Discussion
Diagnosis With Brief Discussion
- Diagnosis
- Pulmonary tuberculosis showing the galaxy sign
- Radiologic Findings
- Fig 1. Chest radiograph shows disseminated tiny nodules and multifocal patchy confluent opacities without zonal predominance in both lungs.
Figs 2-5. Axial and coronal chest computed tomography images with lung window setting show multiple disseminated irregular centrilobular nodules and irregular patchy consolidations composed of coalescent tiny irregular nodules in both lungs, sparing the subpleural areas.
- Brief Review
- The galaxy sign represents a mass-like lesion, composed of innumerable coalescent granulomatous nodules, more concentrated in the center than at the periphery. It was initially described in patients with sarcoidosis and was referred to as the 'sarcoid galaxy' sign. It is now known to be present in other entities such as tuberculosis, lung cancer, and progressive massive fibrosis in pneumoconiosis.
Although tuberculous and sarcoid clusters of small nodules themselves appear indistinguishable on CT, some features might be helpful for differentiating them. First, a single cluster of small nodules is far more common in patients with tuberculosis than in those with sarcoidosis. Second, sarcoid clusters of small nodules are usually seen in the upper and middle lobes with almost the same frequency and are rare in the lower lobes, whereas most tuberculous clusters are in the upper lobes and the superior segments of the lower lobes in the same frequency, reflecting the typical distribution of post-primary pulmonary tuberculosis. Thus, clusters of small nodules in the middle lobe favor the diagnosis of sarcoidosis, and those in the lower lobe favor the diagnosis of tuberculosis. Finally, lymphadenopathy is common in patients with sarcoid clusters but is rare in patients with tuberculous clusters. Tree-in-bud lesions, one of the characteristic features of tuberculosis, should suggest the diagnosis of tuberculosis.
- References
- 1. Nakatsu M, Hatabu H, Morikawa K, et al. Large coalescent parenchymal nodules in pulmonary sarcoidosis:“sarcoid galaxy” sign. AJR 2002;178:1389–1393.
2. Heo JN, Choi YW, Jeon SC, et al. Pulmonary Tuberculosis: Another Disease Showing Clusters of Small Nodules. AJR 2005;184:639–642.
- Keywords
- Lung, Pulmonary tuberculosis, Galaxy sign,