January 21, 2010

Adrenal Mass Characterization

Fig 1: Precontrast axial CT image shows a 3-cm left adrenal mass with an attenuation of 1.3 HU, indicating a lipid-rich adenoma.
Fig. 2: Precontrast axial CT image of a different patient shows a right adrenal mass with an attenuation of 20.8 HU, which is indeterminate. Note that the region of interest (ROI) measurement should cover at least half the size of the mass.

  • Lipid-rich adenomas contain intracellular fat (microscopic level) that can be shown on CT as low attenuation
  • Adenomas wash out contrast more rapidly than malignant masses
  • Extension into IVC suggests malignancy, particularly adrenocortical carcinoma

Adrenal Mass: Adenoma Vs. Others
  1. Size: can not be definitively used to distinguish benign from malignant adrenal masses. In general, patients without known malignancy and a mass greater than 5 cm, surgical resection is advised
  2. Precontrast attenuation: less than 10 HU (sensitivity 70%, specificity 98%)
  3. Postcontrast (venous phase) attenuation: at 60-70 second delay after contrast injection, absolute enhancement of a mass of > 110-120 HU likely pheochromocytoma
  4. Delayed postcontrast attenuation: used to calculate absolute and relative percentage washout. Absolute Percentage Washout (APW) >60% or Relative Percentage Washout (RPW) >40% suggests an adenoma.
Our cases: Both cases are adrenal adenomas, the first is a lipid-rich adenoma and the second is a lipid-poor adenoma (confirmed with dynamic scans, not shown).


Johnson PT, Horton KM, Fishman EK. Adrenal imaging with multidetector CT: evidence-based protocol optimization and interpretative practice. RadioGraphics 2009;29:1319-1331.

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