the bone should begin with a width of about 1.5 to 2 cm., but this aperture may be widened if it is necessary to enter very deeply. The external opening should be immediately behind, and its center 2 or 3 mm. below the level of the upper wall of the meatus. The upper border must be below the linea temporalis. The anatomic anomalies to be feared are protrusion of the sigmoid fossa (lateral sinus) toward the antrum or low level of the middle cerebral fossa. The lateral sinus, generally a trifle lower on the right than on the left side, is usually fully 1 cm. behind and slightly above the posterior upper wall of the meatus. The more pneumatic the bone structure, the greater the probability of a normal distance between meatus and sinus; the more compact the bone, the more likely is a dangerous proximity of the sinus to the meatus (see Figs. 87, 89, 104 to 107). In extreme cases there may only be a distance of 5 mm. or even a trifle less separating the two. The exposed sinus, if normal, appears as a bluish-gray vessel, the walls of which can be easily indented by the probe. The danger of wounding the lateral sinus is least if the chisel is only directed downward and (alternatingly) forward after the first few external strokes. The shallowness of the wound is favored by resecting the external portion of the posterior wall of the bony meatus by chiseling in a forward direction. It should be the aim to enter the antrum at its lowest level. As soon as the antrum is exposed, any intervening spongy bony substance can be more safely scooped out with a curet. But if the apex of the conic hole is lower than the center of the meatus, the antrum will generally be missed. In young children the first few strokes of the chisel suffice to break down the thin external wall. In adults 12 to 15 mm. is the average depth of the requisite hole in the bone as measured from the spina supra meatum, a short spur at the upper posterior angle of the entrance of the exposed bony meatus, a landmark present in about three-fourths of all subjects. Measured from the external surface of the mastoid bone

itself, the distance is more variable. As soon as this distance is exceeded, the utmost caution is required in order not to wound the facial nerve or the external semicircular canal. When the antrum is not reached at this depth, careful measurements should be made of the depth of the meatus up to the membrana tympani, and if at

FIG. 133.-Operative exposure of the mastoid antrum in a moderately pneumatic process. Appearance after completed operation and before closure of the wound.

the corresponding distance from the surface of the mastoid the antral cavity is not found, the operation should be abandoned. It is a singular and not yet explained fact that a number of cases with urgent symptoms have done well after such incomplete operations in which the diseased cavity was not reached (Fig. 133).

The bleeding on cutting the soft parts varies with their congestion, as also does the bleeding from the bone. When the antrum is filled with granulations, these bleed very profusely until thoroughly scooped out. When the sinus is accidentally wounded, a big gush of venous hemorrhage occurs, which can be controlled by pressure with gauze. This accident has usually proved harmless in the end, but it may necessitate temporary abandoning of the operation until a firm clot has formed after a few days. Very few deaths have ever occurred from the entrance of air into the opened sinus. Should the cerebral plate be damaged and the dura exposed, no evil consequences result, as a rule, if the operation is done aseptically and all sharp spiculæ of bone are carefully removed. As in all major operations, all details regarding asepsis of instruments, the hands of the surgeon, and of the field of operation should be rigidly carried out. The hair should be shaved far beyond the wound, and the head inclosed in sterile towels or a rubber cap. The instruments required are scalpels, scissors, several forceps, needles, and ligature threads, two retractors, a periosteum elevator, a set of chisels, a hammer, two sizes of sharp curets, and a few artery forceps. The several steps may be summarized as follows:

General anesthesia; incision down to the bone, 1 cm. behind and parallel to the auricle, from its tip to the end of the mastoid process. If this is insufficient, a short posterior transverse cut is made above the middle of the wound. Arrest of bleeding by compression, artery forceps, torsion, and occasionally a ligature. Blunt detachment of the periosteum, both forward and backward. Chiseling of the bone with successively smaller chisels, at first from the entire periphery toward the center of the wound, but subsequently only in the forward and downward direction, and merely upward from the lower edge with care. The chiseling should extend through the posterior wall of the meatus, at least in the external half. If a carious fistula shows the way, this path should be followed by goug

ing. As soon as the antrum is reached, the granulations usually present are scraped out with the curet, and the bony channel is smoothened with the same tool. The purulent infiltration must be followed as far as it extends. In some instances it is necessary to gouge out the contents of the entire mastoid process through the pneumatic cells to the tip. It is best to remove any overhanging thin cortical shell of bone. The bleeding stops soon after emptying the antrum. In recent cases syringing is uncalled for. When there is retained and foul pus, it is better to irrigate with sterile salt solution. There may be or may not be at the time communication between the antrum and the tympanic cavity, with escape of the fluid through the meatus. in the bone with iodoform gauze. above and sometimes below the pad is put over the wound. Meanwhile the ear has been filled with a fresh sterile gauze drain, whereupon the dressing is completed.

Packing of the wound Suture of the soft parts drain. A large gauze

When a carious spot is found leading into some cells below the antrum, and on scooping them out nothing points to involvement of the antrum itself, the operation may be finished at this point, provided the clinical signs did not clearly indicate empyema of the antrum.

371. The first dressing may be left as long as five days if neither pain, rise of temperature, nor excessive discharge calls for its removal. The subsequent dressings should also be changed only at the longest intervals proper. The patient is kept in bed for a few days until comfortable. When afebrile from the start, the operation should cause either no rise of temperature or only a transient mild aseptic fever. After a properly done operation the discharge from the ear ceases very speedily. discharge from the wound rarely disappears in less than two to three weeks, and sometimes as much as six or eight weeks are required, if the wound is not wide enough externally. It is often difficult to keep the wound open, and the gauze drain should not be dispensed with until

The

the wound is dry. When the discharge remains offensive, which is very rare, it is better to depend on accurate tamponing than on syringing. Attempts have been made to close the wound by a complete suture and to let it heal under a blood-scab. Although this may often be successful in the hands of a thoroughly competent surgeon, it involves considerable risk. It is proper, however, in the case of an incomplete operation in which the antrum is not reached. When the diminished discharge does not require a voluminous dressing, a serviceable form of band

age is the one shown in Fig. 134, which is kept from becoming distorted by the insertion of whalebone at its two edges, while the bands of tape prevent it from slipping.

The mortality of mastoid operations is below 8 per cent. in recent years; in some published series of cases even very far below this figure or nearly zero. The majority of deaths are due to the extension of neglected disease, and only a small proportion of the accidents can be ascribed to the operation. The mortality of mastoiditis without operation is not known, but must be very high.