Thoracic CT Findings Following Endovascular Stent-Graft Treatment for Thoracic Aortic Aneurysm

Quantitative analysis of dynamic computed tomography angiography for the detection of endoleaks after abdominal aorta aneurysm endovascular repair: A feasibility study

Objectives

To assess the feasibility of quantitative analysis of dynamic computed tomography angiography (dCTA) for the detection of endoleaks in patients who underwent endovascular repair of abdominal aortic aneurysms (EVAR).

Material and methods

Twenty patients scheduled for contrast-enhanced CT angiography (CTA) of the abdominal aorta post-EVAR were prospectively enrolled. All patients received a standard triphasic CTA protocol, followed by an additional dCTA. The dCTA acquisition enabled reconstruction of color-coded maps depicting blood perfusion and a dCTA dataset of the aneurysm sac. Observers assessed the dCTA and dynamic CT perfusion (dCTP) images for the detection of endoleaks, establishing diagnostic confidence based on a modified 5-point Likert scale. An index was calculated for the ratio between the endoleak and aneurysm sac using blood flow for dCTP and Hounsfield units (HU) for dCTA. The Wilcoxon test compared the endoleak index and the diagnostic confidence of the observers.

Results

In total, 19 patients (18 males, median age 74 years [70.5–75.7]) were included for analysis. Nine endoleaks were detected in 7 patients using triphasic CTA as the reference standard. There was complete agreement for endoleak detection between the two techniques on a per-patient basis. Both dCTA and dCTP identified an additional endoleak in one patient. The diagnostic confidence using dCTP for detection of endoleaks was not significantly superior to dCTA (5.0 [5–5] vs. 4.5 [4–5], respectively; p = 0.11); however, dCTP demonstrated superior diagnostic confidence for endoleak exclusion compared to dCTA (1.0 [1–1] vs 1.5 [1.5–1.5], respectively; p <0.01). Moreover, the dCTP endoleak index was significantly higher than the dCTA index (18.5 [10.8–20.5] vs. 3.5 [5–2.7], respectively; p = 0.02).

Conclusions

Quantitative analysis of dCTP imaging can aid in the detection of endoleaks and demonstrates a higher endoleak detection rate than triphasic CTA, as well as a strong correlation with visual assessment of dCTA images.

TEVAR: Endovascular Repair of the Thoracic Aorta

The development of thoracic endovascular aortic repair (TEVAR) has allowed a minimally invasive approach for management of an array of thoracic aortic pathologies. Initially developed specifically for exclusion of thoracic aortic aneurysms, TEVAR is now used as an alternative to open surgery for a variety of disease pathologies due to the lower morbidity of this approach. Advances in endograft technology continue to broaden the applications of this technique.

Computed tomography angiography of hybrid thoracic endovascular aortic repair of the aortic arch

Endovascular repair of the aorta has traditionally been limited to the abdominal aorta and, more recently, the descending thoracic aorta. However, recently hybrid repairs (a combination of open surgical and endovascular repair) have made endovascular repair of the aortic arch possible. Hybrid repair of the aortic arch typically involves an open surgical debranching procedure that allows for revascularization of the aortic arch vessels and subsequent endovascular stent placement. These approaches avoid the deep hypothermic circulatory arrest required for full, open surgical repair of the aortic arch. In hybrid repairs, the stent landing zone determines which branch vessels will be covered and therefore need revascularization. This article will review the preprocedure assessment with computed tomography angiography, techniques for revascularization and postprocedure complications.

Endovascular repair of the thoracic aorta

The emergence of endovascular repair of the thoracic aorta (TEVAR) quickly followed the development of technology for the exclusion of infrarenal abdominal aortic aneurysms. Stent grafts comprised of metal struts covered with fabric made of Dacron/polyester or polytetrafluoroethylene were developed for the purpose of achieving an adequate seal at the proximal and distal aspects of thoracic aneurysms, thus excluding sac flow. The recognition of the decreased morbidity of this approach compared with open repair was readily apparent, as it avoided left thoracotomy, aortic cross-clamping, and left heart bypass. Since then, TEVAR is increasingly being used for other aortic pathologies such as complicated type B dissection, traumatic aortic transection, and aneurysmal disease extending into the arch or visceral segment, requiring debranching procedures.

Time-resolved computed tomography imaging of the aorta: a feasibility study

PURPOSE

The aim of this study was to test the feasibility and the additional value of time-resolved computed tomography angiography (CTA) of the aorta, using multiple low-dose phases.

