Emphysema centrilobular

Parenchymal changes affect the gas-exchanging units of the lungs (alveoli and pulmonary capillaries). Smoking-related disease most commonly results in centrilobular emphysema that primarily affects respiratory bronchioles. Panlobular emphysema is seen in AAT deficiency and extends to the alveolar ducts and sacs. 

Morphologically, emphysema is associated with a destruction of the alveolar septum, which results in a dilation and consequent enlargement of the alveolar spaces (Fig. 19). This is apparently caused by a breakdown of the interstitial connective tissue proteins (primarily elastin) that provide the major structural framework of the lung parenchyma. Two types of emphysema have been defined on the basis of the types of destruction of the alveolar septa observed and the type of dilation of the terminal respiratory unit (the acini) that is observed. A typical acinus branches from a terminal bronchiole and consists of the respiratory bronchioles that have alveolated walls and lead to the alveolar ducts and ultimately to the alveolar sacs (see Fig. 3). In centrilobular (or centriacinar) emphysema, the sites of degradation and dilation are limited to the region of the terminal and respiratory bronchioles. In panlobular (or panacinar) emphysema, the entire acinus (including the alveolar ducts and sacs) is more uniformly affected. 

Fig. 26.8. RB-ILD in a 44-year-old female cigarette smoker. Coronal CT image shows scattered, poorly defined centrilobular nodules that are predominantly located in the upper lung lobes. Note mild coexisting centrilobular emphysema (arrows)...

Fig. 26.9. RB-ILD. Axial CT image shows centrilobular nodules (thin black arrow), patchy ground-glass opacities (arrowheads), and mild bronchial wall thickening (white arrow). Note discrete paraseptal emphysema (thick black arrow)...

HRCT often discloses a complex admixture of lesions, termed rheumatoid lung. Bronchiectasis is present in 8% to 75% of patients, but the distinction between primary bronchiectasis and traction bronchiectasis due to pulmonary fibrosis is often difficult (139,140,149,151,152,155,166,177). Bronchiolitis is also frequent, manifesting as centrilobular nodules, tree-in-bud sign, mosaic perfusion, or air trapping (139,149,151,152,155,166,177). Emphysema is present in 5% to 43% of patients (13,139,140,149,151,152,155,166,174,177) and is widely viewed as a trait of RA-ILD, unlike findings in other CTDs. Emphysema is more frequent with an HRCT pattern of UIP, as opposed to NSIP (155). Other features include pulmonary rheumatoid nodules and pleural effusion or thickening can be observed. Pulmonary artery enlargement has been observed in nearly half of patients with RA-ILD, in spite of the fact that overt PH is rare in RA (155). 

Fig.3.1.8a-c. Thin-section computed tomography images from the upper (b) and lower (c) lobes of a 67-year-old male smoker with asbestos exposme demonstrate centrilobular emphysema in the upper lobes and thickened septal lines in the subpleural region on the left (arrows). The extent of emphysema and interstitial change is not readily apparent on the chest radiograph (a). An area of rounded atelectasis with a typical comet s tail appearance is seen within the right lower lobe (arrowhead)... 

There is some evidence that coal-dust exposure causes centrilobular emphysema, based on postmortem lung sections, there being a relationship between emphysema score and lung-dust burden (Cockcroft et al. 1982). The relationship is easier to demonstrate when dust-related fibrosis is present (Ruckley et al. 1984). The relationship between emphysema score and lung-dust burden is stronger in non-smokers than smokers (Leigh et al. 1994). 

Fig. 4.1. Mixed thin-section computed tomography patterns in an adult smoker. There is generalised ground-glass opacification in both lungs (taken to represent a component of respiratory bronchiolitis). In addition, there are signs of fibrosis a fine superimposed reticular pattern is seen, and there is evidence of traction bronchiectasis thin arrows) in the right lung. There is also centrilobular emphysema, of limited extent, in the right lung thick arrow)...

Fig. 4.2. Centrilobular emphysema on thin-section computed tomography. There is characteristic symmetrical and permeative lung destruction...

On individual CT images, the appearances of pulmonary LCH may be mistaken for those of bronchiectasis. However, review of adjacent sections will generally confirm the cystic nature of lesions in LCH. Another problem in diagnosis is the differentiation on CT between emphysema and LCH. True cysts, in contrast to the low attenuation lesions of centrilobular emphysema, generally have a definable wall (Austin et al. 1996) however, when the lesions of emphysema extend to the periphery of the secondary pulmonary lobule, the distinction can become difficult (Fig. 4.5). Multiple intrapulmonary cysts are also a feature in... 

Fig. 4.5. Thin-section computed tomography through the upper zones in a patient with severe centrilobular emphysema. Many of the low attenuation lesions of emphysema appear to have a well-defined wall, and the appearances may be mistaken for those seen in end-stage Langerhans cell histiocytosis...

Foster WL Jr, Pratt PC, Roggli VL, Godwin JD, Halvorsen RA Jr, Putman CE (1986) Centrilobular emphysema CT-patho-logic correlation. Radiology 159 27-32 Fraig M, Shreesha U, Savici D, Katzenstein AL (2002) Respiratory bronchiolitis a clinicopathologic study in current... 

Fig.5.10a,b. A 68-year-old retired construction site worker, a Thin-section CT scan through the upper lobes shows bilateral progressive massive fibrosis (PMF) with surrounding paracicatricial emphysema, b Thin-section CT scan through the lower lobes shows confluent centrilobular emphysema (asterisks) in the right lower lobes and bullae in the left lower lobe (arrows)... 

Fig.6.9a,b. Coal worker s pneumoconiosis computed tomography scan showing with more severe micronodular lung, subpleural and peribronchovascular involvement, a, b Axial views with slice thickness of 1 mm. Multiple micronodules are seen in both lungs. The distribution of the micronodules is diffuse, and, except for the left upper lobe (b), where micronodules can be seen in the interlobular septa (black arrows) and centrilobular, the relationship between the micronodules and the secondary pulmonary lobule is difficult to appreciate. Notice also the peribronchovascular (white arrowheads) and the subpleural micronodules, as well as focal emphysema surrounding some of the micronodules (white arrows)... 

Thin-section CT delineates the changes of the thorax in kaolinosis more than chest radiography. Small nodules distributed mainly in centrilobular regions. The appearance of large opacity resembles that of complicated coal workers pneumoconiosis or complicated silicosis (Fig. 12.10c). Peripheral emphysema typically occurs with such masses. Unlike with silicosis, hilar and mediastinal lymph node enlargement more than 1 cm in diameter is not usually seen. 

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