Chapter 11 – Blood Vessels: Aneurysms and Dissection Flashcards
What is aneurysm?
An aneurysm is a localized abnormal dilation of a blood vessel or the heart ( Fig. 11-17 ); it can
be congenital or acquired.
What is true aneurysm?
When an aneurysm involves an intact attenuated arterial wall or thinned ventricular wall of the heart, it is called a true aneurysm
Give example of true aneurysm.
Atherosclerotic, syphilitic, and
congenital vascular aneurysms, and ventricular aneurysms that follow transmural myocardial
infarctions are of this type
What is a false aneurysm?
a false aneurysm (also called pseudo-aneurysm) is a
- *defect in the vascular wall leading** to an extravascular hematoma that freely communicates with
- *the intravascular space (“pulsating hematoma”)**
Give example of False Aneurysm.
Examples include a ventricular rupture after
myocardial infarction that is contained by a pericardial adhesion, or a leak at the sutured
junction of a vascular graft with a natural artery
What are arterial dissection?
An arterial dissection arises when blood enters
the arterial wall itself, as a hematoma dissecting between its layers.
Dissections are often but
not always aneurysmal (see also below)
Dissections are always aneurysmal.
T or F
FALSE
Dissections are often but
not always aneurysmal
Both true and false aneurysms as well as dissections
can rupture, often with catastrophic consequences
T or F
True
FIGURE 11-17 Aneurysms.
- A, Normal vessel.
- B, True aneurysm, saccular type. The wall focally bulges outward and may be attenuated but is otherwise intact.
- C, True aneurysm, fusiform type. There is circumferential dilation of the vessel, without rupture.
- D, False aneurysm. The wall is ruptured, and there is a collection of blood (hematoma) that is bounded externally by adherent extravascular tissues.
- E, Dissection. Blood has entered (dissected) the wall of the vessel and separated the layers. Although this is shown as occurring through a tear in the lumen, dissections can also occur by rupture of the vessels of the vaso vasorum within the media.
Aneurysms are generally classified by what?
shape and size
What are Saccular aneurysms?
spherical outpouchings (involving only a portion of the vessel wall); they vary from 5 to 20
cm in diameter and often contain thrombus
What are Fusiform aneurysms ?
Fusiform aneurysms involve diffuse, circumferential
- *dilation of a long vascular segment**; they vary in diameter (up to 20 cm) and in length, and can
- *involve extensive portions of the aortic arch,** abdominal aorta, or even the iliac arteries.
These
types are not specific for any disease or clinical manifestations.
Arteries are dynamically remodeling tissues that maintain their integrity by constantly
synthesizing, degrading, and repairing damage to their ECM constituents.
So how does aneurysm can occur?
Aneurysms can occur
when the structure or function of the connective tissue within the vascular wall is compromised.
Although we cite here examples of inherited defects in connective tissues, weakening of vessel
walls is important in the common, sporadic forms of aneurysms as well
What is important in the pathogenesis of commom. sporadic forms of aneurysms?
weakening of vessel
walls is important in the common, sporadic forms of aneurysms as well
Pathogenesis of Aneurysms
- The intrinsic quality of the vascular wall connective tissue is poor
- The balance of collagen degradation and synthesis is altered by local inflammatory infiltrates and the destructive proteolytic enzymes they produce.
- The vascular wall is weakened through loss of smooth muscle cells or the inappropriate
synthesis of noncollagenous or nonelastic ECM.
Give examples of intrinsic quality of the vascular wall connective tissue is poor
- Marfan syndrome
- Loeys-Dietz syndrome
- Ehlers-Danlos syndrome
MEL you are so Poor
What is defective in Marfan syndrome that leads to intrinsic quality of the vascular wall connective tissue is poor?
Marfan syndrome, for example ( Chapter 5 ), defective synthesis of the **scaffolding protein fibrillin** leads to **aberrant TGF-β** activity and **progressive weakening of elastic tissue**; in the aorta, the consequence is **progressive dilation due to remodeling of the inelastic media**
What is defective in Loeys-Dietz syndrome that leads to intrinsic quality of the vascular wall connective tissue is poor?
another recently recognized cause of aneurysms; in this
disorder, mutations in TGF-β receptors lead to abnormalities in elastin and collagen I
and III.
Aneurysms in such individuals can rupture fairly easily (even at small size).
What is defective in Ehlers-Danlos syndrome that leads to intrinsic quality of the vascular wall connective tissue is poor?
altered collagen crosslinking
associated with vitamin C (ascorbate) deficiencyis an example of anutritional
basis for aneurysm formation.
What is an example of a nutritional
basis for aneurysm formation.
Ehlers-Danlos syndrome
How does MMP production contributes to aneurysm dev?
MMP production, especially by macrophages in atherosclerotic plaque or in vasculitis,
probably contributes to aneurysm development [56] ; these enzymes have the capacity
to degrade virtually all components of the ECM in the arterial wall (collagens, elastin,
proteoglycans, laminin, fibronectin).
What regulates the balance of collagen degradation and synthesis that is altered by local inflammatory
infiltrates and the destructive proteolytic enzymes they produce which contribute to the formation of aneurysm?
- TIMP
- MMP
Genetic predisposition to aneurysm formation in the setting of inflammatory
lesions (such as atherosclerosis) may be related to polymorphisms of MMP and/or TIMP
genes, or to the nature of the local inflammatory response that results in increased
production of MMP.
What factors contribute tovascular wall is weakened through loss of smooth muscle cellsor theinappropriatesynthesis of noncollagenous or nonelastic ECM.
- Ischemia of the inner media occurs when there is atherosclerotic thickening of the intima, which increases the distance that oxygen and nutrients must diffuse.
- Systemic hypertension can also cause significant narrowing of arterioles of the vasa vasorum (e.g., in the aorta), which can cause outer medial ischemia. Ischemia is reflected in “degenerative changes” of the aorta, whereby smooth muscle cell loss—or change in synthetic phenotype—leads to scarring (and loss of elastic fibers), inadequate ECM synthesis, and production of increasing amounts of amorphous ground substance (glycosaminoglycan).
Where is ischemia is reflected ?
in “degenerative changes” of the aorta,
Smooth muscle cell loss—or change in synthetic phenotype—leads to what?
leads to scarring (and loss of elastic fibers), inadequate ECM synthesis, and production of increasing amounts of amorphous ground substance (glycosaminoglycan).
What is cystic medial degeneration?
Ischemia is reflected in “degenerative changes” of the aorta, whereby smooth muscle cell loss—or change in synthetic phenotype—leads to scarring (and loss
of elastic fibers), inadequate ECM synthesis, and production of increasing amounts of
amorphous ground substance (glycosaminoglycan).
Histologically these changes are
collectively called cystic medial degeneration ( Fig. 11-18 ). These changes are
nonspecific and can be seen in a variety of settings, including Marfan disease and
scurvy.
FIGURE 11-18 Cystic medial degeneration. A, Cross-section of aortic media from a patient
with Marfan syndrome, showing marked elastin fragmentation and formation of areas devoid
of elastin that resemble cystic spaces (asterisks). B, Normal media for comparison, showing
the regular layered pattern of elastic tissue. In both A and B, elastin is stained black.
What are the two most important disorders that predispose to aortic aneurysms?
- atherosclerosis and
- hypertension
What is a greater factor in abdominal aortic aneurysms?
atherosclerosis
What is the most common condition associated with aneurysms of the ascending
aorta.
hypertension is the most common condition associated with aneurysms of the ascending
aorta.
What are Other conditions that weaken vessel walls lead to aneurysms?
- trauma,
- vasculitis (see below),
- congenital defects (e.g., berry aneurysms typically in the circle of Willis; Chapter 28 ), and
- infections (mycotic aneurysms).
Mycotic aneurysms can originate from what:
- (1) from embolization of a septic embolus, usually as a complication of infective endocarditis;
- (2) as an extension of an adjacent suppurative process; or
- (3) by circulating organisms directly infecting the arterial wall.
Tertiary syphilis is now a rare cause of aorticaneurysms
Tertiary syphilis is now a rare cause of aorticaneurysms
T or F
True
How does Tertiary syphilis cause of aorticaneurysms
The obliterative
endarteritischaracteristic oflate-stage syphilisshows apredilection for small vessels, including
those of the vasa vasorum of the thoracic aorta.
This leads to ischemic injury of the aortic media and aneurysmal dilation, which sometimes involves the aortic valve annulus.
FIGURE 11-19 Abdominal aortic aneurysm.
A, External view, gross photograph of a large
aortic aneurysm that ruptured; the rupture site is indicated by the arrow.
B, Opened view, with the location of the rupture tract indicated by a probe. The wall of the aneurysm is
exceedingly thin, and the lumen is filled by a large quantity of layered but largely
unorganized thrombus
FIGURE 11-20 Aortic dissection.
A, An opened aorta with proximal dissection originating
from a small, oblique intimal tear (identified by the probe) , allowing blood to enter the media
and creating an intramural hematoma (narrow arrows) . Note that the intimal tear has
occurred in a region largely free of atherosclerotic plaque and that propagation of the intramural hematoma is arrested at a site more distally where atherosclerosis begins (broad
arrow).
B, Histologic view of the dissection demonstrating an aortic intramural hematoma
(asterisk). Aortic elastic layers are black and blood is red in this section, stained with the
Movat stain.
FIGURE 11-21 Classification of dissections. Type A (proximal) involves the ascending aorta,
either as part of a more extensive dissection (DeBakey I) or in isolation (DeBakey II). Type B
(distal or DeBakey III) dissections arise beyond the takeoff of the great vessels. The serious
complications predominantly occur in type A dissections.
