspaces distal to the terminal bronchiole accompanied by destruction of alveolar walls and without obvious fibrosis.
List the different types of emphysema:
What type of emphysema is most common?
-Centrilobular
-Panlobular
-Paraseptal
-Paracicatricial or irregular

-Centrilobular emphysema is most common
Describe centrilobular emphysema:
-Centrilobular emphysema is the most common and is characterized by airspace distention in the central portion of the lobule, with sparing of the more distal portions of the lobule.
-This form of emphysema affects the upper lobes to a greater extent than the lower lobes
Describe panlobular emphysema:
-Panlobular emphysema results in uniform distention of the airspaces throughout the substance of the lobule, from the central respiratory bronchioles to the peripheral alveolar sacs and alveoli.
-In contrast to centrilobular emphysema, this form has a predilection for the lower lobes
Describe paraseptal emphysema:
-Paraseptal emphysema is seen as selective distention of peripheral airspaces adjacent to interlobular septa, with sparing of the centrilobular region.
-This form of emphysema is most often seen in the immediate subpleural regions of the upper lobes
-Paraseptal emphysema may coalesce to form apical bullae; rupture of these bullae into the pleural space may give rise to spontaneous pneumothoraces.
What is paracicatricial emphysema?
-Paracicatricial or irregular emphysema refers to destruction of lung tissue associated with fibrosis that bears no consistent relationship to a given portion of the lobule.
-It is most often seen in association with old granulomatous inflammation
What syndrome is associated with accelerated emphysema formation?
α-1-antitrypsin deficiency

