Fig. 7.3 CT galaxy sign in a 53-year-old man with active pulmonary tuberculosis. (a, b) Lung window of thin-section (2.5-mm section thickness) CT scans obtained at levels of the aortic arch (a) and azygos arch (b), respectively, shows CT galaxy sign (arrows) in both upper lobes and superior segment of the left lower lobe

Key Points for Differential Diagnosis

1.The presence of single rather than multiple CT galaxy sign favors the diagnosis of pulmonary tuberculosis.

2.Zonal predominance is more prominent in tuberculous galaxy sign with speciÞc involvement of the upper lobes (upper zone) and the superior segments (middle lung zone) of the lower lobes.

3.In tuberculous galaxy sign, it is accompanied by tree-in-bud sign, whereas enlarged hilar or mediastinal lymph node enlargement is much more frequent in sarcoidosis [2].

CT galaxy sign on HRCT reßects a coalescence of multiple granulomas. Granulomas are much more concentrated toward the center of the cluster than in its periphery, and individual macroscopic granulomas can be identiÞed when granulomas are not so densely assembled [1] (Fig. 7.2).

Patient Prognosis

Cure rate for drug-sensitive tuberculosis is more than 95 % with the current standard four-drug treatment regimen of Þrstline drugs (isoniazid, rifampicin, pyrazinamide, and ethambutol) for 6 months [4]. Prolonged medication for at least 20 months with second-line drugs is necessary for multidrugresistant (MDR) tuberculosis. Extensively drug-resistant (XDR) tuberculosis is extremely difÞcult to treat. When the disease of MDR or XDR tuberculosis is localized, surgical resection of the lung lesion can be done with medical therapy.

Galaxy Sign in Pulmonary Tuberculosis

Pathology and Pathogenesis

The histologic reaction of tuberculosis is primarily granulomatous and necrotizing with cavitation; lesions may progress to Þbrosis and calciÞcation [3]. Coalescence of multiple granulomas may form galaxy sign (clustered tuberculous granulomas) (Figs. 7.2 and 7.3).

References

1.Nakatsu M, Hatabu H, Morikawa K, et al. Large coalescent parenchymal nodules in pulmonary sarcoidosis: Òsarcoid galaxyÓ sign. AJR Am J Roentgenol. 2002;178:1389Ð93.

2.Heo JN, Choi YW, Jeon SC, Park CK. Pulmonary tuberculosis: another disease showing clusters of small nodules. AJR Am J Roentgenol. 2005;184:639Ð42.

3.Leung AN. Pulmonary tuberculosis: the essentials. Radiology. 1999;210:307Ð22.

4.Zumla A, Raviglione M, Hafner R, von Reyn CF. Tuberculosis. N Engl J Med. 2013;368:745Ð55.