Thoracoabdominal Aortic Aneurysm: Repair Options and Spinal Cord Protection

The aorta carries blood from the heart through the chest and abdomen, giving off the arteries to the spinal cord, the liver, bowel and kidneys along the way. A thoracoabdominal aortic aneurysm (TAAA) is a dilatation that involves both the descending thoracic aorta and the abdominal aorta, and therefore the segment from which those vital branches arise. That is what makes it different from a standard abdominal aneurysm: repairing it means dealing with the branch arteries as well as the aorta itself, and protecting the spinal cord while doing so.

What a thoracoabdominal aneurysm is

Surgeons describe the extent of a TAAA using the Crawford classification, because the extent determines the operation and its risks:

• Extent I – from just beyond the left subclavian artery down to above the renal arteries.
• Extent II – from the left subclavian artery to below the renal arteries: the most extensive, and the highest risk for the spinal cord.
• Extent III – from the mid-descending thoracic aorta (about the sixth rib) to below the renal arteries.
• Extent IV – confined to the abdominal aorta but involving the visceral and renal arteries.
• Extent V – from the mid-descending thoracic aorta to just above the renal arteries.

A separate group is the post-dissection aneurysm: after an aortic dissection, the weakened outer wall of the false channel can slowly enlarge over years, producing a TAAA with a complex, two-channel anatomy that needs its own planning.

Causes and who is affected

Most TAAAs are degenerative, developing over decades in people with high blood pressure, smoking history and atherosclerosis, typically in the sixties and seventies. A substantial minority follow a chronic aortic dissection. A smaller group arise in people with heritable aortic conditions – Marfan syndrome, Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome and familial thoracic aortic disease – who may be much younger and in whom the usual size thresholds and device choices do not apply. Infection and inflammatory aortitis are rarer causes.

Most TAAAs cause no symptoms and are found on a scan done for another reason. When symptoms occur they may include back, flank or chest pain, hoarseness from pressure on the laryngeal nerve, difficulty swallowing, or breathlessness. New or worsening pain in someone with a known aneurysm is treated as a warning of impending rupture.

When repair is advised

The decision balances the risk of rupture against the risk of the operation, which for a TAAA is considerably higher than for a standard abdominal aneurysm. International guidance generally advises considering repair of a degenerative TAAA at a diameter of around 6 cm, or at smaller diameters when the aneurysm is growing quickly, is symptomatic, or occurs in someone with a heritable aortic condition, where thresholds of 5 to 5.5 cm or lower are used. Women, who have smaller aortas, may reach the threshold at a lower absolute size. Chronic post-dissection aneurysms are often repaired at 5.5 to 6 cm because the dissected wall is weaker than it looks.

Fitness matters as much as size. Heart, lung and kidney function are assessed formally before any TAAA repair, and for some people the right decision is continued surveillance with blood-pressure control rather than an operation whose risks outweigh the benefit.

Open repair

Open thoracoabdominal repair replaces the diseased segment with a fabric graft through an incision that runs from the chest to the abdomen (a thoracoabdominal incision), with the visceral and renal arteries reattached to the graft either as an island or as individual branches. Modern open repair uses a range of adjuncts to protect the organs: partial left heart bypass to keep the lower body perfused while the upper aorta is clamped, selective perfusion of the kidney and gut arteries with cold or blood-based solutions, cerebrospinal fluid drainage, and careful blood-pressure management. For patients with heritable aortic disease, and for younger, fit patients, open repair remains the most durable option and is the reference standard against which newer techniques are judged. Recovery involves a stay in intensive care, typically one to two weeks in hospital and several weeks to months of convalescence.

Fenestrated and branched endovascular repair

Fenestrated and branched stent-grafts (FEVAR and BEVAR) extend the principle of EVAR to aneurysms involving the branch arteries. The main graft has openings (fenestrations) or small side-arms (branches) that are aligned with the kidney and gut arteries, into which smaller covered stents are placed to keep each branch open. Devices may be custom-made to a patient's CT measurements, which takes several weeks to manufacture, or chosen from off-the-shelf multibranch designs when time does not allow. Endovascular repair avoids the large incision and aortic clamping, so the early physical burden is much lower, and most people are home within a few days. The trade-offs are the same as for standard EVAR but amplified: more components that can leak or occlude, lifelong imaging surveillance, and a meaningful chance of further procedures to maintain the repair. Spinal cord ischaemia remains a risk because the stent-graft covers the intercostal and lumbar arteries that supply the cord.

