Explain Indications for Surgery in Aortic Aneurysm?
Indications for Surgery : Thoracic aortic aneurysms are classified by the portion of aorta involved - ascending, arch, descending thoracic and thoraco-abdominal aorta. 60 per cent of them occur in the ascending aorta and are mostly caused by cystic medial necrosis. Very often aortic root is also involved in this fusiform type of aneurysm causing aortic regurgitation. Cystic medial necrosis in youilg patients is a manifestation of Marfans syndrome. Instead of classical Marfans syndrome a variant or forme frustae of the syndrome can be the aetiological factor. The other common causes are athersclerosis, syphilis or infectious aortitis.
At least 50 per cent of the patients with early thoracic aortic aneurysms are asymptomatic and are picked up during investigations. The symptoms may be due to aortic regurgitation and heart failure, thrombo embolism causing stroke or lower extremity ischaemia and renal or mesentesic infarction. Dilatation of the aorta may cause compression of adjacent anatomical sbuctures and cause varied symptoms. These include pain in the neck and jaw, pain in the interscapular area,
pleuritic pain, back pain or left shoulder pain. Pressure effects may cause superior venacaval obstruction, hoarseness, dysphagia, dyspnoea, stridor due to compression of trachea, cough and wheezing and collapse of left lung. The most dangerous complication is either leaking or frank rupture causing cardiac tamponade, haemothorax, haeinoptysis or haematemesis. Chest X-ray may reveal the presence of aneurysm. The previous gold standard was aortography, which is now effectively replaced by CT and MRI. Three dimensional imaging and reconstruction give the exact measurements needed for treatment. Transthoracic echocardiogram is useful in measuring the size of proximal aorta but is of limited accuracy in the rest of thoracic aorta. TEE gives much better information. Currently surgery is indicated when diameter of ascending aorta is 5.5 cm or larger and descending thoracic aorta six cm or larger. In patients who carry high operative risk, diameter of 6 or 7 cm is taken as indication for surgery. In patients of known Marfans syndrome, as there is high risk of dissection, 4.5 or 5 cm dilatation warrants surgery. Another important point to be taken into consideration is the rapid rate of expansion and onset of symptoms. If a patient with bicuspid aortic valve needs aortic valve replacement, it is better to do replacement of ascending aorta even if the diameter is only four cms. Before surgery is undertaken, proper evaluation of cardiac, pulmonary, renal, hepatic and neurologic function is mandatory.