ANEURISM. 329 



Serious consequences may follow these changes in the arterial 

 walls. In the coronary arteries the obstruction of the circu- 

 lation may be the immediate cause of fatty degeneration of 

 the heart-muscle and death. In the brain the anaemia result- 

 ing from such an obstruction may result in areas of softening. 

 In the aorta, aneurismal dilatation is a frequent result. The 

 heart is generally hypertrophied in consequence of the obstruc- 

 tion to the circulation offered by the thickened and rigid 

 arterial walls. 



Aneurism. 



An aneurism (Fig. 145) is a localized dilatation of an artery, 

 resulting from any cause which weakens its walls as arter- 

 itis and injury, and from increased arterial pressure. Aneur- 

 isms may be classified according to their shape into fusiform, 

 cylindrical, and saccular. 



In fusiform and cylindrical aneurisms there is a general dila- 

 tation of all the coats of the artery. A cirsoid aneurism is one 

 in which the vessel is rendered tortuous and convoluted as the 

 result of its elongation and unequal dilatation of different 

 parts. 



In sacculated aneurisms, the most important variety, there 

 is a unilateral dilatation of the vessel. First, the media gives 

 way, and then there is a dilatation of the intima and adven- 

 titia, and thus is formed a sac which communicates w r ith the 

 artery by a narrow opening. As the sac increases in size it 

 may finally rupture. The blood may be retained subsequent 

 to rupture by the surrounding tissues ; the term false aneurism 

 is used to designate such a cavity, communicating with an 

 artery and containing blood, the walls of which are not formed 

 by the coats of the vessel. A dissecting aneurism is one in 

 which rupture of the intima occurs and the blood burrows a 

 false passage between the coats of the artery. 



The results of the continued presence of the aneurism may 

 be extensive necrosis of neighboring tissues. Erosion of the 

 vertebrae and pressure of the aneurism on the spinal cord have 

 been the unsuspected cause of a paraplegia. In a similar 

 manner the sternum and ribs may be eroded and the aneurism 

 project beneath the skin. 



