The temporal fascia is next incised—slightly below the line of the skin incision. Finally, the temporal muscle is divided—again at a lower level than the fascial incision. Skin, fascia, and muscle are then turned down to a zygomatic base. Some surgeons split the temporal muscle in the direction of its fibres, a course, however, that tends somewhat to cramp the operative field.
The trephine is applied to the bone, the surgeon aiming at striking the angle between the anterior and posterior branches of the middle meningeal artery. The bone-disk is removed. With the aid of craniectomy forceps the bone is nibbled away, more especially in the downward direction towards the base of the skull. It is essential that the operator should get down as low as possible, for the lower the line of attack the easier the approach to the ganglion and the less the damage incurred by the brain (from retraction).
The opening in the bone, oval in shape, should present a diameter in the vertical direction of about 1 to 11⁄4 inches, and an antero-posterior diameter of about 11⁄2 inches.
The dura is stripped away from the base of the skull, partly with the fingers and partly with the blunt dissector, and a flat, slightly malleable retractor introduced along the floor of the middle fossa, the dura and overlying temporo-sphenoidal lobe being gently lifted upwards. The surgeon should take upon himself the responsibility of retracting the brain, holding that instrument with the one hand and working inwards with the other, directing his course towards the foramen spinosum (middle meningeal) and foramen ovale (third division of the fifth nerve).
During this stage hæmorrhage, derived mainly from the branches of the middle meningeal, is often troublesome. It may be controlled by the insertion of dry or wet gauze—in the latter case the gauze is soaked in saline solution or sterilized water (at a temperature of about 110° Fahrenheit)—or by the introduction of cotton-wool plugs to each of which a silk thread is attached, for the purpose of facilitating their final removal.
The middle meningeal artery acts as a guide to the foramen spinosum, a foramen that lies immediately posterior and external to the foramen ovale. In many cases the position of this artery so hampers the operator in his manipulation that ligature is demanded. For this purpose Cushing’s silver ‘clips’ will be found most serviceable. One clip is applied to the artery immediately after its entry into the skull, the other a short distance above, the vessel being divided between the two (see [Fig. 6]).
The foramen ovale is then identified, the dura being stripped away from the nerve trunk by blunt dissection. The surgeon then works inwards and forwards to the second division of the nerve and its foramen, the foramen rotundum. Hæmorrhage, in this case derived from emissary veins, may again be troublesome. Considerable perseverance is required, and, although each attempt at further separation of the dura from the bone entails more oozing, the difficulties—except in the most exceptional cases—may be overcome.
The second and third divisions may now be resected. For this purpose it is essential that the two nerves should be exposed from the point of their exit from the skull right up to the margin of the ganglion. Their dural coat seldom requires to be incised with the knife, the membrane being readily stripped away with the blunt dissector. When fully exposed, the nerve trunks are picked up with a blunt aneurysm needle and divided in two places, flush with the basal foramina and close up against the ganglion. The intermediate parts are removed.
To prevent regeneration of nerve fibres—with consequent return of symptoms—the basal foramina are blocked up with small ivory pegs—well driven home—or with amalgam.
All gauze plugs are removed, the field of operation well dried, and dura and brain allowed to fall back into position. The wound is closed, if possible without drainage. In the event of considerable oozing a cigarette drain should be inserted for twenty-four hours. The scalp-flap is sewn up, skin, muscle, and fascia being united separately.