After the sinus has been exposed well beyond the region of the thrombus, the bone forceps may safely be used, especially in exposure of the transverse sinus; and this is a much more rapid method than removing the bone by means of the gouge and mallet. To prevent the inner blade of the forceps from nipping the sinus wall between it and the bone, the dura mater forming the outer wall of the sinus should be separated from the overlying bone by means of a dura mater separator. In the region of the infected area the sinus wall may be adherent to the bony wall as a result of the inflammatory adhesions, and, in addition, may be extremely friable and so easily torn through.
In exposure of the sinus two points should be remembered: firstly, that it is sometimes difficult to differentiate it from the dura mater covering the temporo-sphenoidal lobe above and the cerebellum below; and secondly, that the transverse sinus is a very much broader vessel than is imagined, being even half an inch in width. Not much force is required to obliterate its lumen, but care must be taken to pack the gauze evenly across its whole width.
Fig. 245. The Lateral Sinus exposed and opened. The lumen of the sinus is obliterated above and below the region of the infected thrombus by plugs of ribbon gauze pressed in between the sinus wall and the overlying bone. In this case it is not necessary to tie the jugular vein.
After the sinus has been occluded above and below the area of infection, it should be incised with a small knife along its whole length between the obstructing plugs of gauze (Fig. 245). If there be bleeding, it may be due to the sinus being obliterated incompletely, or it may come from the superior petrosal sinus. To find out where the bleeding comes from, the finger should be pressed upon the sinus at its upper and lower limits, close to the obstructing plugs of gauze. If the bleeding stops, it shows that the sinus has not been obliterated completely; this can now be done by further plugging with gauze. If, in spite of this, bleeding still continues, it presumably comes from the petrosal sinus.
All clot and granulations are now rapidly curetted out and the lateral sinus plugged with gauze. After a moment the gauze is withdrawn and another small piece is pressed into the lateral sinus at the point of entrance of the petrosal sinus. After the bleeding has been arrested, the outer wall of the lateral sinus is excised by cutting it away with blunt-pointed scissors. The interior of the sinus is then inspected, special attention being given to the lower portion to see if its lining is normal. If this be not the case, even if there be no signs of thrombosis, it means that the surgeon has failed to get well below the infected area, and therefore the internal jugular vein must be ligatured. If, however, it be normal, the gauze plug already placed between the sinus wall and the overlying bone is left undisturbed.
If there be no bleeding from the sinus (excepting a slight amount from the blood contained within the isolated portion), the thrombus is curetted out and the inner surface of the sinus inspected. After excising the outer wall, search is made for the superior petrosal sinus, which presumably is thrombosed, although perhaps only by normal clot. To expose this tributary, which enters the lateral sinus at the point at which it turns downwards to form the sigmoid sinus, bone must be removed in front of the lateral sinus along the angle forming the roof and inner wall of the mastoid and antrum; that is, along the superior margin of the petrosal bone. If the inner surface of the lateral sinus in its neighbourhood be normal, nothing need be done. If, however, the sinus wall be infected, the petrosal sinus should be followed out, if possible, its outer wall being incised and the clot removed, bleeding being afterwards arrested by pressure.
As a final step, the gauze plugging which still obliterates the lumen of the sinus in its upper part is removed. If the sinus be normal at this point, free hæmorrhage will occur; this is arrested at once by again introducing a strip of gauze between the sinus and the bone. Although during the earlier stages of the operation the inner lining of the posterior portion of the sinus may have seemed to be normal, yet it occasionally happens that hæmorrhage does not at once occur on removing the plug of gauze; but after a moment or two a long smooth clot, gradually tapering at its end, may be shot out from the opening within the sinus, being followed by a gush of blood. The terminal portion of this clot is non-infective and of recent formation. Its appearance is always a matter of satisfaction, as it means that the sinus has been freely exposed and opened behind the infected area.
If on exposure of the sinus it be found that the clot extends so low down that it will be impossible to obliterate the sinus well below the infected area, the jugular vein should be ligatured at once before interfering further with the sinus from the mastoid wound.