Thoracic aortic aneurysms

Thoracic aortic aneurysms

A true aneurysm is a localised dilatation of a blood vessel involving all three layers of the vessel wall, whereas a false aneurysm has compressed supporting tissue as its wall and is usually the result of a defect in the vessel intima (from trauma, dissection or previous surgery). Aneurysms are described as fusiform when the whole circumference is a ff ected or saccular when only part of the circumference is involved. When the whole length of a vessel is a ff ected, the clinical and anatomical situation is referred to as ectasia. Aortic aneurysms can develop anywhere along its length, but thoracic aortic aneurysms, including those that extend into the upper abdomen (thoracoabdominal aneurysms), account for 25%, typically occurring in men in the fifth to seventh decade or younger in those with connective tissue disorders. Although a national UK screening pr ogramme exists for abdominal aortic aneurysm, this is not true for thoracic disease. Aetiology The most common aetiology is atherosclerosis, but connective tissue disorders account for many aneurysms in the aortic root and ascending aorta now that tertiary syphilis is rare. Marfan syndrome is associated with cystic medial degeneration involving the vessel wall and causes widening of the proximal aorta and aortic root, leading to aortic valve insu ffi ciency . Hugh Henry Bentall , 1920–2012, Professor of Cardiac Surgery , The Royal Postgraduate Hospital, Hammersmith, London, UK. Sir Magdi Yacoub , b. 1935, Professor of cardiac surgery , Imperial College, UK. Tirone David , b. 1944, Professor of Surgery , Toronto, Canada. associated with aneurysm formation and dissection include Ehlers–Danlos syndrome, which is associated with a range of complica tions including aortic dissection, joint dislocations, scoliosis and osteogenesis imperfecta. Many aneurysms are asymptomatic and are discovered incidentally on routine chest radiographs. Others present as a space-occupying lesion in the thorax with pain caused by pressure on adjacent structures (v ertebra), hoarseness (left - recurrent laryngeal nerve), dysphagia (oesophagus) and respi - ratory symptoms (left main bronchus). Aortic root aneurysms te a may lead to dilatation of the aortic root annulus and aortic regurgitation. Rupture can lead to cardiac tamponade or haemorrhage into the left pleural space, leading to dyspnoea and, if the tra - c heobronchial airway or oesophagus is involved, haemoptysis or haematemesis. Investigations The diagnosis is confirmed by CT or MRI. Arteriography is not necessary for diagnosis but is often required to demonstrate the relation of the arch vessels to the aneurysm. Indications for surgery Without treatment the aneurysm is likely to expand and ultimately rupture. Important factors to consider when plan - ning treatment are age, comorbidity and coexisting coronary disease. In ascending aneurysms, the presence of progressive aortic valve insu ffi ciency is an important indication for surgery . Other indications in this g roup, including Marfan-related aneurysms, are a diameter of 4.5–5 /uni00A0 cm and the presence of symptoms. In descending aneurysms, indications for surgery include symp - toms, acute enlargement and a diameter of approximately 6 /uni00A0 cm. Surgical options The approach adopted for surgical treatment depends on the location of the aneurysm, but typically involves a median sternotomy , CPB and occasionally cooling the patient to 18°C before cross-clamping the aorta above the aneurysm at the distal ascending aorta just before the innominate artery ( Figure 59.27 ). If the aortic root is involved, the aorta, together with its annulus and valve, is resected and a composite graft is sutured to the aortic root. The circulation is arrested and, after removal of the aortic cross-clamp, the distal anastomosis is completed. The coronary ostia require reimplantation into the graft (Bentall’s operation). More recently there has been increased interest in valve-sparing root surgery or valve repair and root replacement, which is based on two original tech - niques, namely the remodelling technique described by Magdi Yacoub and the reimplantation technique described by Tirone David. These techniques are associated with reduced throm - boembolic complications, but ar e usually demanding with a small increased risk of requiring reoperation at a later stage. If the ascending aorta is involved, it is resected and replaced with a tube graft. For aortic arch aneurysms, surgery on this section of the aorta is a formidable undertaking because the cerebral and subclavian vessels have to be anastomosed to the graft, either separately or en bloc. Typically , it involves a period of circulatory arrest and some form of cerebral protection. Excision of a descending aortic aneurysm is with graft replace ment under CPB, with exposure via a left thoracotomy or with a heparin-bonded shunt. Increasingly , thoracic aneurysms at the aortic arch or more distal are repaired using a percuta neous approac h via the femoral artery , with insertion of an endovascular stent graft under radiological guidance. Surgical outcome The operative mortality rate is variable depending on the location and type of repair required, but electively is between 5% and 15% and is considerably higher in emergency repairs. Long-term survival depends on underlying pathology but, for ascending aneurysm repairs, the 5-year survival rate is approximately 65%. The major complications of descending aneurysm repairs include paraplegia, renal failure and ventric ular dysfunction.

Figure 59.27 A large thoracic aortic aneurysm.