I. Thoracic aortic aneurysm Thoracic aorta includes the aortic root, aortic arch and thoracic descending aorta. The middle layer of the aorta is broken and the wall is weak. Under the action of the pressure in the lumen, the aneurysm is formed by local outward expansion and enlargement. The etiology is most commonly due to hypertension, atherosclerosis and Marfan syndrome, while a few cases are due to congenital dysplasia, infection and trauma. (A) Classification and typing of aneurysms according to anatomical sites: 1. Root aneurysms: lesions involving the aortic valve annulus, aortic sinus, sinotubular junction and proximal ascending aorta. It is often combined with upward shift of coronary artery opening, aortic valve insufficiency and left ventricular enlargement and myocardial hypertrophy. 2, ascending aortic aneurysm: simple ascending aortic aneurysm is relatively rare, and most of them are caused by dilatation after aortic valve stenosis. 3.Aortic arch aneurysm: distal arch aneurysm is more common. 4.Thoracic descending aortic aneurysm: isthmus aneurysms are congenital, with limited lesions and often combined with aortic constriction. Atherosclerotic aneurysms involve a wide range. Atherosclerotic aneurysms are classified by etiology: 1.Arteriosclerotic aneurysms: They are mostly seen in the elderly, often combined with coronary artery disease, hypertension and diabetes mellitus and other geriatric diseases. 2. Congenital aneurysm: mainly located in the aortic sinus and the aortic isthmus. Mostly seen in young adults, the surgery is easier and the treatment effect is good. 3.Hereditary aneurysm, such as Marfon syndrome, most often involves the aortic root. 4.Infected aneurysm. 5.Traumatic aneurysm. Classification by morphology: 1.True aneurysm. 2.Pseudoaneurysm. 3.Aortic coarctation. (B) Pathologic anatomy and pathophysiology Thoracic descending aortic aneurysms are most common, while others are located in the aortic root, ascending part and arch, in that order. Atherosclerotic aneurysms are mostly located in the thoracic descending aorta and ascending aorta, and aneurysms caused by Marfan syndrome mostly involve the aortic root; congenital aneurysms are mostly located in the arch and descending arch; traumatic aneurysms are mostly located near the arterial duct ligament in the isthmus, and infected aneurysms are most common in the ascending aorta. Most aneurysms are solitary and very few are multiple. The main pathological changes are degeneration, dissection or necrosis of the elastic fibers in the middle layer of the arterial wall and loss of elasticity, resulting in local fragility. Due to the impact of high pressure blood flow in the aorta. (C) Thoracic aortic aneurysms are more common in middle-aged and elderly people Marfan syndrome mostly develops in 30-40 years old, and atherosclerotic aneurysm mostly develops in 50 years old and above. Infectious and traumatic aneurysms tend to occur in young adults, while congenital aneurysms tend to be diagnosed in the 20s and 30s. They are asymptomatic early in the course of the disease and are often detected on x-ray. When the aneurysm grows to a certain size, pain and pressure symptoms may appear, and there may be signs of arterial embolism due to thrombus dislodgement. The pain is mostly persistent and dull, but rarely severe. The painful site of ascending and arch aneurysm is mostly located in the anterior chest, and the painful site of descending aortic aneurysm is mostly in the interscapular region of the back. (D) Treatment Once aneurysm is diagnosed, in principle, surgery should be performed as soon as possible. 1.Simple ascending aortic aneurysm The aneurysm is confined to the ascending aorta and does not involve the coronary artery opening and the cephalic artery opening, so the ascending aorta should be replaced. (1) Basic method: General anesthesia with moderate hypothermic extracorporeal circulation. An arterial perfusion tube is inserted into the iliac artery (or femoral artery) or right axillary artery (in case of distal open anastomosis requiring cerebral perfusion to stop the circulation), a second-step venous drain is inserted into the right atrium, and a left heart drain or main pulmonary artery suction is inserted into the right superior pulmonary vein. The coronary artery is directly perfused with cardiac arrest fluid, and the heart surface is cooled by placing ice water and ice chips, and the nasopharyngeal temperature is lowered to 25℃～28℃. (2) Surgical method: median longitudinal sternotomy, extracorporeal circulation with intubation at the above mentioned site, partial freeing of the normal aorta on the distal side of the aneurysm in parallel, blocking at the site after ventricular fibrillation, dissecting the aneurysm and exposing the coronary artery opening for infusion of stopping fluid. The aneurysm is removed and the aneurysm wall is excised, taking care to prevent damage to the coronary artery, superior vena cava and pulmonary artery, and the area with close adhesions to the surrounding tissues may not be excised to prevent the thrombus from entering the left ventricle and coronary artery. The thrombus should be prevented from entering the left ventricle and the coronary artery. The corresponding artificial vessel should be used for replacement. 