Successful treatment of pheochromocytoma requires accurate diagnosis and localization of tumors. Herein, we investigated the accuracy of PET using 3,4-dihydroxy-6-(18)F-fluoro-phenylalanine ((18)F-FDOPA), an amino acid transporter substrate, as an independent marker for detection of benign and malignant pheochromocytomas.
Methods: The study comprised 25 consecutive patients (9 men, 16 women) whose median age was 51 y (range, 25-68 y), with known or suspected pheochromocytoma. Eleven patients underwent standardized (18)F-FDOPA PET and 14 patients underwent (18)F-FDOPA PET/CT studies, with a median of 511 MBq of (18)F-FDOPA (range, 206-625 MBq). Two readers, unaware of the reports of other imaging studies and clinical data, analyzed all scans visually and quantitatively (maximum standardized uptake value [SUVmax] and maximum transverse diameter). Histology and long-term clinical follow-up served as the gold standard. Correlation between SUVmax of tumors and biochemical markers was evaluated. SUVmax of the benign and malignant tumors was compared.
Results: Seventeen patients underwent surgery. Histology confirmed pheochromocytoma or paraganglioma in 11 cases (8 adrenal, including 2 malignant tumors, and 3 extraadrenal, including 1 malignant tumor). The diagnosis of pheochromocytoma was established by follow-up in 2 additional patients (1 adrenal and 1 unknown location) and ruled out in 6 patients. Visual analysis detected and localized pheochromocytoma in 11 of 13 patients without false-positive results (sensitivity, 84.6%; specificity, 100%; accuracy, 92%). These lesions had an SUVmax of 2.3-34.9 (median, 8.3). Evaluation of the false-negative cases revealed a 13 x 5 mm lesion with an SUVmax of 1.96 in 1 case; no lesion was localized in the second case using multiple additional modalities. Spearman nonparametric analysis did not show statistically significant correlation between SUVmax of the tumors and biochemical markers. The Mann-Whitney nonparametric test did not demonstrate a statistically significant difference between the SUVmax of (18)F-FDOPA in malignant and benign tumors.
Conclusion: (18)F-FDOPA PET and PET/CT are highly sensitive and specific tools that can provide additional independent information for diagnosis and localization of benign and malignant pheochromocytomas.