What studies are used to localize a pheochromocytoma?
Imaging studies are generally indicated only after biochemical screening is positive. Using a scan as a screening test increases the risk of discovering an “incidentaloma” (i.e., a nonfunctioning tumor).
CT scan or MRI of the abdomen is about 95% sensitive and 65% specific; the T2-weighted MRI has a higher specificity because chromaffin tumors usually “light up.” 123 I-metaiodobenzylguanidine (MIBG) scintigraphy is about 80% sensitive and 99% specific for chromaffin tissue; it is usually used for large (>10 cm) tumors or to evaluate extra-adrenal tumors.
When imaging studies are equivocal, somatostatin receptor imaging, positron emission scanning, or even selective venous sampling of the vena cava at various levels can help locate the tumor.
