Normal Anatomy and Variants

The blood supply to the intra-abdominal organs derives from three major branches of the abdominal aorta: the celiac artery (CA), the SMA and the IMA. Although numerous anatomical variants exist, in the majority of cases CE MRA allows a detailed depiction of the typical and atypical vascular anatomy of the splanchnic vessels [2, 11, 17, 33]. Of principal interest for the arterial supply of the liver are the CA and the SMA, however, since collateral supply between the three major branches exists, all of these branches will be discussed (Fig. 1).

Celiac Artery (CA)

The CA is typically located at the level of the T12 to L1 vertebral body. It arises from the ventral part of the abdominal aorta and supplies the upper abdominal viscera. In about two thirds of patients the CA branches into the common hepatic artery, the splenic artery and the left gastric artery (Fig. 2). However, in the remaining one third of individuals, anatomical variants exist in which the common hepatic artery, the splenic artery and the left gastric artery arise from either the SMA or directly from the aorta.

The common hepatic artery divides into the proper hepatic artery and the gastroduodenal artery. In about 75% of cases the gastroduodenal artery thereafter branches into two further vessels;

the right gastroepiploic artery and the superior pancreaticoduodenal artery. The superior pancre-aticoduodenal artery forms an anastomosis with the inferior pancreaticoduodenal artery which derives from the SMA.

In about 50% of cases the proper hepatic artery divides into the left and right hepatic arteries. The remaining 50% of individuals show variants or accessory hepatic arteries. The main variants are shown in Fig. 3.

Superior Mesenteric Artery (SMA)

The SMA usually arises about 1 cm distal to the celiac artery at the anterior aspect of the aorta. In rare cases, a common single celio-mesenteric trunk is present. The first branch from the SMA is the inferior pancreaticoduodenal artery which forms an anastomosis with the superior pancreati-coduodenal artery deriving from the celiac artery. The jejunal and ileal branches arise from the proximal and left side of the SMA, forming multiple arcades. Right sided branches are the ileocolic artery, the right colic artery and the middle colic artery (Fig. 4).

A common variant is the origin of the right hepatic artery from the SMA or even the origin of the common hepatic artery from the SMA.

Inferior Mesenteric Artery (IMA)

The IMA arises from the abdominal aorta at approximately the level of the third lumbar vertebra. Compared to the other main abdominal branches

Mra Renal Arteries Branches

Fig. 1a, b. Maximum intensity projection (a) and volume rendered (b) displays of a 3D CE MRA dataset acquired in the early arterial phase demonstrate the arterial vascular anatomy of the abdomen. Beyond the aorta and both renal arteries, branches of the celiac trunk and the SMA are well-depicted.

A Celiac artery (CA). B Splenic artery. C Common hepatic artery. D Superior mesenteric artery (SMA). E Inferior mesenteric artery (IMA). a Left renal artery. b Right renal artery. c Left gastric artery. d Gastroduodenal artery. From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 233. Springer, 2005

Fig. 1a, b. Maximum intensity projection (a) and volume rendered (b) displays of a 3D CE MRA dataset acquired in the early arterial phase demonstrate the arterial vascular anatomy of the abdomen. Beyond the aorta and both renal arteries, branches of the celiac trunk and the SMA are well-depicted.

A Celiac artery (CA). B Splenic artery. C Common hepatic artery. D Superior mesenteric artery (SMA). E Inferior mesenteric artery (IMA). a Left renal artery. b Right renal artery. c Left gastric artery. d Gastroduodenal artery. From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 233. Springer, 2005

Gastroduodenal Artery

Fig. 2. Normal anatomy of the celiac trunk. A Celiac artery (CA). B Splenic artery. C Common hepatic artery. D Superior mesenteric artery (SMA).

