Endocrine Abstracts

Introduction: Pheochromocytomas are characterized by a high attenuation value on unenhanced computed tomography (CT). It is not known whether pheochromocytoma can be outruled as a cause of adrenal incidentalomas based on unenhanced attenuation values only. We evaluated the outcome of routine biochemical screening for pheochromocytoma in a series of patients with adrenal incidentalomas in relationship to the unenhanced attenuation values on CT.

Design and methods: An unenhanced CT was available in 174 of 184 patients with altogether 214 adrenal incidentalomas. All patients were screened for pheochromocytoma with 24hr urinary metanephrines and normetanephrines and for hypercortisolism (1 mg DXM-test and ACTH). Patients with hypertension were screened for aldosterone overproduction (aldosterone/renin ratio and 24hr urinary aldosterone).

Results: One hundred and forty-six incidentalomas in 115 patients had an unenhanced attenuation value < 10 Hounsfield units (HU), but none of these patients had increased 24hr fractionated urinary metanephrines or normetanephrines indicating pheochromocytoma. Sixty-eight incidentalomas in 59 patients had an unenhanced attenuation value ≧10 HU and nine (15.2%) of these patients had surgi-cally and histologically verified pheochromocytoma. Incidentalomas with a HU ≧ 10 were characterized by significantly larger size (2.6±1.5 vs. 2.3±1.2 cm; P<0.001), were more often functional (27.9% vs. 8.9%, P<0.001) and more often operated (44.1% vs. 10.2%; P<0.001) than those with a HU < 10.

Conclusion: Pheochromocytoma was outruled as a cause of adrenal incidentaloma if the attenuation value on unenhanced CT was < 10 HU. The results challenge the need for routine biochemical screening of pheochromocytoma in adrenal incidentalomas discovered on unenhanced CT and characterized by a HU <10. However, if the incidentaloma is first discovered on contrast enhanced CT imaging, measurements of urinary or plasma fractionated metanephrines is mandatory in order to rapidly exclude the possibility of pheochromocytoma.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.