Aneurysms Aortic Aneurysms The two most important causes

Aneurysms

Aortic Aneurysms - The two most important causes of aortic aneurysms are atherosclerosis and hypertension - Atherosclerosis is the dominant factor in abdominal aortic aneurysms - The most important factor in ascending aortic aneurysms is hypertension

I. Abdominal aortic aneurysms Main causes: 1. Atherosclerosis 2 - Genetic factors such as Marfan syndrome which is caused by deficiency of fibrillin an important component of elastic fibers

Atherosclerotic aneurysms occur most frequently in abdominal aorta, but can involve iliac arteries, aortic arch, and descending thoracic aorta - Occur most frequently in men and smokers, and rarely in men younger than 50

Mechanism - The atherosclerotic intimal plaques 1. compress the underlying media 2. and also compromise nutrient and waste diffusion from the vascular lumen into the arterial wall. The media consequently undergoes degeneration and necrosis, thus allowing the dilation of the vessel

Morphology: - Typically occurs between the renal arteries and the aortic bifurcation - Can be up to 15 cm in diameter and 20 cm in length - Microscopically: atherosclerosis with destruction and thinning of the underlying aortic media

Clinical consequences 1. Rupture massive potentially fatal hemorrhage - risk of rupture is directly related to the size of the aneurysm (of 5 cm or more) - operative mortality for unruptured aneurysms 5%, emergency surgery after rupture the mortality rate is more than 50%

2. Obstruction of a vessel branching off the aorta (e. g. the renal, iliac, vertebral or mesenteric } resulting in ischemia of kidneys, spinal cord, legs or Gastrointestinal tract. 3. Embolism from atheroma or mural thrombus 4. Compression of ureter or erosion of

II. Thoracic aortic aneurysms - Most commonly associated with hypertension and Marfan syndrome • Manifestations 1. Enchroachment on mediastinal structures 2. Persistent cough from irritation of recurrent laryngeal nerves

3. Pain from erosion of bone 4. Aortic rupture Note: Thoracic aortic aneurysms can result from syphilis which mainly affects ascending thoracic aorta

Aortic dissection - Occurs when blood splays apart the laminar planes of the media to form a blood-filled channel within the aortic wall - This development can be catastrophic if the dissecting blood ruptures through adventitia and escapes into adjacent tissue

Predisposing factorsn A. men aged 40 -60 with antecedent hypertension in more than 90% B. Younger patients with connective tissue abnormalities that affect the aorta—Marfan C. It can be iatrogenic (arterial cannulation D. Rarely it occurs in pregnant woman Note: Dissection is unusual in the presence of substantial atherosclerosis

- The trigger for the intimal tear and subsequent intramural hemorrhage is not known - Once the tear has occurred , blood under the systemic pressure dissects through media along laminar planes

- The intimal tear is found in the ascending aorta within 10 cm of the aortic valve - Such tears usually are transverse or oblique and 1 -5 cm in length - The dissection plane can extend retrograde toward the heart or distally , occasionally as far as as the iliac and femoral arteries and lies between the

- The classic clinical symptom of aortic dissection is the sudden onset of excruciating tearing or stabbing usually begins in the anterior chest , radiating to the back between the scapula and moving downward - The most common cause of death is rupture of the dissection into the pericardial, pleural or peritoneal cavity

classification 1 -Proximal lesions (called type A dissections) - The most common (and dangerous), involving either the ascending aorta only or both the ascending and descending aorta (types I and II of the De. Bakey classification) 2 -Distal lesions not involving the ascending part usually beginning distal to the subclavian artery (called type B dissections or De. Bakey type III)

Classification of dissections. Type A (proximal) involves the ascending aorta, either in isolation (De. Bakey I) or as part of a more extensive dissection (De. Bakey II). Type B (distal, or De. Bakey III) dissections arise after the take off of the great vessels. The serious complications predominantly occur in Type A dissections, which therefore mandate surgical intervention

Dissection

Vasculitis I. Immune mediated II. Infectious •

• It is critical to distinguish between infection and immunologic mechanisms because immunosuppressive therapy is appropriate for immune –mediated but contraindicated in infectious vasculitis

I. Immune mediated vasculitis A. Giant cell (temporal arteritis) - is the most common type - it is a chronic , typically granulomatous inflammation - affects large to small –sized arteries

Principally affects the arteries of the head-especially temporal arteries but also the vertebral and ophthalmic arteries as well as the aorta - ophthamic artery involvement can lead to sudden and permanent blindness - - Lesions also occur in other arteries, including the aorta (giant cell aortitis).

• MORPHOLOGY Segmental lesions - Classic lesions show granulomatous inflammation within the inner media centered on the internal elastic lamina - There is a lymphocyte and macrophage infiltrate, with multinucleated giant cells and fragmentation of the internal elastic lamina -

Clinical features - Mainly affects people older than 50 years - Symptoms a. are vague and constitutional such as fever, fatigue or weight loss b. or may involve facial pain or headache mostly intense along the course of the superficial tempotal