MRA of the Adamkiewicz artery: a preoperative study for thoracic aortic aneurysm

Neuromonitoring during descending aorta procedures

Thoraco-abdominal aneurysm (TAA) repair carries a significant risk of spinal cord infarction. The latter results from irreversible changes in the spinal cord arterial network, e.g., sacrifice of the segmental arteries. Intra-operative neurophysiology with somatosensory and especially motor evoked potential (SEP and MEP respectively) monitoring, has emerged as an effective tool to assess the efficiency of the collateral blood flow, detect reversible spinal cord ischemia and guide the peri-operative multidisciplinary management to prevent postoperative paraplegia. The main roles of such monitoring include diagnosis of spinal cord vs peripheral limb ischemia, titration of mean arterial pressure during aortic clamping, the guidance of selective re-implantation of critical segmental arteries, and management of hemodynamics in the immediate postoperative period. In addition, manipulation of the aortic arch and proximal descending aorta, adds the risk of cerebral infarction from both low flow state and/or thromboembolic events. As such, EEG monitoring may be a useful add-on for either assessment of the efficiency of cerebral cooling as a neuroprotective method and/or for detection and treatment of reversible cerebral ischemia. This chapter presents the multimodality approach to open TAA monitoring as a versatile tool for the prevention of devastating postoperative neurologic deficits.

Impact of preservation of the latissimus dorsi muscle through a left anteroaxillary thoracotomy on spinal cord protection in descending thoracic and thoraco-abdominal aortic operations†

OBJECTIVES

The presence of collateral network circulation to the spinal cord, which is reflected in the repair of a descending thoracic aortic aneurysm (dAo) and a thoraco-abdominal aortic aneurysm (TAAo), has been demonstrated in clinical and animal experimental data. The latissimus dorsi muscle (LDM) including the thoracodorsal artery might be one of the major sources of this collateral network. The objective of this study was to evaluate the impact on spinal cord safety of a left anteroaxillary thoracotomy with minimal muscle division including preservation of the LDM in surgery for dAo and TAAo.

METHODS

Sixty-nine patients [64 (23-85) years old; 56 men] who underwent surgical repair for dAo and TAAo were divided into 2 groups: 29 [65 (23-84) years old] with an anteroaxillary thoracotomy with LDM preservation (PL group) and 40 [61 (28-85) years old] with a lateral thoracotomy without LDM preservation (NL group).

RESULTS

Aortic repairs were performed at the dAo in 30 patients including 14 in the PL group vs 16 in the NL group and at the TAAo in 39 patients including 15 in the PL group vs 24 in the NL group. There were 2 (2.9%) 30-day deaths; 2 (7.9%) in the PL group vs none in the NL group (P = 0.173). No strokes occurred. In patients with a femoro-femoral partial cardiopulmonary bypass with mild hypothermia, the incidence of loss of signal of motor-evoked potentials (>50%) was significantly lower in the PL group; 5.6% vs 31.8% (P = 0.039). The frequency of signal reduction of the remaining motor-evoked potential after surgery was also significantly lower in the PL group: 3.7% vs 25% (P = 0.040). Subsequently, the rate of spinal cord complications were lower in the PL group: 3.4% vs 12.5% (P = 0.188).

CONCLUSIONS

The left anteroaxillary thoracotomy with minimal incision of the muscles including the LDM might have potential advantages for spinal cord protection via preserved intramuscular collateral circulations to the spinal cord in dAo/TAAo open repairs.

The Initial Exploration of Adamkiewicz Artery Computed Tomographic Angiography With Monochromatic Reconstruction of Gemstone Spectral Imaging

OBJECTIVE

The study aimed to explore whether optimal monochromatic reconstruction can improve the depiction of the Adamkiewicz artery (AKA) on gemstone spectral computed tomographic angiography (GSCTA) compared with the polychromatic reconstruction protocol.

METHODS

The prospective study was approved by the ethics committee, and written informed consent was obtained from each patient. The 58 consecutive patients suspected of aortic aneurysm or dissection underwent aortic GSCTA. All images were reconstructed with both polychromatic (group A) and optimal monochromatic (group B) protocol. The CT values of the descending aorta and muscle, background noise, and the contrast-to-noise ratio were measured and calculated. With the criterion standard display of AKA, characteristic hairpin curve sign, 2 blinded radiologists analyzed data independently with the paired samples t, χ, and Mann-Whitney U test.

RESULTS

The CT value of the descending aorta and the contrast-to-noise ratio of group B were significantly superior to group A (t = 12.7, P < 0.01; t = 15.2, P < 0.01). The visual rate of AKA (94.8%) in group B was significantly higher (χ = 4.2, P = 0.04) than group A (82.8%). Using a 5-point scale to assess, the score of the visualization efficiency of group B (226) was significantly higher (Z = -2.4, P = 0.02) than group A (192).

CONCLUSIONS

The optimal monochromatic reconstruction for GSCTA can improve the visualization efficiency and quality of the AKA compared with the polychromatic reconstruction protocol.

Feeding Arteries of the Spinal Cord at CT Angiography before and after Thoracic Aortic Endografting

Purpose:

To study the visualization of spinal cord feeding arteries in patients with complex thoracic aortic pathology undergoing endovascular aortic repair (EVAR) using an optimized protocol for multislice computed tomographic angiography (MSCTA).

Methods:

Eighteen consecutive patients (13 men; mean age 63 years, range 45–79) with aortic type B dissections (n=5), chronic expanding aortic dissections (n=5), thoracic aortic aneurysms (n=6), or penetrating aortic ulcers (n=2) underwent 16-slice CTA before and after (mean interval 9 days) EVAR. Pulse rate and neurological status were documented. Quantitative density measurements were taken at regions of interest (ROI) in the ascending thoracic aorta and at the level of the diaphragm. Two experienced radiologists qualitatively assessed the posterior intercostal arteries (PIA; fully visible, partially visible, non-visible), dorsal branches (DB; visible/non-visible), and artery of Adamkiewicz (AKA; visible/non-visible) on multiplanar reformations and maximum intensity projection reconstructions.

