# Washout on Contrast-Enhanced Ultrasound of Benign Focal Liver Lesions—A Review on Its Frequency and Possible Causes

## TL;DR

This paper reviews how contrast-enhanced ultrasound can help distinguish benign from malignant liver lesions by analyzing late-phase enhancement patterns.

## Contribution

The paper provides a comprehensive review of washout and late-phase hypoenhancement in benign liver lesions and their diagnostic implications.

## Key findings

- Late-phase hypoenhancement is not uncommon in benign liver lesions and can be normal for certain types.
- Understanding contrast patterns and exceptions is crucial for accurate diagnosis of focal liver lesions.

## Abstract

In all imaging methods, including contrast-enhanced ultrasound (CEUS), enhancement in the late phase (LP) is an important criterion for differentiating between benign and malignant focal liver lesions (FLLs). In general, malignant liver lesions are characterized by hypoenhancement and washout in the LP. A lesion with LP hyperenhancement or isoenhancement in the non-cirrhotic liver is usually benign. However, LP hypoenhancement in benign lesions is not so rare, and is even normal and the standard for some lesions, and there are exceptions for each tumor entity that can represent a diagnostic challenge. Knowing these contrast patterns and exceptions is key for correct diagnosis and patient management. The following narrative review describes the contrast behaviors and the frequency of washout and LP hypoenhancement for common as well as rare benign liver lesions and analyzes its causes.