IS BIOCHEMICAL ASSESSMENT OF PHEOCHROMOCYTOMA NECESSARY IN ADRENAL INCIDENTALOMAS WITH MAGNETIC RESONANCE IMAGING FEATURES NOT SUGGESTIVE OF PHEOCHROMOCYTOMA?

Objective: Currently, it is unclear whether pheochromocytomas can be ruled out based on low intensity on T2-weighted sequences and signal loss on out-of-phase magnetic resonance imaging (MRI) sequences. Hence, in this study, we investigated whether biochemical screening for pheochromocytoma in patients with adrenal incidentalomas (AIs) showing MRI features not suggesting pheochromocytoma would prove beneficial.

Methods: We performed MRI for 300 AIs in 278 consecutive patients. All patients were screened for pheochromocytoma with plasma metanephrine and normetanephrine. Patients with high plasma levels of metanephrine and/or normetanephrine were also assessed for pheochromocytoma by urinary metanephrines.

Results: Hyperintensity was detected on T2-weighted MRI sequences in 28 (9.3%) of the 300 AIs. Among these 28 incidentalomas, pheochromocytoma was diagnosed in 13 (46.4%) of the cases by histopathologic analysis. Hyperintensity on T2-weighted MRI was significantly higher in pheochromocytomas compared to the remaining AIs (P<.001). All 13 pheochromocytomas were characterized by hyperintensity on T2-weighted sequences and the absence of signal loss on out-of-phase MRI sequences. Pheochromocytoma was not detected in any of the 272 AIs that appeared hypointense or isointense on T2-weighted MRI sequences or in the 250 cases with signal loss on out-of-phase sequences.

Conclusion: The results of this study suggest that AIs that appear hypointense or isointense on T2-weighted MRI sequences and those with signal loss on out-of-phase sequences may not require routine biochemical screening for pheochromocytoma. Further studies including a higher number of pheochromocytomas are required to confirm our results.