Fig. 16.4 Pulmonary lymphangitic carcinomatosis in a 35-year-old woman with poorly differentiated tubular adenocarcinoma of the stomach. (a–c) Lung window images of thin-section (2.5-mm section thickness) CT scans obtained at levels of right upper (a) and middle (b) lobar bronchi and basal segmental bronchi (c), respectively, show smooth and nodular (arrows)

thickening of interlobular septa. Also note thickening of axial interstitium (open arrows). (d) High-magnification photomicrograph (×200) of transbronchial lung biopsy specimen obtained from a different patient discloses tumor cells (arrows) packing lymphatics in interstitium which causes smooth or nodular thickening of interlobular septum on CT scan

Pulmonary Lymphangitic Carcinomatosis

Pathology and Pathogenesis

PLC is a condition of metastatic carcinoma involving the lung, primarily within lymphatics. The tumor type is most often adenocarcinoma. Variable amounts of tumor may be present throughout the lung, involving the interstitium of the alveolar walls, the air spaces themselves, and the lumens of small muscular pulmonary arteries [4, 15] (Fig. 16.4).

Symptoms and Signs

Because of the large degree of reserve in pulmonary function, patients may present with minimal or no respiratory symptoms. Nonspecific symptoms of cough, dyspnea, or chest pain can result from extensive lymphatic infiltration. Severe dyspnea with hypoxemia can be found as the disease progresses.

Fig. 16.5 Pulmonary lymphangitic carcinomatosis in a 52-year-old woman with breast cancer who underwent left mastectomy. Lung window image of thin-section (1.0-mm section thickness) CT obtained at level of right inferior pulmonary vein shows nodular and band-like interlobular septal thickening (arrows), particularly in the right lung. Also note axial interstitial thickening (open arrows) of the right lung as compared with the left lung. Right major fissural effusion (arrowheads) is noticed

Fig. 16.6 Nodular septal thickening in a 53-year-old man with pulmonary sarcoidosis. (a–c) Lung window images of thin-section (1.5-mm section thickness) CT scans obtained at levels of the main bronchi (a), liver dome (b), and suprahepatic inferior vena cava (c), respectively, show nodular (arrows) thickening of interlobular septa and interlobular fissure, axial interstitial thickening (open arrows), and patchy areas of

ground-glass opacity (arrowheads) in both lungs. (d) Highmagnification (×100) photomicrograph of surgical lung biopsy obtained from a different patient discloses noncaseating granulomas located in interlobular septum (arrows), alveolar walls (open arrows), and subpleural interstitium (arrowhead). Granulomas in interlobular septum constitute nodular interlobular septum on CT scan

CT Findings

The characteristic HRCT findings of PLC consist of smooth or nodular thickening of the interlobular septa and peribronchovascular interstitium with preservation of normal lung architecture [4, 15] (Figs. 16.4 and 16.5). Tumor spread in the pleural interstitial tissue lead to smooth or nodular thickening of the interlobular fissures (Fig. 16.5). The abnormalities may be initially subtle, but tend to progress to extensive bilateral disease associated with areas of ground-glass

opacity (Figs. 16.4 and 16.5). Pleural effusion and hilar or mediastinal lymph node enlargement are seen in 30–40 % of patients (Fig. 16.5).

CT-Pathology Comparisons

Thickening of the interlobular septa and the peribronchovascular interstitium on CT is pathologically related to tumor cell infiltration, desmoplastic reaction, and edema