1 Proper hepatic artery. 2 Right hepatic artery. 3 Left hepatic artery. 4 Left gastric artery. 5 Gastroduodenal artery. 6 Right gastric artery. 7 Right gastroepiploic artery. 8 Left gastroepiploic artery. From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 232. Springer, 2005

Hepatic Artery Variants

Fig. 3. Schematic representation of variants of the hepatic vasculature. A Celiac artery (CA). B Superior mesenteric artery (SMA). a Left gastric artery. b Gastroduodenal artery. c Splenic artery. ha Hepatic arteries From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 238. Springer, 2005

Fig. 3. Schematic representation of variants of the hepatic vasculature. A Celiac artery (CA). B Superior mesenteric artery (SMA). a Left gastric artery. b Gastroduodenal artery. c Splenic artery. ha Hepatic arteries From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 238. Springer, 2005

Normal Superior Mesenteric Artery

Fig. 4. Normal anatomy of the superior mesenteric artery. D Superior mesenteric artery (SMA).

1 Gastroduodenal artery. 2 Medial colic artery. 3 Right colic artery. 4 Iliocolic artery. 5 Jejunal- and ilieal arteries. From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 232. Springer, 2005

Fig. 4. Normal anatomy of the superior mesenteric artery. D Superior mesenteric artery (SMA).

1 Gastroduodenal artery. 2 Medial colic artery. 3 Right colic artery. 4 Iliocolic artery. 5 Jejunal- and ilieal arteries. From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 232. Springer, 2005

Mesenteric Artery Anatomy

Fig. 5. Normal anatomy of the inferior mesenteric artery. D Superior mesenteric artery (SMA). E Inferior mesenteric artery (IMA).

1 Left colic artery. 2 Sigmoid arteries. 3 Superior rectal artery. From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 232. Springer, 2005

Fig. 5. Normal anatomy of the inferior mesenteric artery. D Superior mesenteric artery (SMA). E Inferior mesenteric artery (IMA).

1 Left colic artery. 2 Sigmoid arteries. 3 Superior rectal artery. From Magnetic Resonance Angiography, Schneider G. et al (eds.), p 232. Springer, 2005

it is a relatively thin vessel, measuring only 1-6 mm in diameter. For this reason the IMA is often difficult to depict on MRA.

The left colic artery usually represents the first branch of the IMA. This forms the so-called anastomosis of Riolan with the middle colic artery deriving from the SMA (Fig. 5). In cases of severe stenosis or occlusion of the SMA, this anastomosis can serve as a collateral supply for the SMA. Giving off the sigmoid branches, the IMA becomes the superior rectal artery.

Variations in the splanchnic arterial anatomy occur in more than 40% of patients (Fig. 3). For this reason, pre-operative vascular planning for hepatic resections, liver transplantations, resection of retroperitoneal masses, chemoinfu-sion pump placement, surgical shunting, or other abdominal operations may require accurate mapping of the visceral arterial anatomy. Generally, this is achieved by conventional angiogra-phy because of the fine detail needed to identify variations involving tiny arteries. However, to evaluate the origins of the splanchnic artery and major branches, 3D CE MRA is frequently sufficient.

The most common variation is a replaced (17%) or accessory (8%) right hepatic artery, most commonly from the SMA (Figs. 6,7). Less common variations include the left hepatic artery arising from the left gastric artery (Fig. 8), the common hepatic artery arising from the SMA (2.5%) (Fig. 9) or directly from the aorta (2%) (Fig. 10), the left gastric artery arising from the aorta (1-2%) (Fig. 11), or a celio-mesenteric trunk (<1%). Other more complex variations may also occur.

Although the main indication for arterial imaging of the hepatic vasculature is the evaluation of vascular anatomy, there are other indications for which CE MRA may be helpful. For example, in the case of liver tumors such as pedunculated adenoma or focal nodular hyperplasia (FNH), preoperative CE MRA may help to optimize the therapeutic approach by displaying the arterial supply and venous drainage of the lesion (Fig. 12). Imaging of vascular pathologies such as aneurysms of the splanchnic arteries can also be performed in a non-invasive manner using CE mRa (Fig. 13) and therapeutic approaches, if necessary, can be planned.

