[¹¹C]Metahydroxyephedrine and [¹⁸F]fluorodeoxyglucose positron emission tomography improve clinical decision making in suspected pheochromocytoma

Background: Pheochromocytomas are rare tumors of chromaffin cells for which the optimal management is surgical resection. Precise diagnosis and localization may be elusive. We evaluated whether positron emission tomography (PET) scanning with the combination of [¹⁸F]fluorodeoxyglucose (FDG) and the norepinephrine analogue [¹¹C]metahydroxyephedrine (mHED) would allow more exact diagnosis and localization. Methods: Fourteen patients with suspected pheochromocytoma were evaluated by anatomical imaging (computed tomography or magnetic resonance imaging) and [¹³¹I] metaiodobenzylguanidine (MIBG) planar imaging. PET imaging was performed by using mHED with dynamic adrenal imaging, followed by a torso survey and FDG with a torso survey. Images were evaluated qualitatively by an experienced observer. Results: Eight patients had pathology-confirmed pheochromocytoma. Of the other six, two patients had normal adrenal tissue at adrenalectomy, and the other four had subsequent clinical courses inconsistent with a diagnosis of pheochromocytoma. In four of eight patients with pheochromocytoma, MIBG failed to detect one or more sites of pathology-confirmed disease. The mHED-PET detected all sites of confirmed disease, whereas FDG-PET detected all sites of adrenal and abdominal disease, but not bone metastases, in one patient. MIBG and FDG-PET results were all negative in the six patients without pheochromocytoma. One patient with adrenal medullary hyperplasia had a positive mHED-PET scan. PET scanning aided the decision not to operate in three of six patients. The resolution of PET functional imaging was superior to that of MIBG. Conclusions: PET scanning for pheochromocytoma offers improved quality and resolution over current diagnostic approaches. PET may significantly influence the clinical management of patients with a suspicion of these tumors and warrants further investigation.