Dr Nick Ng Zhi Peng Consultant, SingHealth Duke-NUS Vascular Centre; Department of Vascular Surgery, Singapore General Hospital

General practitioners play an essential role in the initial diagnosis of and surveillance for aortic aneurysms. Read more about what to look out for in primary care, and how to assess if the risk of rupture warrants active management or consideration of surgery.

INTRODUCTION

The aorta is the largest artery in the body, measuring about 1-2cm in diameter. It distributes oxygen-rich blood straight from the heart to the rest of the body.

From the heart, the aorta arches down the chest and traverses into the abdominal cavity through the diaphragmatic hiatus. It gives off branches that supply the upper limbs, spinal cord, brain, liver, pancreas, stomach, intestines, adrenal and kidneys before dividing to form arteries that supply the pelvic organs and lower limbs.

What is an aortic aneurysm?

Aortic aneurysms occur when the aorta is enlarged or dilated by more than 50% of its native size.

As the aneurysm increases in diameter, the risk of rupture also increases. This can lead to massive bleeding and catastrophic circulatory collapse. The mortality risk from a ruptured aneurysm is as high as 50 to 80%.

General practitioners play an essential role in the initial diagnosis of and surveillance for aortic aneurysms. Read more about what to look out for in primary care, and how to assess if the risk of rupture warrants active management or consideration of surgery.

Aortic aneurysms can occur in the thorax, abdomen, or both. 

• Approximately 75% of aortic aneurysms develop in the abdomen, also known as abdominal aortic aneurysms (AAAs).
• Those that occur in the region between the chest and abdominal are known as thoracoabdominal aneurysms (TAAAs) or juxtarenal aortic aneurysms due to their relation with the renal arteries.
• The remainder occur in the chest and are known as thoracic aortic aneurysms (TAAs).

The most common type of aortic aneurysm is a result of atherosclerosis, which weakens the wall of the aorta.²

The majority are fusiform, abdominal and infrarenal.

RISK FACTORS

Risk factors for atherosclerotic aortic aneurysms include:

• Cardiovascular risk factors: Significant smoking history, hypertension, dyslipidaemia and diabetes mellitus²
• Age: It occurs mostly in older patients
• Male gender

PREVALENCE IN ASIAN POPULATIONS

Fortunately, the overall prevalence of aortic aneurysms in Asian populations is low at about 1.3%. This increases to 2.5-4% when selected for Asian populations with cardiovascular risk factors who are male and aged above 60.²

Screening for AAAs in carefully selected Asian male populations with cardiovascular risk factors could potentially yield benefits. Opportunistic screening with physical examination for AAAs or ultrasound examination of the abdomen or transthoracic echocardiography could be considered.

PRESENTATION

Depending on the location of the aortic aneurysm, some patients may report feeling a pulsatile abdominal mass.

Others may present with vague central abdominal pain or back pain that increases in severity over time.

Less commonly, they may report a vague bloating sensation from compression of the aneurysm along the gastrointestinal tract.

Up to 10% of patients with aortic aneurysms have aneurysms elsewhere and may have felt a strong pulsatile mass or pulsation at the back of their knees in the form of popliteal aneurysms.

Even rarer but catastrophic presentations include gastrointestinal bleeding or haemoptysis often due to aortoenteric or aortobronchial fistulas. These may present with a sentinel bleed. A high index of suspicion is required especially if there is a known history of aortic aneurysms or aneurysm repair.

TAAs or TAAAs may present with deep, throbbing pain in the chest or upper back. TAA may result in compressive symptoms such as dysphagia, breathlessness and voice hoarseness.

CT or ultrasound abdomen are good imaging tools for diagnosis of an aneurysm.

RISK OF RUPTURE

Classically, the risk of rupture for AAA based on size is described in Table 1.

Intervention should be performed when the risks from intervention are lower than the risk of aneurysm rupture per year.

WHEN SURVEILLANCE MAY BE SUFFICIENT

The majority of non-ruptured aneurysms present small and are incidentally discovered. They tend to be slow growing and require only surveillance.

