Functional Imaging of Paragangliomas with an Emphasis on Von Hippel-Lindau-Associated Disease: A Mini Review

Vesicular monoamine transporter (VMAT) regional expression and roles in pathological conditions

Vesicular monoamine transporters (VMATs) are key regulators of neurotransmitter release responsible for controlling numerous physiological, cognitive, emotional, and behavioral functions. They represent important therapeutic targets for numerous pathological conditions. There are two isoforms of VMAT transporter proteins that function as secondary active transporters into the vesicle for storage and release via exocytosis: VMAT1 (SLC18A1) and VMAT2 (SLC18A2) which differ in their function, quantity, and regional expression. VMAT2 has gained considerable interest as a therapeutic target and diagnostic marker. Inhibitors of VMAT2 have been used as an effective therapy for a range of pathological conditions. Additionally, the functionality and phenotypic classification of classical and nonclassical catecholaminergic neurons are identified by the presence of VMAT2 in catecholaminergic neurons. Dysregulation of VMAT2 is also implicated in many neuropsychiatric diseases. Despite the complex role of VMAT2, many aspects of its function remain unclear. Therefore, our aim is to expand our knowledge of the role of VMAT with a special focus on VMAT2 in different systems and cellular pathways which may potentially facilitate development of novel, more specific therapeutic targets. The current review provides a summary demonstrating the mechanism of action of VMAT, its functional role, and its contribution to disease progression and utilization as therapeutic targets.

The utility of 68Ga-DOTATATE PET/CT in localizing primary/metastatic pheochromocytoma and paraganglioma in children and adolescents - a single-center experience

OBJECTIVES

Pediatric pheochromocytoma and paraganglioma (PPGL) are rare tumors with limited data on the diagnostic performance of ⁶⁸Ga-DOTA(0)-Tyr(3)-octreotate positron emission tomography-computed tomography (⁶⁸Ga-DOTATATE PET/CT). We have described our experience of ⁶⁸Ga-DOTATATE PET/CT in overall and von Hippel Lindau (VHL)-associated pediatric PPGL and compared its sensitivity with that of ¹³¹I-meta-iodobenzyl-guanidine (¹³¹I-MIBG), ¹⁸F-fluorodeoxyglucose PET/CT (¹⁸F-FDG PET/CT), and contrast-enhanced CT (CECT).

METHODS

Retrospective evaluation of consecutive PPGL patients (age: ≤20 years), who had undergone at least one functional imaging [¹³¹I-MIBG, ¹⁸F-FDG PET/CT, and/or ⁶⁸Ga-DOTATATE PET/CT], was done. Composite of anatomical and all the performed functional imaging scans, image comparator (IC), was considered as the gold standard for sensitivity analysis.

RESULTS

In a cohort of 32 patients (16 males, age at diagnosis: 16.4 ± 2.68 years), lesion-wise sensitivity of ⁶⁸Ga-DOTATATE PET/CT (95%) was higher than that of both ¹⁸F-FDG-PET/CT (80%, p=0.027) and ¹³¹I-MIBG (65%, p=0.0004) for overall lesions, than that of ¹⁸F-FDG-PET/CT (100 vs. 67%, p=0.017) for primary PPG, and than that of ¹³¹I-MIBG (93 vs. 42%, p=0.0001) for metastases. In the VHL (n=14), subgroup, ⁶⁸Ga-DOTATATE PET/CT had higher lesion-wise sensitivity (100%) compared to ¹⁸F-FDG PET/CT (74%, p=0.045) and ¹³¹I-MIBG (64%, p=0.0145).

CONCLUSIONS

In our pediatric PPGL cohort, overall lesion-wise sensitivity of ⁶⁸Ga-DOTATATE PET/CT was higher than that of ¹⁸F-FDG PET/CT and ¹³¹I-MIBG scintigraphy. Hence, we recommend ⁶⁸Ga-DOTATATE PET/CT as the preferred modality in pediatric PPGL. ⁶⁸Ga-DOTATATE PET/CT may evolve as a preferred imaging modality for disease surveillance in VHL.