2.Aortic root aneurysm involves the aortic sinus, annulus and part of the ascending aorta, often combined with coronary artery opening upward and aortic valve closure insufficiency. (1) Basic method: Same as ascending aortic aneurysm. If the aneurysm involves the arch, the method is the same as that for arch aneurysm. (2) Surgical methods: ①Bentall’s procedure: Excision of the aneurysm wall, freeing the left and right coronary artery openings to make them button-shaped. The aortic valve is removed and replaced by an artificial component made of artificial valve and artificial blood vessel, and the proximal end is sewn to the aortic annulus with a 6X14 double-ended needle with spacer mattress suture, 5 mattress sutures for each sinus, paying attention to the tight sutures at each junction to prevent bleeding; if the annulus tissue is stronger, continuous sutures can be used, with 2-OProlene sutures for 3 sinuses respectively. Finally, push in the artificial component, paying attention to tightening the sutures and not tearing off the tissue ring to cause bleeding. ②David procedure: For aortic disorders not originating from the aortic leaflets and annulus, if the aortic leaflets are normal, the normal structure and function of the aortic valve can be preserved while performing aortic root surgery, and aortic root replacement with preservation of the aortic valve can be performed (referred to as David procedure). This procedure can avoid complications such as bleeding and thrombosis due to valve replacement. According to the type of surgery, it can be roughly divided into David type I and David type II. David type I surgery: the aortic root is clipped and the sinus wall is removed in an arc parallel to the annulus along 3 mm above the aortic valve annulus. (1) Basic method: General anesthesia with moderate hypothermic extracorporeal circulation and total body arrest with head perfusion alone. An arterial perfusion tube is inserted in the right axillary artery, and other cannulae are inserted as in the ascending aortic aneurysm. The aortic root is inserted with a needle to perfuse the cardiac arrest fluid. (2) Surgical approach: Open the chest medially and free some branches of the aortic arch. If the unnamed vein interferes with the visualization of the operative field it can be transected after systemic heparinization and reconnected with a 10 mm diameter artificial vessel at the end of the procedure. A 22-24F arterial cannula is placed in the right axillary artery, a second-step venous drain is inserted from the right atrium, and a left heart drain is inserted through the right superior pulmonary vein to establish extracorporeal circulation and systemic hypothermia. The ascending aorta was first blocked, and after dissection of the ascending aorta, cold-blooded cardiac arrest solution was instilled through the left and right coronary artery openings to protect the myocardium. When the nasopharyngeal temperature is reduced to 20℃, the head is placed in a low position and the flow rate is reduced to 10ml/kg/min and then the branches of the aortic arch are blocked respectively, and unilateral cis-grade cerebral perfusion is performed via the right axillary artery. 4.Descending aortic aneurysm Most of them are located far from the aortic isthmus, and a few involve the proximal left subclavian artery, commonly as a spindle-shaped aneurysm with adhesions between the aneurysm wall and lung tissue. In some cases, there may be thrombus in the lumen of the aneurysm. (1) Basic methods: ① General anesthesia with double-lumen tracheal intubation and simple blockage of both ends of the aneurysm. It is usually required to complete the vascular graft in about 30 minutes. ②If it is estimated that the vascular graft cannot be completed within 30 minutes, normothermic left heart diversion or femoral-iliac artery-femoral-iliac vein diversion can be used, requiring free blockage of both ends of the aneurysm. ⑧ Deep hypothermia to stop circulation. If one end of the aneurysm cannot be free blocked, deep hypothermia is required to stop the circulation. This method has great systemic interference, and the protection of the brain, lungs and kidneys is very complicated, and there are many postoperative complications, so it should be used sparingly. (2) Surgical method: According to the location of the tumor, the left posterior external 4th or 5th rib bed incision is chosen, and the corresponding ribs can be removed if necessary, and the adhesions between the tumor wall and the lung should not be excessively freed. The distal part of the aneurysm should be removed first, then the left subclavian artery should be removed, and finally the aortic arch should be removed. The block is performed in the reverse order of the above. The anterior wall of the aneurysm is cut longitudinally, the thrombus is removed, the opening of the intercostal artery is closed, the neck of the aneurysm is cut, and an artificial vessel of the appropriate caliber is replaced, the proximal end is first anastomosed and sutured continuously with 3-OProlene. If there is any bleeding at the anastomosis, the suture can be replaced; the distal anastomosis is performed in the same way as above. When the suture is nearly completed, the distal blocking clamp is opened and the exhaust is tied. If there is bleeding at the distal anastomosis, the distal end of the anastomosis can be blocked again to make up the needle, and each blocking clamp can be opened in turn from far to near. Pay attention to check whether there is bleeding in the intercostal vessels. A chest drain is placed in the 7th intercostal space in the left axillary midline, and the layers of the incision are sutured. If the aneurysm involves the lower thoracic segment, the intercostal artery below T10 can be reconstructed by molding or reimplantation method.