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Ann Thorac Surg 2004;78:846-851
© 2004 The Society of Thoracic Surgeons
a Departments of Thoracic and Cardiovascular Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan
b Department of Radiology, Sapporo Medical University School of Medicine, Sapporo, Japan
Accepted for publication February 6, 2004.
* Address reprint requests to Dr Kawaharada, Department of Thoracic and Cardiovascular Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan, South 1, West 16, Chuo-ku, Sapporo 060-8543, Japan
nobuyosh{at}sapmed.ac.jp
Presented at the Poster Session of the Fortieth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan 2628, 2004.
| Abstract |
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METHODS: Between April 2000 and December 2003, 120 patients underwent magnetic resonance angiography for detection of the ARM. The morphology of the anterior spinal artery at the ARM junction, as revealed by magnetic resonance angiography, in 99 patients in whom ARM was preoperatively detected was classified into the following three types: noncontinuation of the anterior spinal artery above the ARM junction (type A), continuation of the anterior spinal artery above and below the ARM junction (type B), and noncontinuation of the anterior spinal artery below the ARM junction (type C).
RESULTS: The ARMs were detected in 99 (83%) of 120 patients, and from a total of 110 ARMs 105 (95%) originated from intercostal arteries branching from the left side and 94 (86%) originated between Th9 and Th11. Two ARMs were found in 11 (11%) of 99 patients in whom ARMs were detected. In 107 patients, who underwent magnetic resonance angiography to reveal the morphology of the anterior spinal artery at the ARM junction, the patterns of the anterior spinal artery were type A in 59 patients (55%), type B in 21 patients (20%), type C in 3 patients (3%) and not classified in 24 patients (22%). No spinal cord injury occurred in patients in whom the ARM had been preoperatively detected.
CONCLUSIONS: Preoperative detection of the ARM is possible by magnetic resonance angiography and is very useful for reducing the incidence of ischemic injury of the spinal cord.
| Introduction |
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Magnetic resonance angiography (MRA) [911] and multi-slice computed tomography (MSCT) [12, 13] have been reported to be useful for noninvasive ARM detection. However, it is not clear how these noninvasive imaging modalities can best be used when planning surgical repair and stent-grafting of thoracoabdominal aortic lesions to secure spinal blood flow and to prevent the occurrence of paraplegia/paraparesis. The purpose of this study was to determine whether the ARM and the discrepancy in sizes of the anterior spinal artery (ASA) above and below the junction of the ARM can be detected by MRA and to determine the usefulness of preoperative MRA evaluation of the ARM for predicting the likely outcome of surgical treatment of thoracoabdominal aortic aneurysm or descending thoracic aortic aneurysm.
| Material and methods |
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The 120 patients included 84 men (70%) and 36 women (30%), the patients' ages ranged from 19 to 83 years old (median, 65.6 years old). There were 3 patients (2.5%) with Marfan's syndrome. Forty-three patients (36%) had aortic dissection and 77 (64%) had nondissecting aneurysms. Eighty-seven (73%) of 120 patients had undergone operation for descending thoracic aortic aneurysm or thoracoabdominal aortic aneurysm (Table 1). Fifty-five patients (63%) had descending thoracic aortic aneurysm and 32 (37%) had thoracoabdominal aortic aneurysm. Seventy-one (82%) of 87 patients had undergone operations with reference to information obtained by preoperative detection of ARM.
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Imaging protocol and data processing
The MRAs were performed with a 1.5-T unit (SIGNA Horizon LX Echospeed and with a SIGNA Infinity Excite [from January 2003]; GE Medical Systems, Milwaukee, WI). Since reconstruction of the radicular artery is considered necessary for aortic graft replacement in our institute, a 20-cm field of view (FOV) from above the L2 level was examined in each patient. Dynamic study was carried out by the enhanced three-dimensional fast spoiled GRASS (FSPGR) method (phased array spine coil; TR/TE/flip angle, minimum/minimum/10 to 5 degrees; NEX, 2; matrix, 256x128; slice thickness, 1.6 mm; zero fill interpolation [slice ZIP 4 and in-plane ZIP 512]; no phase wrap; FOV, 20 cm; oblique-coronal section along the posterior line of the vertebral body). Gadolinium-diethylenetriaminopentaacetic acid (Gd-DTPA; MAGNEVIST, Schering, Berlin, Germany) was injected through the cubital vein (0.2 mmol/kg, 4 mL/s) followed by a 20-mL saline flush. A power injector (OPTISTAR MR; Mallinckrodt, St. Louis, MO) was used in all patients. After injection, dynamic studies were carried out five times. Scan times were 22 seconds for each session. After data acquisition, the images were stored as DICOM data sets and displayed on a diagnostic monitor at a 0.4-mm reconstruction pitch.
