Functional Diagnosis of Hibernoma by FDG Imaging Under Propranolol Treatment: A Case Report

Positron Tomography/Computer Tomography (PET/CT) imaging of 18F-Fluorodeoxyglucose (18F-FDG) uptake is frequently used to recognize malignant nature of abnormal findings at anatomical investigations. However, several benign structures can mimic cancer glucose avidity. This case report pertains to a large mediastinal mass, incidentally detected on a coronary Computer Tomography (CT) study and showing heterogeneous signal hyperintensity in T1- weighted sequences at a subsequent Magnetic Resonance Imaging (MRI). CT-guided biopsy failed to provide adequate specimen; 18F-FDG PET/CT documented an extremely high glucose analogue consumption (maximum Standardized Uptake Value: 29). In order to exclude every alternative possibility before attempting a potentially hazardous surgery, we hypothesized the possible presence of a hibernoma. To test this hypothesis, we verified the influence of sympathetic innervation on lesion uptake, by repeating 18F-FDG imaging under beta-blockade: this scan documented the complete disappearance of the anomalous tracer uptake. A 6-months follow-up scan documented stable lesion volume and persistently absent 18F-FDG uptake under the beta-blockers, thus presumably excluding the malignant nature of the increased tracer uptake.