Discussion - Hybrid CTA in Diagnosis and Treatment Planning of Dural Arteriovenous

Chapter 2 Hybrid CTA in Diagnosis and Treatment Planning of Dural Arteriovenous

2.4 Discussion

The difficulty of bone removal limits the application of CTA in the diagnosis of dural AVF. In one re-cent report [19], CTA had a sensitivity of 15.4% in the diagnosis of dural AVF. In our study, we proved that hybrid CTA is a promising tool for the diagnosis of dural AVF. DSA can help in the diagnosis of dural AVF, can depict the supplying arteries, and can aid characterization of the draining system of dural AVF.

The latter determines the clinical presentation, grade, and therapeutic strategy in patients with a dural AVF [15,20,21]. Our results suggest that hybrid CTA could be used to determine the diagnosis in all types and grades of dural AVFs, to demonstrate the feeder artery, to aid localization of the lesion, and to show the pattern of venous drainage. One patient in the control group had a false-positive sign of asymmetric early venous enhancement. From DSA, we found that the patient had dominant drainage of the superior sagittal sinus to the right transverse sinus, which was less enhanced compared with the left side at hybrid CTA. We speculate that the vein of Labbé was diluted more at the dominant right transverse sinus owing to nonopaque blood flow coming from the superior sagittal sinus. Asymmetric opacification of the transverse and

sigmoid sinuses during CTA is a rather common finding, likely secondary to the preferential direction of opacified blood flow to the dominant sinus at the early time of arterial scanning. This asymmetry disappears when late-phase venous scans are obtained. Two patients had a false-positive sign of transosseous enhanced vessels in the occipital bone near the sigmoid sinus. We speculate that these were emissary veins. We were not able to identify the direction of the vessels inside the cranium with hybrid CTA. We need to emphasize that finding at least two imaging signs present is the key to making the right diagnosis in dural AVFs.

Two patients with a dural AVF in the superior sagittal sinus did not have asymmetric sinus enhancement. In general, the vertex superior sagittal sinus becomes densely enhanced near the end of the scan. As such, enhancement asymmetry may not be apparent in a patient with a dural AVF at or close to the vertex superior sagittal sinus.

However, other signs allowed diagnosis of dural AVF even in these patients with dural AVF of the superior sagittal sinus. Dural AVFs can be divided into two major groups according to their locations: cavernous sinus and non-cavernous lesions. In cavernous sinus dural AVFs, frequent findings include asymmetric early sinus enhancement and engorgement of the extracranial veins (frequently superior ophthalmic veins). Engorged arteries are infrequently seen in cavernous sinus dural AVFs because of their relatively small size. In non-cavernous dural AVFs, engorged arteries are more frequently seen.

Engorgement of cortical veins and extracranial veins depend on the size and the drainage patterns of the dural AVF. On the basis of our results, hybrid CTA is highly sensitive for different types of dural AVFs, especially in patients with the osteodural-type lesion. Hybrid CTA has the advantage of demonstrating the transosseous vessels and also the fistula inside the bone structures.

doi:10.6342/NTU201603776 On the basis of our study results, hybrid CTA may also provide sufficient

information for treatment planning. Hybrid CTA can provide additional information for identifying the route of approach to treat dural AVFs. Identification of the draining venous pattern is important for the treatment of dural AVFs [22,23]. Pretreatment planning with hybrid CTA was feasible in our series. Transvenous embolization is one of the treatments of choice for most dural AVFs. Hybrid CTA can be used to eliminate the bone structure, while the image noise in non-bone areas is not increased, and to obtain better three-dimensional volume data.

Our study had limitations. Because this was a retrospective study, the tube current for precontrast scanning could only be reduced by half. The radiation dose for precontrast scanning was slightly higher than that in the scanning protocol recommended for MMBE CTA, in which one-quarter tube current is suggested for a precontrast scan. The effective tube current–time product used in our hybrid CT angiographic scanning protocol was similar to that used in a study on the use of MMBE study [24]; however, the tube voltage is 100 kVp rather than 120 kVp in the proposed hybrid CTA protocol. For example, with the same machine (scanner B in our study) and same irradiated length, the irradiation dose (estimated CT dose index volume) was 9.4 mGy for the precontrast scans and about 18.8 mGy for the post-contrast scans with the hybrid CTA protocol and 7.8 mGy and 28.1 mGy, respectively, in the other MMBE protocols [24]. So, the total irradiation dose is lower with hybrid CTA than with other MMBE methods. A lower peak kilovolt is not used because of the concern about contrast-to-noise ratio on the images.

