Overview
This lecture covers aneurysms, including their definition, types, causes, risk factors, complications, and clinical significance.
Definition and Types of Aneurysms
- Aneurysm means abnormal dilation of a blood vessel, diagnosed when the diameter is 1.5 times larger than normal.
- Aneurysms most commonly affect arteries (aorta, femoral, iliac, popliteal, cerebral), rarely veins.
- Two main types: true aneurysms (all vessel wall layers dilate) and pseudoaneurysms (blood escapes vessel, contained by surrounding tissue).
- True aneurysms: fusiform (symmetrical bulging) and saccular/Berry (asymmetrical bulging).
Common Sites and Epidemiology
- Arterial aneurysms are most common in the aorta.
- 60% of true aortic aneurysms are abdominal; 95% of those are below the renal arteries but above the aortic bifurcation.
Pathophysiology and Risk Factors
- Weakening of blood vessel walls causes aneurysms; can be due to poor oxygen supply or high blood pressure.
- Laplace's law: increased wall tension as vessel diameter increases, causing further dilation.
- Risk factors: male, age over 60, hypertension, smoking.
- Atherosclerosis and tertiary syphilis (endarteritis obliterans) reduce vessel wall strength.
- Mycotic aneurysms result from bacterial (e.g., Bacteroides, Pseudomonas, Salmonella) or fungal infections (e.g., Aspergillus, Candida).
- Genetic disorders (Marfan syndrome, Ehlers-Danlos syndrome) weaken connective tissue, increasing risk.
Clinical Features and Complications
- Many aneurysms are asymptomatic unless compressing nearby structures.
- Ruptured aneurysms cause severe internal bleeding and tissue ischemia.
- Thoracic aneurysm above aortic valve can cause aortic insufficiency and "brassy" cough by stretching the recurrent laryngeal nerve.
- Cerebral aneurysm rupture leads to subarachnoid hemorrhage, sudden headache, and neck stiffness.
- Blood clots can form in aneurysms, causing vessel blockage or emboli.
- Classic triad for ruptured abdominal aortic aneurysm: severe pain (flank/abdominal/lower back/groin), pulsating mass, hypotension.
Diagnosis and Treatment
- Aneurysms are often found incidentally on ultrasound, CT, or MRI.
- Surgical treatment is considered for large or risky aneurysms.
Key Terms & Definitions
- Aneurysm — abnormal localized dilation of a blood vessel.
- True aneurysm — all layers of the vessel wall expand.
- Pseudoaneurysm (false aneurysm) — blood leaks through vessel wall, contained by surrounding tissue.
- Fusiform aneurysm — symmetrical, spindle-shaped bulging.
- Saccular/Berry aneurysm — asymmetrical, pouch-like bulging.
- Laplace's law — wall tension increases with vessel diameter.
- Mycotic aneurysm — aneurysm caused by infection.
- Aortic insufficiency — failure of the aortic valve to close properly, causing blood backflow.
Action Items / Next Steps
- Review imaging examples of aneurysms (ultrasound, CT, MRI).
- Read about genetic syndromes (Marfan, Ehlers-Danlos) and their effects on connective tissue.