What percentage of adrenal incidentalomas exhibit mild autonomous cortisol secretion (MACS)?

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Last updated: October 14, 2026 • View editorial policy

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Percentage of MACS in Adrenal Incidentalomas

Among adrenal incidentalomas, MACS (mild autonomous cortisol secretion) represents the most common hormonal abnormality, occurring in approximately 19-30% of cases, with the most recent high-quality guideline data indicating that MACS is the predominant finding among the approximately 30% of functioning adenomas. 1

Evidence-Based Prevalence Data

The 2025 American College of Endocrinology guideline on adrenal mass imaging provides the most authoritative framework for understanding MACS prevalence 1:

  • 80-85% of adrenal incidentalomas are benign adrenocortical adenomas
  • Up to 70% of these adenomas are nonfunctioning
  • The remaining ~30% are functioning adenomas, among which:
    • MACS is the most common hormonal abnormality
    • Primary aldosteronism occurs less frequently
    • Overt Cushing syndrome is rare

Supporting Research Data

Recent high-quality research corroborates these guideline figures:

  • A 2025 Asian cohort study found MACS in 23.5% of all adrenal incidentalomas (the most common functional abnormality among 34.1% with any hormonal excess) 2

  • A 2026 comprehensive surgical review reported MACS prevalence of 5-30% among adrenal incidentalomas 3

  • A 2025 primary care study documented MACS in 23.33% of consecutive adrenal incidentaloma patients 4

  • A 2024 Nature Reviews Endocrinology article states MACS is diagnosed in 20-50% of patients with adrenal adenomas (not all incidentalomas) 5

Clinical Context and Interpretation

The wide range (5-30%) in reported MACS prevalence reflects differences in:

  • Patient selection criteria - whether subcentimeter nodules are included (16% of nodules <1 cm can be functional) 2
  • Diagnostic thresholds used - cutoffs for the 1-mg dexamethasone suppression test vary between studies
  • Population characteristics - age, comorbidities, and bilateral vs. unilateral involvement affect rates
  • Referral patterns - tertiary centers may see enriched populations

Key Clinical Implications

Every adrenal incidentaloma requires hormonal evaluation because MACS:

  • Is the most prevalent hormonal abnormality encountered 1, 2
  • Associates with increased cardiovascular morbidity, mortality, fragility fractures, and decreased quality of life 5
  • Can occur even in subcentimeter nodules 2
  • May progress to overt Cushing syndrome in <1% of cases 6

Important caveat: Up to 4% of patients with positive dexamethasone suppression tests may have inadequate dexamethasone bioavailability rather than true autonomous cortisol secretion 7, highlighting the importance of measuring serum dexamethasone levels when results are equivocal.

References

1
Guideline

imaging of adrenal masses.

Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologist, 2025

2
Research

Prevalence of Mild Autonomous Cortisol Secretion in Adrenal Incidentalomas and the Significance of Subcentimeter Adrenal Nodules: A Single-Center Cohort Study.

Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists, 2025

3
Research

Management Approach of Adrenal Incidentaloma.

Journal of laparoendoscopic & advanced surgical techniques. Part A, 2026

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.