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Magnetic resonance imaging in patients with postoperative spinal cord injury: ‘one step at a time towards safer aortic repair’

Magnetic resonance imaging in patients with postoperative spinal cord injury: ‘one step at a time... Magnetic resonance imaging, Spinal cord injury, Aortic repair, Spinal cord infarction, Collateral network, Spinal cord protection In this issue of the European Journal of Cardio-Thoracic Surgery, Yasuda et al. [1] present their study on magnetic resonance imaging (MRI) for a detailed depiction of spinal cord tissue infarctions in patients who underwent aortic repair with subsequent spinal cord injury (SCI). Ischaemic SCI after extensive aortic repair of any modality or acute aortic events in general remain a frequent and devastating complication with profound impact on individual long-term outcome, subsequent healthcare cost and quality of life [2]. Despite various contemporary adjuncts to mitigate intervention-associated SCI, the incidence of paraplegia after aortic repair remains high [3]. Extensive translational research over the past 2 decades has led to a better understanding of the dynamic arterial network ensuring the integrity of spinal cord perfusion, progressively challenging historical perspectives and suggesting new strategies for spinal cord protection [4, 5]. In their study, Yasuda et al. describe MRI features of 9 patients suffering from SCI subsequent to aortic repair of various modalities and extent. The authors describe a rather heterogeneous arterial infarction pattern at the thoracic and lumbar levels. Based on their findings, the authors conclude that MRI is capable of demonstrating the exact infarction area in relation to different arterial perfusion patterns, and that MRI may be of value for investigating the aetiology of ischaemic SCI following aortic surgeries and events. In order to understand the heterogeneous anatomic manifestations of spinal cord infarction in a cause-and-effect relation, it is important to recognize the various perfusion patterns underlying the clinical problem of postoperative paraplegia. In recent years, it has been proposed that a dynamic, complementary interaction between 2 major pathways (i.e. intra- and paraspinal system) is the key component of a comprehensive spinal cord perfusion network. The ‘intraspinal/epidural’ collateral network (CN)—consisting of ‘longitudinal and transversal connections’ and the anterior radiculomedullary arteries—serves as a common final pathway of ‘2 synergistic back-up systems’ to the anterior spinal artery. These 2 back-up systems include the (i) direct ‘segmental system’ consisting of intercostal and lumbar arteries arising from the aorta, and the extensive rather indirect (ii) ‘paraspinal CN’, which connects to this segmental system [6]. The intraspinal CN ensures spinal cord viability during acutely diminished direct inflow, while the plasticity of the paraspinal CN functions as a larger scale auxiliary supply system capable of maintaining adequate long-term spinal cord perfusion. Based on this concept, the extent and configuration of spinal infarctions—e.g. due to embolism of an end-arterial intraspinal pathway—might depend on the individual (pre)formed vascular territory and collaterals. Therefore, even if the same arterial territory is compromised, the resulting damage pattern might vary considerably from individual to individual. Yasuda et al. describe various infarction patterns in detail and confirm that MRI is capable of reliably depicting the infarction site and extent [7, 8]. This study serves as an additional step towards understanding the complex and individual interaction between aortic interventions, anatomical manifestation and clinical outcome. A major limitation regarding conclusions drawn from their descriptive study, however, is that most patients underwent arch procedures with a frozen elephant trunk (56%) without extending coverage beyond thoracic segmental level 10. Only 1 patient had undergone extensive thoraco-abdominal aortic aneurysm repair. Except for this thoraco-abdominal aortic aneurysm patient, all elective patients suffering from postoperative SCI had spinal cord infarctions in segments limited to the thoracic region. For comparison, in a study by Tanaka et al. [8], 18 patients with postoperative SCI were examined using MRI. The authors identified 3 types of infarction patterns: (i) sporadic, (ii) focal and (iii) diffuse as opposed to the arterial territory infarction classification system used by Yasuda et al. Tanaka et al. found 20% to be diffuse infarctions, most likely caused