*6.1.3.2 MRI evaluation*

Some MRI findings of HAs are similar to CT findings, but MRI is usually more sensitive in detecting fat from hemorrhage. The appearance of HAs on MRI is highly variable, especially in T1, but if contrast medium is used, then it may be better characterized, showing early arterial enhancement and becoming nearly isointense to liver on delayed images.

On T1-weighted images (T1wi), HA appears as a heterogeneous signal intensity mass. The increased signal of HA is due to fat and recent hemorrhage, and the decreased signal intensity is due to necrosis, calcification, or old hemorrhage. A fibrous pseudocapsule may be seen in HA as a hypointense rim. In T2wi, the mass appears heterogeneous; increased signal intensity corresponds to old hemorrhage or necrosis, and the decreased signal intensity is due to the fat or recent hemorrhage. The peripheral rim (fibrous pseudocapsule) in HA appears hypointense in liver parenchyma (**Figure 16**). After contrast injection (T1wi + C) in arterial phase, adenomas are heterogeneous hypervascular masses (inflammatory HA+++) and in delay phase a pseudocapsule, which is hyperintense comparative to the normal liver, can be seen. After Gadoxetate-enhanced MR (Gd-EOB-DTPA), in HA there is no substantial contrast uptake or retention on hepatobiliary phase [40].

#### **Figure 16.**

*MRI evaluation: liver adenoma with central necrotic area and pseudocapsule hyperintense to the surrounding liver (arrow).*

MRI with hepatobiliary agents is an important tool not only in differential subtype definition but even in surveillance with early identification of complications and discovery of some signs of HA malignant degeneration [41]. Lesion enlargement and heterogeneity of signal intensity and of contrast enhancement are signs of malignant transformation [42].

*Imaging recommendations*: the best imaging tool is represented by Gadoxetateenhanced MRI including multiphase and hepato-biliary phase acquisition [43]. The best sequence to evaluate fat into HA is T1wi with in and opposed TE.
