THE NERVOUS SYSTEM. 833 



TUMORS. 



Tumors occurring in the nervous system may be of the types found 

 in the other organs or of types peculiar to nervous tissue. They may be 

 primary, or secondary to similar growths in other parts of the body. 



TUMORS OF THE BRAIN. 



Myxoma, fibroma, lipoma, and osteoma are rare forms of brain tumor. 



Neuroglioma Ganglionare. This is a form of tumor probably due to 

 disturbances in the development of the brain. It is peculiar to nervous 

 tissue and occurs in the form of circumscribed tumors or of diffuse en- 

 largements of portions of the brain. The pia mater over these tumors 

 is unchanged and the convolutions retain their shape. The tumors are 

 formed of neuroglia, in which are contained little groups of ganglion 

 cells (Ziegler). 



Glioma. This is the most common tumor of the brain, and like the 

 preceding is found only in the nervous system. It occurs with especial 

 frequency in children and young adults. Such tumors occur in all 

 parts of the brain, but they are found most frequently in the cerebrum. 

 There may be a single tumor, or there may be several such tumors in 

 different parts of the brain ; some of them attain a large size. Bramwell 

 reports a case in which considerably more than one-half of a hemisphere 

 was involved. These tumors may be sharply circumscribed, or merge 

 imperceptibly into the brain substance ; sometimes the tumor is arranged 

 so as to form the wall of a cyst which contains clear serum. They may 

 be white and hard; gray, soft, and gelatinous; infiltrated with small 

 haemorrhages or partly degenerated and softened. The centre of a gli- 

 oma may break down and become soft and necrotic or even fluid. In 

 this way a cyst is formed having a wall of gliomatous tissue. The brain 

 tissue around these tumors may be inflamed or uecrotic. These tumors 

 arise from the ueuroglia. The relative quantity of cells and fibrils varies 

 in different tumors. They are composed of neuroglia cells and their 

 delicate interlacing processes (for minute structure see "Glioma"). If 

 the tissue is of a loose formation with wide meshes between the fibres it 

 presents a myxomatous appearance, and has been described as myxo- 

 glionia. When the cellular elements are very numerous the tumor is 

 often referred to as a glio- sarcoma. In some cases the vascularity is such 

 a marked feature that the name of telangiectatic glioma is applied to it. 

 (According to Ziegler, a simple preponderance of cells, so long as they 

 are of the neuroglia type, does not warrant classing the tumor as a sar- 

 coma, and he insists that the latter term should be reserved for those 

 gliomata in which an active proliferation of the connective tissue of the 

 walls of the blood-vessels occurs. ) Osier reports three out of five cases 

 of gliomata as made up of large cells in contradistinction to the small- 

 cell variety. 

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