PATHOLOGY OF PINEAL TUMOURS 433 



Pinealomata : the other main type is that which more closely approxi- 

 mates to the adult or mature type of pineal. They are slower in growth 

 and less invasive. Haemorrhages and cysts are less common. Micro- 

 scopical section shows an alveolar pattern ; the cells are chiefly of the 

 large vesicular type, and are separated by strands of fibrous tissue. 



Thus we see the importance of recognizing the developmental stages 



P.M 



c.t. cap. 



Fig. 285. — Section through Pineal Body showing a Central Cavity, the 

 Wall of which is stained deeply and contains numerous Corpora 

 Arenacea. 



Art. : artery. 



Cav. : central cavity. 



C. Ar. : corpora arenacea. 



c.t. cap. : connective tissue capsule. 



Ep. : ependyma. 



gl. sh. : glial sheath. 



Pig. : pigment. 



P.M. : pia mater. 



Ps. Ep. : pseudo-epithelium. 



V. : vein. 



ves. : vessel. 



(Drawn from a specimen in Professor Barclay-Smith's collection at King's College, 



London.) 



through which the pineal passes when attempting to understand the 

 histology of these tumours. 



General Changes. — The associated changes in the brain are due to 

 direct displacement and invasion of the brain substance. The cerebellum 

 is often invaded. The growth extends beneath the tentorium and invades 

 the cerebellum both in the midline and in either of the lateral lobes. 



The midbrain is pressed upon, and especially the corpora quadri- 

 gemina. This distortion gives rise to the characteristic eye signs and 

 may also occlude the aqueduct of Sylvius. Occlusion of the aqueduct 

 may also be brought about by direct invasion of the third ventricle by 

 the growth. The outcome of these changes is that the whole ventricular 



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