A, Zygomatic ridge; B, Spine of Henle: behind and above it is the suprameatal triangle; C, Fibrous portion of cartilaginous meatus, not separated from bony. (In this and the following diagrams the gouge or chisel is drawn small. In actual practice they may be much larger.)
Exposure of the field of operation. The periosteum and overlying soft tissues are then reflected forwards and backwards with a rugine, until the following points are brought into view: namely, the upper posterior margin of the bony meatus (taking care not to separate the fibrous from the bony portion of the meatus) and Henle’s spine in front, the zygomatic ridge above, and the fibres of the sterno-mastoid muscle below (Fig. 217). The tip of the mastoid process should just be seen. To do this it may be necessary to cut away some of the fibres of the sterno-mastoid muscle.
If the surgeon has two assistants, the duty of one of them is to hold apart the edges of the wound by means of retractors, whilst the other is employed in keeping the wound dry. If there be only one assistant, the edges of the wound may be held apart by metal retractors.
Careful examination of the field of operation should now be made. There may be no external signs of disease. As a rule, however, as a result of the inflammatory process having already extended to the surface, the periosteum is found to be much thickened, with extreme vascularity of the underlying bone, or there may be a subperiosteal mastoid abscess of varying size.
Excepting in infants, in whom pus may escape through the squamo-mastoid suture, a subperiosteal abscess is always secondary to a fistula in the bone, which is usually situated over the body of the mastoid process just behind the suprameatal triangle. It may, however, occupy some other position.
In the case of Bezold’s mastoid abscess (see [p. 389]), although no fistula may be seen on the surface of the bone, pus may be found to well up from beneath the mastoid process on cutting through the fibres of the sterno-mastoid muscle. In other cases there may be actual necrosis of the bone, as a rule involving the lower margin of the squamous portion of the temporal bone (see [p. 390]).
The method of opening the antrum in a straightforward case will first be described.
Fig. 218. Schwartze’s Operation. Showing exposure of the antrum. Note sloping position of gouge in removal of bone in region of lateral sinus.
Opening the antrum. The approximate surface marking of the antrum is the suprameatal triangle and the region just behind it, which, however, as has been mentioned, is an uncertain guide. It is wiser, therefore, in all cases of operation on the mastoid process to assume that the case is one in which the lateral sinus extends far forward and is superficial, and that the middle intracranial fossa is low lying.