What CT scans should be ordered for a patient with hypercortisolism?

CT Imaging for Hypercortisolism

Order CT chest, abdomen, and pelvis with IV contrast using an adrenal protocol to evaluate for adrenal tumors, metastases, and ectopic ACTH-producing tumors. 1

Initial Imaging Strategy Based on ACTH Levels

The CT imaging approach depends critically on whether the hypercortisolism is ACTH-dependent or ACTH-independent:

For ACTH-Independent Hypercortisolism (Low/Undetectable ACTH)

CT abdomen with adrenal protocol is the primary imaging study needed. 1 This indicates a primary adrenal source requiring focused adrenal imaging.

• Use an adrenal protocol CT that includes unenhanced imaging to measure Hounsfield units (HU), followed by contrast-enhanced imaging with 15-minute delayed washout imaging 1
• Unenhanced CT with HU >10 suggests possible malignancy and requires enhanced CT with washout assessment 1
• Enhancement washout >60% at 15 minutes indicates a benign lesion 1
• Extend imaging to chest and pelvis if the adrenal mass appears malignant (>5 cm, inhomogeneous, irregular margins, or local invasion) to evaluate for metastases 1

For ACTH-Dependent Hypercortisolism (Elevated ACTH)

CT chest, abdomen, and pelvis is required to locate ectopic ACTH-producing tumors. 1

• Elevated ACTH indicates the excess cortisol is not from the adrenal gland itself 1
• Ectopic tumors commonly occur in the lung, thyroid, pancreas, or bowel 1
• MRI of the pituitary with high-resolution protocol should be obtained first to exclude pituitary adenoma (Cushing's disease), as this is the most common cause of ACTH-dependent hypercortisolism 1
• If pituitary MRI is negative or equivocal, proceed with CT chest/abdomen/pelvis for ectopic sources 1

Critical Technical Specifications

The adrenal protocol CT must include specific technical elements: 1

• Thin-section imaging (1-3 mm slices) through the adrenal glands
• Unenhanced phase to measure attenuation in Hounsfield units
• Contrast-enhanced phase with IV contrast
• Delayed washout imaging at 15 minutes post-contrast
• Multiplanar reconstructions to assess size, heterogeneity, and margin characteristics 1

Features Suggesting Malignancy on CT

Watch for these high-risk imaging characteristics that warrant expanded imaging: 1

• Tumor size >5 cm (adrenal carcinoma should be strongly suspected in tumors >4 cm) 1
• Inhomogeneous appearance with irregular margins 1
• HU >10 on unenhanced CT 1
• Enhancement washout <60% at 15 minutes 1
• Evidence of local invasion 1
• Adjacent lymphadenopathy or liver metastases 1

Common Pitfalls to Avoid

• Never skip the unenhanced phase of adrenal CT, as HU measurement is critical for distinguishing benign from malignant lesions 1
• Do not rely on contrast-enhanced CT alone if the patient presents initially with enhanced imaging; obtain dedicated unenhanced and delayed washout imaging 1
• Do not order CT without measuring ACTH first, as this determines whether you need focused adrenal imaging versus whole-body imaging for ectopic sources 1
• Ensure pheochromocytoma is excluded biochemically before any CT with contrast, as undiagnosed pheochromocytoma can cause hypertensive crisis with IV contrast 2

When MRI is Preferred Over CT

MRI with chemical-shift imaging is more sensitive and specific than CT for differentiating benign from malignant adrenal tumors because benign adenomas contain fat while malignant tumors typically do not. 1 MRI also better demonstrates local invasion and inferior vena cava involvement. 1 However, CT remains the initial imaging modality in most cases due to availability and cost considerations.