by haemodynamic deterioration, and the remaining 80% being focal or sporadic infarctions, presumably caused by embolism. Furthermore, all infarctions post-thoracic endovascular aortic repair were sporadic, asymmetric and limited to 1 or 2 spinal segments, leading the authors to conclude that embolism represents one of the major causes of SCI in this setting [8]. When applying their categorization to the imaging findings by Yasuda et al., only 2 cases can be classified as sporadic, while most cases presented with rather diffuse infarction patterns. Drawing generalized conclusions as to the physiological cause of the described infarction patterns carries the risk of comparing ‘apples and oranges’. The presented cohort comprises patients with various pathologies and therapeutic interventions (predominantly procedures limited to the arch and proximal descending aorta), including acute dissections as well as elective cases. Moreover, the exact timing of SCI remains unknown, making a differentiation between early (procedure-related) and late-onset SCI impossible. This in turn makes conclusions as to the underlying mechanism leading to the infarction—haemodynamic deterioration versus embolism or perfusion compromise due to segmental artery obstruction—even more difficult. For example, the only thoracic endovascular aortic repair case described by Yasuda et al. presented with an asymmetric sporadic infarction pattern—corresponding to the anterior spinal and posterior spinal artery territory—which is in line with Tanaka et al. embolism theory. However, this particular patient did also suffer from previous type B aortic dissection and was treated not only by total arch replacement with frozen elephant trunk but also by abdominal aortic replacement prior to endovascular repair. The influence of these previous interventions on the patient’s CN (hence paraspinal CN priming through segmental artery sacrifice) in conjunction with the lack of information regarding the timing of clinically overt SCI (early vs delayed neurological deficit) makes it difficult to derive conclusions regarding the underlying pathomechanism. Yasuda et al. clearly elaborate on the limitations of their study, primarily the heterogeneous patient cohort and small sample size. It should be noted, however, that quality MRI data of patients suffering from SCI post aortic interventions is generally hard to come by and only few systematic studies comprising comparable small sample sizes are available. Despite all limitations, this study should incite other researchers and clinicians to investigate treatment associated SCI using MRI more liberally. Not only does MRI allow for non-invasive imaging and reliable infarction verification when SCI is suspected, it potentially serves as a tool for functional perfusion analyses and reference imaging on a larger scale prior to various elective aortic interventions. Such systematic descriptions might promote adjustments of centre protocols, both peri- and postoperatively, once enough data are available to draw conclusions regarding the aetiology of SCI in the setting of aortic interventions. For this purpose, the authors state that in their opinion a ‘large-scale, multicentre study with precise neurological observation is necessary to determine the usefulness of postoperative spinal MRI following aortic surgery’, which based on the characteristics and versatility of MRI seems justified. In that regard, the on-going prospective, randomized trial on minimally invasive priming of the CN prior to extensive thoraco-abdominal aortic aneurysm repair (PAPA-ARTiS, NCT: 03434314) may deliver valuable clinical insights in the near future [9]. With their study, Yasuda et al. add a valuable piece to the puzzle towards understanding the dynamic and complex arterial perfusion network of the spinal cord. However, answers to important clinical key questions as to how postoperative lesion characterization can help to prevent SCI and how it adds to the strategy in the various aortic scenarios remain a future task for intense translational research. REFERENCES 1 Yasuda N , Kuroda Y, Ito T, Sasaki M, Oka S, Ukai R. Postoperative spinal cord ischemia: magnetic resonance imaging and clinical features . Eur J Cardiothorac Surg 2021; doi:10.1093/ejcts/ezaa476 . OpenURL Placeholder Text WorldCat 2 von Aspern K , Haunschild J, Khachatryan Z, Simoniuk U, Ossmann S, Borger MA et al. Mapping the collateral network: optimal near-infrared spectroscopy optode placement . J Thorac Cardiovasc Surg 2020 ; doi: 10.1016/j.jtcvs.2020.07.103. Google Scholar OpenURL Placeholder Text WorldCat 3 Rocha RV , Friedrich