Adrenal Washout Calculator

Adrenal washout analysis uses computed tomography attenuation measurements to help characterize an adrenal mass that is not definitively lipid-rich on an unenhanced scan. Attenuation is measured in Hounsfield units, abbreviated HU, using a consistent region of interest in the lesion on pre-contrast, contrast-enhanced, and delayed images. Some adrenal adenomas take up contrast and then lose it more rapidly than many non-adenomas. Washout percentages quantify that change, but they do not independently establish a diagnosis. Absolute percentage washout equals enhanced attenuation minus delayed attenuation, divided by enhanced attenuation minus pre-contrast attenuation, multiplied by one hundred. Relative percentage washout equals enhanced attenuation minus delayed attenuation, divided by enhanced attenuation, multiplied by one hundred. Absolute washout requires all three phases, while relative washout can be used when a true pre-contrast acquisition is unavailable. This calculator displays both whenever all values are entered. Commonly cited thresholds are absolute washout of at least sixty percent or relative washout of at least forty percent on an appropriately timed delayed protocol. Meeting either threshold may support an adenoma interpretation. Timing matters: many classic references use a delayed acquisition around fifteen minutes, while other protocols use ten minutes and may apply different performance expectations. Scanner technique, reconstruction, contrast timing, lesion size, noise, and region placement can all change a result. Thresholds are not perfectly specific or sensitive. Some pheochromocytomas, metastases, and other lesions can overlap with adenoma washout, and some adenomas do not meet the thresholds. Hemorrhage, necrosis, calcification, heterogeneity, and very small lesions can make measurements unreliable. Unenhanced attenuation, lesion morphology, size and growth, chemical-shift MRI, functional imaging, cancer history, symptoms, and biochemical testing may be more important in a particular case. A pre-contrast value of ten HU or lower in a homogeneous lesion may already indicate a lipid-rich adenoma without washout analysis under many guidelines. Measurements should be taken by trained imaging professionals from corresponding solid portions of the lesion while avoiding edges, necrosis, vessels, and artifacts. The enhanced denominator must be meaningful; if enhancement is absent or values are equal, the formula is unstable and the calculator reports an error. Negative or unusually high percentages should trigger a review of phase labels and measurements rather than automatic classification. This tool reproduces standard arithmetic for education and quality checking. It cannot see the images or determine whether the CT protocol is valid. Final characterization and follow-up decisions belong to a radiologist and the treating clinical team, using current local guidelines and the patient's complete context.