1. What diagnostic tests are available for pheochromocytoma? Laboratory measurement of plasma and urine free catecholamines (CA) (including epinephrine, norepinephrine and dopamine) and their metabolites such as VMA is an important method for the traditional diagnosis of pheochromocytoma. The release of CA from tumors into the blood is “intermittent” and direct detection of CA is prone to false negatives. However, the metabolism of CA in tumor cells is continuous, and its intermediate products, metanephrines (MNs), are continuously released into the blood in the form of “leakage”, and plasma free MNs and urinaryfractionated metanephrines (MNs) are continuously released into the blood. MNs include methoxyprenaline (MN) and methoxynorepinephrine (NMN), which are released into the circulation in free form, mainly from pheochromocytoma/chromophobe tumor cells, and modified to sulfate-bound MNs by related enzymes in the GI tract, spleen, and pancreas, and can be synthesized in the GI tract itself. The 24-hour urine CA is still the main biochemical test for qualitative diagnosis, and a negative result with high clinical suspicion is recommended to be repeated several times and/or measured during hypertensive episodes. Plasma free MNs, including MN and NMN, are suitable for screening and monitoring in high-risk groups. A negative result almost effectively excludes pheochromocytoma/pheochromocytoma, with a false-negative rate of only 1,4%, and small asymptomatic tumors or those secreting only dopamine. It has been performed in only a few units in China and is recommended to be promoted. Besides, 24h urine fractionated MNs, 24h urine total MNs (MN+NMN), 24h urine VMA, and plasma CA detection can also be used for the diagnosis of pheochromocytoma. 2. How to make the local diagnosis of pheochromocytoma? Mainly CT and MRI, both of which have similar diagnostic sensitivity and specificity, and there is no evidence to show which one is better, either one can be chosen. Sensitivity for pheochromocytoma is better than for pheochromocytoma, metastases, and recurrent lesions, but the specificity for excluding pheochromocytoma is only about 50%. The recommended initial scan for CT/MRI is abdomen + pelvis, with the aim of detecting multiple adrenal and/or extra-adrenal lesions; if negative, scan the chest and head and neck. CT scan + enhancement is preferred, with the advantages of affordability, sensitivity and short scan time. Pheochromocytomas of 0.5 cm in the adrenal glands and 1.0 cm or more outside the adrenal glands can be detected. It is characterized by uneven density and significant enhancement within the tumor, which can fully reflect the morphological features of the tumor and its anatomical relationship with the surrounding tissues. The sensitivity of MR is similar to that of CT, with the advantage of no ionizing radiation and no risk of contrast allergy. Pheochromocytoma is often rich in blood supply and is characterized by low signal in T1WI, high signal in T2WI and no signal attenuation in the reverse sequence.