Ground-Glass Opacity without Reticulation, with Small Nodules

Fig. 21.3 Subacute hypersensitivity pneumonitis in a 66-year-old woman. (a, b) Lung window images of thin-section (1.0-mm section thickness) CT scans obtained at levels of azygos arch (a) and distal bronchus intermedius (b), respectively, show the so-called head cheese sign with mixed inÞltrative (ground-glass opacity, arrows) and obstructive (mosaic attenuation, arrowheads) abnormalities. Ground-glass opacity is caused by lung inÞltration, whereas mosaic perfusion with decreased vessel sign is usually caused by small airway disease. (c)

High-magniÞcation (×100) photomicrograph of surgical biopsy specimen obtained from right upper lobe demonstrates bronchiolocentric granulomas (arrows) along with lymphocyte inÞltration (arrowheads) in peribronchiolar interstitium (alveolar walls). Ao arteriole, Br bronchiole. (d) High-magniÞcation photomicrograph (×200) discloses loosely formed granuloma (arrows) comprising epithelioid histiocytes and giant cells and surrounding lymphocyte cuff (arrowheads)

Ground-Glass Opacity without Reticulation, with Small Nodules

Definition

Ground-glass opacity (GGO) is caused by partial displacement of air in lung parenchyma. The opacity is caused by partial Þlling of airspaces, interstitial thickening (due to ßuid, cells, or Þbrosis), partial collapse of alveoli, or increased capillary blood volume. Without reticulation, the GGO areas usually represent active inßammatory or reversible disease state

(repetition see section ÒGround-Glass Opacity without Reticulation, Subpleural and Patchy DistributionÓ). In several diseases, the diffuse areas of GGO may contain small identiÞable poorly deÞned (GGO) nodules within the lesions or be associated with the nodules (Figs. 21.3, 21.4, and 21.5).

Diseases Causing the Pattern

Subacute hypersensitivity pneumonitis (HP) (Fig. 21.3), cytomegalovirus pneumonia (CMV pneumonia) (Fig. 21.4),

Fig. 21.4 Cytomegalovirus pneumonia in a 28-year-old man with acute myeloid leukemia. (a, b) Lung window images of thin-section (1.0-mm section thickness) CT scans obtained at levels of main bronchi (a) and basal trunk (b), respectively, show patchy areas of ground-glass opacity in both lungs associated with branching small nodular structures (tree-in-bud sign, arrowheads) and somewhat larger nodules

(arrows) of acinus size. (c) High-magniÞcation (×100) photomicrograph of surgical lung biopsy specimen obtained from left lower lobe demonstrates organizing pneumonia (arrows) pattern with viral inclusion in epithelial cells consistent with cytomegalovirus pneumonia. (d) High-magniÞcation (×200) photomicrograph discloses viral inclusion bodies (arrows) in epithelial cells

and diffuse alveolar hemorrhage (DAH) particularly associated with pulmonary vasculitis (Fig. 21.5) may exhibit diffuse or extensive areas of GGO containing small poorly formed nodular (mainly GGO nodules) lesions [16].

Distribution

The areas of GGO in subacute HP are usually extensive, bilateral, and symmetric [17]. In some patients, they are patchy or asymmetric. Also in cytomegalovirus pneumonia, the GGO lesions show diffuse or patchy distribution without zonal predominance [18, 19]. The lesions in DAH are diffuse in the upper and lower lobes in approximately 75 % of patients or are localized in the lower part of the lungs in 25 % of patients. In both the cases, the apices and costophrenic angles are usually spared [20].

Clinical Considerations

Bird fancierÕs lung and farmerÕs lung are the two most leading cause of hypersensitivity pneumonitis [21]. CMV pneumonia is a common life-threatening complication seen in immunocompromised patients. It occurs most commonly after bone marrow and solid organ transplantation and in patients with AIDS [19]. The clinical syndrome in DAH includes hemoptysis, anemia, diffuse radiologic pulmonary opacity, and hypoxemic respiratory failure. The most common underlying histology of DAH is of a small vessel vasculitis known as pulmonary capillaritis, usually seen with seropositive systemic vasculitis, or a connective tissue disorder (bland pulmonary hemorrhage), and diffuse alveolar damage due to a number of injuries including, drugs, coagulation disorders, and infection [22] .