CTICasesSarcoidosis (Lower Lobe Predominant / "Upside-Down" Sarcoidosis)
Imaging findings
Chest radiograph shows bilateral hilar and mediastinal lymphadenopathy (donut sign). Initial chest CT confirms symmetric adenopathy and reveals clusters of perilymphatic nodules and septal thickening predominantly in the lower lobes. A follow-up scan without treatment shows spontaneous regression of the lymph nodes and resolution of the septal thickening, rendering the classic perilymphatic nodules more discrete.
Key takeaways
While sarcoidosis classically involves the mid-to-upper lung zones, atypical distributions such as a lower-lobe predominant ("upside-down") pattern can occur. Recognizing the classic symmetric hilar/mediastinal adenopathy and the strictly perilymphatic distribution of the nodules, along with spontaneous regression, helps confirm the diagnosis.
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