An FDG-first functional imaging approach in phaeochromocytoma and paraganglioma

Functional imaging is central to the diagnosis and management of phaeochromocytomas and paragangliomas (PPGLs). This study aimed to compare the diagnostic performance of different functional imaging modalities for the detection of primary and metastatic PPGL.

We conducted a retrospective, cross-sectional comparative study at a tertiary referral centre (2012-2023). Seventy three patients were with diagnosed with PPGL; 38 who underwent triple functional imaging. These 38 patients underwent ¹⁸F-FDG PET CT/MRI (FDG), and ⁶⁸Ga-DOTATATE PET/CT (Dotatate), and ¹²³I-mIBG SPECT/CT (mIBG). Per-patient detection rates for primary and metastatic disease were compared and correlated with SUV_max, metanephrine profiles and germline mutations.

Among the 38 patients who underwent triple functional imaging, 18 (47%) were women, with a median age of 41 years (range 11-81). There were 23 phaeochromocytomas and 15 paragangliomas. Overall detection rates were positive in 36/38 (94.7%) patients on FDG, 35/38 (92.1%) on Dotatate, and 34/38 (89.5%) on mIBG. Among patients with metastatic disease, lesion detection was observed in 16/16 (100%) with FDG, 12/13 (92.3%) with Dotatate, and 11/13 (84.6%) with mIBG. FDG SUV_max correlated significantly with plasma 3-methoxytyramine levels (r = 0.56, p = 0.0034) but not with normetanephrine or metanephrine. FDG demonstrated 100% detection in patients with SDHB (6/6) and VHL (3/3) mutations.

In this study, FDG demonstrated the highest per-patient detection and the strongest association with aggressive biochemical and genetic phenotypes. These findings support an FDG-first functional imaging strategy for diagnosis and staging in PPGL, with additional targeted imaging reserved for theranostic decision-making.