The acquired data sets were transmitted to a workstation (Advantage Windows; GE Medical Systems). The maximum intensity projection (MIP) image was reconstructed in each of five phases. The resulting five MIP images were used for subtraction. The second to fifth phase images were subtracted. The first phase and resulting four subtraction images (total of five MIP) were presented in a movie format that followed the imaging time course.
Criteria for detection of the ARM
Criteria for detection of the ARM on source and MIP images was as follows (1) being continuous to a clear blood vessel supply from the intercostal or lumbar artery in an early phase image; (2) identification of extension of a blood vessel from the dorsal branch of the intercostal or lumbar artery toward the surface of the anterior spinal cord in the early phase; and (3) diminishing vascular signal intensity in late phase.
Surgical procedure
The patients who underwent repair of an aneurym of the descending or thoracoabdominal aorta using a partial cardiopulmonary bypass in elective surgery without profound hypothermic circulatory arrest under double-lumen endotrachealtube anesthesia were treated according to a previously reported procedure [14]. After the left thoracic cavity or left retroperitoneal space had been entered, cannulation into the right femoral artery and femoral vein was performed in all patients. For thoracoabdominal aortic aneurysm repair, a left thoracoabdominal incision was made with circumferential division of the left hemidiaphragm. The segmental arteries below the Th8 level, if patent, were reconstructed using the inclusion or exclusion button technique or by interposition 8-mm tubular grafts for reattachment of individual intercostal or lumbar arteries. The reason for reimplanting all patent arteries between Th8 and L1 is that the blood supply to the spinal cord has been reported to be provided by some arteries from Th8 through to L1 in 91% of cases and the ARM does not always originate from the larger segmental arteries [15, 16]. However, the Th8-through-L1 operative strategy has the following problems: (1) reattaching all of the arteries from Th8 to L1 prolongs the clamping time, which may cause spinal cord injury, and (2) some of the arteries that are reattached may not need to be reattached. Obviously, an accurate and reliable technique for identifying arteries that need to be reattached is needed.
When the ARM existed in the region of graft replacement, only the intercostal or lumbar artery in the aneurysm that was detected as the origin of the ARM was reconstructed to the graft. When the ARM did not exist within the graft replacement region, the cross-clamping level was adjusted, and no intercostal or lumbar arteries were reconstructed. When the ARM could not be detected by MRA, conventional graft replacement (reconstruction of all patent intercostal or lumbar arteries) was performed. Visceral and renal arteries were also reimplanted by an island cuff technique or preserved in a beveled distal aortic anastomosis. During reconstruction, selective visceral and renal perfusion with 10F to 12F balloon cannulas was performed by clamping the outflow tubing to the lower extremities.
In patients treated by stent-graft insertion repair, the following method was used. After general anesthesia, the right (or left) femoral artery was dissected for 20F to 22F delivery sheath placement. Under fluoroscopic control, a Z-based handmade stent-graft was deployed to attach to the proximal or distal aortic neck in order to isolate the aneurysm lumen. To secure the ARM branching radicular artery in distal aortic neck, the stent-graft was adjusted in length when it was formed. Most of the cases treated by stent-graft insertion repair were descending thoracic aortic aneurysms (Table 2). Surgical repair was performed on all aortic aneurysms cases whether ARM was detected by MRA or not. In patients with thoracoabdominal aortic aneurysm, stent-grafting with bypass procedure of celiac artery and superior mesemteric artery was performed.
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| Results |
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Data on the patients who underwent surgical operations are presented in Table 2. Eighty-seven (73%) of 120 patients underwent surgical operations; thoracoabdominal aortic aneurysm repair in 32 patients (including stent-grafting in 1 patient), descending thoracic aortic aneurysm repair in 55 (including stent-grafting in 24 patients). Paraplegia did not occur in any of the patients in whom the ARM was detected preoperatively by MRA (Table 3).
