spicuous or absent. Alveolar spaces often contain mucin. When stromal invasion is seen, the malignant cells may show less cytoplasmic mucin and more atypia. These tumors differ from mucinous adenocarcinoma in situ and minimally invasive adenocarcinoma by one or more of the following criteria: size (>3 cm in diameter), amount of invasion (>0.5 cm in thickness), multiple nodules, or lack of a circumscribed border with military spread into adjacent lung parenchyma. There is a strong tendency for multicentric, multilobar, and bilateral lung involvement, which may reßect aerogenous spread [23].

Symptoms and Signs

Most patients are asymptomatic. Cough and exertional dyspnea are the most common respiratory symptoms when it progresses diffusely to bilateral lung. Due to abundant mucin production of the cancer cells, patients with invasive mucinous adenocarcinoma can complain of copious amount of sputum, so-called bronchorrhea. Constitutional symptoms including anorexia, weight loss, and malaise may be present.

CT Findings

Diffuse nonmucinous or mucinous adenocarcinoma or AIS may be seen as three predominant patterns: GGO (4 of 38, 10 %) (Fig. 20.9), consolidation (22 of 38, 58 %), and multiple nodules (12 of 38, 32 %) [24]. When reticular attenuation is superimposed on GGO lesions, the tumor may manifest crazy-paving pattern.

CT–Pathology Comparisons

The GGO reßects the low-density intra-alveolar material (glycoprotein), whereas the superimposed reticular attenuation is due to inÞltration of the interstitium by inßammatory or tumor cells [24, 25].

Patient Prognosis

The overall prognosis for patients with invasive mucinous adenocarcinoma is worse than for those with the nonmucinous adenocarcinoma. Invasive mucinous adenocarcinoma has a strong tendency for multifocal, multilobar, and bilateral lung involvement, which may reßect aerogenous spread. Even if surgically resected in the localized stage, it frequently recurs in the remaining lung.

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Ground-Glass Opacity without Reticulation, Subpleural

and Patchy Distribution

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) (Figs. 21.1 and 21.2), partial collapse of alveoli, and increased capillary blood volume. Without reticulation, the GGO areas usually represent active inßammatory or reversible disease state.

Diseases Causing the Pattern

Cellular nonspecific interstitial pneumonia (NSIP) (Fig. 21.1), desquamative interstitial pneumonia (DIP) (Fig. 21.2), cryptogenic organizing pneumonia (COP), and eosinophilic pneumonia (allergic lung disease) depict GGO lesions without reticulation on thin-section CT (TSCT).

Distribution

The distribution of GGO lesions in cellular NSIP is subpleural, usually without obvious upperÐlower lung zone gradient (this gradient, overt in usual interstitial pneumonia with lower lung zone predominance) [1]. In DIP, the opacity had subpleural and lower lung zone predominance [1]. In twothirds of patients, the opacity lesions in COP are distributed along the bronchovascular bundles or subpleural lungs [2]. In chronic eosinophilic pneumonia, CT shows subpleural opacity with slight upper lung zone predominance [3].

Clinical Considerations

The presence of asthma history suggests the diagnosis of eosinophilic lung disease (approximately 40 % of patients with chronic eosinophilic lung disease have asthma) [3]. In drug-induced lung disease and lung involvements of collagen vascular diseases, lung abnormalities can be assessed with pattern approach, namely NSIP, DIP, COP, and eosinophilic lung disease-like patterns [4, 5].

Fig. 21.1 Cellular nonspeciÞc interstitial pneumonia manifesting as diffuse ground-glass opacity without reticulation in a 10-year-old girl. (a, b) Lung window images of CT scans (2.5-mm section thickness) obtained at levels of right upper lobar bronchus (a) and inferior pulmonary veins (b), respectively, show diffuse ground-glass opacity in both lungs. (c) Low-magniÞcation (×40) photomicrograph of surgical lung biopsy specimen obtained from right lower lobe demonstrates diffuse alveolar wall thickening with inßammatory cell inÞltration. Lesions are

temporally homogeneous and uniform in alveolar wall thickening. Areas of focal organizing pneumonia (arrows) are associated. (d) HighmagniÞcation (×200) photomicrograph discloses alveolar wall thickening with chronic inßammatory cell inÞltration and mild alveolar pneumocytes hyperplasia and many intra-alveolar macrophage aggregation. (e, f) Two-year follow-up CT scans obtained at similar levels to a and b, respectively, exhibit complete disappearance of ground-glass opacity in both lungs. Patient received corticosteroid therapy

Fig. 21.2 Desquamative interstitial pneumonia presenting as patchy areas of ground-glass opacity without reticulation in a 51-year-old smoker man. (a, b) Lung window images of CT scans (1.5-mm section thickness) obtained at levels of suprahepatic inferior vena cava (a) and liver dome (b), respectively, show patchy and extensive but subpleural areas of ground-glass opacity in both lungs. (c) Coronal reformatted CT image (2.0-mm section thickness) demonstrates subpleural patchy

areas of ground-glass opacity (arrows) in both lungs. Also note bullae in upper lung zones. (d) Low-magniÞcation (×40) photomicrograph of surgical lung biopsy specimen obtained from right lower lobe exhibits areas of uniform accumulation of inßammatory cells in intra-alveolar spaces and mildly in interstitium (alveolar walls) (arrows). (e) HighmagniÞcation (×200) photomicrograph discloses intra-alveolar macrophage accumulation and mild interstitial Þbrosis (arrowheads)