Following appropriate intervention, the patient’s neurological function returns to normal. The patient’s recovery is otherwise uneventful, and he is discharged on postoperative day 8 with clean incisions, intact neurological status and adequate analgesia.

Question 9

Following a successful recovery from his surgery, this gentleman’s approximate predicted 5-year survival is:

A.  20%

B.  50%

C.  70%

D.  90%

Question 10

Is there a role for endovascular or hybrid repair of this TAAA?

5.1  Commentary

TAAAs are less common than infrarenal abdominal aortic aneurysms. One populationbased study suggested an incidence of 5.9 TAAAs per 100,000 person-years.1 Although TAAAs are more common in males, the male:female ratio of 1.1–2.1:1 is not as weighted as the ratio of abdominal aortic aneurysm (AAA). The aetiology of TAAAs is related to atherosclerotic medial degenerative disease (82%) and aortic dissection (17%) in most cases.2 About 45% of TAAAs are asymptomatic and detected during work-up of other systems, usually on chest X-ray or cardiac echocardiography examinations. Patients with TAAAs tend to be older than AAA patients and, therefore, may have more severe comorbidities. When present, symptoms are usually chest or back pain related to compression of adjacent structures by the aneurysm or cough from compression/erosion of airways. Fistulization is rare but erosion into the bronchial tree presents with massive haemoptysis, while erosion into the esophagus presents with upper-gastrointestinal bleeding. Presentation with acute, severe pain may reflect leak, acute expansion or dissection of the aneurysm and require urgent evaluation and treatment. The risk factors associated with TAAA are smoking, hypertension, coronary artery disease, chronic obstructive pulmonary disease (COPD), and disease in other vascular beds. Syphilitic aneurysms are a rare cause of TAAA in this era but, when present, usually involve the ascending aorta.

Other causes of vague chest and back pain in a patient such as this include myocardial ischemia,pulmonaryneoplasm,acutedissection,pneumonia,andbonymetastases.[Q1:C]

The clinical and X-ray findings in this particular case argue against these other possibilities. The work-up of patients with TAAA requires assessment of the aneurysm extent, size, and condition of the remaining aorta. Before any studies are carried out, a thorough history and physical examination, including vascular assessment, are needed. [Q2: B] With marked improvements in non-invasive imaging in the past decade, computed tomography angiography (CTA) has replaced invasive aortography for defining the extent of TAAA, status of aortic branches, delineation of any associated dissection, and presence of leak. Magnetic resonanceimaging(MRI)andmagneticresonanceangiography(MRA)havealsoimproved dramatically and offer unique benefits over CT, such as lack of radiation and non-nephro- toxic contrast agents. However, MRA has yet to achieve the resolution of CTA and its use is contraindicated in unstable patients. Transesophageal echocardiography can assess the status of the aortic valve as well as cardiac function. Significant aortic insufficiency is a contraindication to thoracic aortic cross-clamping, unless a shunt or pump is used to bypass the left heart.

The Crawford classification [Q3: B] is used to characterise TAAAs.3 According to this system,aneurysmsbeginningjustdistaltotheleftsubclavianarteryandinvolvingtheaorta up to, but not below, the renals are termed type I. Type II TAAAs are the most extensive – they begin just beyond the left subclavian and continue into the infrarenal aorta. Type III aneurysms involve the distal half of the thoracic aorta, usually originating at the level of T6, and varying extents of the abdominal aorta. Type IV TAAAs refer to those aneurysms involving the entire abdominal aorta, up to the diaphragm and including the visceral segments. This classification scheme has been useful for predicting morbidity and mortality following repair of TAAAs.

In addition to assessment of the aneurysm, the high incidence of comorbidities in this patient population mandates thorough evaluation of cardiac, as well as pulmonary reserve. Preoperative studies should include electrocardiography and cardiac stress testing. Further work-up is dictated by the presence of positive findings. Screening chest X-ray and preoperative ABG provides information regarding the patient’s pulmonary status. Formal pulmonary function tests should be reserved for those patients with evidence of significant pulmonary compromise. Since the risk factors for TAAA are the same as those for atherosclerotic disease, a careful history and physical will dictate whether there is a need to work up disease in other vascular beds (carotid, mesenteric, renal, lower extremity). Carotid duplex studies may be done routinely preoperatively and significant carotid stenoses are treated before TAAA repair. The status of the patient’s clotting system must be determined and optimized, if necessary. In the absence of indications to carry out other operations first, this patient with a TAAA of >6 cm should undergo elective repair of his aneurysm.

