For a patient with a large pheochromocytoma, how would you evaluate for possible autonomous cortisol co-secretion prior to adrenalectomy to assess need for risk of glucocorticoid withdrawal postoperatively?

From a practical standpoint, and given that this is rare, it is reasonable to check a postoperative day 1 (POD1) AM cortisol and decide then whether cortisol replacement is needed.

You can also check ACTH, AM and PM cortisol to assess diurnal variation, and DHEAS pre-op to get some idea.