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Eur J Cardiothorac Surg 2007;31:249-255. doi:10.1016/j.ejcts.2006.11.024
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved
a Department of Radiology, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan
b Department of Thoracic & Cardiovascular Surgery, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan
Received 17 October 2006; received in revised form 13 November 2006; accepted 14 November 2006.
* Corresponding author. Tel.: +81 952 34 2309; fax: +81 952 34 2016. (Email: nojirij{at}cc.saga-u.ac.jp).
| Abstract |
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Key Words: The artery of Adamkiewicz Computed tomography (CT) Angiography Computed tomographic angiography (CTA) Aortography Aorta
| 1. Introduction |
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Improved contrast resolution is essential to increase the detectability and visualization of minute vessels. In this regard, we performed CT angiography with intraarterial contrast injection (IA-CTA) to increase the bolus characteristic of the contrast medium, and we investigated detectability and visualization of the ARM, branching level of innate origin, and right/left frequency as well as continuity from the origin to the ARM. Furthermore, the bolus characteristic of contrast medium in IA-CTA was investigated and compared with IV-CTA.
| 2. Materials and methods |
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Concerning the devices, a simple angio-CT system that combined portable digital subtraction angiography (DSA) (OEC Series 9600; GE Yokogawa Medical Systems Co., Ltd., Tokyo, Japan) and a 4-row MDCT (Light Speed QX/I; GE Yokogawa Medical Systems Co., Ltd., Tokyo, Japan) was used in the first 19 cases, and an angio-CT system (AXIOM Artis dTA; Siemens-Asahi Medical Technologies Ltd., Tokyo, Japan, 6-row MDCT as the CT device) was used in the eight more recent cases.
As to the procedure, a 4-Fr pigtail catheter was inserted from the right femoral artery or left brachial artery to the descending aorta immediately below the left subclavian artery, and DSA was performed (a total of 16 ml of contrast medium was injected at 8 ml/s in aneurysm cases and a total of 20 ml was injected at 10 ml/s in the dissection cases). Subsequently, IA-CTA was performed. Scanning parameters of 4-row MDCT were as follows: 120 kV; 300350 mA; field of view (FOV), 2027 cm; 0.8 s per rotation; slice collimation, 1.25 mm x 4; and table speed, 9.4 mm/s (pitch 6). Reconstruction was done at 1.25-mm section thickness and intervals of 0.71.25 mm. Scanning parameters of 6-row MDCT were as follows: 110 kV; 120150 eff mA; FOV, 20 cm; 0.6 s per rotation; slice collimation, 1 mm x 6; and table speed, 16.7 mm/s (pitch 10). Reconstruction was done at 1.25-mm section thickness and intervals of 0.7 mm. A total of about 100 ml of Iomeprol 400 mg I/ml (Eisai Co., Ltd., Tokyo, Japan), Iopamidol 370 mg I/ml (Nihon Schering K.K., Osaka, Japan), or Iohexol 300 mg I/ml (Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan) contrast medium was injected at 4 ml5 ml/s in aneurysm cases. For the dissection cases, a total of about 120 ml was injected at 7 ml/s. CT scan was started at 4.57 s after the start of injection. At first, the scanning range was from the upper margin of the 7th thoracic vertebra to the lower margin of the 1st lumbar vertebra, according to a report that 91% of ARMs branched out from the 8th thoracic vertebra to the 1st lumbar vertebra level (16). However, because we encountered some cases of branching from the more caudal side, the scanning range was set from the upper margin of the 7th thoracic vertebra to the lower margin of the 3rd lumbar vertebra, and the procedure was performed in all cases under breath hold.
Analysis was performed on a workstation (Advantage Windows 3.1; GE Yokogawa Medical Systems Co., Ltd., Tokyo, Japan). Using the paging method, multi planar reformation (MPR) of 0.51.5 mm section thickness and curved planar reformation (CPR) of 0.51.5 mm section thickness, detectability and visualization of the ARM, and the number of vessels, branching level of innate origin, left/right frequency, and the continuity from the origin to the ARM were investigated. In this study, assessment was made by defining the ARM as a large radiculomedullary artery that leads to the anterior spinal artery and shows a characteristic hairpin curve.
