As a rule a fusiform aneurysm contains fluid blood, but when the intima
is roughened by disease, especially in the form of calcareous plates,
shreds of clot may adhere to it.
It has little tendency to natural cure, although this is occasionally
effected by the emerging artery becoming occluded by a clot; it has also
little tendency to rupture.
#Sacculated Aneurysm.#--When a _limited area_ of the vessel wall is
weakened--for example by atheroma or by other form of arteritis--this
portion yields before the pressure of the blood, and a sacculated
aneurysm results. The internal and middle coats being already damaged,
or, it may be, destroyed, by the primary disease, the stress falls on
the external coat, which in the majority of cases constitutes the sac.
To withstand the pressure the external coat becomes thickened, and as
the aneurysm increases in size it forms adhesions to surrounding
tissues, so that fasciae, tendons, nerves, and other structures may be
found matted together in its wall. The wall is further strengthened by
the deposit on its inner aspect of blood-clot, which may eventually
become organised.
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