-This disease is inherited as an autosomal recessive trait.
-Individuals who are homozygous for both recessive genes (ZZ phenotype) develop panlobular emphysema by middle age.
-Heterozygotes (MZ phenotype) have only a slightly increased incidence of emphysema.
Why do emphysema patients become hyperinflated?
Hyperinflation is caused by loss of elastic recoil of lung
Why do emphysema patients get pulmonary arterial hypertension and right heart enlargement?
Emphysema destroys the pulmonary capillary bed; the associated chronic hypoxemia causes increased pulmonary vascular resistance
Describe findings of hyperinflation on chest x-ray:
-The abnormal increase in lung volumes is best detected by noting inferior displacement and flattening of the normally convex superior hemidiaphragms, right or obtuse angles to the normally acute-angled costophrenic sulci, and an increase in anteroposterior chest diameter (best appreciated by noting an increase in the depth of the retrosternal clear space)
Define bullae:
Bullae are thin-walled cystic spaces that exceed 1 cm in diameter and are found within the lung parenchyma
List radiographic findings in emphysema:
-Diffuse hyperlucency (panlobular)
-Flattening and depression of the hemidiaphragms; increased retrosternal airspace (panlobular >centrilobular)
-Bulla
-Enlarged central pulmonary arteries; right heart enlargement (centrilobular)
-Increased peripheral vascular markings (centrilobular)
What is vanishing lung syndrome?
an accelerated form of paraseptal emphysema seen in young adult men
Name some causes of primary bullous lung disease:
-Familial
-Vanishing lung disease
-Marfan syndrome
-Ehlers Danlos syndrome
-Intravenous drug use
-HIV infection
What is bronchiolitis?
-Bronchiolitis refers to an inflammation of the small noncartilaginous airways
-It can be infectious (RSV, adenovirus) or inflammatory (RB-ILD related to cigarette smoke)
-Bronchiolitis is also a prominent feature of patients with subacute hypersensitivity pneumonitis
What is follicular bronchiolitis?
What does it look like on imaging?
-Follicular bronchiolitis reflects a form of diffuse lymphoid hyperplasia of peribronchiolar lymphoid follicles of unclear clinical significance seen in patients with rheumatoid arthritis or Sjögren syndrome.
-Thin-section CT shows ill-defined centrilobular ground-glass nodules and occasional bronchial dilatation.
What does infectious bronchiolitis look like on CT?
tree-in-bud opacities
What does RB-ILD look like on CT?
Centrilobular and geographic ground-glass opacities
What does subacute hypersensitivity pneumonitis look like on CT?
Centrilobular ground-glass nodules; air trapping on expiratory scans
What is constrictive bronchiolitis?
What causes it?
-Constrictive bronchiolitis, also known as bronchiolitis obliterans, is a subacute disease characterized pathologically by a mononuclear cell inflammatory process within the walls of respiratory bronchioles that leads to the formation of granulation tissue, which plugs small airways.
-This results in dyspnea and functional airways obstruction.
-This disorder may be idiopathic or secondary to viral infection, toxic fume inhalation, drug reaction, collagen vascular disorders, organ transplantation, or chronic aspiration.
-Lung, heart-lung, and bone marrow transplant patients are particularly prone to constrictive bronchiolitis.
-Constrictive bronchiolitis in the adult may be the result of an early childhood lower respiratory infection with adenovirus, in which case it is known as unilateral hyperlucent lung or Swyer-James syndrome.
What is Swyer-James syndrome?
What does it look like on imaging (including nucs)?
-Constrictive bronchiolitis in the adult may be the result of an early childhood lower respiratory infection with adenovirus, in which case it is known as unilateral hyperlucent lung or Swyer-James syndrome.
-In Swyer-James syndrome, the bronchiolitis causes diffuse small airways obliteration, air trapping, and destruction of alveolar walls and emphysema owing to overdistention of peripheral airspaces.
-Because postinfectious bronchiolitis obliterans affects the lungs asymmetrically and usually occurs during a period of lung growth and development, the affected lung is typically small and hyperlucent and the ipsilateral pulmonary artery is hypoplastic.
-Most patients with the Swyer-James syndrome are asymptomatic, while some patients complain of dyspnea or recurrent lower respiratory tract infections.
-In patients with Swyer-James syndrome, the affected lung is normal or small in volume, and marked unilateral air trapping is seen on fluoroscopy or expiratory films.
-The air trapping is caused by bronchiolar obstruction with collateral air drift to the distal airspaces on inspiration that cannot escape on expiration.
-The ipsilateral hilum is small and the pulmonary vasculature is reduced, accounting for the hyperlucency seen radiographically and on CT
-Perfusion lung scanning shows decreased perfusion of the affected lung, while the ventilation study shows decreased ventilation with markedly delayed radioisotope washout.
-This latter finding helps distinguish the Swyer-James syndrome from primary central pulmonary artery occlusion or hypoplastic lung, conditions in which ventilation is maintained.
What does bronchiolitis look like on HRCT?
Why does it have this appearance?
-The direct sign of small airways disease is centrilobular opacities, which represent diseased preterminal bronchioles.
-This is seen on HRCT as sharply defined or ground-glass nodules or Y- or V-shaped tubular branching opacities centrally situated within the secondary pulmonary lobule within 1 cm of the pleural surface
-Pathologically, the opacities reflect dilatation and mucus plugging of small bronchioles or peribronchiolar inflammation and fibrosis.
-The indirect signs of small airways disease result from expiratory air trapping and are most easily seen on HRCT.
-Those portions of lung most severely affected by small airways disease are poorly ventilated and perfused and appear relatively hyperlucent adjacent to areas of normal lung.
-This results in an appearance on HRCT, termed “mosaic attenuation,” that is virtually indistinguishable from the changes seen in primary pulmonary arterial occlusive disease.
-The presence of small airways disease is confirmed on expiratory HRCT by noting air trapping within the hyperlucent regions
What's your differenital for mosaic attenuation?
How can you tell them apart?
-Air-trapping from bronchiolitis, either infectious (RSV, adenovirus) or inflammatory (RB-ILD)
-Primary pulmonary arterial occlusive disease.
-Infiltrative processes such as
Pneumocystis jiroveci pneumonia and desquamative interstitial pneumonitis, which
produce patchy ground-glass opacification, also result in a mosaic attenuation appearance on HRCT.

-The use of both inspiratory and expiratory HRCT scans helps distinguish between these various disorders.
-In a patient with mosaic attenuation, attenuated vessels within the lucent regions of lung indicates that the lucent regions are abnormal because of decreased perfusion.
-This finding allows distinction from ground-glass opacification, where the caliber of vessels in normal and abnormal lung are comparable.
-The presence of small airways disease is confirmed on expiratory HRCT by noting air trapping within the hyperlucent regions