Results:

MSCTA was performed successfully in 17/18 patients before and after EVAR (1 patient was excluded after EVAR owing to rising creatinine levels). Before EVAR, MSCTA revealed 197/203 PIAs within the stented area, of which 179 were fully and 18 partially visible. No significant (p=0.37) difference was noted for overall PIA detection within the stented area on post-EVAR MSCTA (185/203 PIA), although only 124 were fully and 61 partially visible. Similar results were obtained for DB visualization. The AKA were seen in 10/17 patients pre EVAR and 9/17 post EVAR. In 2 patients, the AKA was localized within the stented aortic segment. ROI analysis revealed contrast densities of 427±89 HU and 398±84 HU on pre- and post-EVAR MSCTA, respectively. No neurological events were observed.

Conclusion:

The majority of posterior intercostal arteries and dorsal branches remain open after EVAR due to retrograde perfusion. High-resolution MSCTA permits accurate pre-and post-EVAR visualization of spinal cord feeding arteries in patients with thoracic aortic pathology.

Spinal intraarterial computed tomography angiography as an effective adjunct for spinal angiography

OBJECT

Spinal digital subtraction angiography (DSA) is indispensable for the precise diagnosis of spinal vascular lesions and the assessment of blood supply to the spinal cord. However, comprehensive spinal DSA covering multiple segments requires repetition of selective catheterization into small segmental arteries, which is time consuming, sometimes difficult, and hazardous. The authors investigated the usefulness of CT angiography with intraarterial contrast injection (IA-CTA) as a preliminary study preceding spinal DSA. With the advent of multidetector CT, it is feasible to obtain images of the spinal cord vasculature instantaneously overa number of segments.

METHODS

A total of 56 patients with lesions involving the spinal vasculature underwent IA-CTA with 64- or 320-row detector CT in advance of comprehensive spinal DSA. Contrast material was injected via a pigtail catheter placed at the aorta in proximity to the segments of interest. Scanning was repeated twice to obtain arterial- and venous-phase images to differentiate between the arterial and venous components. The spinal arteries were identified by paging the various multiplanar reconstruction images and tracing the vessels from the aorta. Spinal DSA was subsequently performed by guiding selective catheterization to the feeding segments in reference to the IA-CTA findings. Visualization of the segmental arteries, normal spinal arteries, and abnormal vessels during IA-CTA was investigated and compared with that obtained during spinal DSA.

RESULTS

In all 56 patients, spinal IA-CTA successfully enabled visualization of the spinal vessels, including the radicular arteries and the anterior spinal artery. Below the aortic arch, all segmental arteries were identified clearly. The segmental arteries, radiculomedullary arteries, spinal arteries, and abnormal vessels were traced from the aorta, which would be the target of selective catheterization. In 3 (6.8%) patients, IA-CTA revealed severe aortic atherosclerosis and occlusion of some segmental arteries. The information obtained was useful for directing selective catheterization studies. The findings of IA-CTA corresponded well with those of spinal DSA.

CONCLUSIONS

IA-CTA is a useful adjunct to spinal DSA for surveying the vasculature surrounding the spinal cord and for orienting selective catheterization. IA-CTA can complement spinal DSA, curtail unnecessary segmental injections, and thus reduce procedural complications.

Preoperative visualization of the artery of Adamkiewicz by dual-phase CT angiography in patients with aortic aneurysm

To improve our ability to visualize the Adamkiewicz artery (AKA), we developed a modified intravenous CT angiography technique, which we refer to as right atrial CT (RA-CT) angiography. In this study, AKA detection rate and visualization of the arterial continuity from the aorta to the anterior spinal cord artery (ASA) was evaluated using RA-CT angiography.We performed RA-CT angiography in 110 patients with abdominal, thoracic descending, or thoracoabdominal aortic aneurysms. In RA-CT angiography, contrast medium with a high iodine concentration (370 mg/dl) was injected twice into the right atrium at a high injection rate (8.0 ml/sec), and two CT scans, starting at 20 sec after the first injection and at 35 sec after the second injection, respectively, were performed. All CT images were obtained using an 8- or 16-detector CT scanner at a slice thickness of 0.625 mm. The AKA was defined as the largest radiculomedullary artery with a characteristic hairpin turn, and with continuity from the aorta to the ASA.The AKA with hairpin turn was detected in all patients (100%), and continuity from the aorta to the ASA was confirmed in 99 of the 110 patients (90.0%). The AKA arose between Th8 and L1 in 86 of these patients (86.8%), and originated from the left side in 71 patients (71.7%).RA-CT angiography may be useful for visualizing the AKA and the arterial continuity from the aorta to the ASA in patients with aortic aneurysm, although the use of more advanced CT machines will provide safe and easy identification of the AKA and arterial continuity with a small amount of contrast medium and a single scan.

Clinical-radiological severity mismatch phenomenon: patients with severe neurological deficits without matching infarction on computed tomographic scan

OBJECTIVE

The objective was to determine the long-term outcome of patients with severe persistent neurological deficits without a large infarction on computed tomographic (CT) scan.

METHODS

We analyzed the prospectively collected data as part of the randomized, placebo controlled trial in patients with ischemic stroke presenting within 3 hours of symptom onset. Volume of infarction was measured from CT scan acquired at 3 months. Favorable outcome defined by no significant or slight disability on a modified Rankin scale at 12 months. We determined the outcome of patients with National Institutes of Health Stroke Scale score (NIHSS score) ≥ 10 at 24 hours.

RESULTS

Of the 277 patients with NIHSS score ≥ 10 at 24 hours, 88 (32%) met the criteria of clinical-radiological severity mismatch. Compared with patients with NIHSS score ≥ 10 with infarct volume ≥ 20 cc, the patients with NIHSS score ≥ 10 and infarct volume <20 cc were older but there were no differences in the gender, race or vascular risk factors. Patients with clinical-radiological severity mismatch were more likely to have a favorable outcome at 12 months compared with those without mismatch (odd ratio 4.3, 95% confidence interval 1.5-12.6, P = .0063) after adjusting for potential confounders.