[Q4: D] Observation with follow-up imaging studies is dangerous and puts the patient at risk of death due to aneurysm rupture. The natural history of TAAAs is related to size and growth rate. Understanding the behaviour of these lesions is of crucial importance when determining treatment. Crawford’s series of 94 TAAAs followed for 25 years demonstrated 2-year survival of 24%, with about half of deaths due to rupture.4 This series included dissected as well as non-dissected aneurysms. A more recent series of non-dis- sected TAAAs revealed rupture rates of 12% at 2 years and 32% at 4 years; for aneurysms greaterthan5cmindiameter,ruptureratesincreasedto18%at2years.5 Ruptureisuncommon in aneurysms measuring less than 5 cm in diameter. Another risk factor for rupture

seems to be an increased expansion rate, with aneurysms growing more than 5 mm in 6 months at higher risk than those growing more slowly. Survival in non-operated patients was 52% at 2 years and 17% at 5 years. Patients who underwent repair of TAAA had a 5-year survival of 50%. Another series revealed 61% 5-year survival following TAAA repair. Survival decreased to 50% for patients with dissecting TAAA.6

Operative repair is usually through a left thoracotomy with a paramedian abdominal extension, depending on the distal extent of the aneurysm. A retroperitoneal approach to the abdominal segment is used. The distal extent of the aneurysm determines which intercostal space will be used for a thoracotomy. The incision is made in the fourth or fifth intercostal space for type I or high type II TAAAs, while an incision in the seventh, eighth or ninth intercostal spaces is appropriate for types III or IV.7 Careful identification and reimplantation of visceral vessels is important, as is re-attachment of intercostal arteries when feasible. Successful repair of TAAA results from careful yet quick technique, as well as maintenance of optimal physiology by the anaesthesia and surgical teams. Distal aortic perfusion is accomplished either with left heart bypass and selective visceral perfusion or an axillary-femoral artery bypass before thoracotomy. Distal aortic perfusion manoeuvres are important for the prevention of major systemic morbidity following TAAA repair.

Patients undergoing TAAA repair frequently are older and have significant cardiac, pulmonary and other vascular comorbidities. These factors, combined with the magnitude of the operation and extent of aortic replacement, can lead to significant rates of mortality and serious morbidity. [Q5: D] Pulmonary complications remain the most common and result from a combination of preoperative tobacco use, chronic obstructive pulmonary disease (COPD), and the effect of the thoracoabdominal incision on postoperative pulmonary mechanics. Reperfusion injury may also lead to pulmonary microvascular injury and subsequent pulmonary dysfunction.8 Cardiac complications remain the next most common, in spite of preoperative cardiac optimisation. Avoidance of hypotension, close monitoring perioperatively with pulmonary artery catheters, and minimisation of strain on the left ventricle can help decrease postoperative cardiac dysfunction. Using the bypass circuit to control ventricular afterload can reduce the risk of cardiac complications.9 Renal insufficiency preoperatively increases the risk of postoperative renal failure and mortality. Minimising ischaemic time, selective renal perfusion during cross-clamping, distal aortic perfusion techniques, and avoidance of hypovolaemia are important in preventing renal failure.10

PerhapsthemostdevastatingcomplicationfollowingTAAArepairisparaplegia.Despite yearsofresearchanddevelopmentofprotectivestrategies,paraplegiaratesfollowingTAAA repairremainbetween5%and30%,withanaverageof13%.6 Riskfactorsforpostoperative paraplegia include extent of aneurysm (and therefore most common in Type II TAAAs), cross-clamptime,postoperativehypotension,previousabdominalaorticreconstruction,and oversewing of intercostal arteries. Cross-clamp times of less than 30 min are generally safe, whilethose in the range of 30–60 min areassociated withincreasing risk; cross-clamp times of more than 60 min carry the highest risk for neurological complications. Minimizing cross-clamp time and avoiding hypotension will decrease the risk of paraplegia. Sequential reperfusion of intercostal vessels by moving the cross clamp caudally as segments are reimplanted is useful to re-establish flow to these vessels quickly. In addition, avoiding prolonged mesenteric ischemia, which may worsen reperfusion injury to the lungs, heart and possibly spinal cord through release of cytotoxic cytokines, is beneficial.

Numerous adjuncts have been studied for their ability to prevent paraplegia. [Q6: A] The use of cerebrospinal fluid (CSF) drainage to keep CSF pressure at less than 10 mmHg has been shown to decrease the incidence of postoperative paraplegia, when combined with distal aortic perfusion and/or moderate hypothermia.11 Reimplantation of intercostal vessels, particularly in the important segment of T8–T12, is most likely beneficial in preventing postoperative paraplegia, provided this manoeuvre does not excessively prolong clamp time.12 Epidural cooling by continuous infusion of cool saline via catheter has been reported to decrease the incidence of paraplegia following TAAA repair in a high-volume centre.13 Preoperative angiographic localisation of the artery of Adamkiewicz followed by successful reimplantation of this vessel during surgery has resulted in no neurological sequelae in another Centre’s series.14 Patients who did not have preoperative localisation, or in whom reimplantation was unsuccessful, had a 50% paraplegia rate. These results have not been reproduced, and angiographic localisation has not gained widespread acceptance. General anesthetic agents can also help to prevent paraplegia, with propofol being the most protective. When left heart bypass is performed using pump techniques, moderate hypothermia can be used to protect the spinal cord. Other pharmacological adjuncts that may be beneficial include steroids and mannitol. Free-radical scavengers and inhibitors of excitatory neurotransmitter pathways have shown benefit experimentally but have not been proven clinically.15 At present, the best strategy for preventing spinal cord complications appears to involve a combination of physiological optimization of the patient perioperatively, avoidance of intra-operative hypotension, intraoperative use of spinal drainage and some form of distal aortic perfusion, reimplantation of patent intercostal vessels, and minimisation of cross-clamp time. Other protective adjuncts are used based on surgeon preference and experience.

