DISCUSSION

An aneurysm is typically defined as an increase in size of more than 50% above the normal arterial diameter. It can occur anywhere along the aorta – from the aortic root to the bifurcation. Majority of these aneurysms are degenerative in nature such as in our patient. Other less common causes are associated with infection such as a mycotic infection, inflammation and connective tissue disease.² TAAs are classified into aortic root or ascending aortic aneurysms (60%), followed by aneurysms of the descending aorta (35%) and aortic arch (10%).³

Aneurysms are usually silent unless an imaging study happens to have been performed; thus, true incidence is hard to estimate. Lethal thoracic aortic dissections are also often misdiagnosed as myocardial infarctions.⁴ A local study reported that ruptured aortic aneurysm has a higher mortality rate than myocardial infarction (MI) wherein 75 to 80 percent with ruptured aortic aneurysm die compared to 10 to 20 percent of people coming with MI.

Sudden onset of severe chest and back pain is the most typical symptom of an acute aortic syndrome. The pain may be described as sharp, ripping, tearing, or knife-like and is usually different from other causes of chest pain. The abruptness of its onset is the most specific characteristic.⁵ Minor and less specific symptoms such as chronic back pain which results from direct pressure on nearby structures or by distension of visceral organs which was the presenting symptom of the patient.

Differential diagnoses of the patient’s case aside from an aortic aneurysm include musculoskeletal pain, pulmonary embolism, pericarditis and an acute coronary syndrome. Musculoskeletal pain can easily be ruled out because of the absence of any reproducible pain on palpation of the affected area and the pain is not provoked by posture, motion or pressure. Pulmonary embolism can be considered because it can occasionally present with back pain and sudden onset of dyspnea. However, because of the absence of hypoxia and the typical pleuritic chest pain, deep vein thrombosis, calf swelling or tenderness makes the diagnosis unlikely. Pericarditis can also be considered because of the onset of chest pain however it is considered unlikely because it was not aggravated or relieved with any position changes typical of acute pericarditis. Acute coronary syndrome can be highly considered because of the onset of left sided chest pain however ECG and cardiac biomarkers are needed to fully establish the diagnosis.

Prompt diagnosis is important in patients with an acute aortic syndrome.² A chest radiograph shows widening of the mediastinal shadow as seen in our patient. It may also show displacement or compression of the trachea or left mainstem bronchus. Computed tomography (CT) is the most reliable diagnostic tool in patients with acute aortic dissection or ruptured aortic aneurysm. Arteriography is not a substitute,⁶ although angiography is appropriate for surgical planning.

Two-dimensional echocardiography, and particularly transesophageal echocardiography, can be used to assess the proximal ascending aorta and descending thoracic aorta. Contrast aortography is frequently required preoperatively to assess the length of the aneurysm and involvement of branch vessels.

Routine work up for surgery in our patient revealed a congenital aortic anomaly. Normally, the aortic arch is almost always left sided and gives rise to the three great vessels; first the brachiocephalic trunk (BCT), then the left common carotid artery, and finally the left subclavian artery. The BCT branches into right subclavian artery and right common carotid artery. This branching pattern occurs in 64.9–94.3% of cases and is described as “normal”.⁷

In our patient, an aberrant right common carotid artery was incidentally noted on the work-up of the aneurysm. It has an estimated prevalence of <1% in 4-vessel aortic arch anomalies. It is uncommon and a result from an aberrant development of one or more components of the embryonic pharyngeal arch system. The variations of the aortic arch can be explained by persistence of segments of the aortic arches that normally regress or the disappearance of segments that normally remain.^{8, 9}

The initial management of our patient included the control of the heart rate and blood pressure to slow down the expansion rate and reduce the risk of dissection or rupture. Patients with aortic aneurysm should be treated aggressively to control hypertension to the lowest tolerated blood pressure. Beta-blockers have the desired effect of reducing the inotropic state of the heart which decreases the impact force of the ejected blood on the aorta resulting to a lower heart rate and blood pressure.¹² For most patients, systolic blood pressure should be controlled between 100 and 120 mmHg with a heart rate of approximately 60 bpm. Medical therapy to control pain and decrease lipids is also essential in all patients. Smokers, such as in our patient, have twice the aneurysm expansion rate of nonsmokers and higher dissection rates; hence are advised smoking cessation.¹³

In this case report, we describe an elderly patient with a thoracic aortic aneurysm and aberrant right common carotid artery who was treated with a hybrid procedure wherein a combination of surgery and endovascular methods was done for a less invasive approach, which is the first reported case in this institution. The advances in procedures and device development for TEVAR led to the development of hybrid procedures for aortic arch repair in the last decade. Their common concept involves bypass grafting of the supra aortic branches and ligation of the native branches followed by endovascular stent grafting of the aortic arch with or without subsequent TEVAR of the aorta.

TEVAR has gradually replaced open repair with equal safety and efficacy; and consistently yielded lower rates of early mortality and common postoperative complications than open repair. One study reports perioperative mortality rates of 2.1% versus 11.7%, spinal cord ischemia rates of 3% versus 14%, respiratory failure rates of 4% versus 20%, and renal insufficiency rates of 1% versus 13% in low-risk patients after endovascular and open repair, respectively. TEVAR carries the additional risk of embolic stroke due to the passage of endovascular wires, catheters, and other devices through the aortic arch; nevertheless, the rates are minimal.¹⁴ These complications were not seen in our patient.

The type of approach used should be tailored to the anatomic variables associated with the aortic anomalies. The technical challenges of stent graft deployment, such as proximity to the great vessels and arch tortuosity, have been and remain a focus of device engineering.¹⁵

Aside from CT angiogram, a conventional CT aortogram was done in our patient to better visualize the aberrant vessels along with its blood flow along its critical supra aortic branches. Detailed evaluation of the aortic arch anatomy is important for planning thoracic surgery and endovascular intervention since the presence and pattern of arch variants and anomalies may influence the surgical incision, cardiopulmonary bypass cannulation and interventional approach. In addition, decisions regarding whether to repair coexisting lesions in the same procedure should be considered.^{15, 16}

Both open and hybrid approaches have been advocated when aortic reconstruction is necessary. It may be necessary for aneurysmal degeneration such as in our case. A thorough understanding of the anatomic landmarks and cerebral perfusion is necessary to guide management options. Standard open aortic reconstruction with or without cardiopulmonary bypass has been described historically which is performed through a left thoracotomy or median sternotomy. The operative mortalities in standard open aortic repair has been reported to be as high as 23%.¹⁷ The introduction of thoracic endografting has changed the available management options avoiding cardiopulmonary bypass and circulatory arrest resulting to better patient outcomes and earlier recovery.