1. In serous meningitis a certain amount of clear fluid may escape and the brain surface may be only slightly congested. After removal of the bone and of the dura mater over the infected area the surface of the brain should be scarified in various directions to make certain that the pia-arachnoid has been incised, and fine drainage tubes should be inserted between the latter and the dura mater. In these cases a hernia seldom occurs, although the brain surface may bulge slightly into the wound.
2. In purulent meningitis the surface of the brain is usually covered with turbid fluid or purulent lymph, which may be localized to the site of the diseased bone, or may have spread from this point to a varying extent over its surface.
If the limit of the infection cannot be reached, in spite of removal of a considerable extent of bone and dura mater, all that can be done is to irrigate the exposed area with warm saline solution and to insert fine drainage tubes between the brain and dura mater, at the same time (as in the case of serous meningitis) incising the meninges in various directions.
3. Purulent lepto-meningitis is usually accompanied by encephalitis. If localized by adhesions an accumulation of pus may occur, forming an abscess on the surface of the brain, which also may be superficially ulcerated or necrosed. If there be intracranial pressure from encephalitis, the brain tissue usually protrudes as a dark, hæmorrhagic friable mass, in which shreds of necrotic brain tissue will be seen. In other cases, if there be no increased intracranial pressure and if the condition be quite localized, no hernia may occur, but the surface of the brain may be rough or eroded.
Any purulent secretion should be removed by irrigation, care being taken not to disturb the brain more than is necessary, so as to diminish the risk of breaking down the surrounding adhesions. A hernia may or may not form immediately. If no hernia takes place, it is wiser to do nothing further; that is, provided sufficient bone and dura mater have been removed to reach the limits of the infected area. Some authorities, however, consider that the necrosed portion of the brain should be curetted out. Although in other parts of the body the removal of necrosed tissue is a proper procedure, yet in the case of the brain there is considerable risk of setting up further œdema or septic cerebritis, the progress of which may have become arrested at the time of the operation.
If the inflamed brain tissue protrudes to an excessive degree during the operation itself, the opening in the skull should be enlarged, if it be not already of considerable magnitude, and the dura mater incised to the full limits of the opening. The protruding mass may then be cleanly excised by means of a scalpel. If, however, the brain tissue continues to prolapse, the wound cavity should be simply cleansed and protected by a dressing of sterilized gauze. If the encephalitis subsides, the hernia will not increase in size, and if the wound cavity be kept aseptic, it may gradually shrink.
After-treatment. This consists in covering the wound surface lightly with gauze so as to permit of free drainage, and changing the dressing as often as may be necessary.
In serous meningitis a large quantity of cerebro-spinal fluid may escape, and the dressings must be changed frequently. If recovery be going to take place, the temperature gradually becomes normal and the symptoms of meningitis disappear. In involvement of the posterior fossa, the head retraction gradually diminishes and after a few days free movement is noticed. Adhesions form rapidly, binding together the surface of the brain, meninges, and the overlying bone. For this reason the drainage tubes, already inserted between the dura mater and brain, can be removed within a day or two. The exposed dura mater usually becomes covered with granulations from which a certain amount of purulent discharge may be secreted. The duration of the after-treatment depends on the extent of the operation and the size of the wound. Eventually the skin flaps grow together and cover the brain, which afterwards may be felt pulsating through the scar. In these cases it is usually necessary to provide the patient with some protection, such as an aluminium plate.
If, however, a hernia forms and gradually increases in size, the brain should be explored again to see if another abscess can be discovered; or the lateral ventricle itself may be tapped in case of it being distended with fluid. Both these operations, however, must be looked upon as extreme measures.
If the patient otherwise recovers and a hernia still persists, the question arises what to do. Conservative treatment should first be employed, aseptic dressings being maintained, and slight pressure applied with compresses soaked in rectified spirits. If these measures fail, then the projecting portion of the hernia may be excised (see Vol. III).