Definition:
Usage:
- Applies to: Observations that, by visual assessment, appear to “washout” in whole or in part
- Type of feature: Major
- How it should be assessed or characterized:
- Delayed phase preferred over venous phase.
- Rational: Delayed phase may be superior to portal venous phase for depicting washout appearance. Some observations may show washout appearance only in the delayed phase.
- The enhancement of the observation should be compared to that of the adjacent liver parenchyma. If the liver parenchyma visually consists of both nodules and fibrosis, then enhancement of the observation should be compared to that of the composite liver tissue (i.e., a visual average of the nodules and fibrosis)
If unsure about feature:
- Do not characterize as washout appearance.
Synonyms:
- Synonyms: Washout, Venous or delayed phase washout.
- Preferred terms: Washout appearance and “washout” (with quotation marks) are preferred over the term washout.
- Rationale for preferred terms: The visually assessed temporal reduction in enhancement relative to liver may be due to progressive enhancement of the liver rather than actual de-enhancement of the observation.
Background
- Washout appearance is a LI-RADS major feature for categorization of masses that are neither definite benign entities nor probable benign entities and that lack features of non-HCC malignancy or tumor in vein. For such masses, those with washout appearance may be categorized LR-3, LR-4, or LR-5, depending on the observation’s arterial phase enhancement, diameter, and other features.
- Washout appearance is also an imaging feature used in both AASLD guidelines and OPTN policy for the imaging diagnosis of HCC
Potential pitfalls and challenges
- As washout appearance is assessed visually, LI-RADS does not mandate objective assessment using ROI measurements, time-enhancement curves, or subtraction images.
- Radiologists at their discretion may use ROI measurements, time-enhancement curves, or, at MRI, subtraction images (e.g., arterial phase minus portal venous or delayed phase) to evaluate “washout”.
- For ROI measurements, time-enhancement curves, or subtractions to be valid, arterial phase and portal venous or delayed phase images need to be acquired with the same technique. In addition, subtractions require co-registration of the source images.
- Washout can be present in only part of the observation. The component with washout does not need to correspond to the component that demonstrates arterial hyperenhancement, however the component does need to enhance for this feature to be present.
- Washout of the periphery of an observation, however, should be characterized as peripheral washout rather than washout appearance. Washout of the periphery of an observation is a finding suggestive of intrahepatic cholangiocarcinoma rather than HCC. Peripheral washout is not a major feature and its presence favors a category of LR-M rather than LR-3, LR-4, or LR-5.
- Washout may be difficult to assess in patients with diffuse hepatic fat deposition. In this instance, subtraction images may be helpful.
- Hepatobiliary phase hypointensity is not considered washout appearance. Washout appearance should only be assessed during the portal venous phase of enhancement with gadoxetate disodium, prior to the transitional or hepatobiliary phases.
- In individuals with normal hepatic function, some hepatocellular uptake of gadoxetic acid may be evident in the portal venous phase; therefore, in at risk patients with relatively preserved hepatic function, hepatocyte uptake in the portal venous phase potentially could result in a “pseudo-washout appearance”, although no studies to date have documented this potential pitfall.
- Hypointensity in the transitional phase can be present in non-hepatocellular lesions (metastases, hemangiomas, cholangiocarcinomas) due to the above described enhancement of the liver parenchyma and lack of transporter expression. This finding should be considered pseudo-washout rather than washout appearance.
References:
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