K.E.M. Radiology

Introduction:

The development of thoracic endovascular aortic repair (TEVAR) has allowed a minimally invasive approach for the management of an array of thoracic aortic pathologies. TEVAR is now used as an alternative to open surgery for a variety of diseases due to the lower morbidity of this approach (1,2). Initially utilized in the treatment of aortic aneurysmal disease, TEVAR indications have expanded to include treatment of Type B aortic dissection with malperfusion or rupture, traumatic aortic transection, and penetrating aortic ulcer (PAU). Although there are no randomized controlled trials directly comparing TEVAR to open surgery, numerous studies suggest that TEVAR is associated with decreased morbidity compared with open repair (3,4). Benefits of the endovascular approach include avoidance of thoracotomy or sternotomy incision, avoidance of aortic cross-clamping, decreased blood loss, and decreased end-organ ischemia (5).  

Case presentation:

A 66 yrs old man presented with an episode of massive hemoptysis with approximately 300 ml blood loss. The patient had no prior history of pulmonary TB considered to be one of the common cause of hemoptysis.  THe chest radiograph showed mediastinal widening with soft tissue opacification in left upper zone.  For further evaluation of the soft tissue opacity in the left upper zone CECT of chest and abdomen was performed. This showed a large partially thrombosed aneurysm of the descending thoracic aorta just distal to origin of the left subclavian artery.  The patient was referred to our department for further evaluation. A review of the CT scan showed a wide necked partially thrombosed aneurysm measuring 6.8 cm x 5.3 cm x 7.5 cm just distal to the origin of the left subclavian artery. The left vertebral artery was dominant, the right being hypoplastic. 

To protect the left upper limb circulation and posterior fossa circulation it decided to perform debranching surgery followed by TEVAR. (Fig 1, Video 1, Video 2).

Based on the post debranching CT and DSA , it was decided to occlude the subclavian artery stump with a plug followed by TEVAR.

After adequate pre-procedural patient and relative counselling and obtaining an informed consent, and pre-operative preparation-medical, surgical and anaesthesia fitness was completed. The procedure was performed under general anaesthesia. 

Intraoperative assistance for femoral arteriotomy was provided by our cardiovascular and thoracic surgeons. With aseptic precautions, a right femoral arteriotomy was performed. After proper exposure, the right CFA access was secured with short 6F short sheath. Through a tight brachial access with a 4F sheath. A 4F pigtail catheter with its tip in the ascending aorta. This access was secured to perform multiple angiograms during the procedure. Additional Left CFA access allowed deployment of the  vascular plug in the left subclavian stump.  The subclavian stump was accessed with a 8 Fr 90 cm sheath via left CFA; the vascular plug (14 mm) was  advanced through this long sheath into the stump. The aortic stent graft device was advanced through right common femoral artery overa  stiff wire. An aortogram was performed  for  precise deployment (Fig 5, Video 6). 

Discussion:

Thoracic endovascular aortic repair (TEVAR) has become the preferred approach for treatment of thoracic aortic pathology since the approval of the first endograft device by the U.S. Food and Drug Administration (FDA) in 2005. 

Indication of TEVAR in aortic aneurysm:

TEVAR is indicated if aortic diameteris greater than 6 to 6.5 cm where risk of repair is outweighed by the risk of rupture (6). Patients with aneurysms larger than 6 cm have a 14.1% annual risk of rupture, dissection, or death, compared with 6.5% for patients with aneurysms between 5 and 6 cm (6). Some guidelines have suggested that repair is appropriate for aneurysms as small as 5.5 cm, saccular aneurysms greater than 2 cm, or saccular aneurysms associated with a total aortic diameter greater than 5 cm (7). Symptomatic aneurysms and aneurysms associated with a rapid growth rate of greater than 1 cm per year are considered to be at increased risk for rupture and should also be repaired (7). 

Contraindications to TEVAR

Unfavorable anatomy is the main contraindication to TEVAR, which may include inadequate proximal or distal seal zones, tortuosity, lack of vascular access options, or extremes of aortic diameter. Placement into infected fields should also be avoided.  

Anatomic Considerations

Aortic Arch

The primary features of the thoracic aorta are its relatively large diameter compared to the abdominal aorta, and the anatomy of the aortic arch. There can be significant variability in both the origin of the arch vessels and the degree of arch angulation. The large diameter of the aorta necessitates larger endografts, and the degree of angulation requires a relatively long seal zone (2 cm). Earlier generation stent grafts were characterized by failure of the proximal stent graft to conform to the aortic anatomy leading to “bird beaking,” increasing the risk of graft failure, migration, or collapse. Current-generation devices are all characterized by their improved flexibility, a design feature employed to allow improved conformability to the aortic arch. Aortic arch debranching via ascending aortic-to-innominate and left common carotid artery bypass, carotid–carotid bypass, or left carotid-to-subclavian artery bypass may be required to obtain an adequate seal zone (8). 

Access Vessels

Access vessel anatomy is also critical, as the relatively large size of the thoracic endografts in turn requires larger diameter delivery systems. The femoral and iliac systems should be carefully assessed to ensure that passage of the sheath will be possible, and evaluated for small diameter or heavy calcification. 

Intercostal Arteries and Spinal Cord Perfusion

Paired intercostal branches are derived from the descending thoracic aorta and provide collateral flow to the anterior spinal cord via the artery of Adamkiewicz and other radicular branches. The degree of coverage of these branches must be assessed during TEVAR, as extensive coverage is a major risk factor for spinal cord ischemia and postoperative paraplegia. Consideration should also be given to prior EVAR or open aortic repair, as well as to occluded or embolized internal iliac arteries given that lumbar arteries and the internal iliac arteries provide collateral blood flow to the spinal cord (9). 

