Dual-tracer 18F-FDG and 18F-AlF-NOTA-octreotide PET/CT imaging in oncocytic thyroid adenoma: a case report and literature review

Introduction oncocytic thyroid adenoma (OA), a rare benign neoplasm, poses diagnostic challenges in conventional imaging modalities. The study investigates the diagnostic utility of dual-tracer 18 F-fluorodeoxyglucose ( 18 F-FDG) and 18 F-AlF-NOTA-octreotide ( 18 F-OC) positron emission tomography/computed tomography (PET/CT) in characterizing OA. Methods We present a histopathologically confirmed OA case evaluated through simultaneous 18 F-FDG and 18 F-OC PET/CT imaging. Quantitative analysis included maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), and metabolic tumor volume (MTV). A systematic literature review was conducted to contextualize the imaging findings within existing evidence. Results A 44-year-old female presenting with ACTH-independent Cushing syndrome (morning cortisol 632.8 nmol/L, non-suppressed on dexamethasone suppression tests) underwent comprehensive endocrine evaluation. Incidentally detected thyroid nodule demonstrated discordant tracer uptake: 18 F-FDG PET/CT revealed intense hypermetabolism (SUVmax=31.68; SUVmean=9.18; MTV=4.33 cm 3 ), while 18 F-OC PET/CT showed moderate uptake (SUVmax=6.86; SUVmean=4.41; MTV=1.72 cm 3 ). Histopathology confirmed OA with negative SSTR2 expression. Postoperative cortisol levels remained elevated. After nearly two years of clinical follow-up with conservative management using symptomatic medication, she underwent pituitary lesion resection, which confirmed a pituitary adenoma/pituitary neuroendocrine tumor (PitNET) consistent with a densely granulated corticotroph tumor. Conclusion This case demonstrates the complementary diagnostic value of dual-tracer PET/CT in OA characterization, particularly in SSTR2-negative variants. The discordant uptake patterns suggest distinct metabolic pathways in OA pathophysiology. Prospective multicenter studies with larger cohorts are warranted to establish standardized diagnostic criteria and explore theranostic applications of these imaging biomarkers in OA.