CONCLUSIONS

We observed that approximately one-fourth of patients with severe neurological deficits have clinical-radiological severity mismatch. Such patients appear to have a high rate of favorable outcomes at 1 year.

Simultaneous Evaluation of the Whole Aorta and Artery of Adamkiewicz by MDCT

Recent technical advancement has allowed simultaneous visualization of the artery of Adamkiewicz and whole aorta by multidetector-row-CT (MDCT). Although we could visualize the artery of Adamkiewicz in a high percentage of patients with thoracoabdominal aortic diseases, CT scanning with an adequate protocol and careful post-processing are necessary for accurate evaluation. Noninvasive evaluation of the artery of Adamkiewicz is useful in planning surgery. Preoperative evaluation of the intercostal arterial level from which the artery of Adamkiewicz originates is reportedly important for preventing postoperative spinal cord ischemia. Although, the usefulness of preoperative information on the artery of Adamkiewicz is still controversial, preoperative identification of the artery of Adamkiewicz by imaging has gradually spread since our first report, and has been included in preoperative evaluation items at many institutions, revealing its contribution to improvement in surgical results. (*English Translation of J Jpn Coll Angiol, 2004, 44: 693-699.).

Imaging of the thoracic aorta

Three-dimensional vascular imaging techniques offer a significant advantage over traditional imaging techniques. Spatial resolution of current state-of-the-art allows sufficient depiction of anatomical detail. Pre-operative planning of complex endovascular procedures is facilitated by state-of-the-art imaging. Cone-beam CT holds great promise in guiding complex endovascular procedures.

How to manage the left subclavian artery during endovascular stenting for thoracic aortic dissection? An assessment of the evidence

BACKGROUND

Despite the publication of recent guidelines for management of the left subclavian artery (LSA) during endovascular stenting procedures of the thoracic aorta, specific management for those presenting with dissection remains unclear. This systematic review attempts to address this issue.

METHODS

Systematic assessment of the published data on thoracic aorta dissection was performed identifying 46 studies, which incorporated 1,275 patients. Primary outcomes included the prevalence of left arm ischemia, stroke, spinal cord ischemia, endoleak, stent migration, and mortality. Outcomes were compared between patients with and without LSA coverage and revascularization incorporating factors such as the number of stents used, length of aorta covered, urgency of intervention, and type of dissection (acute or chronic). Statistical pooling techniques, χ(2) tests, and Fisher's exact testing were used for group comparisons.

RESULTS

As compared with other outcomes, LSA coverage without revascularization in the presence of aortic dissection is much more likely to be complicated by left arm ischemia (prevalence increased from 0.0% to 4.0% [p = 0.021]), stroke (prevalence increased from 1.4% to 9.0% [p = 0.009]), and endoleak (prevalence increased from 4.0% to 29.3% [p = 0.001]). However, revascularization was not shown to reverse these effects. Longer aortic coverage (≥ 150 mm) was associated with an increased prevalence of spinal cord ischemia (from 1.3% to 12.5% [p = 0.011]) and mortality (from 1.3% to 15.6% [p = 0.003]).

CONCLUSION

In patients undergoing endovascular stenting for thoracic aortic dissection, in cases where LSA coverage is necessary, revascularization should be considered before the procedure to avoid complications such as left arm ischemia, stroke, and endoleak, and where feasible, an appropriate preoperative assessment should be carried out.

MRI and MRA of Aortic Disease

Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) play a critical role in diagnosing aortic disease such as aortic dissection and aneurysm. Additionally, the advent of contrast-enhanced MRA has allowed MRA to advance markedly and several new imaging techniques to emerge as well. While computed tomography (CT) angiography using multidetector-row CT is a significant innovation, MRA may generate more useful diagnostic information, such as on the artery of Adamkiewicz.

MR angiography for detecting the artery of Adamkiewicz and its branching level from the aorta

PURPOSE

We evaluated the efficacy of magnetic resonance angiography (MRA) for detecting the artery of Adamkiewicz (AKA) and the vertebral level of its feeding arteries branching from the aorta.

MATERIALS AND METHODS

Eighty-two patients (67 men, 15 women; aged 34 to 86 years, mean age 68.6 years) with thoracic descending and thoracoabdominal aortic lesions (aneurysm in 55, dissection in 25, coarctation in 2) underwent MRA to detect AKA. MRA was performed using 6-phase, dynamic-enhanced, 3-dimensional, fast spoiled gradient recalled acquisition in steady state (GRASS) on a 1.5-tesla (T) system, with double-dose bolus contrast injection. The vertebral levels of AKA branching and the AKA feeder artery branching from the aorta were determined.

RESULTS

The AKA was detected in 67 patients (81.7%). Branching of AKA occurred at levels T7 to T12 on the left side (n=52) and on the right (n=15). Vascular continuity from the aorta to the anterior spinal artery was demonstrated in 55 patients (67.1%). Comparing the vertebral level of arterial branching from the aorta to that of the AKA at the intervertebral foramen, the AKA branched at the same vertebral level in 44 patients (80.0%), one vertebral level above/below in 10 (18.2%), and 2 vertebral levels above in one (1.8%).

CONCLUSION

MRA can be useful in the preoperative work-up of patients with thoracoabdominal aortic lesions to localize AKA and the segmental trajectories of vessels supplying blood to the AKA.

Albert Wojciech Adamkiewicz (1850-1921): unsung hero behind the eponymic artery

The artery of Adamkiewicz is an important radiculomedullary artery supplying the spinal cord, especially the lumbar enlargement. Anatomical knowledge of this artery is important for avoiding serious neurological complications during surgery performed in this region--for neurosurgeons and interventional radiologists treating intramedullary tumors and spinal arteriovenous malformations, traumatologists performing spinal fusions, thoracic surgeons treating aortic aneurysms, and urologists and pediatric surgeons conducting retroperitoneal dissections. However, the biography of the talented Polish pathologist Albert Adamkiewicz, after whom the landmark artery is named, has not been described adequately in the existing neurosurgical literature. The authors bring to light the historical perspective of the eponymic artery and provide a recapitulation of other significant contributions made by Adamkiewicz, mostly involving the nervous system. His research papers on the histology of neuronal tissues and neurodegenerative diseases had high scientific merit, but the discovery of the anticancer antitoxin "cancroin" and his postulation of a cancer-causing parasite he named "Coccidium sarcolytus" met with harsh criticism and eventually led to his ill fame. The biography is supplemented with a brief overview of the important surgical implications of the artery of Adamkiewicz.