JO, Elbatarny M, Yanagawa B, Al-Omran M, Forbes TL et al. A systematic review and meta-analysis of early outcomes after endovascular versus open repair of thoracoabdominal aortic aneurysms . J Vasc Surg 2018 ; 68 : 1936 – 45.e5 . Google Scholar Crossref Search ADS PubMed WorldCat 4 Etz CD , Debus ES, Mohr FW, Kolbel T. First-in-man endovascular preconditioning of the paraspinal collateral network by segmental artery coil embolization to prevent ischemic spinal cord injury . J Thorac Cardiovasc Surg 2015 ; 149 : 1074 – 9 . Google Scholar Crossref Search ADS PubMed WorldCat 5 Etz DC , Luehr M, Aspern KV, Misfeld M, Gudehus S, Ender J et al. Spinal cord ischemia in open and endovascular thoracoabdominal aortic aneurysm repair: new concepts . J Cardiovasc Surg 2014 ; 55 : 159 – 68 . Google Scholar OpenURL Placeholder Text WorldCat 6 von Aspern K , Haunschild J, Borger MA, Etz CD. Anatomical description of the intraspinal collateral network: bringing the concept full circle-is the devil in the details? Eur J Cardiothorac Surg 2021 ; 59 : 144 – 6 . Google Scholar Crossref Search ADS PubMed WorldCat 7 Weidauer S , Nichtweiß M, Hattingen E, Berkefeld J. Spinal cord ischemia: aetiology, clinical syndromes and imaging features . Neuroradiology 2015 ; 57 : 241 – 57 . Google Scholar Crossref Search ADS PubMed WorldCat 8 Tanaka H , Minatoya K, Matsuda H, Sasaki H, Iba Y, Oda T et al. Embolism is emerging as a major cause of spinal cord injury after descending and thoracoabdominal aortic repair with a contemporary approach: magnetic resonance findings of spinal cord injury . Interact CardioVasc Thorac Surg 2014 ; 19 : 205 – 10 . Google Scholar Crossref Search ADS PubMed WorldCat 9 Petroff D , Czerny M, Kölbel T, Melissano G, Lonn L, Haunschild J et al. Paraplegia prevention in aortic aneurysm repair by thoracoabdominal staging with ‘minimally invasive staged segmental artery coil embolisation’ (MIS2ACE): trial protocol for a randomised controlled multicentre trial . BMJ Open 2019 ; 9 : e025488 . Google Scholar Crossref Search ADS PubMed WorldCat © The Author(s) 2021. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png European Journal of Cardio-Thoracic Surgery Oxford University Press

Magnetic resonance imaging in patients with postoperative spinal cord injury: ‘one step at a time towards safer aortic repair’

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References (11)

Publisher
Oxford University Press
Copyright
Copyright © 2021 European Association for Cardio-Thoracic Surgery
ISSN
1010-7940
eISSN
1873-734X
DOI
10.1093/ejcts/ezab062
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Abstract

Magnetic resonance imaging, Spinal cord injury, Aortic repair, Spinal cord infarction, Collateral network, Spinal cord protection In this issue of the European Journal of Cardio-Thoracic Surgery, Yasuda et al. [1] present their study on magnetic resonance imaging (MRI) for a detailed depiction of spinal cord tissue infarctions in patients who underwent aortic repair with subsequent spinal cord injury (SCI). Ischaemic SCI after extensive aortic repair of any modality or acute aortic events in general remain a frequent and devastating complication with profound impact on individual long-term outcome, subsequent healthcare cost and quality of life [2]. Despite various contemporary adjuncts to mitigate intervention-associated SCI, the incidence of paraplegia after aortic repair remains high [3]. Extensive translational research over the past 2 decades has led to a better understanding of the dynamic arterial network ensuring the integrity of spinal cord perfusion, progressively challenging historical perspectives and suggesting new strategies for spinal cord protection [4, 5]. In their study, Yasuda et al. describe MRI features of 9 patients suffering from SCI subsequent to aortic repair of various modalities and extent. The authors describe a rather heterogeneous arterial infarction pattern at the thoracic and lumbar levels. Based on their findings, the authors conclude that MRI is capable of demonstrating the exact infarction area in relation to different arterial perfusion patterns, and that MRI may be of value for investigating the aetiology of ischaemic SCI following aortic surgeries and events. In order to understand the heterogeneous anatomic manifestations of spinal cord infarction in a cause-and-effect relation, it is important to recognize the various perfusion patterns underlying the clinical problem of postoperative paraplegia. In recent years, it has been proposed that a dynamic, complementary interaction between 2 major pathways (i.e. intra- and paraspinal system) is the