🩺 Adrenal Incidentaloma Workup Simulator

Incidental Discovery of an Adrenal Mass

Found by chance on a scan ordered for something else entirely.

• ~5%: Incidence on abdominal CT (rises with age)
• ~10-15%: Bilateral masses (of incidentalomas)
• >80%: Most are benign (nonfunctioning adenomas)
• 50-70: Peak detection age (years old)

What counts as an incidentaloma

A mass ≥1cm found on imaging not aimed at the adrenal gland.

Why prevalence is rising

Wider CT/MRI use for unrelated complaints detects more incidental masses.

Every incidentaloma needs a structured workup, even if it looks harmless.

Initial framing questions

Is it benign or malignant? Is it hormonally active? Does size matter?

CT Density (Hounsfield Unit) Assessment

Unenhanced CT attenuation separates lipid-rich benign lesions from denser ones.

• <10 HU: Benign cutoff (lipid-rich adenoma)
• 10-20 HU: Indeterminate zone (needs further imaging)
• >20 HU: Concerning threshold (malignancy possible)
• ~71%: Adenoma sensitivity (at <10 HU cutoff)

Reading the Hounsfield scale

Fat reads dark, dense tissue reads bright on unenhanced CT.

Low-HU adenomas

Lipid-rich content gives low attenuation and reassures benignity.

Below 10 HU is a strong, validated marker of a benign adenoma.

When density is ambiguous

Indeterminate or high HU prompts washout CT, MRI, or biopsy.

Hormonal Function Screening

Every incidentaloma is tested for hormone excess, no matter how it looks.

• ~5-30%: Autonomous cortisol (of incidentalomas)
• ~5%: Pheochromocytoma (catecholamine excess)
• ~1-2%: Aldosteronoma (Conn) (if hypertensive)
• 1mg DST: Screening test (dexamethasone suppression)

Cortisol excess screening

Overnight dexamethasone suppression test flags autonomous secretion.

Catecholamine excess

Plasma or urine metanephrines rule out pheochromocytoma before biopsy.

Never biopsy an adrenal mass before excluding pheochromocytoma.

Aldosterone excess

Aldosterone-renin ratio is checked in hypertensive or hypokalemic patients.

Mass Size and Malignancy Risk

Bigger masses carry a meaningfully higher chance of malignancy.

• <4 cm: Low-risk size (lower malignancy odds)
• 4-6 cm: Intermediate (individualized decision)
• >6 cm: High-risk size (surgery favored)
• ~25%: ACC risk at >6cm (adrenocortical carcinoma)

Size as a risk multiplier

Larger diameter correlates with rising carcinoma probability.

Surgical threshold

Masses over 4cm are often favored for resection, especially with other risk features.

Size alone rarely decides — it is weighed with density and function.

Growth on follow-up

Interval growth on repeat imaging also raises surgical priority.

Combined Risk & Management Decision

Imaging, hormone status, and size together choose the care pathway.

• 6-12 mo: Surveillance imaging (low-risk masses)
• MRI/PET: Further workup (indeterminate cases)
• Adrenalectomy: Surgical referral (high-risk features)
• Annual: Repeat hormone testing (up to 5 years)

Low-risk pathway

Small, low-HU, nonfunctioning masses go to surveillance imaging.

Intermediate pathway

Indeterminate density or borderline size prompts further workup.

A single high-risk feature can override an otherwise reassuring picture.

High-risk pathway

Functioning tumors, large size, or high HU favor surgical removal.