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Short answers

1 The angiogram shows a thoracic aortic dissection (fig 2).

View larger version (95K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 2 Three dimensional reconstruction from the computed tomography angiogram showing the aortic arch and the iliac bifurcation. The left arrow shows the intimal flap and the right arrow indicates the occluded left commom iliac artery

2 The most common classification system is the Stanford classification. This is a Stanford type B dissection. It starts distal to the left subclavian artery.

3 The intimal flap has occluded the left common iliac artery causing acute ischaemia of the left leg.

4 Complicated type B dissections should be treated by endovascular insertion of an aortic stent graft or open surgery to replace the affected aortic segment. Uncomplicated dissections should be treated by aggressive blood pressure management.

1 Diagnosis
The angiogram shows a thoracic aortic dissection (fig 2). An intimal flap is visible within the aortic lumen. The step-like nature of the flap is normally caused by a pulsation or movement artefact from the heart, rather than a defect in the flap.

Patients with acute aortic dissection or lesser pathologies such as intramural haematoma or penetrating aortic ulcers are often referred to as having "acute aortic syndrome." Acute aortic dissection is the most common non-traumatic acute aortic emergency. Mortality is about 1% per hour for the first 48 hours.

The aetiology is often unknown. Dissection has been associated with many underlying conditions including hypertension, Marfan’s syndrome, and Ehlers-Danlos syndrome (caused by cystic medial degeneration of the aortic wall), aortic coarctation, aortitis, trauma, pregnancy, and the use of cocaine.

Dissection results from a tear in the aortic intima, which cleaves a plane in the media and allows blood to enter the false lumen. Arterial pressure extends the dissection for a variable distance distally and sometimes proximally.

2 Classification
More than one classification system exists for aortic dissection. The most widely used system is the Stanford classification.¹ This classifies the dissection according to the most proximal extent of the intimal flap.

Stanford type A—This normally presents with anterior chest pain; it accounts for around 75% of all cases of dissection. The treatment of choice is emergency cardiothoracic surgery because mortality approaches 50% without treatment.^{2 3} Mortality results from cardiac tamponade, aortic rupture, and acute myocardial infarction caused by occlusion of the coronary ostia or acute severe aortic regurgitation or insufficiency.

Stanford type B—This normally presents with interscapular back pain, typically of sudden onset with a tearing or ripping sensation. Type B dissections are divided clinically into uncomplicated and complicated. Our patient’s angiogram shows a Stanford type B dissection. In the aorta it starts distal to the left subclavian artery. (Although the intimal flap extends into the left subclavian artery it is still considered to be a Stanford type B dissection.)

3 Complications
The intimal flap has occluded the left common iliac artery. The patient developed acute limb ischaemia. The intimal flap is not visible in the abdominal aorta because the false lumen is so large that it virtually obliterates the true lumen.

Other acute complications include end organ ischaemia caused by the dissection flap occluding the branch vessel. This can cause renal, splenic, hepatic, and mesenteric infarction, and less commonly spinal cord ischaemia. Acute aortic rupture can occur and is often fatal. Acute complications occur in around 20% of patients.⁴

The major late complication is aneurysmal dilatation of the aorta. This can lead to late rupture and death. Around 70% of patients with an aortic diameter exceeding 40 mm at presentation will develop an aneurysm by five years.⁵ Overall, about 20% of patients with a type B dissection will develop an aneurysm.⁶

4 Treatment options
Uncomplicated dissections are treated medically because mortality is similar for medical management and surgery.⁶ Management aims to control hypertension with adequate analgesia, a β blocker, and nitrates. This usually requires admission to a high dependency unit.

Complicated dissections require either open surgery or an endovascular intervention. Intervention is reserved for patients with aortic rupture, aortic dilatation, malperfusion of branch vessels, and persistent symptoms.

Open repair comprises resection and replacement of the affected segment of aorta or resection of the intimal membrane to restore flow. Operative mortality in the largest series was 29%,⁷ with high rates of other complications such as paraplegia, stroke, and renal failure. Unfortunately, surgery often fails to treat malperfusion problems. Thrombosis of the false lumen occurs in about 50% of cases. All patients require follow-up to monitor aneurysmal dilatation of the aorta.

The high mortality and morbidity associated with open repair mean that endovascular techniques are often the first line of treatment. Techniques vary depending on the complication caused by the dissection. The mainstay of treatment is insertion of an aortic stent graft to close the proximal intimal tear and reduce the pressure in the false lumen. The left subclavian artery is usually preserved to maintain perfusion to the arm but can be covered if necessary (with or without a surgical subclavian bypass). The distal landing zone is usually the midthoracic aorta. The stent restores flow in the aorta and its branches and obliterates the false lumen.

This procedure often reopens occluded branch vessels, but adjunctive procedures such as fenestration of the intima or the placement of additional bare metal stents into the branch vessels may be needed. Stenting of the branch vessels without treating the proximal tear is generally unsuccessful because the pressure in the untreated false lumen often causes the stent to collapse. A meta-analysis of many small series showed mortality of 9.8% in acute dissection treated with stent grafts. Neurological problems such as stroke and paraplegia occurred in 2% of patients.⁸ No studies have demonstrated the long term efficacy of endovascular techniques so close follow-up remains mandatory.

This patient underwent a thoracic aortic stent graft with additional stenting of the left common iliac artery (fig 3). The false lumen in the thoracic aorta thrombosed and flow was restored into the left leg. Unfortunately he had prolonged limb ischaemia but is otherwise well. A portion of false lumen in the abdominal aorta remains patent and he will need prolonged clinical follow-up and repeated imaging to look for aneurysmal dilatation.

View larger version (160K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 3 An intra-arterial angiogram after deployment of a thoracic stent graft into the aortic arch (arrows show the proximal and distal ends of the stent). The stent graft intentionally covers the origin of the left subclavian artery. The primary intimal tear is covered and flow restored in the true lumen of the aorta. The false lumen is occluded

Long answers

Cite this as: BMJ 2009;338:a3114