Fig. 244. Diagram to show the usual Points at which the Lateral Sinus is primarily infected. A, High up; from the posterior mastoid cells. In this case it may not be necessary to tie the jugular vein. B, Low down; involving the jugular bulb. This necessitates ligature of the vein.
Indications. The sinus should always be opened as soon as it is certain that septic thrombosis has occurred.
Contra-indications. The only contra-indication for opening the sinus and removing the thrombus is the certainty that either the patient’s general condition will not permit of the operation being performed, or that the septic thrombosis has spread beyond the region from which it is possible to remove it.
For this reason, operation is unjustifiable if the patient is already suffering from septic pneumonia, pericarditis, or acute septicæmia; or, on the other hand, if there are symptoms of cavernous sinus thrombosis on both sides, or general meningitis. If, however, the patient’s general condition be good, operation may be attempted as a last resource even although a pulmonary empyema or a one-sided cavernous sinus thrombosis already exists.
Operation. After exposure of the lateral sinus, the next point to determine is the site and extent of the infected area (Fig. 244). On this will depend whether it will be necessary or not to tie the jugular vein in the neck.
The sinus is first exposed towards the jugular fossa until its surface appears normal for at least half an inch. It is wiser, however, always to expose the sinus as low down as possible. A strip of sterilized gauze is then pressed in between the bone and the outer wall of the sinus so as to obliterate its lumen at this spot. Instead of removing the bone from above downwards, the sinus may be exposed first at its lowest limit by chiselling directly through the tip of the mastoid process. In this way it can be obliterated by a strip of gauze before attacking the area of infection. The overlying bone is afterwards removed from below upwards until the thrombosed area is reached.
In removal of the bone from above downwards there is a certain risk of small particles of clot being dislodged into the circulation, or, if the sinus wall is injured, of hæmorrhage taking place if the thrombus at this particular point does not completely occlude the sinus. If, however, the sinus be first exposed and obliterated at its lowest limit, these risks are greatly minimized. There is no special technique in removing the bone beyond that already given in the description of the complete mastoid operation.
The next step is to expose the lateral sinus behind the infected area and follow it backwards until the dura mater appears normal for at least three-quarters of an inch. If necessary, the skin incision must be prolonged still farther backwards, in order to permit of removal of the bone overlying the transverse sinus, which may, perhaps, have to be exposed even to the torcular Herophili.
In removing the bone overlying the infected thrombus, the gouge and chisel should be used rather than the bone forceps or burr. With the latter there is greater risk of dislodging particles of clot into the circulation, owing to pressure of the instrument on the sinus wall.