Endocrine studies yield results highly suspicious of a neuroendocrine tumor. Which of the following is the best next step in management of this patient?
- A. Beta-blocking agent [11 %]
- B. Chromogranin A measurement [3%]
- C. Metaiodobenzylguanidine scan [12%] .,
- D. MRI of the abdomen [64%]
- E. Removal of tumor [11 %]
Abdominal imaging is the next step for localizing a pheochromocytoma after biochemical confirmation of the tumor. Both CT and MRI are highly sensitive for localizing pheochromocytomas, which are usually located in the adrenal glands. Clinically active pheochromocytomas are typically >4-4.5 em in diame ter and have a high tissue density on CT scan (generally 40-50 Hounsfield units). Larger tumors are more likely to have central necrosis and calcification. MRI usually shows high intensity on T2-weighted images.
Patients with negative abdominal imaging usually require further testing such as the me taiodobenzylguanidine (MIBG) scan, which is a functional scintigraphy with I’" labeled MIBG (Choice C). MIBG resembles norepinephrine, is taken up by adrenergic tissue, and can detect tumors not detected by CT or MRI. In addition, MIBG is also performed in patients with large tumors (>5 em diame ter) as they have a higher risk of malignancy and possible extra-adrenal disease. Younger patients and those with a familial disorder also require MIBG after initial CT or MRI as they have a higher risk of extra-adrenal and multiple tumors.
(Choices A and E) Removal of the tumor is performed only after localization, adequate preoperative control of blood pressure for 10-14 days with an alpha blocker, and intravascular fluid volume repletion with liberal fluid and salt. Intraoperative complications are much higher with inadequate preoperative alpha blockade and intravascular fluid deficiency. Beta blockers are given only to patients with adequate and complete alpha blockade. Beta-blocking agents started before alpha blockade can lead to paradoxical increase in blood pressure.
(Choice B) Chromogranin A (CGA) is stored and released from dense-core secretory granules of neuroendocrine cells and is elevated in nearly 80% of patients with pheochromocytoma. However, elevated CGA levels are not specific for pheochromocytoma and can be elevated in other neuroendocrine tumors (eg, carcinoid) or in patients with mild renal insufficiency. CGA is some times used in addition to measuring catecholamine and me tanephrine levels in patients with possible drug interference to biochemical testing.
Educational objective: Abdominal imaging (CT or MRI) is the next step for localizing a pheochromocytoma after biochemical confirmation of the tumor. Patients with negative abdominal imaging usually require further testing, such as the metaiodobenzylguanidine scan. Removal of the tumor is performed only after adequate preoperative control of blood pressure for 10-14 days with an alpha blocker, and intravascular fluid volume repletion with liberal fluid and salt. Beta blockers are given only to patients with adequate and comple te alpha blockade.