WANDEEING SPLEEN. 299 



Infarctions of the spleen may be due to embolism or 

 thrombosis of the splenic artery. The terminal branches of 

 this artery have only a capillary connection with each other. 

 When they are occluded a conical area of splenic tissue under- 

 goes necrosis. The base of the cone is applied to the splenic 

 capsule, and the apex is directed towards the hilus. A thin 

 stratum next the capsule sometimes escapes necrosis, being 

 nourished by capsular branches. Splenic infarcts are usually 

 white, but occasionally they are red with blood which 

 regurgitates into them from vessels in their neighbourhood. 



Passive congestion of the spleen is due to increased pressure 

 in the portal area. The splenic vein is a tributary of the portal 

 trunk, and when this trunk is obstructed in any way enlarge- 

 ment of the spleen may result. The intimate connexion of the 

 spleen with the portal system explains the rapid diminution in 

 the size of splenic tumours, which may be brought about as the 

 result of diarrhoea. 



A wandering spleen is uncommon. The organ is occasionally 

 found in regions very remote from its normal situation. It may 

 become fixed in its new positions and cause considerable diffi- 

 culty in diagnosis. The condition is sometimes a part of general 

 visceral prolapse. The wandering spleen has a pedicle formed 

 by the gastro-splenic omentum and lieno-renal ligaments, with 

 the included vessels. Occasionally the tail of the pancreas 

 retains its connexion with the organ, the whole gland becoming 

 elongated and twisted. The pedicle of a wandering spleen may 

 become twisted and produce acute symptoms. The splenic 

 vessels in their normal condition are well supported at the back 

 of the abdomen, but when the spleen is loose or enlarged they 

 are subject to traction and may show signs of endarteritis, or 

 small aneurysms of the splenic artery may occur. Communi- 

 cation between the artery and vein has been described, pro- 

 ducing the characteristic murmur of arterio-venous aneurysm. 

 Thrombosis also results occasionally. 



Accessory spleens are very common in the gastro-splenic 

 omentum and other peritoneal folds connected with the organ. 



