What is an aneurysm of the ascending aorta?

Ascending Aortic Aneurysm: Definition, Diagnosis, and Management

An ascending aortic aneurysm is a pathological dilation of the ascending portion of the aorta, defined as a diameter greater than 1.5 times (>50%) the expected normal diameter, with significant risk of rupture, dissection, and death when reaching critical dimensions. 1

Definition and Anatomy

Ascending aortic aneurysms can be classified anatomically into three types:

1. Aortic root aneurysms (including sinuses of Valsalva):

   • Also called annulo-aortic ectasia
   • Common in heritable thoracic aortic disease (HTAD) and bicuspid aortic valve (BAV) patients (20-30%)
   • Typically affects younger patients (30-50 years)
   • Often associated with aortic regurgitation
   • Equal sex distribution (1:1 ratio)

2. Supra-coronary aortic aneurysms (above sinuses of Valsalva):

   • Primarily caused by atherosclerosis related to hypertension
   • Affects older patients (59-69 years)
   • Male predominance (3:1 ratio)
   • Can be related to medial degeneration (isolated or with aortic valve disease)
   • Less common causes: bacterial infection, syphilis, arteritis

3. Aortic arch aneurysms:

   • Often extend from adjacent ascending or descending aorta
   • Primarily linked to atherosclerosis
   • Can be associated with cystic medial degeneration
   • May result from deceleration injuries or coarctation 1

Epidemiology and Risk Factors

• Incidence: 5-10 per 100,000 person-years
• Distribution: ~60% affect root/ascending aorta, ~10% arch, ~30% descending aorta
• Primary risk factor: Hypertension (80% of cases)
• Genetic factors: Present in approximately 20% of cases
• Male predominance: 2-4:1 ratio
• Mean age at diagnosis: 59-69 years 1

Pathophysiology

The pathophysiology varies by etiology:

• Degenerative: Medial degeneration with elastin fragmentation and smooth muscle cell loss
• Genetic disorders: Marfan syndrome, Loeys-Dietz syndrome, Ehlers-Danlos syndrome
• Congenital: Bicuspid aortic valve (BAV)
• Inflammatory: Arteritis (Takayasu's, giant cell arteritis)
• Infectious: Bacterial (rare), syphilis (uncommon)
• Traumatic: Deceleration injuries 1, 2

Diagnosis

Most patients with ascending aortic aneurysms are asymptomatic, with diagnosis often made incidentally during imaging performed for other reasons. The diagnostic approach includes:

1. Initial imaging: Transthoracic echocardiography (TTE) is the first-line modality for assessing aortic valve anatomy, function, and aortic root/ascending aorta dimensions 3

2. Confirmatory imaging: CT or MRI is required to:

   • Adequately visualize the entire aorta
   • Identify affected parts
   • Measure diameter perpendicular to the longitudinal axis
   • Search for co-existing intramural hematoma, penetrating atherosclerotic ulcer, or branch vessel involvement 1, 3

3. Normal dimensions:

   • Ascending thoracic aorta: 34.1 ± 3.9 mm for men and 31.9 ± 3.5 mm for women
   • Aortic dilation (ectasia): Diameters greater than 2 standard deviations above the mean diameter (adjusted for age, sex, and body surface area)
   • Aneurysm: Diameter ≥5.0 cm for the ascending aorta 3

Natural History and Risk Assessment

The natural history of ascending aortic aneurysms involves progressive enlargement with risk of rupture or dissection:

• Growth rate: Average 1.9-3.4 mm per year (higher in genetic disorders)
• Critical diameter: When the aorta reaches 57.5 mm, yearly rates of rupture, dissection, and death are 3.6%, 3.7%, and 10.8%, respectively 1

High-risk features beyond aortic diameter include:

• Relation to patient's height
• Saccular aneurysm associated with penetrating atherosclerotic ulcer
• Uncontrolled resistant hypertension
• Growth rate ≥3 mm/year
• Root vs. ascending phenotype 1

Management

Management decisions are based primarily on aortic diameter, growth rate, symptoms, and underlying etiology:

Surgical Intervention Thresholds

• Standard threshold: Elective surgical repair at diameter ≥55 mm for men and ≥50 mm for women 3
• Lower thresholds for genetic disorders:
  • Marfan syndrome, Ehlers-Danlos, Turner syndrome, BAV: 40-50 mm
  • Loeys-Dietz syndrome: ≥42 mm (internal diameter) or ≥44-46 mm (external diameter) 1, 3
• Other indications:
  • Growth rate ≥5 mm/year
  • Symptoms (pain, compression)
  • Family history of aortic dissection
  • Need for concomitant cardiac surgery 1, 3

Medical Management

• Blood pressure control: Target <135/80 mmHg
• First-line medications: Beta-blockers (especially for Marfan syndrome)
• Alternative options: Angiotensin receptor blockers (ARBs) or ACE inhibitors
• Lifestyle modifications:
  • Regular moderate exercise
  • Avoidance of contact/competitive sports and isometric exercises
  • Smoking cessation (doubles aneurysm expansion rate)
  • Avoidance of fluoroquinolones 3

Surveillance

For non-surgical candidates or those below surgical thresholds:

Aneurysm Size	Surveillance Frequency
< 4.0 cm	CT/MRI every 12 months
≥ 4.0 cm	CT/MRI every 6 months

Post-operative follow-up:

• Early imaging within 1 month
• Yearly imaging for first 2 years
• Every 5 years thereafter if stable 3

Common Pitfalls and Caveats

1. Relying solely on absolute diameter: Body size affects normal aortic dimensions; consider indexed measurements (aortic size index or aortic height index) for more accurate risk stratification, especially in small or large individuals 1

2. Overlooking growth rate: A rapid increase in size (≥5 mm/year) warrants intervention regardless of absolute size 3

3. Missing associated conditions: Patients with ascending aortic aneurysms should be evaluated for:

   • Aortic valve disease (especially BAV)
   • Other aneurysms (abdominal aortic, peripheral)
   • Genetic disorders 1

4. Underestimating risk in women: Women have a four-fold higher rupture risk compared to men with similarly sized aneurysms 3

5. Inconsistent measurement technique: Measurements should be taken perpendicular to the flow axis, and the same imaging modality should be used for serial measurements to ensure consistency 1, 3