SDHB and extra-adrenal sympathetic paraganglioma: Currently, only three predictors of metastatic potential in patients with pheochromocytomas and sympathetic paragangliomas are well recognized: primary tumor location (adrenal pheochromocytomas vs. extra-adrenal sympathetic paragangliomas), primary tumor size, and germline mutations of the SDHB (succinate dehydrogenase complex, subunit B, iron sulfur) gene.