Magnetic resonance angiography of collateral blood supply to spinal cord in thoracic and thoracoabdominal aortic aneurysm patients

OBJECTIVE

Preservation of spinal cord blood supply during descending thoracic (TAA) and thoracoabdominal aortic aneurysm (TAAA) surgery is mandatory to prevent neurologic complications. Although collateral arteries have been identified occasionally and are considered crucial for maintaining spinal cord function in the individual patient, their critical functionality is poorly understood and very little experience exists with visualization. This study investigated whether the preoperative and postoperative presence or absence of collateral arteries detected by magnetic resonance angiography (MRA) is related to spinal cord function during the intraoperative exclusion of the segmental supply to the Adamkiewicz artery.

METHODS

Spinal cord MRA was used to localize the Adamkiewicz artery and its segmental supplier in 85 patients scheduled for open elective surgery for TAA or TAAA. The segmental artery to the Adamkiewicz artery was inside the cross-clamped aortic area in 55 patients, and spinal cord supply was consequently dependent on collateral supply. In these 55 patients the presence of collaterals originating from arteries outside the cross-clamped aortic segment was related to changes in the intraoperative motor-evoked potentials (MEPs) that occurred before corrective measures. Twenty-one patients returned for postoperative MRA.

RESULTS

A highly significant (P < .0015) relation was found between the presence of collaterals and intraoperative spinal cord function. In 30 of 31 patients (97%) in whom collaterals were identified, MEPs remained stable. The collaterals in most patients originated caudally to the distal clamp (eg, from the pelvic arteries), which were perfused by means of extracorporeal circulation during cross-clamping. The MEPs declined in 9 of 24 patients (38%) in whom no collaterals were preoperatively visualized. Postoperatively, the 21 patients who had MRA, including 10 in whom preoperatively no collaterals were found, displayed a well-developed collateral network.

CONCLUSION

Collateral arteries supplying the spinal cord can be systematically visualized using MRA. Spinal cord blood supply during open aortic surgery may crucially depend on collateral arteries. Preoperatively identified collateral supply was 97% predictive for stable intraoperative spinal cord function. Patients in whom no collaterals can be depicted preoperatively are at increased risk for spinal cord dysfunction.

Optimal contrast medium injection protocols for the depiction of the Adamkiewicz artery using 64-detector CT angiography

AIM

To determine the optimal contrast medium injection protocol for demonstrating the Adamkiewicz artery (AKA) using 64-detector CT angiography (CTA).

MATERIALS AND METHODS

CTA was performed using 64-detector CT. The study population consisted of 80 patients (mean age 67.2 years) with aortoiliac diseases. In the first 60 patients 540 mg I/kg body weight was administered over 25s. The patients were randomly assigned to three protocols with imaging started at 15 (protocol A-1), 18 (A-2), or 21s (A-3) after triggering (threshold 150 HU). The other 20 received 720 mg I/kg body weight with an imaging delay of 18s (protocol B). Two radiologists evaluated the presence of the AKA and measured the attenuation of the aorta and AKA.

RESULTS

Aortic enhancement was 360.4, 348, 279.3, and 372 HU for protocols A-1, A-2, A-3, and B, respectively. There was no significant difference between the A-1 and A-2 protocols (Tukey-Kramer test, p=0.73); however, aortic enhancement was significantly lower in A-3 than A-1 and A-2 (p<0.01). There was no significant difference between A-2 and B (p=0.40). AKA attenuation was 69.3, 91.9, 94.6, and 105.4 HU for protocols A-1, A-2, A-3, and B, respectively. There was no significant difference between the A-2 and A-3 protocols (p=0.91); however, AKA attenuation was significantly lower with A-1 than A-2 or A-3 (p=0.01). AKA attenuation was significantly lower with A-2 than B (p=0.03) and there was a significant difference between A-2 (50%) and B (95%) in the depiction of the hairpin configuration of the AKA (p=0.02).

CONCLUSION

For the demonstration of the AKA at CTA, the optimal protocol used an imaging delay of 18s after triggering and an iodine dose of 720 mg I/kg body weight.

Preoperative visualization of the artery of Adamkiewicz by intra-arterial CT angiography

BACKGROUND AND PURPOSE

CT and MR angiographies have been reported to visualize the artery of Adamkiewicz (AKA) noninvasively to prevent spinal cord ischemia in surgery of thoracic descending aortic aneurysms. The purpose of this work was to compare the usefulness of CT angiography (CTA) with intra-arterial contrast injection (IACTA) with that of conventional CTA with intravenous contrast injection (IVCTA).

MATERIALS AND METHODS

We enrolled 32 consecutive patients with thoracic or thoracoabdominal aortic aneurysms who were scheduled for surgical repair or endovascular stent-graft treatment. All of the CTA images were obtained using a 16-detector row CT scanner and 100 mL of contrast material (370 mg/mL) injected at a rate of 5 mL/s. Contrast was injected via the antecubital veins of 15 patients and via a pig-tail catheter placed at the proximal portion of the descending aorta in 17 patients who underwent IVCTA and IACTA, respectively. Two datasets were reconstructed from 2 consecutive scans. The AKA was identified as a characteristic hairpin curved vessel in the anterior midsagittal surface of the spine and by the absence of further enhancement in the second rather than in the first phase. Continuity between the AKA and aorta was confirmed when the vessel could be traced continuously by paging the oblique coronal multiplanar reconstruction or original axial images.

RESULTS

Intra-arterial contrast injection was significantly more sensitive in identifying the AKA than IVCTA: 16 (94.1%) of 17 versus 9 (60.0%) of 15 (P = .033). Continuity between the AKA and aorta through intercostal or lumbar artery was confirmed in 14 (87.5%) of 16 and 5 (55.6%) of 9 of the IACTA and IVCTA groups, respectively.

