Galaxy Sign

Definition

A large pulmonary nodule composed of multiple small nodules and surrounded by many very smaller satellite nodules is called a galaxy sign [1] (Fig. 7.1).

Diseases Causing the Sign

The nodule(s) with CT galaxy sign is (are) observed in patients with pulmonary sarcoidosis and active pulmonary tuberculosis [2] (Table 7.1) (Figs. 7.2 and 7.3).

Distribution

The CT galaxy sign in pulmonary sarcoidosis, as in the cases of other pulmonary sarcoidosis, is usually located in the upper and middle lung zones but can also be seen in the lower lung zones. In tuberculosis, the galaxy sign is noticed speciÞcally in the upper lobes or the superior segments of the lower lobes.

Clinical Considerations

Tuberculous galaxy sign indicates active disease, thus reversible to antituberculous chemotherapy [2]. Also the galaxy sign in sarcoidosis is reversible. According to a report of Heo and his colleagues, a single galaxy sign is far more frequent in patients with tuberculosis than in those with sarcoidosis [2].

a

b

Fig. 7.1 CT galaxy sign in a 23-year-old man with pulmonary sarcoidosis. (a, b) Consecutive thin-section (2.5-mm section thickness) CT scans obtained at levels of the right upper lobar bronchi show multifocal areas of CT galaxy sign (arrows) that are comprised of multiple small nodules and surrounded by many very small satellite nodules, particularly in the right upper lobe. Mediastinal window images (not shown here) demonstrated enlarged lymph nodes in the mediastinum and hilum, bilaterally

Table 7.1 Common diseases manifesting as galaxy sign

a

c

b

d

Br

Fig. 7.2 CT galaxy sign in a 44-year-old man with active pulmonary tuberculosis. (a, b) Consecutive (5.0-mm section thickness, low-dose technique) CT scans obtained at level of the right bronchus intermedius show CT galaxy sign (arrows) in superior lingular segment of the left upper lobe. On these relatively thick-section CT images, caution should be given not to interpret this galaxy sign as ground-glass opacity lesion, thus invasive lung adenocarcinoma. (c) Gross pathology specimen

obtained from the left upper lobe with surgical lung biopsy demonstrates nodular aggregation (arrows) of small granulomas. (d) LowmagniÞcation (×4) photomicrograph discloses nodular aggregation of granulomas having central necrosis in the peribronchiolar interstitium. Granulomas are concentrated toward the center of nodular cluster (arrows) than in its periphery. Br bronchiole