The patient, male, 46 years old, developed back pain in November 2009 with no obvious cause, which was persistent dull pain with paroxysmal intensification, radiating to the anterior chest when the pain was severe, accompanied by cough, fever, occasionally coughing up a small amount of white foamy sputum, not related to position change, without obvious regularity, no night sweats, wasting, no chest tightness, hemoptysis, dyspnea, and so on, and was treated locally with symptomatic treatment such as pain relief and anti-infection, without significant improvement. Later on, he gradually developed epigastric pain, which was obvious under the sword prominence and persistent, accompanied by nausea and no vomiting, and was suspected of “gastrointestinal perforation? Acute pancreatitis?” The abdominal plain film and gastroscopy did not show any abnormality, and after symptomatic treatment, the appeal symptoms did not improve, so he was admitted to the hospital. Chest CT showed that: a small amount of cord-like shadow with clear boundary was seen in the left lung apices, a lamellar high-density shadow with blurred boundary was seen in the dorsal segment of the right lower lobe, no focal abnormal density was seen in the remaining lung fields, a mass of about 3.5 cm in diameter was seen in the left middle mediastinum with unclear demarcation from large blood vessels, local pleural thickening was seen in the left posterior chest wall, and no pleural effusion was seen. Impression: 1. left middle mediastinal mass, consider tumor; 2. inflammation of the dorsal segment of the lower lobe of the right lung, old tuberculosis of the left pulmonary apex, and thickening of the left pleura. Electronic laryngoscopy showed: left vocal cord paralysis. The cause of the left middle mediastinal mass was investigated as “1, tumor? 2. Right lower pneumonia” was admitted to the Department of Respiratory Medicine. Physical examination: body temperature 38.2℃, blood pressure 100/64 mmHg, respiration 22~24 times/min, clear consciousness, slightly shortness of breath, no jugular vein anger, liver and neck reflux sign (a). No dry rales were heard in both lungs. The heart border was not large, the heart rate was 125 beats/min, the heart rhythm was uniform, and a grade 2/6 systolic murmur could be heard between the 2nd ribs at the right edge of the sternum, jet-like, and no pericardial friction sounds could be heard. The abdomen was soft, the liver and spleen were not detected, and there was no edema in both lower limbs. After admission, CT was performed again to show that the lumen of the descending aorta below the level of the aortic arch was bulbous and dilated to the left, with a maximum diameter of about 5.2 cm, and the enhancement scan showed a crescent-shaped low-density shadow without contrast filling in the dilated ascending aorta, a small amount of cord-like shadow with clear borders in the upper lobe of the left lung, and a sheet-like high-density shadow with blurred borders in the dorsal segment of the lower lobe of the right lung. The possibility of aortic pseudoaneurysm was considered (Figure 1, 2, 3). On January 1, 2009, a surgical operation was performed. Intraoperatively, tight adhesions between the lung and chest wall were seen, and the pseudoaneurysm was wrapped by lung tissue. Transfer 173min, deep hypothermia stopped circulation for 36min, ventilator assisted for 15h, and discharged 14 days after surgery. Discussion: Pseudoaneurysm is a limited pulsatile hematoma formed by the rupture of the arterial wall due to trauma and other causes and encapsulated by the surrounding soft tissues. Aortic pseudoaneurysm is rare, and its formation depends on the size of the arterial wall rupture and the specific structure of the surrounding tissues, because the aortic blood flow pressure is very high, it is not easy for the surrounding tissues to stop bleeding after bleeding, and only 2% to 5% develop into local aneurysm or Pseudoaneurysm. Moreover, pseudoaneurysms have no obvious symptoms in early stages, and are easily ignored because they are detected only after months to decades of trauma, infection, and cardiovascular surgery. Most patients with late-onset thoracic aortic pseudoaneurysms present with symptoms of pressure such as chest tightness and breath-holding after activity, and some are accompanied by low-grade fever and cough; acute thoracic aortic pseudoaneurysms have an intact outer membrane, while the inner membrane completely breaks and curls inward to occlude the distal end, forming acute aortic constriction The above signs are diagnostic clues, such as loss of pulse and blood pressure in upper or lower extremities, anuria, paraplegia, interscapular murmur, mediastinal widening >8 cm on X-ray chest film (mediastinal/thoracic ratio >0.28), blurred aortic outline, and displacement of trachea and esophagus. Detailed medical history, especially the history of chest trauma and surgery, is essential for the diagnosis of this disease. x-ray chest X-ray has no special value for the diagnosis of this disease. CT and MRI are of great help in diagnosing this disease and determining the surgical plan. Pseudoaneurysm management principles: once the diagnosis is clear, remove the aneurysm as soon as possible, repair the ruptured aneurysm, and perform aortic valve replacement at the same time to control the systolic pressure.