When present, the arc of Riolan is an important connection between the SMA and IMA in the setting of arterial occlusion or significant stenosis. In proximal SMA. embryologic development of the mesenteric structures and their blood . collaterals include the arch of Bühler and gastroduodenal arcade. SMA to inferior mesenteric artery (IMA) collaterals include the arc of Riolan and the marginal artery of. The marginal artery of Drummond is the major collateral arcade between the SMA and IMA, is Differentiation of the Arc of Riolan from the Marginal artery of.
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The arcde and clinical data of consecutive mesentery CTA images were retrospectively analyzed. The 47 cases with ARE and 47 patients without expansion were involved. The average diameter of arc of Riolan was measured. Two radiologists after reaching consensus analyzed the shapes of mesenteric artery, CT findings and the occurrence and causes of ARE.
The mean diameter of arc of Riolan was 1. The expansion of arc of Riolan was the most significant following obstruction of SMA. The diameters of arc of Riolan were significantly different between the upward flow group and the downward or the two-way flow groups, and between the colon tumor group and the active ulcerative colitis group.
CT findings such as bowel wall thickening, contrast enhancement, intestinal obstruction, marginal artery expansion, riolna node enlargement varied and were help to identify the cause of ARE. ARE often suggests the occurrence of obstructed intestinal feeding artery or intestinal lesions. Arcare can clearly display the situation of arc of Riolan and collateral circulation, and together with CT symptoms, can guide the selection of diagnosis and treatment schemes in clinic.
The arc of Riolan AORalso known as the central anastomotic mesenteric artery or meandering mesenteric artery, is an inconstant artery which links the proximal superior mesenteric artery SMA or one of its principal branches to the proximal inferior mesenteric artery IMA or one of its primary branches [ 1 ].
It made the connection between the middle colic branch of the SMA and the left colic branch of the IMA and can form a short loop that runs close to the root of the mesentery. According to the location of the stenosis, the direction of blood flow may be anterograde or retrograde [ 2 ].
It also provides collateral flow from SMA to IMA to iliac vessels and then to the lower limbs in distal abdominal aortic occlusion. Recessive AOR is the common state, with small amount of blood or even without blood inside of it. So normally it presents minuteness in the images. arcad
The expansion has much relationship with the occurrence of acute and chronic ischemia. Considering the invasion and complications of DSA, many researches focus on the application of CT angiography on the studying of vascular structures in many diseases [ 4 – 6 ].
Keeping track of the collateral circulations in SMA and IMA is not only beneficial for prognostic evaluation of acute and chronic ischemia, but also for ensuring intestinal arrcade supply in selection of schemes for colon surgery [ 7 ].
In this study, the retrospectively analysis was performed by studying a large amount of patients who arcadr abdominal large-vascular lesion or intestinal disease with treatment of the detector-row spiral CTA in the recent 5 years and finally we summarize the manifestations of the arc of Riolan expansion. We retrospectively analyzed patients clinically suspected as aorta or abdominal intestinal lesions and received CTA in aorta abdominal or mesenteric artery between June and June The major clinical manifestations include: Five patients were excluded from CTA because of severe contrast-agent contraindications, such as history of adverse reactions 1 case and renal inadequacy 4 cases.
Marginal artery of the colon
Finally, after informed consent was obtained, subjects age range between years; the mean value, 51 years were examined, including males and females MDCTA shows that arc of Riolan expansion occurred in 47 cases consisted of 29 males and 18 females age range, years; mean 53 arcace. A control group was sampled from patients without vasodilation of the arc, exclusion criteria including: As a result, 47 subjects consisted of 27 males and 20 females age range years, mean 50 years were selected into the control group.
In our standard CT protocol for abdomen examinations, dual scan gram area from Diaphragm to the pubic symphysis in a supine position was adopted as field of view FOV. Ltd, Tokyo, Japanrespectively.
The region of interest was positioned at the thoracoabdominal aorta, and the threshold for CT angiography was set as HU. Arterial phase scan delay was established with the automatic bolus tracking technique.
When the threshold was surpassed, helical scanning was automatically initiated. Portal venous phase acquisition was set 25 sec delay after the previous protocol. In addition to the axial source data, post-processed multiplanar-reconstruction MPRmaximum-intensity projection MIPand 3D volume-rendering VR images were evaluated by two radiologists with 4 and 6 years of experience in CT angiographic imagingand the decisions were made in consensus.