Another limitation of our study was the small number of cases. We could not conclude that hybrid CTA can be used for the diagnosis in all patients with a dural AVF.

False-positive and false-negative rates may be under-estimated because it is difficult to have a large number of patients who undergo DSA without positive hybrid CT angiographic, MR imaging, or MR angiographic findings. In addition, we used subjective findings that have not been well established for diagnosing retro-grade cortical veins. These need to be better defined with further research. In conclusion, we found that hybrid CTA is a valuable tool for the diagnosis of dural AVF. It can provide the key information necessary for treatment planning. Further studies in larger series of patients are warranted.

Note:

This part was published on Radiology 2010.

Lee CW, Huang A, Wang YH, Yang CY, Chen YF, Liu HM. Intracranial Dural Arteriovenous Fistulas: Diagnosis and Evaluation with 64-Dector Row CT Angiography.

Radiology. 2010; 256: 219-228.

doi:10.6342/NTU201603776 Figure 2-1: Patient 8. (a) Lateral DSA image after left external carotid injection shows

isolated left transverse sigmoid sinus dural AVF. (b) Coronal hybrid CT angiogram shows asymmetric sinus enhancement (large arrows), engorged cortical veins (small arrows), and incidental small right proximal transverse sinus dural AVF (arrowheads).

Images from (c) hybrid CTA and (d) MMBE CTA show isolated, occluded transverse sinus. Transosseous enhanced vessels (arrows on c) could be demonstrated only on hybrid CT angiogram.

Figure 2-2: Patient 15. Images in 48-year-old man with pulsatile tinnitus and dizziness.

(a) Maximum intensity projection image from hybrid CTA shows dural AVF (arrow) with early enhancement and engorged drainage vein at the left clivus to the paraspinal area. (b) hybrid CTA source image shows fistula in the left clivus (arrow). (c) DSA image of left external carotid artery (L ECA) demonstrates a fistula (arrow) at the left hypoglossal-clival area with paraspinal drainage. The lesion was treated with the transvenous approach according to findings from hybrid CTA through the route of the anterior internal spinal venous plexus. (d) Precontrast image obtained after embolization shows coils inside left clivus.

doi:10.6342/NTU201603776 Figure 2-3:Patient 13. Images in 60-year-old man with pulsatile tinnitus. (a) Lateral

projection of left external carotid artery demonstrates a type IIA dural AVF (Cognard et al [4] classification) at the left transverse-sigmoid sinus area. (b) Left common carotid artery angiogram obtained in the venous phase shows the left vein of Labbé (arrows) also draining into the left transverse sinus. (c) Hybrid CT angiogram obtained with volume rendering shows the fistula (red arrows) actually located at the dura next to the sigmoid sinus. The vein of Labbé (open arrows) is next to the fistula and drains into the transverse sinus.

Figure 2-4: Images in 56-year-old woman with pulsatile tinnitus. (a, b) DSA images of bilateral external carotid arteries demonstrate the fistula, engorged cortical vein, and superior sagittal sinus. The relationship between the fistula and the superior sagittal sinus is not clearly shown. (c) Hybrid CT angiogram obtained with volume rendering depicts the fistula inside the bilateral paramedian posterior frontal bones (red), the engorged cortical drainage vein (red), and patent superior sagittal sinus. After transarterial approach with coils deploying in the venous side of the fistula, complete obliteration of the lesion was achieved. (d) Plain radiograph shows platinum coils inside the bilateral paramedian posterior frontal bones.

doi:10.6342/NTU201603776 Table 2-1: Summary of Demographic Information, Clinical Manifestations, Lesion

Locations, Treatments, and Outcomes in 22 Patients with 24 Dural AVFs

Patient

No./Sex/Age(y)

Location Clinical Manifestation Treatment Outcome

Cavernous sinus

10b/F/77 Hypoglossal Incidental None -

14/M/50 CH Tinnitus TVE Good

20/M/53 Occipital dura Tinnitus TAE Good

21/M/63 Cerebellar falx SAH TAE Good

22/F/62 Parietosphenoid

osseous-dura

Tinnitus TVE Good

Note: Patient 8 and 10 had two dural AVFs (8a and 8b and 10a and 10b, respectively) For patients 8a, 10b, 18, and 19, in the Clinical Manifestation column, incidental means that there were no AVF-associated clinical manifestations, and AVF was detected incidentally when CTA was performed for other diseases.

At presentation, patient 18 had transient ischemic attack, and vertebral artery dissection was diagnosed.