For asymptomatic patients at diameters of < 5.5 cm or < 5 cm in males and females respectively, surveillance is the mainstay of management along with modification of cardiovascular risk factors.

These include smoking cessation and compliance to medication for hypertension, ischaemic heart disease and diabetes.

Though slightly controversial and based on centre experience, surgeon preference and counselling, smaller (4-5 cm) and asymptomatic aneurysms in surgically fit patients are sometimes considered for treatment as the anatomy of these aneurysms may become more challenging over time (and the patient becomes less fit).

Nevertheless, in general, the risk of rupture per year for such aneurysms is low and hence surveillance and conservative management is advised.

General practitioners (GPs) or vascular surgeons may elect to image these aneurysms at 3-6 monthly or even yearly intervals, depending on the size at presentation as well as the rate of growth.

• Imaging can be performed with abdominal ultrasound (for size) or contrasted CT aortography.
• CT gives more information about the aneurysm in relation to the visceral branches and allows for measurement of all aspects of the aorta. However, the use of contrast and the patient’s baseline kidney functions are important considerations, especially if surveillance needs to be done at close intervals.

WHEN ACTIVE MANAGEMENT OR SURGERY SHOULD BE CONSIDERED

Aortic aneurysms that need to be more actively managed or considered for surgery are those that are:

• Larger than 5.5 cm (6 cm for thoracic)
• Growing at more than 0.5 cm / 6 months or1 cm / year
• Symptomatic – abdominal, back or chest pain
• Symptomatic – embolic showers or thrash todistal, downstream vessels
• Saccular, eccentric dilatation
• Non-atherosclerotic in aetiology (connective tissue disorders, inflammatory, autoimmune, mycotic)
• Related to injury

Symptomatic aneurysms

When symptomatic for pain, this may represent that the aneurysm is increasing in size at a faster rate than previously. This may also represent a risk for impending rupture.²

Due to the atherosclerotic nature and non-laminar, sluggish blood flow within aneurysms, the walls of aneurysms are often layered with thrombus which may break loose, travel through the bloodstream and lodge into a distal blood vessel causing blockage.

In such cases, patients may present with dusky discolouration or gangrene in the extremities. Less commonly, they may present with severe abdominal pain from bowel or visceral ischaemia. Certainly, this would also be an indication to treat the aneurysm regardless of size.

Saccular and non-atheroscleroticaetiology aneurysms

Aortic aneurysms that are saccular in morphologymay be at an increased risk of rupture due to theless uniform expansion. Often, these may be of non atherosclerotic aetiologies and thus the risk of rupture based purely on size as described earlier may not beas accurate, rendering the threshold for intervention lower. Saccular aneurysms may also be mycotic innature (see next section on mycotic aneurysms).

Aneurysms resulting from systemic lupus erythematosus (SLE), aortitis or connective tissue disorders such as Marfan syndrome may be extensive along the entire aorta and other arteries. They may originate from the root of the heart or be a result of malignant aneurysmal degeneration from chronic dissection.

Fortunately, these aneurysms are less common, butare also thus best managed at high-volume centres.

Mycotic/infective aneurysms

A mycotic aneurysm suggests that there is anunderlying haematogenous pathogen that has beenembedded in the wall of the aorta, giving rise toaneurysmal degeneration. These patients may havesevere septicaemia and intervention can be highlytime-sensitive.^4,5

Four mechanisms of mycotic aneurysms have been proposed, which include:

• Bacterial wedding of existing intimal injury oratherosclerotic plaque
• Septic emboli into the arterial vasa vasorum
• Contiguous infective focus that extends into the aortic wall
• Direct bacterial inoculation during penetrating trauma

Gram-positive bacteria such as Staphylococcus,Enterococcus, and Streptococcus account for 60%of causative organisms, whereas Salmonella accounts for the majority of infections caused by gramnegative bacteria. Other causative organisms include Mycobacterium tuberculosis and Treponema pallidum.

Salmonella has an inclination for adherence to diseasedvascular endothelium, and non-typhoidal Salmonella constitutes the majority of cases in East Asia whereinfection often develops after the consumption of uncooked eggs and meat.

