Mesenteric Ischemia

Selective angiography has been considered the gold standard for the diagnosis of chronic mesen-teric ischemia [17]. The demonstration of significant stenoses in two of the three main mesenteric vessels in conjunction with appropriate clinical symptoms verifies the diagnosis of mesenteric ischemia [3] (Fig. 3). MRA has the potential to become a definitive noninvasive tool for the diagnosis of chronic mesenteric ischemia. It can provide information about patency and stenosis in mesen-teric vessels and is becoming a modality of choice for the selection of patients suspected of having mesenteric ischemia who may benefit from surgery.

Chronic mesenteric ischemia generally occurs when there is insufficient blood supply to the intestine during periods of high metabolic demand, such as following a meal. It is most commonly caused by severe stenosis or occlusion of at least two of the three main splanchnic arteries. The clinical syndrome of mesenteric ischemia is rare. Symptoms may include abdominal pain, weight loss and food aversion [3,18-19].Atherosclerosis of the splanchnic arteries is considered to be the main pathophysiologic mechanism for chronic mesenteric ischemia [1,5]. However, the diagnosis of mesenteric ischemia is frequently perplexing in clinical practice. Reflecting the risks associated with arterial catheterization, the clinical diagnosis of mesenteric ischemia has been mostly one of exclusion. The median time-delay between clinical presentation and diagnosis is 18 months for patients with new symptoms and one month for patients with recurrent symptoms. Symptoms of mesenteric ischemia may overlap with those of more common intestinal disorders such as peptic ulcer or chronic cholecystitis. Recent advances in MR technology permit adequate assessment of the splanchnic arterial system [2,9,16, 20-21]. Hence, MRA in combination with flow quantification [10,12-13,22] or oximetry [23] has been proposed for the diagnosis of mesenteric ischemia. However, despite the availability of non-invasive MRA, a reliable diagnosis remains difficult in a high percentage of cases: atherosclerotic changes are often based on the level of arterioles and therefore cannot be captured by luminographic procedures

Fig. 3. MIP display of a 3D CE MRA data set acquired in the early arterial phase; the sagittal, reformatted view reveals stenoses (arrows) of the celiac trunk and SMA

Ultrasound Images Celiac And SmaSma Embolus

Fig. 4a, b. MIP (a) and volume rendered (b) displays of a 3D CE MRA data set (0.1 mmol/kg Gd-BOPTA) in the early arterial phase showing a high-grade stenosis of the celiac trunk (arrow). Collateral flow from the SMA via the gastroduodenal artery (arrowheads) is noted, indicated by the enlarged diameter of the gastroduodenal artery. In general, an enlarged, pronounced gastroduodenal artery on CE MRA images is almost pathognomonic for a stenosis of either the celiac trunk or the SMA [Images courtesy of Dr. G. Schneider]

Acute Mesenteric Ischemia

Fig. 5a, b. Patient with aortic dissection extending into the SMA. On the whole volume MIP (a) of the 3D CE MRA data set (0.1 mmol/kg Gd-BOPTA) the dissection membrane extending into the right iliac artery can be appreciated (arrows), however the involvement of the SMA is difficult to evaluate. Nevertheless extension of the dissection membrane into the SMA (arrow) can be appreciated with an additional VIBE sequence (b), performed immediately after the CE MRA study [Image courtesy of Dr. G. Schneider]

Fig. 5a, b. Patient with aortic dissection extending into the SMA. On the whole volume MIP (a) of the 3D CE MRA data set (0.1 mmol/kg Gd-BOPTA) the dissection membrane extending into the right iliac artery can be appreciated (arrows), however the involvement of the SMA is difficult to evaluate. Nevertheless extension of the dissection membrane into the SMA (arrow) can be appreciated with an additional VIBE sequence (b), performed immediately after the CE MRA study [Image courtesy of Dr. G. Schneider]

[24]. In addition, the mesenteric circulation is frequently supported by arterial collaterals. Therefore, completely asymptomatic patients can be seen even though severe stenotic changes are present in the main mesenteric vessels [25-26] (Fig. 4). A solution to this problem might be the evaluation of mesenteric ischemia using perfusion values of the small bowel wall before and after caloric stimulation (see below). Mesenteric ischemia may occur in conjunction with aortic dissection due to extension of the dissection membrane into a mesenteric artery. Typically, clinically relevant in volvement is due to an extension of the dissection into the SMA (Fig. 5). Acute onset of symptoms due to mesenteric ischemia is found in conjunction with thromboembolic events, in which the lack of collaterals indicates an acute (Fig. 6) stage. In contrast, those cases in which a collateral supply is already visible are examples of a subacute stage (Fig. 7).

Finally, mesenteric ischemia may also be present in the context of inflammatory diseases, which can occur as part of a vascular inflammation syndrome such as Takayasu arteritis (Fig. 8).

Mra Mesenteric Vessels

Fig. 6. A contrast enhanced MRA study (0.1 mmol/kg Gd-BOPTA) in a patient with left atrial thrombus formation and sudden onset of abdominal pain shows peripheral embolization of the SMA (arrowin a) and acute thromboembolic occlusion of the celiac artery (arrow in b). Note the absence of collateral vessels but a dilated gastroduodenal artery (arrowheadin a) [Image courtesy of Dr. G. Schneider]

Fig. 6. A contrast enhanced MRA study (0.1 mmol/kg Gd-BOPTA) in a patient with left atrial thrombus formation and sudden onset of abdominal pain shows peripheral embolization of the SMA (arrowin a) and acute thromboembolic occlusion of the celiac artery (arrow in b). Note the absence of collateral vessels but a dilated gastroduodenal artery (arrowheadin a) [Image courtesy of Dr. G. Schneider]

Acute Mesenteric Ischemia Mra

Fig. 7. MIP display of a 3D CE MRA data set (0.1 mmol/kg Gd-BOPTA) of the mesenteric arteries shows multiple wall irregularities of the SMA indicating recurrent thromboembolic events (arrows in a). Furthermore, occlusion of the celiac artery can be noted (arrow in b). In contrast to the case in Fig. 6 collateral vessels (arrowheads) have developed in this patient due to recurrent, subacute emboli [Image courtesy of Dr. G. Schneider]

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a

Takayasu Arteriitis

Fig. 8. Involvement of the mesenteric arteries in a patient with Takayasu arteritis. The True-FISP axial image (a) reveals an almost complete occlusion of the abdominal aorta (arrow). The high grade stenosis (arrow) is confirmed on a whole volume MIP reconstruction (b) of the 3D CE MRA data set (0.1 mmol/kg Gd-BOPTA). Additionally, the Arc of Riolan (arrowheads) is visible which on CE MRA images typically indicates stenosis either of the SMA or the IMA since it serves as a collateral between these vessels [Image courtesy of Dr. G. Schneider]

Celiac Trunk

Fig. 9. Schematic representation of variants of the hepatic vasculature.

A Celiac artery

B Superior mesenteric artery a Left gastric artery b Gastroduodenal artery c Splenic artery ha Hepatic arteries

Fig. 9. Schematic representation of variants of the hepatic vasculature.

A Celiac artery

B Superior mesenteric artery a Left gastric artery b Gastroduodenal artery c Splenic artery ha Hepatic arteries

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