CT value of mesenteric artery greater HU was considered as an appropriate and evaluable imaging. Depending on this diameter and the whole imaging profiling, we evaluated the fineness of arc of riolan and make a degree of it. Referred to mesenteric artery expansion and cerebral artery expansion were described by CTA or DSA [ 89 ], criterion on arc of Riolan expansion: Axial source data, MPR, MIP and VR images were independently and blindly evaluated by two radiologists with 3 and 5 years of experience in CT angiographic imagingand the decisions were made in consensus.
Conversely, the blood flow direction was defined as downward or bi-directionally depending on body position. Therefore, the observed of obstruction or severe stenosis of SMA were divided into upward group; the cases suffered from obstruction or severe stenosis of IMA, sigmoid colon cancer and active ulcerative colitis were grouped in downward or bi-directionally.
Patients without arc of Riolan expansion had an alternative diagnosis confirmed either at biphasic CT scan or on the basis of appropriate laboratory values and clinical findings, or they had no diagnosis and recovered spontaneously with out treatment.
Charts were also reviewed for documented evidence that information provided by the CT angiogram affected ultimate patient care, either by influencing the decision to perform surgery or endovascular interventional treatment.
For continuous data, average diameter and range min-max values were used for descriptive statistics, respectively. A Kolmogorov-Smirnov test was used to assess normal distribution. P values less than 0. Statistical analysis was done with the Statistical Package for the Social Sciences version Large-scale cases were examined. No patients experienced a reaction to the contrast agent.
Three patients were excluded because the concentration of contrast collected at arterial phase was not high enough. In the control group, only Table 1 presents the diameter degree of the expanding arc of Riolan on account of following different diseases. Female, year-old, VR image shows severe SMA stenosis long arrowheadshort arrowhead indicates arc of Riolan expansion.
Images showed severe stenosis in SMA white arrowarc of Riolan expansion dovetail arrowby atherosclerosis, complicated with intestinal wall, mesentery oedema dovetail arrowsmall intestine incomplete obstruction and expansion arrowheadmesenteric edema virtual tail arrow ; DSA artery displays arc of Riolan white arrowlack of view.
A VR image shows SMA obstruction long arrowheadshort arrowhead indicates arc of Riolan expansion; b arterial phase axial view, indicating arc of Riolan section white arrowslight oedema and ileus in intestinal wall dovetail arrow.
Male, year-old, VR image shows IMAobstruction, proximal segment not displayed, compensated via Riolan white arrowhead. Male, year-old, descending colon tumor, MIP image shows arc of Riolan expansion long arrowhead and marginal arc short arrowheadobviously strengthened intestinal wall. Female, year-old, ulcerative colitis at active phase, coronal slap-MIP AVR B at arterial phase, white arrowhead indicates expanded arc of Riolan, red arrowhead indicates suffused intestinal wall thickening, obvious strengthening.
Box figure shows the diameter of arc of Riolan on account of following different diseases. The diameter degree of arc of Riolan in the upward group, the downward group, and the bi-directional group are showed in Table 2. The upward group was significantly different from the other two groups. Comparison of afcade of Riolan diameter between the upward group, the bi-directional group, and the downward group mm. Due to the different course, intestinal mucosa enhancement and bowel dilation were different accordingly.
Irolan, bowel wall thickening, contrast enhancement, intestinal obstruction ,marginal arcadd expansion, lymph node enlargement were not seen in most IMA obstruction, whereas showed commonly in advanced sigmoid colon cancer and active UC respectively, with no difference between the two groups.
Arc of Riolan, named by Jean Riolan, an anatomist from France, is a crucial connection between the SMA and IMA in the setting of arterial occlusion or significant stenosis besides Drummond marginal artery, which located in mesocolon, striking along the medial margins [ 3 ].
Usually, the fineness of artery is very small and recessive state keeps in most time. Previous studies suggest the arc will obviously expand only following obstruction of SMA, but normally, arc of Riolan undergoes little and slow blood flow, and cannot be displayed fully in angiography [ 3 ].
However, all cases of this study in the control group display full arc of Riolan with CT angiography. DSA is regarded as the golden standard for the evaluation and description of vascular structures. Nevertheless, some variations can be overlooked when this technology is used in cases where description of the collateral circulation system between SMA and IMA is difficult, where the catheter tip is far from where it should be in the SMA or IMA during selective angiographic processes in spite of using vasodilator [ 12 ].