Management of these aneurysms is often challenging and performed in conjunction with infectious physicians. We will discuss more about the approach and treatment of these aneurysms at SingHealth inthe next issue of Defining Med.

THE GP’S ROLE IN CARE

As the first point of contact for many patients, GPs play an essential role in making the initial diagnosisand ensuring timely referrals.

By leveraging their expertise with chronic disease management, GPs are also well-positioned to optimise the control of cardiovascular risk factors such as blood pressure and lipid management. As our partners in the community, GPs can continue to encourage these patients to adopt a healthy lifestyle and quit smoking.

Management of aortic aneurysms is broadly divided into acute management of a ruptured aneurysm and elective management to prevent catastrophic events.

While management largely lies in the realm of vascularsurgeons and interventional radiologists, multidisciplinary care is important for risk factor modification, pre- and postoperative surveillance, as well as management of any complications arising from both disease and treatment.

Treatment is seldom ‘one-size-fits-all’, but rather atailored approach based on size, location and occasion, and importantly, a centre’s cumulative experience.¹

Find out more about the treatment of aortic aneurysms, and special considerations that guide surgical management, in the next issue of Defining Med.

REFERENCES

1. Ng, N.Z.P.; Pang, J.H.Q.; Yap, C.J.Q.; Chao, V.T.T.; Tay, K.H.; Chong, T.T. Custom-Made Device (CMD) for the Repair of Thoraco-Abdominal Aneurysm (TAA): Mid-Long

Term Outcomes from a Single Southeast Asian Centre Experience in Singapore. J. Clin. Med. 2024, 13, 6145. https://doi.org/ 10.3390/jcm13206145

2. Chan WK, Yong E, Hong Q, Zhang L, Lingam P, Tan GWL, Chandrasekar S, Lo ZJ. Systematic review and meta-analysis of the prevalence of abdominal aortic aneurysm

in Asian populations. J Vasc Surg. 2021 Mar;73(3):1069-1074.e1. doi: 10.1016/j.jvs.2020.08.140. Epub 2020 Sep 26. PMID: 32987145.

3. Ng NZP, Chong TT. Endovascular Aneurysm Repair (EVAR) of an Infrarenal Abdominal Aortic Aneurysm (AAA) in a Young Patient with Systemic Lupus Erythematosus

(SLE). EJVES Short Rep. 2017;37:8-11. doi: 10.1016/j.ejvssr.2017.09.003. eCollection 2017. PubMed PMID: 29234732; PubMed Central PMCID: PMC5678881.

4. Dayna SPY, Peng NNZ, Shaun LQ. Off-the-Shelf, Hybrid, Innominate Chimney Thoracic Endovascular Aneurysm Repair for Treatment of Mycotic Thoracic Aortic

Aneurysm: A Case Report. Vasc Specialist Int. 2024 Apr 24;40:11. doi: 10.5758/vsi.230126. PubMed PMID: 38679430; PubMed Central PMCID: PMC11056280.

5. Cheok S, Gan LSC, Chung SJ, Ch’ng JK. Aortic endograft infection secondary to Burkholderia pseudomallei: A case report and review of the literature. J Vasc Surg

Cases Innov Tech. 2021 May 21;7(3):421-424. doi: 10.1016/j.jvscit.2021.04.023. PMID: 34278075; PMCID: PMC8263529.

Dr Nick Ng Zhi Peng is a Vascular and Endovascular Surgical Consultant at the Department of Vascular Surgery, Singapore General Hospital. He graduated from the Yong Loo Lin School of Medicine, National University of Singapore in 2011 and completed his surgical training with the SingHealth General Surgery Residency Programme in 2018. He obtained his Masters of Medicine (Surgery) in 2017 and FRCS (Edinburgh) in March 2019. Dr Nick performs both open and endovascular surgery, and his areas of interest include aortic, carotid, limb salvage for chronic limb-threatening ischaemia and renovascular diseases. His aim is to manage these challenging diseases as best as possible to give patients the best quality of care and life.

GPs can call the SingHealth Duke-NUS Vascular Centre for appointments at the following hotlines: