The Human Cardiovascular System - Computational Hemodynamics: Theory, Modelling and Applications - page 38

commonly known as cerebral, intracranial or brain aneurysms, discussed in depth
in Chap. 7. In the abdominal artery the aneurysm is known as Abdominal Aortic
Aneurysm (AAA) which is a localized dilation of the abdominal aorta by more than
half of its original diameter.
Aneurismal conditions can also be hereditary resulting in congenital aneurysm,
which deteriorates the vascular wall structure. With aging, aneurysms increase in
size resulting in the rupture and initiation of bleeding within the brain. This causes a
medical condition known as stroke that can result in death or disability.
Aneurysms are classified as saccular or fusiform is based on their geometry
(spherical- or spindle- shape) and dimension, which reaches up to approximately
5-20 mm in diameter. A saccular aneurysm is spherically shaped, affects a short
length of the vessel, and typically occurs in the cerebral arteries. A fusiform aneu-
rysm, which is typically spindle-shaped, is variable in dimension and is affected by
arterial length. They typically affect a longer length of the ascending and transverse
aortic arch, the abdominal aorta.
An aneurysm can grow large and rupture leading to severe haemorrhage, and
other complications, death. Nearly 8.9 % of the population above 65 years old is
diagnosed with this disease. As it normally remains asymptomatic, surgical inter-
vention or follow a wait-and-watch strategy is preferred for vascular surgeons if the
rupture risk is being assessed at a low level. Currently, the maximum diameter cri-
terion is widely used in clinical practice. When the diameter exceeds 55 mm or the
expansion of the aneurysm is greater than 10 mm/year, a surgery is recommended
(Brady et al. 2004).
Treatment of aneuryms can be made by inserting stents into the arteries. The af-
fected arterial region is generally treated using angioplasty with stents or by open
surgery that involves inserting a clip across the aneurysm in order to prevent blood
from entering the aneurysmal bulge and aggravating its dilation (Fig. 2.18 ). For
AAA stenting, an endovascular stent graft is delivered to the aortic aneurismal site
via a catheter and a stent graft is released, and positioned to reinforce the weak
arterial section caused by the aneurysm. This channels the blood through it without
exerting pressure on the aneurismal bulge (Fig. 2.18 ).

2.3.4 Thrombosis

A thrombus is formed on a blood-contacting surface or in flowing blood which
blocks circulation at a micro-level. We discuss two possible causes of thrombosis.
When a calcified cap within a plaque is unable to withstand stresses by the flow-
ing blood exerted on its wall it ruptures and exposes the interior of the artery to the
blood stream. This causes blood to coagulate about the rupture and form blood clots.
The blood clot gives rise to a thrombus, which essentially adds a further blockage
to the already narrow channel -this condition is referred to as thrombosis. Should
the blockage be severe, it can cut off the blood supply through the artery. If this oc-
curs in the coronary artery, the result is a heart attack. If the thrombosis occurs in
the cerebral artery, it can trigger a transient ischemic attack or a stroke. A blockage