*6.1.2 Computer tomography*

One of the most accurate imaging tools in diagnosing a HA is contrast enhanced computed tomography (CECT), on which it appears as a well demarcated tumor, with characteristic peripheral enhancement during the early phase with subsequent centripetal flow during the portal venous phase. A heterogeneous consistency is usually a sign of necrosis, hemorrhage, or fibrosis [5].

Multiphasic computed tomography (CT) has a detection rate of 100% for adenomas, which is however different per type of examination: nonenhanced 86%, hepatic arterial-dominant phase (HAP) 100%, portal venous-dominant phase (PVP) 82%, and delayed 88%. Tumor margins are well defined by a low-attenuation pseudocapsule in 86% of adenomas and the surface appears smooth, without lobulated contour, in 95%. Tumor fat and calcifications are uncommon (7%, respectively 5%). Other than areas of fat, hemorrhage, or necrosis, the adenomas show homogenous enhancement, especially on PVP and delayed-phase scans [39].

#### **Figure 13.**

*HA located in segment VII as shown by imaging on NECT (A), CECT—arterial phase (B), portal venous phase (C), parenchymal phase (D), MRI T1w (E), and T2w (F). Atoll sign characterized by a hyper intense band in the periphery and isodensity in the center of the lesion with respect of the surrounding liver is relevant on CT in portal venous phase (C). A hyperintense rim in T2 wi is described in inflammatory adenoma (arrow in F).*

*MSCT technique*: nonenhanced CT and enhanced triphasic CT: in arterial (30–35 s after the bolus tracker detection), portal venous (60–80 s after contrast medium injection), and equilibrium/late phases (after 3–5 min). 1.5 ml/kg of nonionic iodinated contrast material is injected into an antecubital vein with a rate of 3 ml/s using a power injector.

CT findings are depending on HA subtype. On nonenhanced CT (NECT), hemorrhage within tumor is seen on as hyperdense foci, intratumoral lipid as hypodense foci (negative density), and focal coarse calcifications are rarely seen (**Figure 14**). On contrast-enhanced (CECT), encapsulation is present in ~20% of HAs, best seen on the late phase (**Figure 14**). Hypervascularity is most intense and persistent in inflammatory subtype of HA (**Figure 15**).

CT is most useful in distinguishing a HA from other liver tumors or lesions: (1) focal nodular hyperplasia which has a characteristic central star-shaped hypodense scar, (2) hemangiomas with their peripheral enhancement on arterial phase and progressive centripetal fill-in pattern, (3) liver cell carcinoma which has a particular wash-in, wash-out pattern, and (4) singular liver metastases with no fat or hemorrhage.

#### *6.1.3 Magnetic resonance imaging (MRI)*

#### *6.1.3.1 MRI technique*

Unenhanced conventional sequences: T2w is useful in detection of focal liver lesions. T2\* is important in the evaluation of iron content and chemical shift artifact sequences; T1 in/out of phase is important to delineate steatosis or intralesional lipomatous content; ssFSE short TE/long TE makes differentiation between cysts and solid mass; and diffusion is the most sensitive sequence for liver lesion detection.

Contrast enhanced T1: multiphase dynamic 3D acquisitions without and with intravenous injection of 0.1 ml/kgbw of extracellular or liver-specific contrast paramagnetic agents (Gd-EOB-DTPA) in arterial phase (AP): detection of hypervascular lesions, portal venous phase (PVP), late phase (LP), and hepatobiliary phase (HBP).

*Imaging key* features in HAs are: hypervascularity, fat content, hemorrhage, and encapsulation. MRI shows some elements better than CT (lipid and hemorrhage). HA shows no substantial uptake or retention in contrast enhanced MRI with Gadoxetate (Primovist). MRI features for adenomas are distinct from FNH. T1WI: mass with heterogeneous signal intensity; increased signal intensity (due to fat or recent hemorrhage); decreased signal intensity (necrosis, calcification, old hemorrhage) T1 + C: heterogeneous, hypervascular liver mass with foci of fat or hemorrhage in a young woman.

#### **Figure 14.**

*NECT with large liver mass with central calcifications, small lipomatous inclusions, solid components and necrosis (A), CECT—arterial phase (B), portal venous phase (C), and parenchymal phase (D).*

**131**

**Figure 16.**

*liver (arrow).*

*Challenging Issues in Hepatic Adenoma DOI: http://dx.doi.org/10.5772/intechopen.87993*

*6.1.3.2 MRI evaluation*

**Figure 15.**

to liver on delayed images.

ary phase [40].

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

*CT evaluation: liver adenoma with central necrotic area and encapsulation (arrow).*

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 hepatobili-

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

*Liver Disease and Surgery*

hemorrhage.

*6.1.3.1 MRI technique*

rhage in a young woman.

of 3 ml/s using a power injector.

inflammatory subtype of HA (**Figure 15**).

*6.1.3 Magnetic resonance imaging (MRI)*

*MSCT technique*: nonenhanced CT and enhanced triphasic CT: in arterial (30–35 s after the bolus tracker detection), portal venous (60–80 s after contrast medium injection), and equilibrium/late phases (after 3–5 min). 1.5 ml/kg of nonionic iodinated contrast material is injected into an antecubital vein with a rate

CT findings are depending on HA subtype. On nonenhanced CT (NECT), hemorrhage within tumor is seen on as hyperdense foci, intratumoral lipid as hypodense foci (negative density), and focal coarse calcifications are rarely seen (**Figure 14**). On contrast-enhanced (CECT), encapsulation is present in ~20% of HAs, best seen on the late phase (**Figure 14**). Hypervascularity is most intense and persistent in

CT is most useful in distinguishing a HA from other liver tumors or lesions: (1) focal nodular hyperplasia which has a characteristic central star-shaped hypodense scar, (2) hemangiomas with their peripheral enhancement on arterial phase and progressive centripetal fill-in pattern, (3) liver cell carcinoma which has a particular wash-in, wash-out pattern, and (4) singular liver metastases with no fat or

Unenhanced conventional sequences: T2w is useful in detection of focal liver lesions. T2\* is important in the evaluation of iron content and chemical shift artifact sequences; T1 in/out of phase is important to delineate steatosis or intralesional lipomatous content; ssFSE short TE/long TE makes differentiation between cysts and solid mass; and diffusion is the most sensitive sequence for liver lesion detection. Contrast enhanced T1: multiphase dynamic 3D acquisitions without and with intravenous injection of 0.1 ml/kgbw of extracellular or liver-specific contrast paramagnetic agents (Gd-EOB-DTPA) in arterial phase (AP): detection of hypervascular lesions, portal venous phase (PVP), late phase (LP), and hepatobiliary phase (HBP). *Imaging key* features in HAs are: hypervascularity, fat content, hemorrhage, and encapsulation. MRI shows some elements better than CT (lipid and hemorrhage). HA shows no substantial uptake or retention in contrast enhanced MRI with Gadoxetate (Primovist). MRI features for adenomas are distinct from FNH. T1WI: mass with heterogeneous signal intensity; increased signal intensity (due to fat or recent hemorrhage); decreased signal intensity (necrosis, calcification, old hemorrhage) T1 + C: heterogeneous, hypervascular liver mass with foci of fat or hemor-

*NECT with large liver mass with central calcifications, small lipomatous inclusions, solid components and necrosis (A), CECT—arterial phase (B), portal venous phase (C), and parenchymal phase (D).*

**130**

**Figure 14.**

**Figure 15.** *CT evaluation: liver adenoma with central necrotic area and encapsulation (arrow).*
