A comparative study of 131I-MIBG and 99mTc-octreotide in diagnosing pheochromocytoma

Purpose: To evaluate and compare the clinical value of 131I-MIBG and 99mTc-Octreotide in diagnosing pheochromocytoma. Methods: Both 131I-MIBG and 99mTc-Octreotide imagings were performed in 18 patients suspicious of pheochromocytoma using a SPECT/CT. Pathological results were obtained in 15 cases by operation or biopsy (12 pheochromocytomas, 2 metastatic paraganglionomas, and 1 adrenal lipoma). The remaining 3 cases of pheochromocytoma were not proved pathologically, but the diagnoses were supported by clinical signs, biochemical measurements and CT findings. All patients also underwent CT study. Results: In 7 cases both 99mTc-Octreotide and 131I-MIBG imagings were positive. 2 of them were ectopic pheochromocytomas located at para-abdominal aorta and had multiple lesions in which 99mTc-Octreotide detected more lesions than 131I-MIBG. 6 cases were positive in 99mTc-Octreotide imaging but negative in 131I-MIBG. Among them 4 had multiple lesions, and 2 were ectopic pheochromocytomas originated from or near the heart(One of the cases was shown in Fig 1). There were 3 cases with negative 99mTc-Octreotide but positive 131I-MIBG. Of the 2 cases with both 99mTc-Octreotide and 131I-MIBG negative findings, one was a pheochromocytoma with cystic change and the other was an adrenal lipoma. The detective rates of 99mTc-Octreotide and 131I-MIBG were 80.2% (13/17) and 64.7% (11/17) respectively. Conclusion: 99mTc-Octreotide is superior in 131I-MIBG in diagnosing pheochromocytoma especially with multiple lesions and ectopic in location, 131I-MIBG might be the first choice in case of normally located pheochromocytoma. However, a negative finding off 131I-MIBG cannot rule out the diagnosis of pheochromocytoma and a 99mTc-Octreotide study must be performed. (authors)