Part 70 (1/2)

In this connexion must be mentioned--(1) Serous meningitis: a name given to an increase of the cerebro-spinal fluid within the subdural or subarachnoid s.p.a.ce, or the ventricles, the hypersecretion being probably caused, as Merkens suggests (_Deutsche Zeitsch. fur Chir._, vol. lix), by the toxic infection induced by the suppurative focus in contact with the external surface of the dura mater. The symptoms of serous meningitis may closely simulate an intracranial abscess or a purulent meningitis, except that frequently there is no pyrexia. (2) Purulent meningitis, which may be diffuse or localized. (3) Pseudo-meningitis: that is, a condition simulating meningitis but in reality due to irritation of the meninges as a result of suppuration still confined within the temporal bone--for example, the result of acute middle-ear suppuration in infants.

Clinically it is often difficult to determine before operation which variety is present.

=Indications.= Operation is indicated as soon as the onset of meningitis has been diagnosed and should be performed without delay. Waiting for all the cardinal symptoms of meningitis to occur will never save life.

The only possibility of doing so is to operate while the inflammatory process is still localized. At the same time it must be recognized that whenever symptoms of meningitis occur the prognosis is most serious.

Lumbar puncture should always be performed as an aid to diagnosis. If the cerebro-spinal fluid be clear and sterile, diffuse meningitis can usually be excluded, although at the same time it must be remembered that it does not negative a localized meningitis without increased intracranial pressure. Increased flow of cerebro-spinal fluid indicates increased intracranial pressure, perhaps the result of serous meningitis. Slight turbidity suggests early purulent meningitis, especially if bacteria are present, but not necessarily that the case is hopeless. If the fluid be definitely purulent, operation may be considered out of the question; a case, however, has been recorded in which recovery took place.

The value of cytological examination of the fluid is still doubtful.

Marked increase of polynuclear cells is said to point to acute and intense inflammation, whereas an abatement of the polynucleosis may be taken as a sign of diminution of the meningeal irritation. With this, increased leucocytosis, increasing as recovery progresses, may be looked upon as a hopeful sign.

If it be obvious that the patient is dying, not only from the local infection but also on account of general septic absorption, operation, of course, is excluded. Similarly, at the present time, post-basic meningitis of infants is rightly deemed inoperable.

=Operation.= Although no set operation can be described, the principles of the operation are to expose the infected area widely so as to allow of free drainage and, at the same time, to relieve intracranial pressure. The extent of the operation will therefore depend largely on what is found during the course of the operation itself.

1. In an infant or young child, if the symptoms develop in the course of an acute ot.i.tis media, the tympanic membrane should first be inspected to see if there is sufficient drainage. If not, it should be freely incised, and opening of the antrum and mastoid may be delayed for at least twelve hours.

2. In an adult, immediate exploration of the mastoid and antrum is indicated on the onset of meningeal symptoms, even although they occur during the course of an _acute_ middle-ear suppuration.

If the symptoms of meningitis in these cases be as yet indefinite, and if pus be found under tension within the mastoid cavity, or if an extra-dural abscess exists, the dura mater should not be incised at once, but a delay of twenty-four hours should be advised; in many cases complete recovery will take place. If, however, the symptoms continue, intracranial exploration will be necessary.

3. In chronic middle-ear suppuration, meningitis is usually secondary to, or accompanies, other intracranial complications or internal-ear suppuration, the symptoms of which it may mask.

After performing the mastoid operation any tract of carious bone is followed out to its limits.

According to what he finds, the surgeon may first expose the dura mater covering the lower portion of the middle fossa (Fig. 243), or of the posterior fossa behind and in front of the lateral sinus; these are the usual sites of infection. The removal of bone must be free, in order to get well beyond the limits of the infected area, if possible. The dura mater is incised to the limits of its exposure either crucially or by cutting it through in the form of a large flap.

The dura mater is usually congested, but if an extra-dural abscess or lateral sinus thrombosis be present, it may be thickened and of a leathery appearance; or in the latter case almost gangrenous.

The further steps depend on the conditions met with on incision of the dura mater.

[Ill.u.s.tration: FIG. 243. METHOD OF REMOVAL OF BONE BY THE FORCEPS. In this instance the bone is being removed above the tegmen tympani in order to expose the lower portion of the middle fossa.]

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 acc.u.mulation 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, haemorrhagic friable ma.s.s, 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 dema 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 ma.s.s 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 quant.i.ty 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.