The bolus characteristic of the contrast medium was assessed by determination of the CT value (Hounsfield unit; HU) in the aorta in each of the 16 cases in which both IA-CTA before surgery and IV-CTA at the time of admission were performed. Patients who underwent CT at another hospital or those who underwent IV-CTA without the use of a similar amount of iodine were excluded from the comparison. The assessed level in the aorta was set at the 12th thoracic vertebra level for both IA-CTA and IV-CTA because the origin of the ARM most frequently branches out at the 12th thoracic vertebra and because the level can be easily captured in view of its relation to the ribs. Among the 16 patients used for comparative control, the aorta at the assessed level had a single lumen in nine patients and a double lumen in seven. In the latter cases, the CT value was determined by classifying the lumens as true and false. By taking advantage of the cross-sectional CT image, the CT value was assessed at three sites, namely, anterior, middle, and posterior sites at the above-mentioned level of the lumen. The mean value obtained from these three sites was calculated, and regarded as the mean CT value in the lumen. For IV-CTA, 4-row MDCT (Aquilion TSX-101A; Toshiba Medical Systems Co., Ltd., Tokyo, Japan) was used. Scanning parameters were as follows: 120 kV; 350400 mA; FOV, 3240 cm; 0.5 s per rotation; slice collimation, 2 mm x 4; and table speed, 27.5 mm/s (pitch 5.5). A total of about 100 ml of Iomeprol 350 mg I/ml was injected into an antecubital vein at 3 ml/s. The scan delay was set by means of an automatic triggering system (Real Prep; Toshiba, Tokyo, Japan). Continuous low-dose fluoroscopy (120 kV, 50 mA) at the level of the descending aorta was initiated 10 s after the injection of contrast material. When the attenuation value reached a pre-set threshold (an absolute attenuation value of 100 HU) in sampling point, helical scanning of the thoracolumbar aorta automatically began. Reconstruction was performed at 2-mm section thickness at intervals of 1 mm. Student's t-test was used for statistical analysis, and statistical significance was set at p < 0.05.
| 3. Results |
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Concerning continuity from the origin to the ARM, the innate origin itself was occluded in 20.5% (8/39) of the total ARMs. However, it was possible to observe the continuity from the innate origin to the ARM as well as from the secondary origin to the ARM mediated by collateral vessels in 61.5% of the total ARMs (24/39) (Figs. 1 and 3 ). An artery (intercostal artery) originating from a false lumen of dissection was also noted in one case and continuity to the ARM was confirmed in this case (Fig. 4 ). It was not possible to follow the continuity from the origin to the ARM in four vessels because the origin was outside the scanning range, in two vessels because the FOV was somewhat small and the route mediated by bypass was outside the FOV range, and in nine vessels because imaging of the vessels themselves was poor. However, even if the exact continuity was not followed, it was possible to estimate the origin. Including the estimated origins, information on origin was obtained for 90% of the ARMs (35/39) and at least one ARM to be reserved was determined in each patient.
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| 4. Discussion |
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The average number of ARM per patient was slightly higher than that reported by Koshino et al. [16], who investigated autopsy cases (no case of aortic disease) in Japan. According to Koshino et al. [16], the average number of ARM was 1.3 ± 0.65, definitely demonstrating presence of cases with plurality of ARMs, but the average number was lower than that reported in prior autopsy cases. Koshino et al. [16] explained that the reason was that only a comparatively large radiculomedullary artery was defined as an ARM in their study. Despite the aortic disease involvement, it is considered relatively minute vessels could be detected by our method. Some researchers may oppose the definition of these minute vessels as ARMs. However, if the vessels are clinically imaged, they should be taken into consideration as important vessels for feeding nutrients to the spinal cord, whether or not they are minute.
Concerning the branching level of innate origin of the ARM and the right/left frequency, it was reported that 91% of the vessels branched out between the 8th thoracic vertebra and the 1st lumbar vertebra (87% between the 9th thoracic vertebra and the 1st lumbar vertebra), and that 72% branched to the left [16]. Our results were not much different from these, but the ratio of vessels that branched out of the lower right region was slightly higher in our study.
It was possible to clearly confirm continuity from the origin to the ARM in 61.5% (24/39) of the ARMs. The result was only slightly better than that reported by Yoshioka et al. [15] (56.6% by MRA and 50% by IV-CTA). This was probably because Yoshioka et al. [15] identified only one ARM per patient, there was difference in the percentage of dissection cases (about 30% in the report by Yoshioka et al. vs 50% of our cases), and occlusion of the artery origin was noted in 20% of all ARMs in our study. Even though it was not possible to confirm exact continuity from the origin to the ARM in 15 cases, the assumed origins could be limited to several levels in our study on the basis of the direction of intervertebral foramen from which the ARM originated, the presence or absence of patency in the proximal intercostal and lumbar artery, and the extent of collateral flow development. As a result, we were able to identify the vessels to be reserved at graft surgery in all 27 patients, indicating that sufficient information was obtained before surgery.
