Obstruction of the Larger Arteries. 1111 



3. Obstruction of the larger arteries. Thrombosis et embolia 



arteriarum. 



Etiology. In exceptional cases the aorta and its larger 

 branches may be obstructed by emboli which are derived from 

 the heart or from an aneurysm of the thoracic aorta. Usually, 

 however, the obstruction of a relatively wider vascular lumen 

 occurs through a thrombus originating at a spot in the wall 

 of the vessel which has become roughened or after an embolus 

 has become wedged in, the thrombus becoming gradually larger 

 by deposits of new layers of fibrin. For this reason all causes 

 which are capable of producing an endoarteritis chronica 

 deformans may also constitute the basis of thrombosis of 

 larger vessels. This occurs most frequently in horses jand is 

 usually brought about by the larvae of the Sclerostomum vul- 

 gare (Scl. bidentatum) ; in dogs the Filaria immitis sometimes 

 leads to extensive thrombosis. Exceptionally the vascular 

 lumen may be obstructed when arteries are compressed by a 

 tumor (Mack, Frohner), by exostoses (Grassner, Pirl), which 

 may also produce chronic inflammation, even to complete occlu- 

 sion of the aorta. An acute inflammation, finally (Vennerholm) 

 or contusion of the vessel wall (H. Bouley) may be the causes 

 of occlusion of arteries. 



Anatomical Changes. The thrombosis in horses which is 

 usually produced by larvae of sclerostoma is found mostly in the 

 anterior mesenteric artery, fairly frequently at the posterior 

 end of the abdominal artery and in its, pelvic branches (artt. 

 iliacae, femorales, hypogastricae), from where the thrombus 

 may become continued downward into the tibial arteries; in 

 exceptional cases the vessels of an anterior extremity (art. axil- 

 laris, art. brachialis) or the first portion of the aorta (Berg- 

 strand) is found obstructed. In a case of Filariosis haematica 

 in a dog Hutyra found a large portion of the thoracic and abdom- 

 inal aorta filled up. 



The thrombus is usually attached to the roughened wall of 

 the vessel ; it is dry, tough, and usually arranged in layers. It 

 may cover only a part of the vessel w?ill and thus make the 

 lumen smaller (thrombosis parietalis), or it occupies the entire 

 periphery of the vessel wall, in which case there remains a 

 patent canal in the direction of its longitudinal axis (Thr. 

 canalisatus), or finally it obstructs the vessel entirely (Thr. 

 obturans). The end or the outer surface of a thrombus which 

 does not occlude the blood vessel completely is usually formed 

 by layers of fresh fibrin, which reach into the circulating blood 

 and perhaps into a lateral branch in the form of plugs, and are 

 in all probability usually the result pf post-mortem coagulation. 



An obturating thrombus may in time disintegrate and be 

 absorbed, but in the meanwhile a proliferation of connective 



