The galaxy sign represents coalescing granulomatous inflammation in sarcoidosis. Large nodules with surrounding micronodules are characteristic – even pathognomonic – of sarcoidosis.
Two patients with sarcoidosis demonstrating the galaxy sign:
“Large Coalescent Parenchymal Nodules in Pulmonary Sarcoidosis: “Sarcoid Galaxy” Sign.” Am J Roentgenol 2002.
Black Hole Sign
Patients with angioinvasive fungal pneumonia caused by Mucormycosis develop necrotizing infarction of the lung parenchyma. This portion of the parenchyma will be completely non-enhancing at MRI and appear as a ‘black hole.’
“Pulmonary Mucormycosis: Radiologic Features at Presentation and Over Time” Am J Roentgenol 2018.