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Clinical use and utility of metaiodobenzylguanidine scintigraphy in pheochromocytoma diagnosis.

OBJECTIVE
To examine the indications for metaiodobenzylguanidine (MIBG) scintigraphy and to assess its performance in localizing pheochromocytoma in the post-computed tomography and magnetic resonance imaging era.


METHODS
In this retrospective study, electronic and paper medical records of patients who underwent MIBG scintigraphy at a large academic hospital in Los Angeles, California, between January 1995 and July 2009 were reviewed for indications for MIBG scintigraphy, clinical history, biochemical test results, findings from imaging studies, and pathologic diagnoses. MIBG score was defined as follows: 3 (or intensive uptake) meant MIBG uptake of adrenal gland or other locus was higher than that of the liver; 2 (or moderate uptake) meant uptake was similar to that of the liver; 1 (or borderline uptake) meant uptake was lower than that of liver; and 0 (or negative uptake) meant background signal.


RESULTS
Ninety-eight patients underwent MIBG scintigraphy during the study period; the indication was suspected pheochromocytoma in 75 cases. Pheochromocytoma diagnosis was excluded in 48 and confirmed in 15. The remaining 12 patients had insufficient information in the medical records to render a diagnosis. Among the 63 patients, 47 received 131I-MIBG and 16 received 123I-MIBG. Sensitivity was 73% and specificity was 69% if any adrenal uptake was considered positive, but increased to 90% if borderline uptake was considered negative. False results were more common in younger patients, but not correlated with biochemical test results. In patients with pheochromocytoma either excluded or confirmed, the MIBG scintigraphy results were confirmatory in 63%, but misleading in 37%. MIBG scintigraphy results did not provide additional diagnostic value to any case and contributed to pheochromocytoma overdiagnosis and even unnecessary adrenalectomy.


CONCLUSIONS
MIBG scintigraphy results are either confirmatory or misleading, and this imaging modality is not necessary for most patients in modern practice.