1. In an infant or young child, if the symptoms develop in the course of an acute otitis 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.
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.
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.