CONCLUSION

Intra-arterial contrast injection detected the AKA at a high rate and verified continuity from the aorta to the AKA.

Advances in spinal cord MR angiography

Novel developments in MR angiography are reviewed that enable non-invasive clinical imaging of normal and abnormal vessels of the spinal cord. Current fast contrast-enhanced MR techniques are able 1) to visualize vessels supplying or draining the spinal cord and 2) to differentiate spinal cord arteries from veins. The localization of the Adamkiewicz artery, the largest artery supplying the thoracolumbar spinal cord, has become possible in a reproducible and reliable manner. Knowledge of the anatomic location of this artery and its arterial supplier may be of benefit in the work-up for aortic aneurysm surgery to reduce incidences of ischemic injury. Spinal cord MR angiography is ready to become a diagnostic tool that can compete with catheter angiography for detecting and localizing arterial feeders of vascular lesions and is strongly advised for use prior to invasive catheter angiography. Successful clinical application strongly relies on in depth knowledge of the complex spinal cord vasculature and skills in image postprocessing.

Management of neurologic complications of thoracic aortic surgery

Neurologic complications of thoracic aortic surgery are strongly associated with increased morbidity and mortality. Identifying preoperative risk factors for neurologic injury may enable us to refine our perioperative approach, and to lessen or avoid these complications. Methods to identify stroke and spinal ischemia intraoperatively such as neurophysiologic monitoring may enable us to improve outcomes in these patients by immediately instituting measures to improve brain and spine perfusion. The development of both protocols and therapies to treat these complications has allowed us to mitigate and, at times, reverse neurologic injury both intraoperatively and postoperatively.

Comparison of magnetic resonance with computed tomography angiography for preoperative localization of the Adamkiewicz artery in thoracoabdominal aortic aneurysm patients

OBJECTIVE

Preoperative localization of the Adamkiewicz artery and its segmental supplier in advance of thoracic aortic aneurysm (TAA) and thoracoabdominal aortic aneurysm (TAAA) repair is proposed to be useful to prevent postoperative paraplegia. The diagnostic potential of magnetic resonance angiography (MRA) and computed tomography angiography (CTA) was evaluated for the preoperative localization of the Adamkiewicz artery in white TAAA patients.

METHODS

Thirty-nine consecutive patients with a TAA(A) scheduled for elective open surgical aortic repair preoperatively underwent MRA and CTA. Objective image quality was assessed by measuring the signal-to-noise ratio and contrast-to-noise ratio of the Adamkiewicz artery and was related to patient thickness. Two independent observers scored the location of the Adamkiewicz artery and the subjective image quality of vessel-background contrast of the Adamkiewicz artery, image noise, spinal cord tissue enhancement, epidural venous enhancement, and overall image quality.

RESULTS

Average detection rate for Adamkiewicz artery localization was 71% (67% to 74%) for CTA and 97% (94% to 100%) for MRA. Interobserver agreement was 82% for CTA and 94% for MRA. Signal-to-noise ratio was significantly higher (P < .001) and contrast-to-noise ratio was significantly (P < .001) lower for CTA than for MRA. Contrast of the Adamkiewicz artery (P < .001) and overall image quality (P < .004) were judged to be significantly better for MRA. Spinal cord tissue enhancement was judged stronger at CTA (P < .03), with significantly less epidural venous enhancement (P < .001). No significant difference was found in image noise. Signal-to-noise and contrast-to-noise decreased significantly (P < .001) with increasing patient thickness for CTA but not for MRA.

CONCLUSIONS

Localization of the Adamkiewicz artery in white TAAA patients is possible with both CTA and MRA. Compared with CTA, MRA is more favorable because of the higher Adamkiewicz artery detection rate, the higher contrast-to-noise ratio, and its independence of patient thickness.

Differentiation of spinal cord arteries and veins by time-resolved MR angiography

PURPOSE

To dynamically resolve the inlet arteries and outlet veins of the spinal cord, particularly the Adamkiewicz artery (AKA) and great anterior radiculomedullary vein (GARV), using MR angiography (MRA).

MATERIALS AND METHODS

First, conventional two-phase angiography (acquisition time = 38-55 seconds) utilizing elliptic centric k-space ordering was applied to aortic-aneurysm patients. Changes of vessel intensity were compared between two subsequent dynamic phases. Computer modeling of bolus enhancement and k-space sampling was performed to demonstrate the relation between vessel enhancement, acquisition time, and vessel diameter. Second, time-resolved (TR, or "keyhole") angiography using a reduced number of phase-encoding steps was explored in healthy volunteers and aortic-aneurysm patients using acquisition times (range = 6-8.5 seconds) shorter than the spinal cord circulation time.

RESULTS

Using two-phase angiography the AKA and GARV were covisualized in the early phase, and contrast decreased for the AKA and increased for the GARV in most (70%) but not all cases. Computer modeling showed that the arteriovenous contrast strongly depended on vessel diameter, and complete separation was only obtained with short acquisition times. Using TR MR angiography (TR-MRA), complete temporal separation of the AKA and GARV was realized in all cases (100%).

CONCLUSION

The AKA and GARV can be completely separated by TR-MRA.

MR Angiography and CT Angiography of the Artery of Adamkiewicz: State of the Art

It is very important to assess the artery of Adamkiewicz before repair of the thoracoabdominal or descending thoracic aorta. Several studies have demonstrated the feasibility and advantages of noninvasive assessment of the artery of Adamkiewicz with magnetic resonance (MR) angiography and multi-detector row computed tomographic (CT) angiography. Recent advances in MR angiography and CT angiography have led to changes in the detectability of this artery. In the present study, both MR angiography and CT angiography were performed without complications for preoperative evaluation of 30 patients who underwent repair of the thoracoabdominal or descending thoracic aorta. MR angiography provided detection rates as high as 93% and 80% with the morphologic "hairpin turn" criterion and the anatomic "continuity" criterion, respectively. Sixteen-detector row CT angiography provided detection rates as high as 83% and 60%, respectively. Use of both MR angiography and CT angiography provided higher detection rates of 97% and 90%, respectively. The collateral pathways were depicted in seven cases (23%). MR angiography is superior for depiction of the artery of Adamkiewicz, especially when it arises from the false lumen of a dissecting aneurysm. CT angiography has a wide field of view and allows depiction of significant collateral pathways associated with the internal thoracic artery and intercostal arteries.

