Role of 18F-FDG PET/CT, 123I-MIBG SPECT,and CT in Restaging Patients Affected by Malignant Pheochromocytoma

Purpose

Pheochromocytoma (PH) is a rare catecholamine-secreting tumor that arises from chromaffin tissue within the adrenal medulla and extra-adrenal sites; commonly it is sporadic, and malignant PH accounts for about 10% of all cases. Several imaging modalities have been used for the diagnosis and staging of this tumor: functional imaging using radio-labelled metaiodobenzylguanidine and, more recently, ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET/CT), which offers substantial sensitivity and specificity to correctly detect metastatic PH and helps to identify patients suitable for treatment with radiopharmaceuticals. The aim of our study was to compare CT, ¹⁸F-FDG PET/CT, and ¹²³I-metaiodobenzylguanidine single photon emission tomography (¹²³I-MIBG SPECT) as feasible methods to restage patients diagnosed histologically with PH.

Methods

We retrospectively evaluated 38 patients (27 females and 11 males; mean age: 44 ± 15 years) with malignant PH documented histologically after surgical intervention. These patients underwent CT, ¹⁸F-FDG PET/CT, and ¹²³I-MIBG SPECT.

Results

¹⁸F-FDG PET/CT showed positive results for neoplastic tissue in 33/38 patients (86.8%) and negative in 5/38 (13.2%), in concordance with CT alone. ¹²³I-MIBG SPECT was positive in 30/38 patients (78,9%) and negative in 8/38 (21.1%). No differences in lesion numbers were found between ¹⁸F-FDG PET/CT and CT, whereas a difference could be demonstrated between ¹⁸F-FDG PET/CT and ¹²³I-MIBG SPECT.

Conclusion

¹⁸F-FDG PET/CT could more accurately restage patients with PH than CT and ¹²³I-MIBG SPECT, also in the absence of a staging study.