CS=cavernous sinus, TS=transverse sigmoid sinus, SS=sigmoid sinus, CH=clivo-hypoglossal area, SSS=superior sagittal sinus, ICH=intracerebral hematoma, SAH=subarachnoid hemorrhage, TAE=transarterial embolization, TVE=transvenous embolization, SRS=stereotactic radiosurgery

A fair outcome was defined as partial symptom relief

Table 2-2: Diagnostic Performance of Imaging Signs at Hybrid CTA

Imaging Sign Sensitivity Specificity Positive Predictive Value

Negative Predictive Value

Engorged artery

Value 0.95(19/20) 1.00(18/18) 1.00(19/19) 0.95(18/19)

95% CI 0.75, 1.00 0.85, 1.00 0.85, 1.00 0.74, 1.00

Transosseous enhancing vessels

Value 0.95(19/20) 0.89(16/18) 0.90(19/21) 0.94(16/17)

95% CI 0.75, 1.00 0.66, 0.98 0.70, 0.99 0.71, 1.00

Engorged extracranial veins

Value 0.81(13/16) 1.00(22/22) 1.00(13/13) 0.88(22/25)

95% CI 0.56, 0.94 0.87, 1.00 0.80, 1.00 0.90, 1.00

Engorged cortical veins

Value 1.00(7/7) 1.00(31/31) 1.00(7/7) 1.00(31/31)

95% CI 0.68, 1.00 0.90, 1.00 0.68, 1.00 0.90, 1.00

Asymmetric sinus enhancement

Value 0.96(23/24) 0.93(13/14) 0.96(23/24) 0.93(13/14)

95% CI 0.78, 1.00 0.66, 1.00 0.78, 1.00 0.66, 1.00

Sinus occlusion

Value 0.89(8/9) 1.00(29/29) 1.00(8/8) 0.97(29/30)

95% CI 0.54, 1.00 0.90, 1.00 0.71, 1.00 0.82, 1.00

Overall

Value 0.93(89/96) 0.98(129/132) 0.97(89/92) 0.95(129/136)

95% CI 0.85, 0.97 0.93, 1.00 0.90, 0.99 0.90, 0.98

Note.—Data are for the 22 patients with dural AVFs and 14 control subjects. Numbers in parentheses are numbers of subjects and were used to calculate the values as proportions.

doi:10.6342/NTU201603776 Table 2-3: Interobserver Agreement in Reading Imaging Signs at Hybrid CTA

Imaging Sign κ Value 95% CI

Engorged artery 0.84 0.67, 1.00

Transosseous enhanced vessels 0.95 0.84, 1.00

Engorged extracranial vein 0.56 0.29, 0.83

Engorged cortical vein 0.92 0.78, 1.00

Asymmetric sinus enhancement 0.94 0.83, 1.00

Dural sinus occlusion 1.00 1.00, 1.00

Table 2-4: Comparison of DSA with Readers for Grades Assigned to 24 Dural AVFs

Grade (Cognard) Observed Agreement Region

Cavernous sinus 5/5(100) 5/5(100) 5/5(100)

1 CS I I I

2 CS I I I

3 CS I I I

4 CS I I I

5 CS IIA+B IIA+B IIA+B

Transverse sigmoid sinus 7/9(78) 8/9(89) 7/9(78)

6 TS I I I

Hypoglossal and clival areas 4/4(100) 4/4(100) 4/4(100)

10b Hypoglossal area I I I

14 CH I I I

15 CH I I I

16 CH I I I

Superior sagittal sinus 2/2(100) 2/2(100) 2/2(100)

17 SSS IV IV IV

Overall 22/24(92) 23/24(96) 22/24(92)

Note: Patients 8 and 10 had two dural AVFs each (8a and 8b and 10a and 10b, respectively). Number in parenthesis is the percentage. CS=cavernous sinus, TS=transverse sigmoid sinus, CH=clival-hypoglossal area, SSS=superior sagittal sinus.

doi:10.6342/NTU201603776

Chapter 3 Predicting Procedure Successful Rate and 1-Year Patency After Endovascular Recanalization for Chronic Carotid

Artery Occlusion by CT Angiography

3.1 Introduction

In chronic internal carotid artery (ICA) occlusion, the hemodynamics may be normal, or severely impaired, depending on recruitment of cerebral collaterals [25,26].

When ICA stenosis progresses to occlusion, the reduction of blood supply to the perfused territory is usually compensated by extracranial–intracranial (EC/IC) and intracranial collaterals. In fact, an ICA chronic total occlusion (CTO) bears a considerable risk of ipsilateral ischemic stroke. According to some reports, patients with carotid CTO also have a risk of recurrent stroke of approximately 6.3% [27]. In addition, the risk of recurrent stroke increases to approximately 12% per year in CTO patients who also have compromised hemodynamic status [28,29]. Other researchers have reported a risk of recurrent stroke as high as 86% in a 7-year follow-up study [30].

