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Clinical Study of High-Resolution C-Arm CT in Mechanical Recanalization and Stent Implantation for Chronic Cerebral Artery Occlusion
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.344607
Keywords: C-arm CT, occlusion, stents, therapeutic
Chronic cerebral artery occlusion is a major but rare cause of ischemic stroke; the main pathogenesis of the condition is watershed infarction or a transient ischemic attack[1],[2] due to occlusive stump thrombus or arteriosclerosis plaque embolism and decreased cerebral perfusion pressure. In recent years, with the improvement of interventional instruments and techniques, recanalization by endovascular operation can be achieved in some patients with chronic cerebral artery occlusion.[3],[4],[5],[6] However, complications and restenosis rates remain high due to a lack of surgical experience, non-visualization of the occlusive vascular lumen on digital subtraction angiography (DSA), unknown condition of the distal vascular bed, and unclear stent expansion at the occluded site. Dyna micro-CT is a new generation high-resolution C-arm CT developed by Siemens, Germany. Compared to conventional C-arm CT, Dyna micro-CT affords improved local spatial resolution and stent visibility.[7],[8] Therefore, this study retrospectively evaluated the utility of high-resolution C-arm CT (Dyna micro-CT) for mechanical recanalization and stent placement in patients with chronic cerebral artery occlusion.
Ethics statement Written informed consent was obtained from each patient for the use of the images. The study protocol was approved by the Ethics Committee of Zhengzhou University. All procedures were in accordance with the Helsinki Declaration of 1975 (and its revision in 1983). General data The study cohort comprised 27 patients with chronic cerebral artery occlusion (12 men and 15 women; age range: 35–69 years; mean age: 52.0 ± 8.7 years) who were treated by interventional therapy at the department of interventional radiology of the First Affiliated Hospital of Zhengzhou University (eastern district) from December 2016 to August 2018. The mean disease duration was 9.0 ± 8.7 months (range: 3–36 months). Computed tomography angiography (CTA) and/or magnetic resonance angiography (MRA) showed occlusion in the anterior circulation in 21 cases (15, two, and four cases of occlusion in the middle cerebral artery, C6 segment of the internal carotid artery, and C7 segment, respectively). The patients' initial symptoms included dizziness, numbness, paroxysmal or persistent weakness of the contralateral limb, and aphasia. Occlusion in the posterior circulation was noted in six cases, including basilar artery occlusion in two cases and occlusion in the V4 segment of the vertebral artery in four cases. The initial symptoms of these patients included dizziness, giddiness, ataxia, blurred vision, nausea, vomiting, and dysarthria. MRI showed small subacute infarction in six cases, old infarction in 19 cases, and no obvious infarction in two cases. Procedure, Dyna micro-CT, and post-processing of images Preoperative preparation, mechanical recanalization of the occluded blood vessel, and stent implantation were as those reported previously.[3],[4],[5],[6] Residual stenoses were measured and recorded after stenting based on angiography findings. Anterograde blood flow after reperfusion was evaluated according to the thrombolysis in cerebral ischemia (TICI) grading system, and a score ≥2b indicated successful recanalization.[9] Dyna CT and Dyna micro-CT were used to scan the stent implantation area during and after the operation. The data for the latter were collected using the following parameters: 20S high-resolution flat CT scan (x-ray tube voltage: 109 kV; current: 460 ma); field of view, 22 cm; maximum rotation, 200°; frames, 496; and rotation acquisition, 20 s. After obtaining the image, the image was reconstructed using Siemens workstation (InStudio 3D). Images reconstructed using Dyna CT can show the overall intracranial situation, for example, whether there was high-density contrast media overflow, which helped determine if there was intraparenchymal hemorrhage or subarachnoid hemorrhage or not. Through the local reconstruction using Dyna micro-CT, the details of the stent wires and marks and the degree of stent expansion can be observed. Evaluation of image quality Images obtained using Dyna CT and Dyna micro-CT combined with SMART image quality evaluation were evaluated by two experienced neurointerventional doctors. The evaluation criteria