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| Comment |
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In anatomical studies, the ARM was found to originate from the left side in 72% [16] to 78% of patients [17], between Th8 and L1 levels in 91% of patients [16], and between Th7 to L1 levels in 94% of patients [17]. The results of the present study concur with the results of those studies. Koshino and colleagues [16] reported that there was no significant correlation between the diameter of the ARM and the diameters of the intercostal artery and lumbar artery from which the ARM originated. Furthermore, within the Th8 to L1 vertebral level, the diameters of the intercostal artery and lumbar artery varied considerably and did not correlate with the diameter of the ARM [16]. Morishita and coworkers reported that the ASA was continuous in adult cadavers and that there was a discrepancy between the ASA diameters above and below the ARM. Furthermore, distal spinal blood supply becomes progressively dependent on the ARM as the narrowest point of the ASA becomes narrower [17]. The morphology of the ASA at the ARM junction, as revealed by MRA, in patients in whom the Adamkiewicz artery was detected was classified into three types. Since we could not measure the size of the ASA by MRA, the three types of ASA morphology were determined according to whether there was continuation of the ASA above and below the ARM junction. Noncontinuation of the ASA above the junction of the ARM was visualized by MRA, but continuation was found in some patients, suggesting that there are some patients in whom spinal cord ischemia would not occur even if reattachment of intercostal arteries was not performed. Some surgeons no longer consider reimplantation of the ARM to be the best treatment strategy and now believe it is best to rely on collateral circulation and a short aortic cross-clamping time [18, 19]. Since MRA showed continuation of the ASA above and below the ARM junction (type B) in 20% of the patients, it is possible that spinal cord ischemia will not occur in such cases even without ARM reconstruction.
However, the pattern of the ASA was type A, noncontinuation of the ASA above the ARM junction, in 59 patients (55%). Hollier and coworkers used complete radicular arterial reattachment to prevent spinal ischemia after thoracoabdominal aortic repair [3]. Svensson and associates reported that reattachment of the radicular artery most likely to supply the ARM is important to secure spinal blood supply [20]. They noted that successful reattachment of segmental intercostal or lumbar arteries from Th8 to L1 is important to reduce the risk of paralysis. Therefore, it is very important for us to maintain stable spinal cord circulation achieved by reattaching the intercostal arteries.
The problems with the operative strategy of reattaching all intercostal lumbar arteries, including those within the Th8 to L1 vertebral level, are that some of the arteries may not need to be reattached and that reattachment of all of the arteries from Th8 to L1 prolongs clamp time and operation time. A long clamp time may result in spinal cord injury, and a long operation time may result in other postoperative complications. Obviously, an accurate and reliable technique for identifying arteries that need to be reattached is needed. Therefore, reconstruction of intercostal arteries should be planned on the basis of preoperative detection of ARM for distal spinal blood supply.
Prevention of the intraoperative steal phenomena (blood flow away from spinal cord circulation) and maintenance of high pressure in the proximal descending aorta may allow sufficient blood flow through the ASA during reconstruction of intercostal arteries in thoracobdominal or descending thoracic aortic aneurysm repair. Catheters may be placed in the orifice of intercostal arteries to control back-bleeding and thereby prevent the intraoperative steal phenomena or alternatively ligation of intercostal arteries by clipping can be performed, if the intercostal artery supplying ARM is identified preoperatively by MRA and excluded as a candidate for clipping.
However, Svensson and coworkers [20] reported that a third of neurologic deficits occurred in a delayed fashion and that such delayed complications were closely associated with postoperative hypotension. These findings suggest that postoperative spinal cord circulation is unstable. Therefore, to reduce delayed deficits, we emphasize the importance of stable spinal cord circulation achieved by reattaching the segmental arteries if the ARM can be detected preoperatively.
Preoperative detection of an intercostal artery that may be related to the ARM is very useful for establishing the best operational strategy for descending aortic aneurysm or thoracoabdominal aortic aneurysm repair, because surgical repair can be performed while taking care to revascularize the intercostal and lumbar arteries at or near the level of the ARM, and the occurrence of spinal cord injury can thereby be reduced. In our institute, we have routinely reconstructed or preserved an intercostal artery that may be related to the preoperatively detected ARM during operations for repair of thoracoabdominal or descending thoracic aortic aneurysm.
Because use of the large carrel patch method can result in expansion of the remaining aortic wall after the operation, we used the interposition procedure for reconstruction of intercostal arteries as the first choice in order to minimize the area of the remaining aortic wall. With this reconstruction method, we think that we may be able to reduce operation time, distal perfusion time and clamp time needed for thoracoabdominal aortic aneurysm repair.
In conclusion, preoperative detection of the Adamkiewicz artery is possible by MRA, and detection of this artery is very useful for reducing the incidence of ischemic injury of the spinal cord and noncontinuation of the anterior spinal artery above the junction of the ARM was visualized by MRA.
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