Furthermore, advanced imaging techniques have uncovered microstructural changes in normal appearing brain tissue in such patients [31]. Such findings have been related to functional disability, higher mortality, and a decline in psychomotor speed, executive functions, and working memory [31].

Over the last few decades, the prevention of secondary stroke in patients with carotid disease has improved with more rigorous control of blood pressure and the introduction of statins combined with anti-platelet therapy [32,33]. Medical treatment

has become the prevailing doctrine in treating carotid CTOs and aggressive treatment of carotid CTOs remains controversial [34]. The carotid occlusion surgery study (COSS) compared the benefit of superficial temporal artery — middle cerebral artery (MCA) bypass vs. medical treatment in preventing stroke in carotid CTO [35]. The 30-day event rate in the surgical group was approximately 14.4% and the 2-year outcome rate did not differ significantly between the surgical (21%) and the medical groups (22.7%), although vessel patency was demonstrated in 90% of patients [35,36].

With the latest advancements in stenting and hybrid-surgical technique, some recent non-randomized studies have shown the feasibility of carotid artery stenting (CAS) and carotid endarterectomy (CEA) in carotid CTO [37-40]. In addition, their results suggest that such interventions might improve neurocognitive function in carotid CTO patients [37-40]. CEA success rates were also shown to differ depending on the ultrasound findings in CTO [39].

The patient selection criteria for the treatment of carotid CTOs are still controversial. In few small-series reports, in acute to chronic ICA occlusion from cervical to petrous segment could be endovascularly recanalized with high successful rates with frequent complication such as subarachnoid hemorrhage (SAH), arterial dissection, symptomatic and asymptomatic embolic events [41-43]. It is rare to find report about how to predict the technical success rates, complication rates, and re-occlusion after endovascular recanalization using non-invasive technique such as CTA. In this study, we retrospectively analyzed the pre-procedural CTA in patients with carotid CTO and its relationship to short-term outcomes including technical success rates, complication rates, and re-occlusion after endovascular recanalization.

doi:10.6342/NTU201603776 3.2 Materials and Methods

3.2.1 Subjects

This retrospective study was approved by our Institutional Review Board. All medical images and records were analyzed and reviewed. Patients who were diagnosed and confirmed with carotid CTOs by CTA (and who subsequently underwent endovascular recanalization within 3 months of the CTA) were included in the study.

The endovascular recanalization was performed at least 2 months after initial diagnosis of carotid occlusion. The exclusion criteria were: (1) acute occlusion of the carotid artery; (2) severe carotid stenosis with string sign on CTA but occlusion on angiography before recanalization; (3) history of previous stenting of the occluded artery; (4) viable head–neck malignancy or prominent radiation necrosis; and (5) severe disabling stroke precluding further recanalization. Hybrid CTA images were used for evaluation. The endovascular recanalization procedure was performed, as previously described [37,38].

The medical conditions, results of the recanalization (success or failure), presence of a major event within 30 days, and patency on follow-up imaging studies were recorded.

The patency or re-occlusion was assessed by ultrasound and/or CTA.

Patients were divided into two groups according to the extent of ICA occlusion based on the ICA classification proposed by Bouthillier et al. [44]. In this system, the ICA is divided into seven segments, i.e., C1, cervical; C2, petrous; C3, lacerum; C4, cavernous; C5, clinoid; C6, ophthalmic; and C7, communicating. C5 was used as the landmark, or milestone, to divide the patients into groups A and B. Group A patients had occlusions which involved the ICA up to the clinoid segment and beyond, while group B patients had occlusions which were proximal to the clinoid segment of the ICA or involved only the common carotid artery.

3.2.2 Patient Outcomes

Technical success was defined as complete patency of the occluded vessel shown on immediate post-procedural angiography. A periprocedural major complication was defined as a neurological or cardiovascular event within 30 days. Events which occurred after 30 days were defined as delayed complications. Stent patency was evaluated within 1 year of the recanalization using follow-up CTA or carotid duplex ultrasound.

Re-occlusion was defined as no flow shown on the follow-up imaging studies.

3.2.3 Statistical Analysis

All clinical variables were compared between the two groups. The student t-test was used for continuous data and the chi-square test was used for categorical data. A logistic regression model was used to analyze clinical predictors and clinical outcomes.