were as follows: (1) Platinum-iridium marks (Neuroform EZ stent) or Tantalum marks (Enterprise stent), 0: not seen; 1: unclear; and 2: clear. (2) Nickel-titanium wire, 0: not seen, 1: unclear; and 2: clear. Postoperative management and follow-up After successful operation, patients' vital signs were measured strictly and the systolic blood pressure was controlled in the range of 90-110 mmHg for more than 48 hours. If there were postoperative National Institute of Health Stroke Scale (NIHSS) or modified Rankin Scale (mRS) score changes, head CT and/or MRI were performed to evaluate bleeding or ischemic events. According to the results of thromboelastography or antiplatelet drug gene detection, the patients were prescribed oral clopidogrel for 3- 6 months, followed by long-term aspirin enteric-coated tablets and statins. Postoperative imaging follow-up was performed with DSA, Dyna micro-CT, or CTA to determine whether there was restenosis or occlusion in the stent. The improvement of cerebral perfusion was evaluated by MRI or CT perfusion imaging. A modified Rankin scale (mRS) score of 0–2 was considered to indicate a good prognosis while that of 3–6 was considered to indicate a poor prognosis. Statistical analyses Statistical analyses were performed using SPSS 22.0 software. The (x̄ ± s) is used to describe the measurement data, which accorded with normal distribution and the Chi-square test or Fisher precision test was used to evaluate image quality. P <0.05 was considered statistically significant.
Of the 27 patients, 22 were successfully recanalized and 22 intracranial stents (including 14 Neuroform Ez and eight Enterprise stents) were implanted. Dyna micro-CT was performed for the stent area during the operation. The reconstructed images showed incomplete expansion of seven stents. After balloon dilatation, the stents fully expanded, which was confirmed using Dyna micro-CT [Figure 1]. Immediate postoperative angiography showed a residual stenosis rate of 0%–22% in 22 patients. In these patients, anterograde blood flow returned to TICI 3 in 17 patients and TICI 2B in five patients.
Dyna micro-CT combined with SMART image quality evaluation Compared to reconstruction with normal Dyna CT, image reconstruction using Dyna micro-CT provided significantly improved image quality (P < 0.05). Dyna micro-CT could clearly show the metal wire of the stent, help to evaluate the extent of stent expansion and the situation of wall apposition [Table 1]; [Figure 2].
Complications Of the 22 patients, three showed mild-to-moderate dysphoria after the operation. After sedation and control of blood pressure for 1–3 days, the patients' condition recovered to that before the operation. In one patient, Dyna micro-CT showed a subacute small infarct in the left basal ganglia area with continuous retention and stratification of the contrast agent and bleeding could not be excluded. The patient was treated with neutralizing heparin and double antiplatelet medication was stopped. The patient's condition was closely monitored; 22 hours after the operation, the patient experienced headache. CT showed intraparenchymal hemorrhage in the stent area. Thus, the patient was treated with evacuation of the hematoma plus bone flap decompression. After 3 weeks, the right upper limb muscle strength was grade III, the right lower limb muscle strength was grade IV, and mRS score was 3 [Figure 3]. The remaining 18 patients were stable without acute thrombosis or bleeding complications. Among the six patients who were not recanalized, one patient's language function worsened compared to that before the operation. After conservative treatment for 2 weeks, the patient's language function recovered to the preoperation level; thereafter, roofing of the temporal muscle and bypass surgery were performed.
Follow-up All 22 patients were followed up for 6-26 months (average, 12.0 ± 5.9 months) after stent implantation. The improvement rate of symptoms was 95.5% (21/22), and the complete remission rate was 77.3% (17/22). The mRS scores were as follows: 0 in four cases, 1 in seven cases, 2 in ten cases, and 3 in one case. None of the patients died or showed a recurrent stroke or transient ischemic attack after the operation. All 21 patients underwent imaging follow-up for 6 months (CTA, four cases; DSA, 17 cases), and three patients showed mild-to-moderate stenosis and no reocclusion. CT or MRI perfusion imaging was performed in 15 patients. The results showed a significant improvement in the hypoperfusion area in comparison with that before the operation.
