Aneurysm (Aneurysmal Dilatation)

What is Aneurysm

An aneurysm is a blood-filled balloon in the wall of a blood vessel. They could involve any blood vessel in the body.

An aneurysm dilates and could rupture leading to massive blood loss followed by marked hypovolemia and finally death. The blood vessel could be thin as a result of a hereditary cause or acquired.
Aneurysm could be the site for clot formation and embolization.

Classification of Aneurysm

Aneurysms could be classified by type, morphology, and location.

True or False type of aneurysms

True aneurysm

involve all 3 layers of the arterial wall (intima, media, and adventitia). These are seen in atherosclerosis, syphilis and congenital aneurysms. The ventricular aneurysms that follow transmural myocardial infarction involve all layers of the wall of the heart and are called true aneurysm.

False aneurysms

are also called pseudo-aneurysms is a collection of blood leaking out of the artery wall and confined to the vessel by the surrounding tissue. This blood-filled cavity will eventually thrombose and seal the leak or rupture out of the surrounding tissue. Pseudoaneurysms are caused by trauma that punctures the artery wall like knife and bullet wounds or percutaneous surgical procedures like coronary angiography or arterial grafting or using an artery for injection.

Morphological classification

This is according to the shape and size and may be saccular or fusiform.
Saccular aneurysms
They are rounded in shape and involve only a portion of the vessel wall. They are 5-20 cm in diameter and are filled partially or fully by thrombus.
Fusiform aneurysms
are spindle-shaped and vary both in diameter and length. Their diameter can extend to 20 cm (8 inches). They involve large sections of the transverse and descending aorta and less frequently iliac arteries.

Classification according to the location

They could be:

Arterial and venous aneurysms

Heart – coronary artery aneurysms, ventricular aneurysms, aneurysm of sinus of Valsalva, and aneurysms following cardiac surgery
Aorta – thoracic or abdominal aortic aneurysms
Brain – berry aneurysms, cerebral aneurysms, and Charcot-Bouchard aneurysms
Legs – popliteal artery aneurysms
Kidneys – renal artery aneurysms
Capillaries – capillary aneurysms

Cerebral aneurysms occur in the anterior cerebral artery which is part of the circle of Willis. Its rupture can cause severe stroke leading death. The second commonest site is the internal cerebral artery.