Delusive Nature of Flip-Flop Sign Secondary to Histoplasmosis.

Histoplasmosis, caused by Histoplasma capsulatum, often mimics the appearance of lung cancer on fludeoxyglucose (FDG) positron emission tomography (PET) scans. The "flip-flop fungus," due to its similar presentation on imaging modalities, can lead to false-positive results and unnecessary invasive testing. We present a 46-year-old male patient with a lung nodule and bilateral hilar lymphadenopathy on an FDG-PET scan who initially presented with chest discomfort. Histoplasma infection was confirmed through Grocott's methenamine silver (GMS) stains on bronchoscopy-guided biopsy specimens. An analysis of additional cases from the literature highlighted the diverse clinical presentations and outcomes associated with this condition that may be mistaken for other pathology on PET scans, which in this scenario is known as the "flip-flop fungus" sign. Despite the rarity of this condition, the accurate interpretation of PET findings greatly improves patient management strategies and avoids unnecessary invasive testing.