MATERIALS AND METHODS

Twenty-two consecutive patients underwent a time-resolved CTA protocol (TR-CTA) of the aorta, either for follow-up of endovascular aneurysm repair (EVAR) or aortic dissection, using a CT scanner with the possibility of bidirectional table movements for dynamic CT imaging (Siemens Definition AS+; 12 phases, temporal resolution 2.5 s/scan, 80 kVp, 120 mAs/rot, scan range 27 cm, 60 mL; Imeron 400, flow 5.0 mL/s). The patients had previously undergone standard CTA (120 kVp, 100 mL contrast agent). Standard CTA after EVAR and aortic dissection were triphasic and biphasic protocols, respectively. Effective radiation dose and maximum Hounsfield unit values were compared between the TR-CTA and standard CTA. Image quality was rated for TR-CTA.

RESULTS

Fifteen patients underwent TR-CTA for follow-up after EVAR; 4 were examined for follow-up after dissection and 3 for both, that is, aortic dissection treated with an endovascular stent. Mean effective dose of TR-CTA for the scan range of 27 cm (15.3+/-1.1 mSv) was comparable with the biphasic standard CTA protocols (16.2+/-2.4 mSv; P=0.29). Triphasic protocols resulted in 23.7+/-4.9 mSv (P<0.0001). Hounsfield unit values were not significantly different. Most of the examinations (91%) were fully evaluable, whereas 9% were of limited evaluability because of high image noise. None of the examinations was nondiagnostic.

DISCUSSION

TR-CTA consisting of multiple low-dose phases leads to a clear depiction of the angiographic information and is feasible for follow-up after EVAR and aortic dissection. Considering the limited scan range, radiation dose is comparable with the standard biphasic CTA protocol, but dynamic information may provide additional information.

Evaluation of the diameter of the proximal descending thoracic aorta with age: implications for thoracic aortic stent grafting

BACKGROUND

Long-term anatomical changes of the thoracic aorta which may affect long-term outcome of blunt aortic injuries treated with endovascular stent grafts are unknown. The purpose of this study was to examine the natural history of thoracic aortic diameter with progressing age.

METHODS

One thousand consecutive thoracic computed tomographic scans performed for nonthoracic aortic pathology on patients aged 15-99 (mean 59.4) were examined, and thoracic aortic diameter immediately adjacent to the left subclavian artery was measured. Factors possibly influencing diameter, including age by decade of life, race, gender, history of hypertension (HTN), diabetes mellitus (DM), chronic obstructive pulmonary disease (COPD), and tobacco use, were examined. Factors were compared using Student's t-test.

RESULTS

The differences in mean diameters of the thoracic aorta by gender (male=27.1 vs. female=26.0, p=0.87), race (Caucasian=26.6 vs. non-Caucasian=26.3, p=0.10), presence of HTN (yes=25.8 vs. no=24.9, p=0.36), COPD (yes=26.3 vs. no=25.4, p=0.21), DM (yes=26.1 vs. no=25.3, p=0.12), and tobacco use (yes=26.3 vs. no=25.0, p=0.18) were not significant. However, differences in mean diameter increased significantly over time with age. Patients under 40 years old had mean aortic diameters of 22.92 mm compared to 27.09 mm (p<0.001) for patients over 40. The mean aortic isthmus diameter showed an approximately 1cm increase when comparing octogenarians to teenagers.

CONCLUSION

The diameter of the aortic isthmus increases substantially with age. These findings suggest that long-term surveillance is warranted for trauma patients with aortic stent grafts, to monitor the natural history and to assess for possible late complications.

Assessment of aortic pathology and peripheral arterial disease using multidetector computed tomographic angiography

The development of multidetector computed tomography represents a remarkable diagnostic advancement because this imaging modality has been widely used in the evaluation of the cardiovascular system. With scanner-adjusted image acquisition and contrast medium administration, multidetector computed tomographic angiography provides a cost-effective and accurate imaging assessment in patients with aortic pathologies or peripheral arterial occlusive disease. Multidetector computed tomographic angiography is associated with several advantages, including high image spatial resolution and rapid imaging acquisition speed. This diagnostic methodology allows accurate detection of a variety of intravascular lesions in the carotid artery, thoracic and abdominal aorta, renal arteries, and peripheral arterial systems. This article provides an overview of multidetector computed tomographic angiography in the assessment of arterial disease and reviews current literature about this diagnostic technology in the evaluation of aortic and peripheral arterial pathologies.