key component of a comprehensive spinal cord perfusion network. The ‘intraspinal/epidural’ collateral network (CN)—consisting of ‘longitudinal and transversal connections’ and the anterior radiculomedullary arteries—serves as a common final pathway of ‘2 synergistic back-up systems’ to the anterior spinal artery. These 2 back-up systems include the (i) direct ‘segmental system’ consisting of intercostal and lumbar arteries arising from the aorta, and the extensive rather indirect (ii) ‘paraspinal CN’, which connects to this segmental system [6]. The intraspinal CN ensures spinal cord viability during acutely diminished direct inflow, while the plasticity of the paraspinal CN functions as a larger scale auxiliary supply system capable of maintaining adequate long-term spinal cord perfusion. Based on this concept, the extent and configuration of spinal infarctions—e.g. due to embolism of an end-arterial intraspinal pathway—might depend on the individual (pre)formed vascular territory and collaterals. Therefore, even if the same arterial territory is compromised, the resulting damage pattern might vary considerably from individual to individual. Yasuda et al. describe various infarction patterns in detail and confirm that MRI is capable of reliably depicting the infarction site and extent [7, 8]. This study serves as an additional step towards understanding the complex and individual interaction between aortic interventions, anatomical manifestation and clinical outcome. A major limitation regarding conclusions drawn from their descriptive study, however, is that most patients underwent arch procedures with a frozen elephant trunk (56%) without extending coverage beyond thoracic segmental level 10. Only 1 patient had undergone extensive thoraco-abdominal aortic aneurysm repair. Except for this thoraco-abdominal aortic aneurysm patient, all elective patients suffering from postoperative SCI had spinal cord infarctions in segments limited to the thoracic region. For comparison, in a study by Tanaka et al. [8], 18 patients with postoperative SCI were examined using MRI. The authors identified 3 types of infarction patterns: (i) sporadic, (ii) focal and (iii) diffuse as opposed to the arterial territory infarction classification system used by Yasuda et al. Tanaka et al. found 20% to be diffuse infarctions, most likely caused by haemodynamic deterioration, and the remaining 80% being focal or sporadic infarctions, presumably caused by embolism. Furthermore, all infarctions post-thoracic endovascular aortic repair were sporadic, asymmetric and limited to 1 or 2 spinal segments, leading the authors to conclude that embolism represents one of the major causes of SCI in this setting [8]. When applying their categorization to the imaging findings by Yasuda et al., only 2 cases can be classified as sporadic, while most cases presented with rather diffuse infarction patterns. Drawing generalized conclusions as to the physiological cause of the described infarction patterns carries the risk of comparing ‘apples and oranges’. The presented cohort comprises patients with various pathologies and therapeutic interventions (predominantly procedures limited to the arch and proximal descending aorta), including acute dissections as well as elective cases. Moreover, the exact timing of SCI remains unknown, making a differentiation between early (procedure-related) and late-onset SCI impossible. This in turn makes conclusions as to the underlying mechanism leading to the infarction—haemodynamic deterioration versus embolism or perfusion compromise due to segmental artery obstruction—even more difficult. For example, the only thoracic endovascular aortic repair case described by Yasuda et al. presented with an asymmetric sporadic infarction pattern—corresponding to the anterior spinal and posterior spinal artery territory—which is in line with Tanaka et al. embolism theory. However, this particular patient did also suffer from previous type B aortic dissection and was treated not only by total arch replacement with frozen elephant trunk but also by abdominal aortic replacement prior to endovascular repair. The influence of these previous interventions on the patient’s CN (hence paraspinal CN priming through segmental artery sacrifice) in conjunction with the lack of information regarding the timing of clinically overt SCI (early vs delayed neurological deficit) makes it difficult to derive conclusions regarding the underlying pathomechanism. Yasuda et al. clearly elaborate on the limitations of their study, primarily the heterogeneous patient cohort and small sample size. It should be