Hybrid and staged repair

Hybrid repair combines open and endovascular techniques: the visceral and renal arteries are rerouted surgically from a healthier artery (visceral debranching), after which a standard stent-graft can be used to exclude the aneurysm without needing fenestrations. It avoids clamping the thoracic aorta and a chest incision, at the cost of an abdominal operation and the long-term behaviour of the bypass grafts. Hybrid repair has a role for selected patients whose anatomy is unsuitable for a branched device and whose fitness rules out full open repair.

Whatever the technique, extensive repairs are often staged: treating the thoracic segment first and returning for the abdominal segment weeks later. Staging allows the spinal cord's collateral blood supply to adapt between operations and is one of the most effective ways of reducing paraplegia. The aortic arch may also need treatment in the same programme when disease extends upwards.

Protecting the spinal cord

The spinal cord is supplied by a network of small arteries from the aorta, the subclavian arteries and the pelvic arteries. Any TAAA repair interrupts part of that network, and the feared complication is spinal cord ischaemia, which can cause temporary or permanent weakness or paralysis of the legs. Its risk rises with the extent of aorta treated (highest for extent II), with previous aortic repair, and with low blood pressure around the time of surgery. Reducing that risk is a central part of planning and is why TAAA repair should be done by teams who do it regularly. The measures used include:

• Cerebrospinal fluid drainage – a fine catheter in the lower back lowers the pressure around the cord so that blood can perfuse it more easily during and after the operation.
• Blood-pressure management – keeping the mean arterial pressure deliberately high for the first days after repair, and avoiding anaemia.
• Staging and, where appropriate, temporary perfusion of the aneurysm sac so that the cord's collateral supply can develop.
• Preserving inflow – revascularising the left subclavian artery when it must be covered, and protecting the pelvic (hypogastric) arteries.
• Monitoring – motor evoked potentials under anaesthesia and, increasingly, biochemical markers of cord injury, so that falling perfusion can be corrected before damage becomes permanent. Dr Choong has published a systematic review of biochemical markers of spinal cord ischaemia in thoracoabdominal repair and research on perfusion strategies for open repair, and continues to contribute to work in this area.

Watch: Spinal Cord Ischaemia Biomarkers: Aortic Research

Recovery and follow-up

After open repair, expect several days in intensive care and one to two weeks in hospital; full recovery takes two to three months. After branched endovascular repair most people leave hospital within a few days, although the drain and blood-pressure protocol usually keep them in for a little longer than a standard EVAR. All endovascular and hybrid repairs need lifelong imaging surveillance, typically a CT scan at one month and twelve months and then yearly, with the frequency adjusted to findings. Open repairs are scanned less often. Blood-pressure control, stopping smoking and statin therapy remain important for everyone, and first-degree relatives of people with thoracic aortic aneurysm are usually offered a screening scan.

Watch: Complex Aortic Aneurysms: Why Planning Matters · Read: Complex aortic aneurysms: assessment and treatment planning

Choosing a team

Sudden severe chest, back or abdominal pain, collapse, or new leg weakness in someone with a known aneurysm is an emergency: call 995 in Singapore.

Common questions about thoracoabdominal aneurysm

Is a thoracoabdominal aneurysm the same as an abdominal aortic aneurysm?

No. An abdominal aortic aneurysm sits below the kidney arteries and can usually be treated with a standard stent-graft or a straightforward open repair. A thoracoabdominal aneurysm involves the segment of aorta that gives off the arteries to the kidneys, bowel, liver and spinal cord, so its repair is a much larger undertaking with different risks.

Can a thoracoabdominal aneurysm be treated with a stent?

Often, yes, but with a fenestrated or branched stent-graft rather than a standard one, and sometimes in stages. Whether that is suitable depends on the detailed anatomy on CT, on fitness, and on age, because younger patients may be better served by the durability of open repair.

What is the risk of paralysis?

It depends on the extent of the aneurysm and the technique. In experienced centres using the protective measures described above, permanent paraplegia after extensive repair is uncommon but not zero; temporary weakness that recovers is more frequent. Your surgeon should give you an estimate for your own anatomy rather than a general figure.

How quickly do I need to decide?

For an asymptomatic aneurysm below threshold, there is usually time for surveillance, planning and a second opinion. For a large or symptomatic aneurysm, planning moves faster but is rarely a same-day decision unless rupture is suspected, in which case it is an emergency.

Will I need more operations?

After open repair, further aortic surgery is uncommon unless there is heritable disease. After branched endovascular repair, roughly one in four to one in three people need a further, usually minor, procedure within five years to maintain the repair, which is why surveillance matters.