The predictive value of diagnostic tests for pheochromocytoma.

BACKGROUND: Ascertaining or excluding a pheochromocytoma may be difficult. The purpose of this study is to identify preoperative tests that are good predictors of a pheochromocytoma.
METHODS: Patients presumptively diagnosed with a pheochromocytoma based on clinical assessment, plasma or urinary catecholamines, computed tomography, or magnetic resonance imaging were analyzed. The sensitivity, specificity, positive, and negative predictive values were determined for each test based on the pathologic finding of a pheochromocytoma. Data were analyzed with Student's t test or Fisher's exact test.
RESULTS: Of 14 patients, seven had pathologically proven pheochromocytomas, whereas three had cortical adenomas. In four patients, a pheochromocytoma was excluded by repeat testing. The 24-hour urinary mean metanephrine levels were significantly different between patients with and without pheochromocytomas (5.8 micrograms vs 0.5 micrograms, p = 0.05) and had the best positive predictive value (83%) and negative predictive value (100%) of the biochemical tests. T2-weighted magnetic resonance imaging had a 100% positive and negative predictive value. Age, sex, symptoms, blood pressure, tumor location, tumor size, and plasma catecholamine levels could not accurately predict or exclude a pheochromocytoma.
CONCLUSIONS: T2-weighted magnetic resonance imaging is the imaging study of choice for predicting a pheochromocytoma. The 24-hour urinary metanephrine level is the single best biochemical indicator of a pheochromocytoma. Plasma catecholamine levels and computed tomography are not helpful in diagnosing or excluding a pheochromocytoma.