Recanalization and stenting for chronic cerebral artery occlusion are more difficult and riskier than those for symptomatic intracranial artery stenosis, posing a major challenge to interventional neurologists. The limited available literature suggests that in patients with subacute or chronic cerebral arterial occlusion, the recanalization rate is 85.7%–100%, perioperative complication rate is 8.3%–44.4%, and mortality rate is 44.4%.[10],[11],[12] In order to minimize risks and improve outcomes, in addition to rigorous screening of cases, perioperative care, and fine surgical operations, it is important to use advanced imaging techniques for preoperative evaluation.[2],[13] The development of C-arm CT has solved many problems associated with the presence of invisible structures in previous neurointerventional therapy and has cross-era significance. However, for patients undergoing stent implantation, fluoroscopy and conventional angiography cannot easily reveal stent incomplete expansion, and the application of conventional C-arm CT is limited by the stents' high-density wire artefacts.[14],[15] This is an important risk factor for thrombotic events and long-term stent restenosis. Dyna micro-CT is a new-generation high-resolution C-arm CT system developed by Siemens. It was introduced in Germany in 2016. In comparison with traditional Dyna CT, it uses a smaller scanning area (stent area), a non-binned mode technique instead of the original 2 × 2 pixel binning technique, and optimized exposure conditions and image-processing methods, thereby improving the spatial resolution of local lesions without using low-concentration contrast agents. In comparison with the former technique, Dyna micro-CT shows an obvious improvement in stent visibility, which has been proven in animal experiments.[8] In early clinical studies, we found that with appropriate post-processing of the image and angle selection, Dyna micro-CT can show the tangent position and cross-section of the stent more clearly than traditional Dyna CT. It is helpful to observe the expansion of the stent and the situation of apposition to undertake the corresponding treatment measures. However, only a few previous reports have discussed the clinical effectiveness of Dyna micro-CT in intracranial stent implantation.[7],[8],[16] In this study, Dyna micro-CT detected seven cases of incomplete stent expansion, which was not easy to detect with routine CT and conventional C-arm CT, either because of the metal artefact of the stent or the hard plaque in the occluded part. These seven cases were treated with balloon dilatation and the apposition was improved. Caroff et al.[17] used high-resolution flat CT (Vaso CT) to observe the stent-assisted embolization of cerebral aneurysms and concluded that high-resolution flat CT could reduce the incidence of thromboembolic events. In the present study, this was also confirmed by the absence of severe intraoperative and postoperative complications such as acute thrombosis. In cases of hemorrhage, CT and MRI showed that the primary infarction was located in the left basal ganglia region and the focus was small (<1 cm) and not acute, so it was not clear on C-arm CT after stenting and could be easily ignored or thought to be the overflow of contrast agent from the infarct lesion. Dyna micro-CT can clearly show the stratified state of the contrast agent in the lesion (shown by the arrow, [Figure 3]h, [Figure 3]i), indicating that the possibility of bleeding is high. As the patients' speech and limb movements were normal, they were treated with neutralizing heparin and double antiplatelet therapy was stopped. The hematoma was subsequently enlarged and removal of hematoma plus bone flap decompression was conducted, and the patient recovered well. This suggests that on the one hand, we should strictly control the indications in the selection of cerebral artery occlusive cases, and be cautious in patients with acute-stage large-area cerebral infarctions. After the occlusive artery is recanalized, blood pressure should be strictly controlled to prevent reperfusion hemorrhage. On the other hand, in patients with infarction due to artery occlusion, the integrity of the blood-brain barrier is destroyed, and some patients may show overflow of the contrast agent due to increased vascular permeability in the infarcted area. This situation should be promptly reviewed using CT to assess the status of contrast agent dispersion and rule out the possibility of bleeding. In conclusion, Dyna micro-CT shows good applicability in operations involving chronic cerebral artery occlusion and stent placement, which helps reduce the incidence of postoperative complications and improve the long-term patency rate of the stent. However, this study is a single-center retrospective study and has limitations, and its reliability and long-term efficacy need to be further confirmed by a long-term, large-sample, multi-center, double-blind control study. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship This work was supported by the National Natural Science Foundation of China (Grant No. 81801806) and the Technological Research Project of Henan Provincial Science and Technology Department (172102310397). Conflicts of interest There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3]
[Table 1]
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