From the Guidelines
The best method for detecting and localizing pheochromocytoma tumors is functional imaging with metaiodobenzylguanidine (MIBG) scintigraphy, particularly I-123 MIBG, combined with anatomical imaging such as CT or MRI. This dual approach provides both functional and structural information about the tumors. For initial diagnosis, plasma free metanephrines and normetanephrines blood tests are recommended as they have the highest sensitivity (over 95%) for biochemical confirmation before imaging 1. Once biochemically confirmed, CT or MRI of the abdomen and pelvis should be performed first to locate the primary tumor, as most pheochromocytomas (about 90%) occur in the adrenal glands. For extra-adrenal tumors or metastatic disease, I-123 MIBG is particularly valuable as it specifically targets catecholamine-producing cells. In cases where MIBG is negative or for suspected metastatic disease, newer PET imaging techniques using tracers like 68Ga-DOTATATE or 18F-FDG may provide superior detection 1. These imaging methods work because pheochromocytomas have specific receptors and metabolic properties that allow targeted visualization, enabling precise localization for surgical planning, which remains the definitive treatment for these tumors. Some key points to consider when using these imaging methods include:
- The use of CT or MRI to determine the presence of metastases in PPGLs, although these methods cannot determine whether PPGLs are benign or malignant 1.
- The importance of functional imaging modalities, such as MIBG scintigraphy and PET imaging, in determining the presence of metastases and evaluating the option of radionuclide-based therapy in patients with nonresectable PPGL 1.
- The need to avoid confusing metastases with multiple primary tumors that often occur in patients with hereditary PPGL syndromes, and to not misdiagnose local recurrences as metastases 1.
From the Research
Detection and Localization Methods
The detection and localization of tumors associated with Pheochromocytoma can be achieved through various methods, including:
- Positron emission tomography (PET) scanning with [11C]metahydroxyephedrine (mHED) and [18F]fluorodeoxyglucose (FDG) 2
- High-resolution computed tomography imaging 3
- Magnetic resonance imaging (MRI) 3
- Radiolabeled meta-iodobenzylguanidine (MIBG) or somatostatin scanning 3
- 6-[18F]fluorodopamine positron emission tomographic (PET) scanning 4, 5, 6
- Plasma-free metanephrine measurements coupled with vena caval sampling 6
Comparison of Methods
Studies have shown that PET scanning with mHED and FDG can detect all sites of confirmed disease, whereas MIBG failed to detect one or more sites of pathology-confirmed disease in some patients 2. 6-[18F]fluorodopamine PET scanning has also been shown to be effective in detecting and localizing pheochromocytomas with high sensitivity 4, 5. Computed tomography and MRI have good sensitivity but poor specificity for detecting pheochromocytoma 3, 5.
Clinical Applications
These detection and localization methods can be used in the evaluation of patients with suspected or confirmed recurrent or metastatic disease 3. The choice of method may depend on the specific clinical scenario and the availability of resources. For example, PET scanning with mHED and FDG may be useful in patients with suspected pheochromocytoma who have negative or equivocal results on conventional imaging modalities 2. 6-[18F]fluorodopamine PET scanning may be useful in patients with known disease who require localization of the tumor 4, 5.