[Limitations of scintigraphy using metaiodobenzylguanidine for locating pheochromocytomas. Apropos of 2 cases].
Two cases of MIBG (metaiodobenzylguanidine) scintigraphy are reported: the first case concerns a female patient hospitalized for high blood pressure (HBP) with symptoms evocative of pheochromocytoma. Urinary titration of catecholamines metabolites, which are usually abnormally high, and tomodensitometry permit the visualization of a left adrenal tumor. On the contrary, the MIBG scintigraphy does not show any abnormal fixation. After resection, the pathological examination confirms the diagnosis of pheochromocytoma. The second case concerns a female patient hospitalized for HBP with, on the chest X-Ray, a left postero-inferior density. Serum and urinary catecholamine levels are normal. Tomodensitometry confirms the tumor of the posterior mediastinum and the MIBG scintigraphy demonstrates a focus of thoracic opposite the tumor. After resection, the pathological examination shows an ectopic supernumerary bronchial bud. These two cases illustrate the limitations of MIBG scintigraphy to locate pheochromocytomas. There are false negative (10%) which may be explained by an insufficient uptake of the tracer by the tumor, by an insufficient image formation or by medication interferences. On the contrary, there may be false positives because of histochemical similarities between the chromaffin tissues and certain glandular or neural tumors. Nevertheless, in spite of serious limitations, which we must be aware of, MIBG scintigraphy remains the best primary examination for the location of pheochromocytomas.