Definition of the Galleria Sign
The "galaxy sign" is a radiological finding on high-resolution computed tomography (HRCT) characterized by an irregularly marginated pulmonary nodule formed by the confluence of multiple small nodules, and it is a diagnostic feature of pulmonary sarcoidosis. 1, 2
Detailed Radiological Characteristics
The galaxy sign appears as:
- An irregularly marginated nodular opacity that results from multiple smaller nodules coalescing together 1
- A pattern that resembles a galaxy with a central mass surrounded by satellite lesions 2
- A finding best visualized on thoracic HRCT imaging 1
Diagnostic Significance
The galaxy sign has high specificity for pulmonary sarcoidosis:
- It was present in 23.1% of patients with biopsy-proven pulmonary sarcoidosis compared to only 1.9% of patients with pulmonary tuberculosis (p<0.001) 1
- This makes it a useful discriminating feature when sarcoidosis is in the differential diagnosis 1
Clinical Associations
When the galaxy sign is present in sarcoidosis patients, it correlates with specific clinical features:
- Younger patient age (median 32 years vs. 62 years in those without the sign) 1
- Lower CD4/CD8 ratio in bronchoalveolar lavage fluid (median 2.6 vs. 5.8) 1
- No correlation with disease severity, suggesting it is a morphological pattern rather than a prognostic indicator 1
Important Distinction
Do not confuse the "galaxy sign" with the "Galleria mellonella" infection model, which is an entirely unrelated term referring to a laboratory research tool using wax moth larvae to study bacterial virulence 3. The galaxy sign is purely a thoracic imaging finding.