CTICasesPulmonary Sarcoidosis
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Imaging findings
Chest radiography demonstrates bilateral mass-like hilar and perihilar opacities. Chest CT reveals cluster-like, micronodular parenchymal consolidations demonstrating the reversed halo sign with nodules along the rim (the "black hole" or "galaxy" sign), accompanied by mosaic attenuation reflecting air trapping and modest mediastinal lymphadenopathy.
Key takeaways
The "reversed halo" or "atoll" sign in the lung is most classically associated with organizing pneumonia, but when the rim of the halo consists of distinct micronodules, the differential diagnosis strongly favors granulomatous diseases such as sarcoidosis or tuberculosis. Mosaic attenuation in sarcoidosis is a common manifestation of small airway involvement leading to air trapping.
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