Aneurysms: Pathological Classification
An aneurysm is a localized abnormal dilation of a blood vessel or the heart. They are primarily driven by structural weakness in the vessel wall, often involving the degradation of the media layer.
1. Abdominal Aortic Aneurysm (AAA)
Usually associated with atherosclerosis; occurs most commonly in men >60 years of age, particularly smokers. Often presents as a pulsatile abdominal mass.
- Pathogenesis: Atherosclerosis increases the diffusion distance to the media, leading to ischemia and atrophy of the vessel wall.
- Risk: Rupture when >5 cm in diameter; presents with hypotension, pulsatile abdominal mass, and flank pain.
2. Thoracic Aortic Aneurysm
Associated with hypertension, Marfan syndrome (cystic medial necrosis), and tertiary syphilis (obliterative endarteritis of the vasa vasorum).
- Syphilitic Aneurysm: Characterized by a “tree-bark” appearance of the aortic intima.
- Marfan Syndrome: Defect in fibrillin leads to cystic medial necrosis, significantly increasing the risk of aortic dissection.
3. Aortic Dissection
| Classification | Key Features |
|---|---|
| Stanford Type A | Involves ascending aorta. Requires emergency surgery; high risk of rupture/tamponade. |
| Stanford Type B | Involves descending aorta (distal to left subclavian). Managed medically with beta-blockers. |
4. Exam Must-Knows
Pathology Pearl: Aortic dissection presents as sudden “tearing” chest pain radiating to the back. A discrepancy in blood pressure between the arms is a classic clinical finding. Cystic medial necrosis is the histological hallmark.
- Berry Aneurysms: Small, saccular aneurysms in the Circle of Willis, associated with ADPKD and Ehlers-Danlos syndrome. Increased risk of subarachnoid hemorrhage.
- Mycotic Aneurysm: An aneurysm caused by infection (e.g., bacterial seeding of a preexisting plaque).