MDCTA allows most of the body to be scanned helically in just one breath hold less than 8 seconds, and thus provides high-contrast resolution without any artifacts. Together with axial images, 3D images provide a very good anatomical orientation. Detailed information regarding vascular, bowel and their relations with one another can be obtained, hence, CTA compared with DSA shows the equal or very similar diagnostic value [ 1314 ].
Different from the angiograph, MDCTA belongs to antegrade physiological imaging, and the developing time interval is very close between SMA and IMA, really reflecting the characteristics of anatomy and blood stream in these vessels. The gross success rate of Mesenteric artery CT angiography with bolus triggered technique was The data in this group indicates that the presence of arc of Riolan is closely related to not only the severe obstruction of SMA, but also obstruction of IMA, severe stenosis of SMA not obstruction also cause the expanded arc of Riolan.
In case of severe blood supply deficiency in SMA, arc of Riolan becomes the major collateral vessel. For example, IMA ischemia can not only be compensated by Drummond arc, but can trigger trunk collateral circulation system and plays the role of partial compensation from external iliac artery via rectum arc to internal iliac artery. The reasons causing stenosis or obstruction of SMA or IMA include atherosclerosis, mesenteric artery embolism, aorta lesions, and arteritis.
Marginal artery of the colon – Wikipedia
The 7 cases of IMA obstruction in this group included 6 cases of aorta interlining false lumen and abdomen aorta tumor, forming thrombus complicated with IMA obstruction, and 1 case with history of multiple aorta arteritis. In this study, all of the eight observed colon cancer cases with Riolan expansion were the advance of the sigmoid colon carcinoma infiltrating including sigmoid colon and partial descending colon.
Colon cancer is rich in feeding artery and expanded vein, and the richer blood supply indicates low differentiation of tumor and higher malignant degree [ 15 ]. When the inferior mesenteric artery cannot fulfill the needs of the tumor growth, the collateral circulation will be activated, supplying blood together by Arc of Riolan and Drummond marginal artery. CT signs such as wider range, rich blood supply, obviously strengthened masses at arterial and portal phase, and enlarged metastatic lymph nodes were displayed accordingly.
The transition zone between descending colon and sigmoideum colon is supplied jointly by colon sigmoideum artery and ACS, and the tumors rapidly grow to induce the compensatory blood supply in collateral circulation [ 16 ]. Ulcerative colitis is a recurrent chronic nonspecific inflammatory lesion, and angiography and pathophysiological studies show that the blood flow in intestinal wall was enhanced and small arteries were dense upon the occurrence of enteritis.
Relevant pathological changes are induced by Escherichia coli infection, leading to intestinal wall hyperaemia, vascular expansion, higher blood flow, and lower vascular resistance.
The 5 active UC patients all displayed intestinal vessel expansion, marginal artery expansion and arc of Riolan thickening, and strengthened intestinal wall, which are similar with Doppler ultrasound researches [ 17 – 19 ], namely UC can induce higher IMA blood flow, faster blood flow, and larger inner diameter in blood vessels. All factors affecting artery load will contribute to changes in mesenteric artery blood flow including position and foods [ 20 ]. Therefore, in our study, CT examination schemes adopt supine and scan on an empty stomach, and assumed that arc of Riolan blood flow was only decided by the arterial pressure difference.
In case of SMA stenosis, coeliac trunk artery and IMA can supply blood via pancreaticoduodenal arc and expanded arc of Riolan to small intestine and right hemicolon. In case of IMA stenosis or obstruction, SMA will supply blood via arc of Riolan to the left hemicolon and to some branches in left internal iliac artery. Therefore, due to the different positions of mesenterlc artery stenosis, the directions of blood stream in the arc of Riolan are different.
MDCTA belongs to antegrade image, and the blood flow direction can be determined by the position of stenosis and the size variation of blood vessels. The arc of Riolan expanding degree in the upward group is obviously higher than the downward group and the two-way group. Thus limitations are inevitably showed in this study. First, a bias in selection of patients, which may affect the occurrence rate of arc of Riolan, at the same time it also reflects the real situation in clinic to some degree.
Second, celiac and mesenteric artery variation situation did not be considered in our paper. A previous research [ 21 ] suggested that congenital superior-inferior mesenteric arterial variation or arc of Riolan was due to occlusion of proximal superior mesenteric artery.
Third, we assume that the arc blood flow direction is based on the difference of vascular lumen diameter is raised, not confirmed by doppler. In fact, the intestinal artery blood flow rely mainly on its own pressure difference, may also be affected by the postures, eating, etc besides.