Combined Use of Adamkiewicz Artery Demonstration and Motor-Evoked Potentials in Descending and Thoracoabdominal Repair

BACKGROUND

We retrospectively reviewed the outcome of distal descending aortic and thoracoabdominal aortic repair with preoperative identification of the Adamkiewicz artery by magnetic resonance angiography and intraoperative monitoring of transcranial motor-evoked potentials.

METHODS

We began combined use of demonstration of the Adamkiewicz artery and intraoperative recording of motor-evoked potentials for prevention of spinal cord complications in descending and thoracoabdominal aortic aneurysm repair in 1998. Ninety-two consecutive patients were studied, with descending aneurysm in 53 and thoracoabdominal aneurysm in 39 patients. The repair was performed through a left thoracic or thoracoabdominal incision, using partial cardiopulmonary bypass to prevent spinal cord injury. Magnetic resonance angiography revealed the Adamkiewicz artery in 70.7% of cases. During surgery, spinal cord ischemia was monitored using motor-evoked potentials. Anastomoses were performed using a segmental clamp technique to reduce spinal cord ischemic time. Based on the findings of magnetic resonance angiography and motor-evoked potentials, the Adamkiewicz artery and other relevant intercostals and lumbar arteries were revascularized or preserved, or both.

RESULTS

The mean durations of partial cardiopulmonary bypass, cross-clamping, and surgery, respectively, were 144.4 +/- 232.2, 106.0 +/- 65.5, and 411.8 +/- 170.7 minutes. Three hospital deaths (3.3%) occurred in patients with a thoracoabdominal aortic aneurysm. Motor-evoked potentials changed in 9 patients (9.8%), in 8 (88.9%) of whom they were eventually restored. Although paraplegia developed in 1 patient (1.1%) with a mycotic descending aneurysm, the other patients survived without spinal cord injury.

CONCLUSIONS

Combined visualization of the Adamkiewicz artery and determination of motor-evoked potentials are useful in preventing spinal cord injury in descending and thoracoabdominal aortic repair.

Chronic descending aortic dissections

Aortic dissection involving the descending aorta has a predictable and often debilitating course of progressive dilatation that occurs once patients survive the acute phase of the disease. Important factors that impact the rate and degree of dilatation include the persistence of a false lumen channel (and the amount of thrombus), the control of hypertension, and the presence of an underlying connective tissue disorder. The mainstay of management of chronic descending aortic dissections is antihypertensive therapy including beta-blockade until the dissected aorta becomes significantly aneurysmal. Surgical management is recommended at that point. Multiple advances have been made that have improved the results of operative repair of aneurysmal descending aortic dissections including circulation management methodologies, CSF drainage, neurocerebral monitoring, and more recently, endovascular therapies. The presentation, diagnosis and management of chronic descending aortic dissections are discussed.

Comparison of 0.5-M Gd-DTPA with 1.0-M gadobutrol for magnetic resonance angiography of the supplying arteries of the spinal cord in thoracoabdominal aortic aneurysm patients

PURPOSE

To prospectively compare 0.5-M gadopentetate dimeglumine (Gd-DTPA) with 1.0-M gadobutrol for contrast-enhanced magnetic resonance angiography (CE-MRA) of the blood supplying arteries of the spinal cord in patients referred for open surgical repair of a thoracoabdominal aortic aneurysm (TAAA).

MATERIALS AND METHODS

A total of 11 patients with a TAAA underwent two three-dimensional CE-MRA exams of the aorta, segmental arteries (SAs), artery of Adamkiewicz (AKA), and anterior spinal artery (ASA). Imaging was performed on two separate occasions using Gd-DTPA and gadobutrol as contrast agents at 0.3 mmol/kg. Images were evaluated by measuring signal-to-noise (SNR) and contrast-to-noise (CNR) ratios and were judged for different image quality criteria by two blinded observers.

RESULTS

In all patients both CE-MRA exams were of sufficient image quality to detect the AKA and ASA. No significant differences in SNR and CNR were observed between the two contrast agents. According to the observers, no significant differences in subjective image quality were found.

CONCLUSIONS

Using both contrast agents it was possible to visualize the ultrasmall spinal cord arteries in all cases. The use of the 1.0-M contrast agent did not improve image quality of CE-MRA images of the blood supplying arteries of the spinal cord compared to the 0.5-M contrast agent.

Usefulness of Preoperative Detection of Artery of Adamkiewicz with Dynamic Contrast-enhanced MR Angiography

PURPOSE

To prospectively evaluate the detection of the artery of Adamkiewicz at magnetic resonance (MR) angiography and the effect such detection has on outcome after surgical graft placement in a series of patients with thoracoabdominal aortic disease.

MATERIALS AND METHODS

This study had ethics committee approval, and written informed consent was obtained from all patients. Fifty patients (38 men, 12 women; age range, 47-83 years; mean age, 67.2 years) who were scheduled to undergo thoracoabdominal aortic surgery for treatment of thoracoabdominal aortic aneurysm (n = 42) or thoracoabdominal aortic dissection (n = 8) were enrolled in the study. MR angiography was performed with a 1.5-T system by using dynamic three-dimensional fast spoiled gradient-recalled acquisition in the steady state with a bolus of contrast material and saline injection (4 mL/sec). Differences in the cross-clamping time, bypass time, total surgery time, and spinal complication rate between patients in whom the artery of Adamkiewicz was identified (group A) and those in whom the artery was not identified (group B) were evaluated with chi(2) or Mann-Whitney U testing.

