What are the CT findings in hyperaldosteronism?

CT Findings in Hyperaldosteronism

CT imaging in primary aldosteronism typically shows either a unilateral adrenal adenoma (usually 1-4.75 cm), bilateral adrenal hyperplasia with enlarged adrenal glands (mean limb width >3-5 mm), or normal-appearing adrenal glands, but CT alone cannot reliably determine functional activity and should be combined with adrenal venous sampling (AVS) before surgical decisions 1.

Key CT Findings by Subtype

Aldosterone-Producing Adenoma (APA)

• Unilateral adrenal mass ranging from 1 to 4.75 cm in diameter 2
• Most commonly detected when >1.0 cm in patients <35 years with marked hyperaldosteronism and hypokalemia 1
• CT demonstrates the adenoma clearly in approximately 75% of cases (12/16 patients in one series) 3
• Sensitivity: 85-87% and specificity: 82-93% for detecting APA 2

Bilateral Adrenal Hyperplasia (BAH)

• Significantly enlarged adrenal glands compared to normal controls 4
• Mean adrenal limb width >3 mm achieves 100% sensitivity for BAH diagnosis 4
• Mean adrenal limb width ≥5 mm achieves 100% specificity for BAH diagnosis 4
• May appear as bilateral adrenal enlargement or even normal-appearing glands 3
• Can present with bilateral nodules (micro- or macronodular hyperplasia) 5

Critical Limitations of CT Alone

CT cannot determine functional activity of adrenal tissue, which is the fundamental limitation 1. This creates several diagnostic pitfalls:

• Nonfunctional incidentalomas can mimic APAs, leading to unnecessary surgery 1, 5
• In patients with solitary adrenal nodules on CT, up to 25% (3/12 patients) actually had idiopathic hyperaldosteronism rather than APA 5
• Bilateral nodules don't exclude unilateral disease—some patients with bilateral CT abnormalities have unilateral aldosterone production 5
• Normal-appearing adrenal glands on CT don't exclude PA 3

Advanced CT Techniques

Dual-energy CT with iodine concentration measurements shows promise as a complementary tool 6:

• Iodine concentration difference (ICD) in arteriovenous phase: dominant lesions show 1.18 ± 0.45 vs 0.41 ± 0.42 in non-dominant lesions
• Using ICD threshold of 0.68: sensitivity 88.2%, specificity 82.4% for identifying dominant lesions
• May serve as adjunct to AVS, though not yet standard practice

Clinical Algorithm for Imaging Approach

The 2025 Endocrine Society guideline recommends CT plus AVS before surgery, with one exception 1:

1. Perform CT in all confirmed PA patients considering surgical treatment
2. Proceed directly to surgery without AVS only if: Patient <35 years old AND marked PA with hypokalemia AND unilateral adenoma >1.0 cm on CT
3. All other patients require AVS before surgical decisions, regardless of CT findings
4. CT-based management alone results in lower biochemical cure rates post-surgery (OR: 0.266; 95% CI: 0.103-0.690) 1

CT vs MRI Performance

Both modalities show comparable diagnostic performance 2:

• CT and MRI have similar sensitivity (83-92%) and specificity (82-93%)
• Good interobserver agreement on both (κ=0.71 for CT, κ=0.67 for MRI)
• Choice between modalities can be based on local availability and expertise

Common Pitfalls to Avoid

• Never rely on CT findings alone to determine lateralization for surgical planning (except in the specific scenario above) 1, 5
• Don't assume bilateral nodules mean bilateral disease—AVS may reveal unilateral production 5
• Don't dismiss PA if CT is normal—microadenomas and hyperplasia may not be visible 3
• Measure adrenal limb width systematically when evaluating for BAH—visual assessment alone may miss subtle enlargement 4