noted, however, that quality MRI data of patients suffering from SCI post aortic interventions is generally hard to come by and only few systematic studies comprising comparable small sample sizes are available. Despite all limitations, this study should incite other researchers and clinicians to investigate treatment associated SCI using MRI more liberally. Not only does MRI allow for non-invasive imaging and reliable infarction verification when SCI is suspected, it potentially serves as a tool for functional perfusion analyses and reference imaging on a larger scale prior to various elective aortic interventions. Such systematic descriptions might promote adjustments of centre protocols, both peri- and postoperatively, once enough data are available to draw conclusions regarding the aetiology of SCI in the setting of aortic interventions. For this purpose, the authors state that in their opinion a ‘large-scale, multicentre study with precise neurological observation is necessary to determine the usefulness of postoperative spinal MRI following aortic surgery’, which based on the characteristics and versatility of MRI seems justified. In that regard, the on-going prospective, randomized trial on minimally invasive priming of the CN prior to extensive thoraco-abdominal aortic aneurysm repair (PAPA-ARTiS, NCT: 03434314) may deliver valuable clinical insights in the near future [9]. With their study, Yasuda et al. add a valuable piece to the puzzle towards understanding the dynamic and complex arterial perfusion network of the spinal cord. However, answers to important clinical key questions as to how postoperative lesion characterization can help to prevent SCI and how it adds to the strategy in the various aortic scenarios remain a future task for intense translational research. REFERENCES 1 Yasuda N , Kuroda Y, Ito T, Sasaki M, Oka S, Ukai R. Postoperative spinal cord ischemia: magnetic resonance imaging and clinical features . Eur J Cardiothorac Surg 2021; doi:10.1093/ejcts/ezaa476 . OpenURL Placeholder Text WorldCat 2 von Aspern K , Haunschild J, Khachatryan Z, Simoniuk U, Ossmann S, Borger MA et al. Mapping the collateral network: optimal near-infrared spectroscopy optode placement . J Thorac Cardiovasc Surg 2020 ; doi: 10.1016/j.jtcvs.2020.07.103. Google Scholar OpenURL Placeholder Text WorldCat 3 Rocha RV , Friedrich JO, Elbatarny M, Yanagawa B, Al-Omran M, Forbes TL et al. A systematic review and meta-analysis of early outcomes after endovascular versus open repair of thoracoabdominal aortic aneurysms . J Vasc Surg 2018 ; 68 : 1936 – 45.e5 . Google Scholar Crossref Search ADS PubMed WorldCat 4 Etz CD , Debus ES, Mohr FW, Kolbel T. First-in-man endovascular preconditioning of the paraspinal collateral network by segmental artery coil embolization to prevent ischemic spinal cord injury . J Thorac Cardiovasc Surg 2015 ; 149 : 1074 – 9 . Google Scholar Crossref Search ADS PubMed WorldCat 5 Etz DC , Luehr M, Aspern KV, Misfeld M, Gudehus S, Ender J et al. Spinal cord ischemia in open and endovascular thoracoabdominal aortic aneurysm repair: new concepts . J Cardiovasc Surg 2014 ; 55 : 159 – 68 . Google Scholar OpenURL Placeholder Text WorldCat 6 von Aspern K , Haunschild J, Borger MA, Etz CD. Anatomical description of the intraspinal collateral network: bringing the concept full circle-is the devil in the details? Eur J Cardiothorac Surg 2021 ; 59 : 144 – 6 . Google Scholar Crossref Search ADS PubMed WorldCat 7 Weidauer S , Nichtweiß M, Hattingen E, Berkefeld J. Spinal cord ischemia: aetiology, clinical syndromes and imaging features . Neuroradiology 2015 ; 57 : 241 – 57 . Google Scholar Crossref Search ADS PubMed WorldCat 8 Tanaka H , Minatoya K, Matsuda H, Sasaki H, Iba Y, Oda T et al. Embolism is emerging as a major cause of spinal cord injury after descending and thoracoabdominal aortic repair with a contemporary approach: magnetic resonance findings of spinal cord injury . Interact CardioVasc Thorac Surg 2014 ; 19 : 205 – 10 . Google Scholar Crossref Search ADS PubMed WorldCat 9 Petroff D , Czerny M, Kölbel T, Melissano G, Lonn L, Haunschild J et al. Paraplegia prevention in aortic aneurysm repair by thoracoabdominal staging with ‘minimally invasive staged segmental artery coil embolisation’ (MIS2ACE): trial protocol for a randomised controlled multicentre trial . BMJ Open 2019 ; 9 : e025488 . Google Scholar Crossref Search ADS PubMed WorldCat © The Author(s) 2021. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Journal

European Journal of Cardio-Thoracic Surgery – Oxford University Press

Published: Feb 13, 2021

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