Fig. 18.13 Miliary sarcoidosis in a 47-year-old man. (a, b) Lung window images of thin-section (1.5-mm section thickness) CT scans obtained at levels of right upper lobar bronchus (a) and inferior pulmonary veins (b), respectively, show randomly distributed innumerable small nodules in both lungs. Also note diffuse ground-glass opacity in background lungs. (c) Coronal reformatted image (2.0- mm section thickness) demonstrates randomly distributed small

nodules and ground-glass opacity in both lungs. (d) Lowmagnification photomicrograph of surgical biopsy specimen obtained from the right upper lobe discloses small, noncaseating, and uniform granulomas having random (subpleural [arrows], along bronchovascular bundles [open arrows], and in alveolar walls [arrowheads]) distribution

Miliary Tuberculosis

Pathology and Pathogenesis

When many bacilli enter the circulation simultaneously with subsequent massive hematogenous dissemination, generalized miliary TB develops. Many are filtered out in the pulmonary capillaries to give origin to a preponderance of the miliary tubercles in the lungs. Histologically, a multinucleate giant cell commonly forms the center and is enclosed by a

zone of epithelioid macrophages and an outer shell of lymphocytes [57] (Fig. 18.14).

Symptoms and Signs

Acute miliary TB has a severe and rapidly progressive course, usually after acute infection in young adults. Nonreactive TB develops slowly in older adults with disease reactivation. The most common symptoms of military TB are nonspecific.

Fig. 18.14 Miliary tuberculosis manifesting as acute lung injury in a 27-year-old man who is complaining of dyspnea. (a–c) Lung window images of thin-section (1.5-mm section thickness) CT scans obtained at levels of main bronchi (a), right bronchus intermedius (b), and cardiac ventricle (arrows) (c), respectively, show randomly distributed innumerable small nodules with background diffuse ground-glass opacity in both lungs.

Also note interlobular septal thickening (arrows) and consolidative lesions in dependent portion of the lower lung zones. (d) High-magnification (×100) photomicrograph of transbronchial lung biopsy specimen obtained from the right upper lobe discloses multiple granulomas located along bronchiole (arrows) and in alveolar walls (arrowheads)

Constitutional symptoms including fever, anorexia, weight loss, and night sweats are common. Cough and dyspnea are present more than two-third of patients [58]. Fulminant disease including ARDS and septic shock has been described. Hepatomegaly and splenomegaly are frequently found.

CT Findings

The most common characteristic TSCT finding of miliary TB is innumerable miliary nodules, variable in size from 1 to 3 mm in diameter [59, 60] (Fig. 18.14). The size and profusion of nodules are not significantly different in the upper, middle, lower lung zones, and the nodules have diffuse random distribution in the horizontal plane and within the secondary pulmonary lobule as well. GGO is the second most common finding of miliary TB [54] and reticular pattern of diffuse intralobular lines and interlobular septal thickening has also been frequently

described in miliary TB [59] (Fig. 18.14). The extent is variable and the distribution is random. Other findings include large nodules, necrotic lymph node, and pleural effusion.

CT–Pathology Comparisons

Each focus of miliary infection results in local granulomas that, when well developed, consist of a relatively welldelimited rim of epithelioid histiocytes and fibrous tissue [60] (Fig. 18.13). They appear as both sharply and poorly defined nodules on TSCT. The diversity of the margins presumably reflects the presence of some degree of active inflammation within the center of lobules secondarily affecting adjacent airspaces and thus resulting in poorly marginated nodules. Areas of GGO represent small granulomas resulting in minimal thickening of the alveolar walls and septal interstitium or partly filled alveolar lumen with fluid,

Fig. 18.15 Miliary metastases in a 60-year-old woman who has lung adenocarcinoma. (a, b) Lung window images of CT (2.5-mm section thickness) scans obtained at levels of right upper lobar bronchus (a) and basal trunk (b), respectively, show a primary lung cancer (open arrows) in the left upper lobe and randomly distributed innumerable small nodules in both lungs. Also note diffuse ground-glass opacity in background lungs.

(c, d) High-magnification photomicrographs of surgical lung biopsy obtained from a different patient with lung military metastases discloses tumor nodules located along bronchovascular bundle (arrows in c) and along the pleura (arrows in d). (e) Six-month follow-up CT exhibits progressed disease with increased size of primary mass (open arrows) in the left upper lobe and increased size and number of metastatic nodules