What is the recommended initial imaging study for patients suspected of having adrenal insufficiency?

Recommended Initial Imaging for Adrenal Insufficiency

For patients suspected of having adrenal insufficiency, computed tomography (CT) of the adrenal glands is the recommended initial imaging study. Specifically, non-contrast CT should be performed first to evaluate adrenal gland morphology and detect potential causes of adrenal insufficiency 1.

Diagnostic Approach to Adrenal Insufficiency

Initial Laboratory Evaluation (Before Imaging)

• Morning serum cortisol and plasma ACTH measurements are the first-line diagnostic tests 1, 2
• Low cortisol (<5 μg/dL) with high ACTH indicates primary adrenal insufficiency
• Low cortisol with low/normal ACTH suggests secondary adrenal insufficiency
• In equivocal cases, ACTH stimulation test should be performed 1

Imaging Recommendations

1. Non-contrast CT of the adrenal glands is the initial imaging study of choice 1

   • Allows assessment of adrenal gland size, morphology, and density
   • Can detect calcifications (common in tuberculosis-related adrenal insufficiency)
   • Can identify adrenal atrophy (common in autoimmune adrenal insufficiency) 3
   • Can detect hemorrhage, infiltrative disease, or masses

2. When to proceed with additional imaging:

   • If non-contrast CT is indeterminate, proceed with contrast-enhanced CT with washout protocol 1
   • MRI may be considered as a second-line option, particularly in pregnant women or young patients 1

Imaging Findings in Different Etiologies of Adrenal Insufficiency

Autoimmune Adrenal Insufficiency

• Bilateral adrenal atrophy on CT 3
• Normal or small-sized adrenal glands

Infectious Causes (Tuberculosis, Fungal)

• Bilateral adrenal enlargement with central necrosis and peripheral enhancement 4
• Calcifications often present in chronic cases 4, 3

Hemorrhagic Adrenal Insufficiency

• High attenuation (50-90 HU) on non-contrast CT 4
• Decreasing attenuation on follow-up scans

Metastatic Disease

• Bilateral adrenal enlargement or masses
• Irregular margins and heterogeneous enhancement 1

Special Considerations

• In patients with suspected adrenal crisis, treatment should never be delayed for diagnostic procedures, including imaging 1
• If 21-hydroxylase antibodies are negative in primary adrenal insufficiency, CT imaging is specifically recommended to determine etiology 1
• In male patients with antibody-negative primary adrenal insufficiency, very long-chain fatty acids should be measured to check for adrenoleukodystrophy after CT imaging 1

Pitfalls to Avoid

• Do not delay treatment of suspected acute adrenal insufficiency for imaging studies 1
• Non-contrast CT may miss adrenal pathology that would be visible on contrast-enhanced studies
• Be aware that diffuse, non-metastatic enlargement of adrenal glands can occur in patients with malignant disease, which may not represent true adrenal insufficiency 5
• Avoid relying solely on imaging for diagnosis; laboratory confirmation is essential 1, 2

CT imaging of the adrenal glands provides valuable information about the etiology of adrenal insufficiency and helps guide further diagnostic and therapeutic decisions. The pattern of adrenal involvement on CT can often suggest the underlying cause of adrenal insufficiency, which is crucial for appropriate management.