Iodine 131 metaiodobenzylguanidine scintigraphy of medullary carcinoma of the thyroid.

We have presented a case of sporadic medullary carcinoma of the thyroid with documentation of localization of tracer 131I-MIBG within the primary neoplasm. A review of the nuclear medicine literature of localization techniques for MCT demonstrates that 131I-MIBG, while an excellent choice for diagnosis of pheochromocytoma and neuroblastoma, produces low yield and unpredictable concentration in other neural crest apudomas, including MCT. A low incidence of true-positive results with 131I-MIBG uptake and a high incidence of false-negative results make this radiopharmaceutical a suboptimal choice for diagnostic studies, but a potentially promising one as a therapeutic agent.