Repair of a TAAA represents a major physiological insult. Excellent anesthesia care and post-operative critical care monitoring are essential components of a successful operation. Postoperatively, large volumes of urine output must be replaced on a 1:1 basis in order to avoid hypovolaemia. Use of warmed, balanced electrolyte solutions is preferred. [Q7] Coagulopathy in the postoperative period is usually related to incomplete replacement of clotting factors and hypothermia. In addition, supracoeliac aortic clamping has been shown to result in a state of fibrinolysis that may exacerbate bleeding.17 The aneurysm itself can be responsible for chronic coagulation factor consumption and a subsequent increased tendency to perioperative coagulopathy.18 Ongoing bleeding after TAAA repair may require reoperation, and results in an increase in major morbidity and mortality. It is important to ensure that any increased prothrombin and partial thromboplastin times are corrected with plasma transfusions. Platelets should be replaced if thrombocytopenia occurs in the face of ongoing bleeding. Since hypothermia is often used intraoperatively as a spinal cord protective measure, it may persist as a problem postoperatively. Aggressive correction with warm fluids, blood products and warming blankets is needed to restore normothermia and proper function of coagulation as well as other enzymatic systems. Reoperation is reserved for ongoing significant bleeding following correction of coagulopathy and hypothermia. Reoperation for bleeding results in mortality rates of 25% or greater in these patients.19

Some patients, as in the case we present here, will awake neurologically intact only to develop paraplegia hours to days later. [Q8]This phenomenon of delayed-onset paraplegia

may represent reperfusion injury to areas of the spinal cord at risk from intraoperative hypoperfusion. Avoidance of postoperative hypoperfusion may decrease the incidence of this complication. The epidural catheter is left in place for 3 days postoperatively. In cases of delayed-onset paraplegia, maintenance of CSF pressure below 10 mmHg may permit restoration of function. There are anecdotal reports of reversal of delayed-onset paraplegia byplacementofanepiduralcatheterafteronsetofparalysisandremovalofCSFtodecrease pressure to below 10 mmHg.16 Lowering the CSF pressure may increase cord perfusion pressure enough to rescue the threatened regions of neuronal tissue. Lowering the CSF pressure to below 5 mmHg may cause intracerebral haemorrhage, therefore the pressure must be monitored closely and maintained in the safe range. [Q9: B] Patients undergoing successful TAAA repair have a 5-year survival of 50–61%5, 6 [also please refer to discussion following Q4].

[Q10] Since the patient presented did not have any significant contraindications to an open thoracoabdominal repair, endovascular repair of his TAAA would not have been appropriate at this time. However, various institutional studies have demonstrated the feasibility and safety of endovascular repair of TAAAs for patients at significant risk for open repair.20 Pre-operative planning with high-resolution, thin-cut CTA is mandatory. Fenestrated endografts may be used for treatment of juxta-renal aortic aneurysms or more extensive type IV and other TAAAs. Fenestrations are circular openings in the aortic graft fabric that are circumferentially reinforced with a nitinol ring, which is ultimately matted with a balloon-expandable stent graft into the target visceral vessel. Branched endografts are aortic endografts with side branches pre-sewn to the graft fabric; these in combination with fenestrations, help treat even the most complex TAAAs. A recent French series of 33 patients undergoing treatment of TAAAs with fenestrated and branched endografts for a variety of TAAAs types (type I [3%], II [21%], III [37%], IV [13%]) demonstrated an inhospital mortality of 9%.21 Type II and III endoleaks were present in 15% of patients and transient spinal cord ischemia occurred in 12% of patients, though permanent paraplegia remained in only 3%. A review of six single-institution series encompassing 496 patients with TAAAs, demonstrated a 30-day mortality of fewer than 9%, spinal cord ischemia of 2.7–20%, and remarkably high branch patency rates (96–100%). As potential loss of visceralbranchvesselsisafearedcomplicationoffenestratedandbranchedendograftsrepair, midand long-term results with larger patient populations will be important to determine whether material fatigue and fracture, migration, and/or component separation occur. Aside from fenestrated or branched endograft repair, early follow-up demonstrated no renal of visceral branch vessel occlusion; all 109 vessels were patent in this high-volume centre single centre study.

Recently, Lachat et al. have introduced a novel hybrid open and endovascular approach that may be particularly useful for the treatment of Type IV TAAAs.22 This technique involves placement of a self-expanding stent graft (Viabahn grafts, Gore and Associates, Flagstaff, Az) thru a retrograde Seldinger technique into the origin of the renal or visceral vessel. Using this Viabahn Open Rebranching TEChnique (VORTEC) technique, the distal end of the self-expanding stent graft is deployed in the visceral or renal vessel and partially projects outside the vessel. The proximal end of the graft is then anastomosed to the debranching graft, which may originate from a common iliac artery; the proximal stump of the visceral vessel is ligated to avoid retrograde perfusion of the aneurysm and