February 21, 2010

Lipid Poor Adrenal Adenoma

  • Most adenomas can be characterized as lipid rich on precontrast scan, which will show attenuation value of less than 10 HU
  • Some adenomas are lipid poor, therefore demonstrate a higher attenuation value. This can be further characterized by performing an adrenal mass CT protocol
  • Adrenal mass CT consists of 1) precontrast, 2) portovenous phase postcontrast (60-70 sec) and 3) delayed phase (10-15 min)
  • Measurement of region of interests (ROI) over > half of the mass at different phases. Values are used to calculate absolute and relative percentage washout

Absolute Percentage Washout (APW) = 100 x (portovenous attenuation - delayed attenuation)/(delayed attenuation - precontrast attenuation)

Relative Percentage Washout (RPW) = 100 x (portovenous attenuation - delayed attenuation)/delayed attenuation

Adenomas typically show rapid washout
  • APW > 60% OR
  • RPW > 40%

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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