Opening of a temporo-sphenoidal abscess. A temporo-sphenoidal abscess may be explored either through its lowest point, that is, through the roof of the antrum and floor of the middle fossa, or through its outer wall just above the zygomatic ridge. To obtain a view of the roof of the antrum and mastoid cavities, the head of the patient should lie almost flat on the operating table and be turned well over to the opposite side. The bony roof of the antrum and mastoid is removed by means of the gouge and mallet, and so expose the dura mater covering the floor of the middle fossa (Fig. 252). If a fistula communicates with the antrum cavity and the middle fossa, the bone surrounding it is first attacked. In removing the bone, it must be remembered that the tegmen tympani is exceedingly thin, and unless care is taken pieces of bone may be pressed inwards on to the overlying dura mater. Sufficient bone should be removed to determine whether the dura mater is normal or not. To do this it may be necessary to chisel away the tegmen tympani outwards until the squamous portion of the temporal bone is reached, after which a pair of bone forceps may be used until a sufficient opening is obtained.
The condition found on examination of the dura mater varies. In many cases it is congested or covered with granulations at the site of the infection, and usually it is adherent to the underlying bone. At other times it seems normal.
Increase of the intracranial pressure, as shown by the bulging outwards of the dura mater, and absence of pulsation are suggestive of an abscess. These signs, however, are not conclusive, as on the one hand increased intracranial pressure may be due to other causes and on the other it is quite possible to have pulsation if the abscess be small and deeply placed.
If an extra-dural abscess be present, the intracranial cavity should not be explored at once unless this is absolutely necessary, but this step of the operation should be delayed for at least twenty-four hours. If, however, immediate operation be necessary, special precautions must be taken to render the part as aseptic as possible, and a fine layer of gauze should be packed between the margin of the bone and the dura mater in order to prevent further infection of the brain or meninges. In an uncomplicated case only sufficient bone should be removed to permit of the insertion of a large drainage tube; that is, the dura mater should not be exposed over a larger area than the size of a shilling.
If there be disease of the tegmen tympani and the symptoms point to a temporo-sphenoidal abscess, the brain should be explored through this opening in the bone (Fig. 252), as the abscess is thus not only drained through its most dependent part, but also through its stalk.
If, however, the diagnosis be doubtful, the temporo-sphenoidal lobe may be explored through a fresh opening, just above the tegmen tympani. This will diminish the risk of septic infection from the mastoid cavity. After the dura mater has been exposed sufficiently a small incision is made in it, taking care to avoid wounding any of the vessels. With a pair of forceps the cut edge of the dura mater is drawn outwards and the incision is prolonged in each direction with a pair of blunt-pointed scissors. Similarly, the dura mater is cut through at right angles to the primary incision, so that four small flaps are made and turned back so as to expose the outer surface of the brain.
As a rule the dura mater, arachnoid, and pia mater are fused together by inflammatory adhesions, so that from a practical point of view they need hardly be considered as separate structures. Similarly, at the site of infection, the point of the so-called stalk of the abscess, the cerebral membranes are adherent to the underlying brain, especially if there has been any localized meningitis. For this reason it is sometimes necessary to peel away the dura mater from the brain, in order to expose the latter.
As a rule, very little fluid escapes: if present in considerable quantity, and if it escapes from between the dura mater and brain, it is an unfavourable sign, as it generally signifies early meningitis.
If meningitis be present, purulent lymph or secretion may be seen on the surface of the brain, either localized or spreading from the site of the infection.
If the intracranial pressure be great, the brain will bulge through the opening in the dura mater. If the abscess be very large and situated superficially, the thin layer of brain substance forming its outer wall may rupture as soon as an opening has been made in the dura mater. Sometimes, indeed, the pus may be seen to ooze through an opening in the dura mater, which may be found to communicate with the abscess cavity.