Definition:

• Hypo-intensity of an observation that is due to relative hyperenhancement of the surrounding liver rather than “washout” of the observation.  Pseudo-washout appearance usually occurs in the transitional phase, but potentially could occur in the portal venous phase in individuals with normal or relatively preserved hepatic function.

Usage

• On gadoxetate disodium enhanced studies washout appearance may be more difficult to characterize with certainty. On such studies an observation should be characterized as showing washout appearance only if the “washout” is evident in the portal venous phase. 

If unsure about feature:

• Characterize as pseudo-washout appearance, rather than washout appearance.

 Synonyms:

• Synonyms: transitional phase hypointensity, late dynamic phase hypointensity
• Preferred terms:  Pseudo-washout appearance
• Rationale for preferred terms:  Draw distinction between true “washout” and relative hypointensity of an observation secondary to the progressively increasing intensity of the liver parenchyma.

 Background

• Gadoxetate disodium is a commonly used contrast agent in patients at risk for developing HCC.  In patients with relatively preserved hepatocyte function, hepatocyte uptake in the portal venous phase could result in relative hypo-intensity of an observation that does not take up the contrast as well as the background liver parenchyma, thus potentially producing a pseudo-washout appearance.

Potential pitfalls and challenges

• In individuals with normal hepatic function, some hepatocellular uptake of gadoxetate disodium 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, cholangiocellular carcinomas) due to the above described enhancement of the liver parenchyma and lack of transporter expression.  This finding should be considered pseudo-washout appearance rather than washout appearance.