The sympathetic nervous system is derived from sympathetic germ cells in the primitive neural crest of the ectoderm. During 5-6 weeks of gestation, part of the sympathetic germ cells migrate from the thorax to form the sympathetic chain and other ganglia: the other part migrates to the middle of the adrenal cortex to form the adrenal medulla. The sympathetic germ cells may develop into chromophores and sympathetic neuroblasts; both mature to form chromaffin cells and sympathetic ganglion cells, respectively. Pheochromocytomas are most common in the adrenal medulla, while neuroblastomas, ganglion neuroblastomas, and ganglion neuromas are less common. The latter three are most often found in sympathetic ganglia and pheochromocytomas outside the adrenal glands. Pheochromocytomas originate in the adrenal medulla, sympathetic ganglia, parasympathetic ganglia, or other areas of the pheochromocytoma tissue. It causes hypertension and other signs and symptoms due to the secretion of high amounts of catecholamines such as adrenaline and/or norepinephrine (and sometimes dopamine). The incidence is 0.Ol to 0.001% in adults, accounting for 0.6% to 1% of hypertensive patients, 10% in children, 10% to 20% in malignant, mainly disseminated. 10% is familial, commonly multiple endocrine neoplasia (MEN) type II and III. The majority of cases are monogenic, and only 10% are multiple. The diagnosis of malignant pheochromocytoma is difficult to determine by histological criteria, but is based on local invasion of tissues and the development of non-phenoidal tissues such as lymph nodes, liver, and bone. Extra-adrenal pheochromocytomas may also be named as functional or nonfunctional paragangliomas, depending on whether they secrete catecholamines. Neuroblastoma is a highly malignant tumor of the sympathetic adrenal organs that can occur anywhere in the body, but is more common in the adrenal medulla. It is common in children and most often presents with symptoms before the age of 6 years. This tumor metastasizes early, with approximately 70% having liver, brain, bone marrow, lymph node and bone metastases at the time of diagnosis. Although neuroblastoma cells cannot efficiently synthesize catecholamines, norepinephrine, and epinephrine, they can synthesize the precursor dopamine and excrete its metabolites; therefore, a catecholamine uptake mechanism exists in most neuroblastomas. Sympathoblastoma and ganglioneuroma are tumors that originate from the neural crest and are more completely differentiated. They are mostly found in the posterior thoracic septum next to the thoracic vertebrae and in children and adolescents, and are less likely to metastasize. MIBG (meta-iodobenzylguanidine) has been found to have a similar absorption and storage mechanism with norepinephrine, and has a high affinity with adrenergic tumors. Therefore, 131I-MIBG is not only used for the imaging diagnosis of such tumors, but also for the effective treatment of certain lesions with high uptake by applying high doses of 131I-MIBG.