RESULTS

In 42 of the 50 patients (84% [group A]), at least one artery of Adamkiewicz was seen to arise from an intercostal artery. Two arteries of Adamkiewicz were identified in four of the patients (8%). The artery of Adamkiewicz could not be detected with MR angiography in eight patients (group B). The ranges of cross-clamping, bypass, and total surgery times, respectively, were 30-199 minutes (mean, 78.4 minutes +/- 39.1 [standard deviation]), 30-298 minutes (mean, 96.9 minutes +/- 60.0), and 135-665 minutes (mean, 354.9 minutes +/- 133.9) in group A and 53-124 minutes (mean, 72.8 minutes +/- 29.8), 10-124 minutes (mean, 66.0 minutes +/- 41.0), and 220-405 minutes (mean, 315.6 minutes +/- 68.8) in group B. Spinal complications occurred in two patients in group B but in none of the patients in group A (P < .001).

CONCLUSION

The artery of Adamkiewicz was detected in a large percentage of patients in whom there were no spinal complications, unlike the spinal complications that occurred in the patients in whom the artery was not detected.

Normal Anterior Spinal Arteries within the Cervical Region: High-Spatial-Resolution Contrast-enhanced Three-dimensional MR Angiography

PURPOSE

To determine retrospectively whether the anterior spinal artery (ASA) is visualized in the cervical region with contrast material-enhanced high-spatial-resolution three-dimensional magnetic resonance (MR) angiography of the extracranial carotid and vertebral arteries.

MATERIALS AND METHODS

The institutional research ethics committee approved this study and provided a waiver for informed consent. Data sets were evaluated in 50 consecutive patients referred for contrast-enhanced three-dimensional MR angiography of the carotid arteries (32 male and 18 female patients; age range, 15-80 years; mean age, 59 years). The ASA was defined as a linear area of high signal intensity that is seen anterior to the spinal cord in an arterial phase of enhancement and connects directly to a known arterial structure. If the linear area of high signal intensity was seen in the arterial phase but did not connect to a known arterial structure, it was considered a probable ASA. Venous enhancement was graded on a five-point scale (0-4) with grade 0 (no venous enhancement) or grade 1 (trace venous enhancement) considered to be in the arterial phase.

RESULTS

The ASA was identified with certainty in 37 of 50 patients. A vessel visualized anterior to the spinal cord, which probably represented the ASA, was seen in another 11 of 50 patients. In 29 of 50 patients the vessel was visualized only on the full-volume maximum intensity projection (MIP) image. In the remainder of cases the artery was identified on operator-defined subvolume MIP images. Continuity between the vessel and the vertebrobasilar arterial structures was identified in 35 of 50 patients. The vessel was seen as a continuous structure throughout its length in 34 patients and appeared discontinuous in 14. Radiculomedullary feeders were identified in 24 of 50 patients.

CONCLUSION

The normal cervical ASA was visualized in 48 of 50 of subjects with contrast-enhanced high-spatial-resolution three-dimensional MR angiography.

Gadopentetate dimeglumine-enhanced three-dimensional MR-angiography: dosing, safety, and efficacy

Noninvasiveness, inherent three-dimensionality allowing reformations in any desired plane, and safe contrast agents, coupled with high diagnostic accuracy have driven the rise in popularity of contrast-enhanced MR angiography (CE-MRA) within the medical community. Reflecting its dominant market share as a paramagnetic contrast agent, gadopentetate dimeglumine (Gd-DTPA) has been used for the majority of clinically-performed MRA exams. Over the period January 1994 to February 2002, a total of 172 original studies describing the use of gadolinium-enhanced MRA in more than three human subjects were identified. Of these, 117 described the use of Gd-DTPA as the contrast agent for MRA. A total of 4046 subjects who received Gd-DTPA for MRA are described in these studies. Analysis of these data demonstrate Gd-DTPA to be a safe contrast agent for MRA when applied in a dose ranging from 0.1 to 0.3 mmol/kg of bodyweight. The documented clinical results show Gd-DTPA to be efficacious in the assessment of the arterial system. The effectiveness of Gd-DTPA-enhanced MRA extends beyond the detection, localization, and characterization of arterial disease, and encompasses choice and planning of appropriate therapy, as well as evaluation of therapeutic effectiveness.

Spinal cord feeding arteries at MR angiography for thoracoscopic spinal surgery: feasibility study and implications for surgical approach

PURPOSE

To prospectively investigate the feasibility of contrast material-enhanced magnetic resonance (MR) angiography for visualization of the spinal vasculature in patients referred for video-assisted thoracoscopic surgical treatment of a thoracic herniated disk and to prospectively assess the influence of preoperative imaging of the spinal vasculature on the choice of surgical approach.

MATERIALS AND METHODS

Eight patients (three men and five women; mean age, 58 years; range, 42-83 years) with a thoracic herniated disk underwent contrast-enhanced MR angiography of the thoracoabdominal aorta and posterior branches. Imaging was performed with three-dimensional first-pass contrast-enhanced MR angiographic technique and a triple dose of gadolinium-based contrast agent. Images were analyzed by two observers in consensus to localize the Adamkiewicz artery (AKA) and its connections to the aorta and the anterior spinal artery (ASA). This information was used to determine any change in surgical approach.

RESULTS

In all eight patients, the AKA, the ASA, and the connections with the aorta were identified. The AKA originated between T9 and L2 in all patients and derived from the left side of the aorta in 75% (six of eight) of the patients. In three patients in whom the AKA was observed on the left side, the surgical approach was changed to the right side to preserve spinal cord integrity.

CONCLUSION

Preoperative imaging of the AKA is feasible with contrast-enhanced MR angiography. Contrast-enhanced MR angiography can be used to image the main feeding arteries of the spinal cord in patients undergoing thoracoscopic spinal surgery, and results can be used to change the side of surgical approach.

Magnetic resonance angiographic localization of the artery of Adamkiewicz for spinal cord blood supply

BACKGROUND

The purpose of this study was to determine whether the artery of Adamkiewicz (ARM) can be detected by magnetic resonance angiography and to determine the usefulness of preoperative magnetic resonance angiography evaluation of the ARM.

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.