Fig. 6. A volume rendered 3D CE MRA (0.1 mmol/kg Gd-BOPTA) dataset shows an anatomic variation of the arterial supply of the liver in a patient with liver transplantation planned. Note that the right hepatic artery (arrow) branches from the SMA, whereas the left hepatic artery (arrowhead) branches from the celiac trunk. The small caliber of the vessels is the result of a longstanding inflammatory process that resulted in liver fibrosis

Fig. 6. A volume rendered 3D CE MRA (0.1 mmol/kg Gd-BOPTA) dataset shows an anatomic variation of the arterial supply of the liver in a patient with liver transplantation planned. Note that the right hepatic artery (arrow) branches from the SMA, whereas the left hepatic artery (arrowhead) branches from the celiac trunk. The small caliber of the vessels is the result of a longstanding inflammatory process that resulted in liver fibrosis

Fig. 7a, b. Whereas the MIP reconstruction (a) reveals multiple renal arteries (arrowheads) together with an obvious abnormal course of the right hepatic artery (arrow), the volume-rendered image (b) clearly displays the anatomic variation of a right hepatic artery originating from the SMA (arrow). This example shows that evaluation of vascular anatomy is sometimes easier on volume-rendered images than on MIP reconstructions

Fig. 7a, b. Whereas the MIP reconstruction (a) reveals multiple renal arteries (arrowheads) together with an obvious abnormal course of the right hepatic artery (arrow), the volume-rendered image (b) clearly displays the anatomic variation of a right hepatic artery originating from the SMA (arrow). This example shows that evaluation of vascular anatomy is sometimes easier on volume-rendered images than on MIP reconstructions

Fig. 8a, b. Left hepatic artery (arrowhead) arising from the left gastric artery (arrow) on a CE MRA (0.1 mmol/kg Gd-BOPTA) MIP reconstruction (a) and on a volume-rendered image (b). Note again that the vessels are better appreciated on the volume-rendered image
Mra Great Vessels

Fig. 9a, b. CE MRA in a 3 year old girl with transposition of the great arteries. Whole-body MIP reconstruction (a) reveals an abnormal course of the ascending aorta due to transposition of the great arteries and dextro-positio cordis. In addition, the splenic (arrowhead) and hepatic arteries (arrow) both seem to originate from the celiac trunk. However, a subvolume MIP reconstruction (b) clearly reveals that the common hepatic artery (arrow) branches from the SMA while the splenic artery (arrowhead) originates from the celiac trunk

Sma Mra Mri Anatomy

Fig. 9a, b. CE MRA in a 3 year old girl with transposition of the great arteries. Whole-body MIP reconstruction (a) reveals an abnormal course of the ascending aorta due to transposition of the great arteries and dextro-positio cordis. In addition, the splenic (arrowhead) and hepatic arteries (arrow) both seem to originate from the celiac trunk. However, a subvolume MIP reconstruction (b) clearly reveals that the common hepatic artery (arrow) branches from the SMA while the splenic artery (arrowhead) originates from the celiac trunk

Fig. 10a, b. CE MRA (0.1 mmol/kg Gd-BOPTA) MIP reconstruction (a) reveals multiple stenoses (arrowheads) of the hepatic artery due to vasculitis. However, determining the origin of the hepatic artery is difficult. The corresponding volume-rendered image (b) reveals separate branching of the hepatic artery (arrow) from the aorta. Information regarding this anatomic variation is extremely important for planning liver transplantation

Fig. 10a, b. CE MRA (0.1 mmol/kg Gd-BOPTA) MIP reconstruction (a) reveals multiple stenoses (arrowheads) of the hepatic artery due to vasculitis. However, determining the origin of the hepatic artery is difficult. The corresponding volume-rendered image (b) reveals separate branching of the hepatic artery (arrow) from the aorta. Information regarding this anatomic variation is extremely important for planning liver transplantation

Fig. 11a, b. The volume-rendered image in AP-projection (a) demonstrates the left hepatic artery originating from the left gastric artery (arrow). The lateral view (b) reveals additional separate branching of the left gastric artery from the aorta (arrow)

Liver Enhancement Imaging Variants

Fig. 12a-g. Pedunculated FNH of the liver. The volume-rendered image (a) of the arterial phase 3D CE MRA (0.1 mmol/kg Gd-BOPTA) dataset reveals a dilated hepatic artery with an abnormal course supplying the FNH (arrowheads). The corresponding venous phase MIP reconstruction (b) clearly shows the venous drainage (arrows of the FNH (arrowheads). Additional coronal multiplanar reconstructions from the venous phase dataset (c-g) demonstrate the supplying hepatic artery (arrowin c) as well as the FNH itself (aster/skin e, f), together with the central scar (arrowin g)

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