Preoperative Planning and Landing Zones

Adequate preoperative measurements are critical for the correct sizing of thoracic endografts, and are best facilitated by CT Aortogram with three-dimensional reformatting. This provides information about the landing zones, coverage length, and tortuosity and angulation of the aorta. CTA can also provide information about intraluminal thrombus or wall calcification that may have implications for graft placement. Measurements from the CTA can be used to accurately size the endograft. Magnetic resonance angiography can also be used as a preoperative imaging study, but does not show calcification as well as CT and still has the risk of nephrogenic systemic fibrosis when used in patients with renal insufficiency (10). 

Commercially available thoracic stent grafts all require a 20-mm-long proximal landing zone. It is critical to obtain good apposition throughout this segment to avoid endoleak or device migration. Depending on the patient's anatomy, it may be necessary to cover one or more of the arch branches to obtain an adequate seal. Frequently, coverage of the left subclavian artery is required to obtain an adequate proximal seal, particularly in dissection or traumatic aortic transection cases. When this is necessary, preoperative duplex ultrasound of the carotid and vertebral arteries should be performed, if possible, and consideration given to performing left carotid-subclavian bypass or subclavian transposition prior to procedure. TEVAR can then be completed as a second-stage procedure with embolization of the native subclavian artery to prevent type II endoleak. If the left carotid or innominate artery would require coverage, then antegrade bypass from the ascending aorta (11,12,13) or extra-anatomic bypass via a carotid–carotid bypass (14) may be necessary. 

The distal landing zone is also critical to avoid type Ib endoleak, and also requires a 20-mm seal zone with the currently available devices. In patients with disadvantaged distal seal zones where adequate seal can only be achieved with celiac artery coverage, selective arteriogram and demonstration of an intact gastroduodenal artery providing collateral flow from the superior mesenteric artery are necessary prior to placement of TEVAR. Reports indicate that coverage of this vessel may have a nominal rate of mesenteric ischemia of only  of abpot 6% (14,15,16). 

The Procedure

The procedure is generally performed under general anesthesia, which allows respiratory control by anesthesiologist and provides more precise imaging. 

The procedure can be started with the femoral arteriotomy to obtain femoral access . Additional access can be obtained from either the arm or the contralateral groin to allow for control angiography. Wire access is gained into the ascending aorta and exchanged for a stiff wire to allow tracking of the device. Once the device is positioned, angiography is performed with power injection and respiratory arrest to allow for precise graft positioning. Once the graft is deployed, it may be ballooned at the seal zones and at any overlap zones to ensure full approximation to the aortic wall. Completion angiography is then performed to assess for endoleak, the sheath and device are removed, and the arteriotomy is closed.

Complications

Stroke: Any manipulation of the aortic arch carries the risk of embolization to the carotid artery and subsequent stroke. This risk is magnified in patients with a very proximal seal zone, mural thrombus in the arch, or history of prior stroke (17). Posterior circulation stroke can also occur due to coverage of the left subclavian artery or embolization via the subclavian artery. Posterior circulation strokes have increased morbidity and mortality when compared with anterior circulation strokes (18). Performance of a carotid-subclavian bypass prior to TEVAR can decrease this risk, and has the added benefit of improving risk of paraplegia (19,20) . 

Paraplegia: Paralysis due to spinal cord ischemia is a much-feared risk of TEVAR. Risk factors include extensive coverage of the thoracic aorta (21), prior AAA repair (22) and coverage of the left subclavian artery. Neuromonitoring with early recognition and treatment with lumbar drainage and permissive hypertension are the keys to treatment.

Visceral ischemia: Visceral ischemia can occur with intentional or unintentional coverage of celiac artery origin. An intact pancreaticoduodenal arcade may reduce this risk. 

Access complications: The large diameter of the devices required for TEVAR in turn requires relatively large sheath sizes of 20 to 26F. It is important to assess the patient's access via the femoral and iliac vessels on preoperative CT scan to minimize access problems. Calcified, small, tortuous vessels are most at risk. When iliac rupture occurs, balloon occlusion can be used for temporary vascular control until the artery can be repaired. 

Postimplantation syndrome: Fever and leukocytosis in the immediate postoperative period may be due to endothelial activation from placement of the stent graft. This should be considered in patients with elevated inflammatory markers and pleural effusions with an otherwise negative infectious work-up (23). 

Device migration and endoleak: Postimplantation graft migration occurs with an incidence of 1 to 2.8% (24). Extensive aortic tortuosity and graft oversizing are associated with migration risk. Endoleak is fairly uncommon after TEVAR, with reported rates ranging in the literature from 3.9 to 15% (24). 

Postoperative management/surveillance: Patients are monitored in the ICU postoperatively, with careful monitoring of their hemodynamic and neurologic exam. They are usually transferred out of the ICUr by postoperative day 3 and discharged home within 1 week. If there are any concerns about endoleak based on the technical aspects of the case, a CTA is performed prior to discharge. Graft surveillance is performed with CTA at 1 month, 6 months, and then annually to assess for adequate graft position and endoleak.

Clinical outcome: TEVAR has excellent technical success rate of up to 98%. There is low perioperative mortality compared with open repair, with endovascular repair mortality rates of 1.9 to 2.1%, compared with 5.7 to 11.7% with open repair (25). Perioperative stroke may occur in 4 to 8% (26) and spinal cord ischemia in 3 to 5.6% of patients. 

Conclusion

TEVAR has become the preferred approach for patients with thoracic aortic pathology and anatomy amenable to endograft placement. Adequate seal zones, careful preoperative planning, and proper device sizing are critical to obtain a good result and limit complications. Hybrid approach options and fenestrated endografts may further expand the number of patients who can benefit from this treatment modality.

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