MR angiography of the spine: update

The role of MRA, as an adjunct to conventional MR imaging of the spine and spinal cord, is evolving. The older MRA methods that have been applied to spinal vascular imaging include 2D and 3D phase contrast techniques and a derivative of 3D time-of-flight techniques with data acquired for about several minutes after gadolinium contrast injection (standard 3D CE MRA). Newer 3D gradient-echo techniques, which allow the acquisition of each volume of data in tens of seconds as a contrast bolus traverses the region of interest (fast 3D CE MRA), offer the possibility of temporally resolving intradural arteries and veins. The appearance of normal and abnormal intradural vessels, primarily veins, on the standard 3D CE MRA method has been described for the thoracolumbar region. Normal intradural arteries have been more difficult to detect, although preliminary results with the fast 3D CE MRA method, are promising. Only by establishing the MRA appearance of normal arteries and veins, can one begin to define "abnormal" with greater confidence (presuming that the variability in the appearance of normal vessels is not so great as to preclude differentiation). In striving for this goal, MRA has already encountered competition from CT angiography. In the characterization of spinal vascular lesions, the value of MRA has been demonstrated most convincingly for dural AVF. This lesion is more accurately localized and more sensitively detected (by neuroradiolologists and others experienced in spine imaging) with combined MR imaging and standard 3D CE MRA than with MR imaging alone. Preliminary results suggest that sensitivity and specificity may be further improved if fast 3D CE MRA is combined with conventional MR imaging. Although less well documented, the value of MRA in characterizing other lesions, such as AVMs and vascular tumors, has been reported in recent publications. In the future, the role of MRA will depend on technical advances, such as parallel acquisition techniques and possibly implantable RF coils, which permit improved detection of, and differentiation between, intradural arteries and veins. With these improvements, MRA may play an expanded role in the characterization of spinal vascular abnormalities, encompassing trauma and degenerative spine disease and vascular malformations and tumors.

MR Angiography of the Spine and Spinal Cord

OBJECTIVES

This review has three objectives: 1) to describe spinal vascular anatomy, focusing on thoracolumbar intradural vessels detectable by both magnetic resonance angiography (MRA) and digital subtraction x-ray angiography (DSA), 2) to compare the MRA techniques that have been used to detect the major intradural vessels, and 3) to illustrate the clinical application of these MRA techniques, especially their efficacy in characterizing spinal dural arteriovenous fistulae (AVF).

METHODS

MRA is an adjunct to conventional magnetic resonance imaging. MRA is usually implemented as a three-dimensional (3D) contrast-enhanced (CE) gradient-echo technique, with two approaches to data acquisition: 1) "standard" 3D CE MRA, requiring approximately 10 minutes per 3D volume, and 2) "fast" (bolus/dynamic) 3D CE MRA, requiring approximately 0.5 to 2 minutes per 3D volume depending on k-space sampling schemes. Vessels are displayed on targeted maximum intensity projection images.

RESULTS

Normal intradural vessels detected on standard CE MRA are primarily veins (medullary and median), whereas both arteries and veins are detected on fast CE MRA. Identification of arteries (artery of Adamkiewicz, anterior spinal artery) is limited, and their differentiation from veins can be incomplete. Intradural vessels in patients with dural fistulae have abnormal features on MRI (length of flow voids and postcontrast serpentine enhancement) and standard 3D CE MRA (length, tortuosity, and qualitative size of dominant perimedullary vessel), which differ significantly from those of normal vessels. Standard MRA added to a conventional MRI study significantly (P=0.016) increased the rate of detection of the spinal level of a dural fistula. The correct level +/- one vertebral segment was identified in 73% of true-positive patients.

CONCLUSIONS

Application of spinal MRA requires knowledge of vascular anatomy, specifically the major intradural vessels, and careful implementation of 3D CE MRA techniques. The standard technique allows for more effective noninvasive screening for vascular lesions, particularly dural AVF, than magnetic resonance imaging alone. Preliminary results indicate that the fast technique may further improve characterization of normal and abnormal intradural vessels, especially if continued technical advances yield greater temporal resolution while maintaining adequate spatial resolution.

MR angiography and CT angiography of the artery of Adamkiewicz: noninvasive preoperative assessment of thoracoabdominal aortic aneurysm

It is important to identify the artery of Adamkiewicz in patients with thoracoabdominal aortic aneurysm to aid in surgical planning and to prevent postoperative paraplegia or paraparesis. However, the artery of Adamkiewicz is difficult to visualize and impossible or very dangerous to evaluate with selective intercostal or lumbar angiography. The feasibility, advantages, and limitations of magnetic resonance (MR) angiography and computed tomographic (CT) angiography in the preoperative assessment of the artery of Adamkiewicz were evaluated in 30 patients with thoracoabdominal aortic aneurysm. Initial results indicate that MR angiography and CT angiography are safe, effective, noninvasive procedures that allow clear visualization of the artery of Adamkiewicz by providing detailed depiction of the vascular anatomy from the aorta to the anterior spinal artery. However, further studies will be needed to assess the efficacy of these modalities in decreasing surgical risk.

Demonstration of the artery of Adamkiewicz at multi- detector row helical CT

PURPOSE

To assess the ability of multi-detector row helical computed tomography (CT) to depict the artery of Adamkiewicz.

MATERIALS AND METHODS

Seventy patients with vascular diseases underwent multi-detector row helical CT of the entire aorta and iliac arteries. The artery of Adamkiewicz was examined on multiplanar and curved planar reformation images and on cine-mode displays. The visualization of the artery of Adamkiewicz, as well as its branching level and side of origin, was investigated.

RESULTS

In 63 (90%) of the 70 patients, at least a single artery of Adamkiewicz was clearly visualized from the intervertebral foramen to the hairpin-shaped union with the anterior spinal artery. Two arteries of Adamkiewicz were identified in 15 (24%) of 63 patients. Fifty-five arteries of Adamkiewicz (71%) originated from the left side. Seventy-two (92%) originated between T8 and L1. Neither the intercostal vein nor the posterior spinal vein were visualized in 57 of 63 patients. Continuity of the entire length, starting from the stem of the intercostal or lumbar artery and proceeding to the artery of Adamkiewicz and finally to the anterior spinal artery, was traceable on cine-mode displays or on curved planar reformation images in 20 of 63 patients.

CONCLUSION

Multi-detector row helical CT depicts the artery of Adamkiewicz in a high percentage of patients.