Modified on: Thu, 16 Jun, 2022 at 3:08 PM
FAQ-162: Is washout on CEUS true washout?
Quantitative time-intensity curve measurements show that the appearance of washout on CEUS reflects true washout (1,2). On CT/MRI, the appearance of washout may reflect increased enhancement of surrounding parenchyma, rather than true decline in tumor enhancement, hence “washout”.
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FAQ-163: The lesion shows mild washout initially and then washes out completely to look black. Is it mild or marked?
This depends on the time after contrast injection at which the washout becomes marked. If the washout becomes marked at or before 2 minutes, characterize as marked. If the washout becomes marked only after 2 minutes, characterize as mild. If unsure, characterize as marked (to prevent false CEUS LR-5 categorization for non-HCC malignancies with borderline marked washout).
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FAQ-164: How much growth is “unequivocal growth”?
There is no “threshold” for determining unequivocal growth on CEUS. This is up to the interpreter. As a general rule, more than 5 mm is unequivocal.
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FAQ-165:Does washout apply only to observations with APHE?
No. Washout applies to isoenhancing observations in addition to observations with APHE. For example, both of the following nodules should be characterized as having washout:
Arterial phase isoenhancement followed by late-phase hypoenhancement.
Arterial phase hypoenhancement followed by isoenhancement followed by hypoenhancement
Washout does NOT apply to nodules that remain hypoenhancing in all phases.
See Manual/time-intensity curves (pending).
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FAQ-166: Is there peripheral washout on CEUS?
No. A CT/MRI feature of intrahepatic mass-forming cholangiocarcinomas and other non-HCC malignancies, peripheral washout is characterized by a concentric tumoral architecture (i.e., an arterialized, cellular rim and a fibrotic, watery center). The extracellular and hepatobiliary agents used in CT and MRI drain rapidly from the arterialized, cellular rim, manifesting as peripheral washout appearance. As they drain from the tumor periphery, the agents gradually accumulate in the expanded interstitial spaces of the tumor center, causing progressive/delayed central enhancement, which accentuates the conspicuity of the peripheral washout.
CEUS agents are purely intravascular contrast agents (i.e., they do enter the interstitial compartment). They drain rapidly from all tumor components with low blood volume, including the arterialized cellular rim and the fibrotic, watery center. Hence, they yield an early-onset, marked washout throughout the tumor, not a pattern of central retention and peripheral washout.
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FAQ-167: Why is enhancing “capsule” not a CEUS major feature of HCC?
As pure intravascular agents, CEUS microbubbles do not leak into the large interstitial spaces of the tumor “capsule” and the tumor “capsule” tends to be isoechoic to surrounding liver on late-phase CEUS images. By comparison, the low-molecular-weight agents used in CT and MRI leak readily into the “capsule” interstitium, causing the characteristic enhancing capsule appearance of many progressed HCCs in the postarterial phases.
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