Adrenal incidentaloma and subclinical Cushing's syndrome: a longitudinal follow-up by endoscopic ultrasound (EUS)

Introduction: Adrenal incidentaloma (AI) is one of the most frequent tumors of the human body. Moreover, it can be associated with endocrine alterations (e.g. subclinical Cushing's syndrome (SCS)). In recent years, follow-up of AI was a controversially discussed topic. The aim of this retrospective study was to evaluate the growth rate of AI and SCS as it can be determined by EUS as a method for high resolution imaging.

Methods: This analysis consisted of 93 out of 229 patients with AI or SCS who were investigated longitudinally by EUS in our institution during the last 16 years. The longitudinal follow-up required at least two investigations by EUS and the evaluation of the endocrine function. Therefore, measurements of plasma cortisol, 24h urinary cortisol, plasma renin, serum aldosterone, 24h urinary catecholamines and 2 mg dexamethasone suppression test were made. Based on these tests the study population was divided into two groups: non-functioning masses (NFM) (adenoma and nodular hyperplasia) and SCS.

Results: 86 patients had non-functioning masses (59 adenomas, 48 nodular hyperplasias) and 7 patients had SCS. At baseline the mean diameter was 19,1 (± 8,9)mm (NFM) and 22,1 (± 11,2)mm (SCS). The mean follow-up period was 26,9 (± 24,2) months. The estimated mean growth rates per year were low: The rate of NFM was 0,27 mm/yr and in cases of SCS 0,15 mm/yr. A progression from SCS to an overt Cushing's syndrome could be observed in one case. Furthermore, there was no malignant progression of any mass.

Conclusion: Growth rate as determined by EUS was low for both tumor entities observed in this study. There was no difference in tumor growth between both groups. It remains to be determined in which cases and when follow-up assessment can be stopped, and in which cases longer observation periods seem to be mandatory.