After the hernia has disappeared and the wound is aseptic, steps should be taken to close the gap in the skull. This may be done by an osteo-plastic operation in which a flap, comprising a segment of the outer table, is raised from an adjacent part of the skull and placed in the gap; or by transplanting a portion of periosteum-covered bone from the scapula, tibia, or other suitable source. An alternative method is to implant a plate of celluloid, silver or other metal, or a portion of the fascia lata, in the gap. When a permanent hole is left in the bone, the patient should wear over it a leather or metal shield to protect the brain.
The protrusion of brain resulting after a decompression operation deliberately performed for the relief of intra-cranial tension, unless it becomes infected, has nothing in common with a hernia cerebri.
Surgical Affections of the Cranial Nerve
Irritation, or paralysis, of one or more of the cranial nerves may result from lesions implicating their centres or trunks.
When the trunk of the nerve is affected, the paralysis is on the same side as the lesion, and is of the lower neurone type; when the cortical centre or the upper axons are involved, it is on the opposite side, and is of the upper neurone type ([p. 334]). The lesions of the cerebral centres with which nerve symptoms are most frequently associated are: laceration of the brain, hæmorrhage, meningitis, tumour, and syphilitic gumma.
The nerve-trunks may be contused or torn across, especially in basal fractures which traverse their foramina of exit; blood may be effused into their sheaths as a result of injuries not attended with fracture; or they may be pressed upon by an inflammatory effusion, a tumour, a gumma, or an aneurysm invading the base of the skull. When the nerve is merely contused, or pressed upon by blood-clot, the paralysis tends to pass off in the course of a few days. When it is torn across, or compressed by a new growth, the paralysis is permanent. In some traumatic cases paralysis does not come on until a few days after the injury, and is then due either to gradually increasing pressure from blood-clot, or more probably to the onset of meningitis or of ascending neuritis.
I. The branches of the Olfactory Nerve may be ruptured as they pass through the cribriform plate in fractures implicating the anterior fossa of the skull, and there results complete and permanent loss of smell (anosmia). Hæmorrhage into the nerve sheath or contusion of the nerve may cause a transitory loss of smell. The trunk of the nerve may be implicated also in tumours and meningitis in the anterior fossa. In all cases in which anosmia results there is also interference with the power of recognising different flavours, thus greatly impairing the sense of taste.
II. Optic Nerve.—Temporary paralysis of one or both optic nerves is a comparatively common result of traumatic effusion of blood into their sheaths; the resulting blindness may pass off in a few days, or may last for some weeks. When a large effusion takes place, the prolonged pressure on the nerve may result in optic atrophy and permanent blindness. Complete severance of the nerve by a bullet, the point of a sharp instrument, or a fragment of bone, results in loss of sight in the eye on the same side. In cellulitis of the orbit, intra-orbital tumour, gumma and aneurysm in the region of the cavernous sinus, also, the optic nerve may be implicated.
Lesions implicating the cortical centre for sight in the occipital lobe give rise to hemianopia—that is, loss of sight in the lateral halves of the fields of vision of both eyes—colour-blindness, subjective sensations of light and colour, and other eye symptoms.
Double optic neuritis, followed by optic atrophy, is one of the most constant effects of the growth of a tumour within the skull, and is not uncommon in cases of cerebral abscess and meningitis. Pressure on the optic chiasma, for example by a tumour of the pituitary body, is associated with bilateral temporal hemianopsia.