Radical operation for cerebellar tumours.
Craniectomy may be regarded as the operation of choice in the exposure and removal of cerebellar tumours. The formation of an osteoplastic flap is contra-indicated (see [p. 29]). The operative procedures vary according as to whether it is desired to expose the one or both cerebellar hemispheres. Bilateral exposure, though presenting the great advantage of offering a larger field for exploration, is by far the more serious of the two operations.
Unilateral cerebellar exposure.
The patient being placed in the semi-prone or face-down position, the incision starts at the posterior border of the apex of the mastoid process, curves inwards along the superior curved line of the occipital bone to the occipital protuberance, and then passes straight down the middle line of the neck for 2 to 3 inches. If the incision is deepened at once to the bone, hæmorrhage is severe. The incision should first involve the skin and then the muscles attached to the occipital bone. Each vessel as encountered is clipped and tied. The flap must be turned down right up to the posterior margin of the foramen magnum.
The flap being held aside, the pin of the trephine is placed in such a manner that the disk to be removed will correspond to the thin central portion of the cerebellar fossa. The trephine, placed low down, is directed more or less towards the anterior fontanelle.
The disk being removed, the bone is freely cut away with rongeur forceps—outwards to the posterior border of the mastoid process, upwards to the curved line, inwards to near the middle line, and downwards to the posterior margin of the foramen magnum.
This generally completes the first stage of the operation, for, in cerebellar tumours, it is usually advisable to complete the operation in two stages. The scalp-flap is replaced, lightly sewn into position, and the patient sent back to bed.
A few days later the flap is again turned down, the dura incised, and turned down as a flap the convexity of which corresponds to but falls short of the line of the lateral sinus. The cerebellar substance is then examined and the tumour removed after the lines enumerated in dealing with cerebral tumours. Greater difficulty, however, is experienced in the attempted removal of cerebellar tumours, for the operator is working in a very confined space, and because the cerebellum tends to herniate through the adventitious hole in dura and bone. Two other factors must be taken into consideration: (1) the danger incident to all cerebellar operations of respiratory failure,[48] and (2) the friability of the cerebellar substance. Every care must be taken to avoid unnecessary damage of the brain-matter.
When the tumour is situated in the cerebello-pontine angle, a somewhat favourite site for tumour formation, ‘lateral displacement’ of the cerebellum towards the middle line will aid considerably in the exposure. A flat retractor, bent to a suitable curve, is introduced between the dura and the cerebellum, and the brain-matter gently but firmly retracted towards the middle line. As the brain yields to the pressure the tip of the retractor is insinuated towards the posterior surface of the petrous bone. With the aid of a head-lamp a good view may usually be obtained of the region involved, and, as the tumour is but lightly attached, its removal can be undertaken.
The dura is then carefully sutured and the scalp-flap accurately replaced, deep sutures for the muscles and a few surface sutures for the skin. Drainage should be avoided whenever possible—the discharge of cerebro-spinal fluid is fraught with considerable danger. The gap in the skull requires no other protection than that afforded by the mass of neck muscles.