The regression coefficient was analyzed by the Wald test. Multivariable regression and stratified analysis were used to control confounders. The 1-year vascular patency was also analyzed by Kaplan–Meier survival curve analysis. Patients with a follow-up time of b1 year were considered as right censored. The predictors were compared by Wilcoxon test. The significance level was set at .05. Statistical analyses were conducted using SAS software, version 9.4 (SAS Institute, Inc., Cary, North Carolina).

3.3 Results

From January 2008 to July 2015, 41 patients with a total of 42 carotid CTOs were included in the analysis. The one patient with bilateral occlusions was treated in two sessions. Thirty-two CTO arteries (32/42, 76%) in 31 patients were symptomatic (including 23 ipsilateral minor strokes; nine transient ischemic attach). Ten patients (10/41, 24%) had non-specific symptoms such as dizziness, fainting, or neurocognitive

doi:10.6342/NTU201603776 decline. The extent of occlusion in group A (N = 23) included 13 occlusions from the

carotid bulb to the clinoid segment of the ICA, eight from the bulb to the supraclinoid ICA, and two from the bulb to the MCA. The extent of occlusion in group B (N = 19) included four occlusions at the common carotid artery (CCA) alone, five at the cervical ICA, five from the bulb to the petrous ICA, and five from the bulb to the cavernous ICA (Figure 3-1).

In total, 29 arteries (29/42, 69%) were successfully recanalized. One patient (who failed revascularization) had an acute SAH during the procedure, while the other 12 patients with failed recanalizations had no acute or new onset of symptoms. The technical success rate was 52% (12/23) in group A and 89% (17/19) in group B. The major complication rate in group A was 22% (5/23) and 0 in group B. The 1-year reocclusion rate was 92% (11/12) in group A and 0 in group B. One patient was lost to follow-up after successful recanalization in group B. When comparing group A with group B, technical success rate (P = 0.0093) and stent patency (P b 0.001) were significantly different (Table 3-1). Based on univariable logistic regression analysis of technical success, group B had a higher success rate than group A (odds ratio: 7.79; CI:

1.45–41.73; P = 0.0165). Since diabetes was a possible confounder, it was used to adjust the logistic regression model. The group effect was still significant based on multivariable logistic regression (odds ratio: 12.71; CI: 2.06–78.44; P = 0.0062).

Analysis of stent patency was performed in 28 patients who were successfully recanalized. Chi-square tests showed that the group effect (P=0.001) and diabetes (P=0.004) were associated with stent occlusion (Table 3-2). Stratified analysis showed that the group effect was significant in diabetic patients (odds ratio: 75.00; CI:

1.16–4868.64; P = 0.0027) and non-diabetic patients (odds ratio: 87.00; CI:

2.99–2531.93; P = 0.0002). However, the odds ratio was lower in the pooled estimate (corrected Mantel Haenszel odds ratio: 82.05; CI: 5.96–1129.50). Major complications occurred in five patients in group A (5/23, 21.7%) and four occurred within 7 days. In group A, there was one subarachnoid hemorrhage (SAH), three ischemic infarcts (one immediate post-procedure and two acute in-stent thromboses on the 1st day and 5th day, respectively) and one delayed stroke (1/23, 4.3 due to stent occlusion on the 40th day.

Two patients died (one SAH and one acute in-stent thrombosis). Other 3 had good recovery. No immediate or delayed major complication or death occurred in group B.

On the follow-up images within 1 year, of the 29 successfully recanalized arteries, 17 arteries (one in group A; 16 in group B) were patent, 11 (11 in group A; 0 in group B) were occluded, and one had no follow-up imaging. In group A, the only patent artery was followed-up for only 2 months after recanalization. In group B, five arteries were patent on the follow-up images performed within 8 months.

Based on survival analysis of stent occlusion at one-year follow-up, of the 28 subjects deemed technically successes, six subjects with <1 year of follow-up were considered right-censored. One patient was excluded due to loss of follow-up after successful procedure. Eleven occlusion events, all in group A, were recorded. The median time of re-occlusion was 4 months (95% CI: 1–7 months). Based on univariable analysis of the clinical predictors, only the group effect was significant (P < 0.0001) by Wilcoxon test (Table 3-3). The Kaplan–Meier survival curve for groups A and B is shown in Figure 3-2.

doi:10.6342/NTU201603776 3.4 Discussion

Our results showed that CTA can predict the successful rate and 1-year patency rate after endovascular recanalization in patients with carotid CTO. Patients with an occlusion proximal to the clinoid segment of the ICA (group B) had a higher rate of successful recanalization, fewer periprocedural major complications, and better 1-year

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