Localised hæmorrhages also occur, although less frequently, in the crura cerebri, the pons, the floor of the fourth ventricle, and the cerebellum. In these situations they usually prove fatal by causing rapidly advancing coma and interference with the respiratory and cardiac centres. The temperature immediately rises to 106° or even 108° F., and a modified form of Cheyne-Stokes respiration is present.
(3) Still more gross lesions, in the form of distinct lacerations, are comparatively common at the tips of the frontal, temporal, and occipital lobes, on the surface of the cerebellum, and at the base of the brain. These are usually associated with symptoms of compression in its most typical form, and as a rule prove fatal. The grey matter is torn, and extensive effusion of blood takes place into the brain substance, and on the surface, filling up the sulci, and distending the arachno-pial space ([Fig. 184]). In a compound fracture, brain matter may be extruded through the opening in the skull.
(4) The extravasated blood may burst into the lateral ventricles, in which case the pulse becomes small and rapid—130, 160, or even 170. The respiration also is rapid—45 to 60—and greatly embarrassed, and the temperature suddenly rises to 103° or 104° F., and continues to rise till death ensues.
(5) Traumatic Œdema.—It is not uncommon for a diffuse œdematous infiltration of the brain substance or of the arachno-pial membrane to take place in the vicinity of the injured portion of brain. This serous exude, on account of the natural adhesions of the arachno-pia, usually remains limited to the damaged area, but it may become generalised.
Mechanism.—The explanation of these widespread hæmorrhages is to be found, according to Duret, in the disturbance of the cerebro-spinal fluid which accompanies a severe blow on the head. This fluid not only surrounds the brain, but it also fills the ventricles, and permeates its substance in every direction in the peri-vascular and perilymphatic spaces. As the brain tissue is incompressible, if an area of the skull is momentarily depressed by a localised blow, space is provided for it by displacement of a quantity of cerebro-spinal fluid, which sets up a fluid wave, and this by hydrostatic pressure increases the tension of the fluid throughout the entire brain. Vessels may be lacerated at any point, either by the flow of this wave or during the ebb which follows the recoil. Hence it is that the lesion is not always at the seat of impact, but may be at the opposite side of the skull or at other remote points.
Fig. 184.—Contusion and Laceration of Brain. Note limited lesion at point of impact on left side, and more extensive damage at point of contre-coup on right.
(After Sir Jonathan Hutchinson.)
Repair.—As the disintegrated brain matter is replaced by cicatricial tissue, neither the nerve cells nor the fibres being regenerated, the loss of function of the parts destroyed is usually permanent. A localised extravasation of blood may become encapsulated, and constitute a “hæmorrhagic cyst.” We have experimentally confirmed Duret's observations and agree with his conclusions.