A method that increases the bolus characteristic of contrast medium is preferable for capturing minute vessels. However, it was reported that intravenous injection of contrast medium at a rate exceeding 4 ml/s did not induce a clinically significant increase in aortic enhancement [17,18]. In other words, it is not considered possible to increase the bolus characteristic of contrast medium any more even if the focal region can be quickly photographed by MDCT in IV-CTA. In fact, the CT value in the aorta determined under IA-CTA was significantly higher than that determined by IV-CTA performed at this hospital (p < 0.05). Shinagawa et al. [19] intravenously injected a total 1.5 mg/kg of contrast medium (370 mg I/ml) rapidly at 5 ml/s and determined the CT value in the aorta to be time-dependant. The mean value was reported as 346.3 ± 113.7 HU (n = 20) [19]. The number of cases of aortic disease was not stated, but the result still indicated a significantly lower CT value compared with our results by IA-CTA. The contrast medium administered by IV-CTA is mixed in the right heart, dilutes while it passes through the pulmonary circulation, and some of the contrast material flows to the head and upper limbs. On the other hand, it is possible to inject a large amount of contrast medium at a high concentration directly into the aorta in IA-CTA so that the bolus characteristic of contrast medium is definitely increased in comparison with that in MRA with intravenous contrast injection and IV-CTA. This is the reason for the above-mentioned favorable results. Although there was no statistically significant difference, the CT value in the descending aorta obtained by IA-CTA tended to be higher in the dorsal side in comparison to that of the ventral side. This is attributable to the high specific gravity of contrast medium, and the fact is favorable because the intercostal or lumbar artery that serves as the origin of the ARM generally branches from the dorsal side of the aorta.
Even though ARMs were captured as described above, there were four vessels in which the branching site from the aorta was outside the scanning range. Furthermore, there were two vessels in which the innate origin of the ARM was occluded so that it was difficult to confirm continuity in some part because some of the collateral vessels ran outside the scanning range. To improve procedure results in the future, the present results suggest the need to use a slightly wider CT scanning range from the cephalic to the caudal direction as well as a slightly wider FOV. However, considering that the ARM that branches from the caudal lumbar vertebral level causes fewer clinical problems, the CT scanning range from the cephalic to the caudal direction should be determined depending on the patient and the imaging devices used.
Concerning procedural safety, it was reported that the incidence of complications during general selective angiography is 1.73% overall [20]. However, there has been no report on complications when cases were limited to aortography alone, especially in recent cases in which a small diameter catheter was used. Accordingly, the incidence of complications by this method is assumed to be much lower than that reported above. In fact, we have not had any complications associated with the procedure. No definite changes in renal function were observed except for minor temporal renal dysfunction observed in two patients in whom renal function was poor prior to the procedure.
Surgery was not performed in five patients according to the judgment made after the procedure. However, 22 of the 27 patients underwent surgery later on. Although transient paraplegia occurred after surgery in one patient (4.5%), no paraplegia was observed in the remaining cases, indicating that sufficient helpful information was obtained before surgery. In the transient paraplegia case, the innate origin of the ARM was the left 1st lumbar artery according to the preoperative IA-CTA. However, all near by peripheral intercostal and lumbar arteries were occluded except for the left 11th intercostal artery. Accordingly, surgical reservation of the left 11th intercostal artery was scheduled. However it was not possible due to severe arteriosclerosis, so the surgery was completed after reservation and reconstruction of some proximal intercostal and lumbar arteries that were operable. Paraplegia occurred from the day after surgery and persisted for about 1 month. Gradual improvement was observed thereafter. The causes of paraplegia in this case were assumed to be insufficient blood flow from the reconstructed vessel to the spinal cord, insufficient blood flow in the reconstructed vessels themselves, prolongation of surgery because several vessels had to be reconstructed, and embolism due to atheroma associated with arteriosclerosis.
Currently, in surgery for an aneurysm or dissection of the descending thoracic or thoracoabdominal aorta, postoperative paraplegia is unavoidable in some cases. The hemodynamic pattern in the spinal cord has yet to be clarified in this regard. However, detecting the ARM before surgery is considered necessary to reduce the risk of postoperative paraplegia. Various ideas and measures contrived in this regard may not only reduce the incidence of paraplegia but also elucidate the hemodynamic pattern in the spinal cord.
| Acknowledgments |
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| References |
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