Extra‐adrenal and metastatic pheochromocytoma: The role of131I meta‐iodobenzylguanidine (131I MIBG) in localization and management

From June, 1980, to August, 1983,131I MIBG scintiscans were performed in 353 patients with suspected pheochromocytomas. Extra‐adrenal pheochromocytomas were identified in 15 of 18 patients who at operation were proven to have such tumors and normal adrenal glands. Conventional localization studies, often repeated, had failed to localize these tumors in nearly all cases. Nine of the extraadrenal pheochromocytomas were found within the middle mediastinum. This group of unique tumors required further specialized localization studies with augmented computed tomography (CT) scans for specific anatomical delineation. These complementary studies allowed for precise planning of surgical excision of the tumors, which required cardiopulmonary bypass in some patients. Extraadrenal pheochromocytomas were identified in a family with no other endocrinopathies. The tumors in 3 patients from 3 different generations all were perirenal and involved the vena cava. 131I MIBG scintiscans detected metastatic lesions in 40 patients with malignant pheochromocytomas. Metastases were not readily demonstrated in 4 patients. The diagnosis of malignant and metastatic pheochromocytoma was first made by the scintiscan findings in 5 patients.131I MIBG scans were not false‐positive in any cases and were falsenegative in 10.5% of 95 patients proven to have pheochromocytomas by biochemical evidence or operation. Ten patients have been treated for malignant pheochromocytomas with therapeutic doses of131I MIBG. Five patients have had objective responses with diminution in size of metastases or primary malignant tumor and a decrease in the secretion of catecholamines. This agent has been found to be of great value in detecting pheochromocytomas that often have defied all other means of localization.131I MIBG concentrates in most malignant pheochromocytomas, and preliminary results suggest that it will be very useful in the treatment of this disease.