Abnormal permanent dilation of part of aortic wall, with intact walls which are attenuated and thinned out ,due to a congenital cause or an acquired cause is Known as an Aortic Aneurysm. There are many causes which would lead to aneurysms, as I have discussed in my other blog post called, :Quick look at Aneurysms and Dissection.
Here we are focussing mainly on acquired causes. Out of both congenital and acquired causes, two most contributed causes for aortic aneurysms, especially in abdominal aorta, is atherosclerosis and Hypertension. Tertiary syphilis is another rare cause.
- Hypertension—> narrowing of arterioles in vasa vasorum (Quick look at Pathology in hypertension) —> Inadequate oxygen and nutrient supply to outer media of the aorta —-> medial degeneration —-> Weakening of the wall —-> dilation of vessel
- Atherosclerosis —->Release of Matrix Metallo Proteases —-> Increased degradation connective tissue
- Atherosclerosis —–> Intimal thickening —-> increase the distance of oxygen and nutrient diffusion form the blood in lumen to inner media
All above ultimately leads to Medial ischemia.In response to medial ischemia, following occurs,
- Loss of smooth muscles
- Increased degradation of the matrix
- Defective synthesis of matrix proteins
- increased synthesis of amorphous matter in the matrix (eg :- glycosaminoglycans) which would further apprehend the vascular integrity.
Aortic aneurysms are mainly either thoracic or abdominal. In Abdominal aneurysms, the patient is mainly asymptomatic and most of the times, it is discovered by accident during examination, or patients present as follows;
- Rupture of an abdominal aortic aneurysm leading to massive hemorrhage into abdominal cavity which begets unbearable pain.
- Due to Impingement of the aneurysm on adjacent structures which would give rise to different signs and symptoms (Eg:- Impingement on Ureters cause difficulty in passing urine)
- Inadequate supply of blood to lower limbs, kidneys, gastro intestinal tract as the supply for these originate from the vessels branching from aorta.
- Embolism from atheroma or mural thrombi occurring in the aneurysm.
In contrast Thoracic aneurysms are clinically detected as they have direct complications such as;
- Impingement on recurrent laryngeal nerve leading to persistent dry cough
- Impingement on thoracic vertebrae leading to erosion
- Impingement on esophagus causing dysphagia (difficulty in swallowing)
- Due to encroachment on lungs and airways, patient feels difficulty in breathing.
- Back pressure developing –> dialation of vales in heart near the ostia of coronary arteries supplying myocardium —> narrowing of Ostia —> myocardial ischemia
Aortic Dissections occur mainly due to hypertension. In contrast to aneurysms, Dissections have a distinct breach in the vessel wall, which leads to accumulation of blood, from the intravascular space between the laminar planes of media. This forms a blood filled channel within the media and blood do not communicate with the outside of the vessel as in false aneurysms.
Although even if we say there is a breach in the vessel wall, aortic dissections sometimes can occur without any intimal tear. Aorta is a large artery. It has a very large Tunica media. This layer is so thick, that small blood vessels called, “Vasa Vasorum”are present to supply blood to this layer to provide their nutritional and oxygen requirements. During hypertension due to medial thickening in the arterioles (Quick look at Pathology in hypertension) and loos of their integrity, these can rupture leading to accumulation of blood within the laminar planes of media of aorta.
Aortic dissections are mainly classified in to 2 TYPES depending on the part of the aorta involved.
- Type A – includes Proximal dissections involving only ascending aorta or both in ascending and descending aorta.
- Type B – Includes distal dissections involving descending aorta.
The classic clinical presentation of an aortic dissection is the sudden and abrupt onset of an unbearable excruciating pain from anterior aspect of chest, radiating to the back between the scapulae. This will move down with the progression of the dissection downwards. the most common cause of death would be the collection of blood in cavities such as pericardial, peritoneal and pleural spaces.