of the brain. It is partly with this object that the bone is replaced after trephining. Some surgeons also introduce between the edges of the opening in the dura mater and the brain a piece of gold-foil, or other unirritating thin material, larger in area than the opening in the dura, so as to prevent the two surfaces from coming in contact and adhering. In operations carried out in this manner, hernia cerebri should not occurespecially if the dressing is arranged so as to form a support during healing.

When a hernia of this type has occurred, it is usually sufficient to wait for the subsidence of the oedema, keeping up pressure over the orifice in the skull in the meanwhile; as a rule the hernia will recede in the course of a few days. Should it not do so, the cause is usually too small an opening in the dura mater or adhesion between the latter and the brain.

FIG. 175. ASEPTIC HERNIA CEREBRI. A shows the true primary aseptic form
which occurs after an operation in which there is a defect left in both scalp and dura
mater, which is represented by the thick line. B shows an aseptic hernia cerebri which
is secondary to an increase in the intra-cranial pressure, e.g. from œdema.
The scalp
wound has healed, but the pressure has caused the incision in the dura to give way
and the brain protrude beneath the scalp.

Under such circumstances it may be advisable to turn down the flap again-after the lapse of four or five days-enlarge the opening in the dura mater, and separate any adhesions between its margins and the brain, so as to allow the protrusion to recede into the cranial cavity. After the opening in the dura mater has been enlarged, it is well to incorporate in the dressing a plate of sterilised block tin, or other firm material, rather larger than the opening in the bone, and to keep it in place by an elastic bandage. This will support and prevent increase in the size of the protrusion and lead to its gradual return into the cranial cavity.

CASES IN WHICH THE PARTS HAVE BEEN EXPOSED TO
SEPTIC CONTAMINATION.

(a) In some cases the hernia cerebri occurs at the time of the injury. This is practically a primary hernia cerebri because it occurs before septic

changes have occurred, and only differs from the preceding type in that there is a likelihood of the wound becoming septic.

(b) In other cases, the hernia cerebri occurs two or three days after an operation or injury. This is a much more severe form, and is sometimes spoken of as secondary hernia cerebri.

In this form of hernia cerebri the protrusion of the brain is due to its surface becoming infiltrated with inflammatory exudation and to increase in the intra-cranial pressure from the congestion of the brain beneath. The protruded portion usually contains little cerebral matter, and is mainly composed of granulation tissue with lymph and pus infiltrating it. Suppuration generally occurs on the surface of the hernia, and in some cases, especially when the swelling continues to increase, a collection of pus will be found in its interior,

or even extending into the cranial cavity and forming a superficial cerebral abscess (see Fig. 176).

These secondary hernia vary in size and are generally somewhat mushroom-shaped, for they expand after emerging through the opening in the skull. They are usually very vascular, and have a somewhat constricted pedicle corresponding to the opening in the dura mater. They are covered with granulations which discharge pus freely, and are often gangrenous in patches. Pressure over them may lead to convulsions. A spontaneous cure sometimes results either from gradual cicatrisation of the whole mass, or from gangrene of the herniated portion and cicatrisation of the pedicle. As a rule, however, the condition is followed by septic inflammation of the deeper parts of the brain leading to cerebral abscess, by lepto-meningitis, or by pyæmia.

FIG. 176.-SECONDARY' SEPTIC HERNIA CEREBRI. There is a gap in the skull and the scalp, through which protrudes a mass of septic granulation tissue and brain matter forced out by the increased intra-cranial tension due to inflammation and suppuration (the dark area) in the brain.

TREATMENT.-(a) Of hernia occurring at the time of the injury.— In these cases two conditions favouring the occurrence of hernia cerebri have to be dealt with: namely, the opening in the skin is usually over the hernia, and the parts have, moreover, been exposed to infection. The treatment of a compound fracture of the skull has already been described on p. 342, and it is unnecessary to repeat what has been said there. When protrusion occurs, the best treatment is to see that the base of the hernia is not constricted, and then to cover the protrusion

completely with a piece of Lister's protective or gold-foil, and apply outside that the ordinary gauze dressings in which a piece of block-tin is incorporated and kept in position by means of an elastic bandage. This dressing will require changing daily; if infection does not occur, the hernia may gradually recede, and entirely disappear in a week or ten days. As soon as the hernia has receded sufficiently, an attempt may be made to close the wound; a flap of skin can usually be brought over the opening in the skull, and any raw surface left by raising the flap can be covered by skin-grafts (see Vol. I. P. 52).

(b) of herniæ occurring two or three days after an operation or injury.— The object of treatment in this group of cases should be to render the hernia aseptic, if possible, and then to prevent further protrusion. The surface of the protrusion should be shaved off; there need be no hesitation in removing a considerable portion, seeing that it contains very little healthy cerebral substance. After the bleeding has been arrested by pressure and before any adhesions are separated, the raw surface is thoroughly swabbed with undiluted carbolic acid. It is important to disinfect the surface before separating adhesions, so as to avoid carrying septic material into the deeper structures. As a rule, all this can be done without an anæsthetic because the protruded mass is insensitive. The surface is then powdered with sterilised iodoform, and a piece of Lister's protective oiled silk or thin sheet-rubber applied over it; a gauze dressing which overlaps the protective widely in all directions is then put on. A piece of block-tin may be incorporated with the dressings and additional pressure exerted by means of an elastic bandage. If the sepsis has been got rid of in this way, and if no intra-cranial inflammatory mischief (such as an abscess in the brain) is going on, the surface of the herniated portion will often granulate, and the mass shrinks and disappears. An attempt should then be made to cover in the surface of the brain if it is large, and with this object the edges of the wound should be freed for some distance and stitched together, or a flap may be turned in over the hernia if there is much tension, and the space from which it has been taken may be skin-grafted.

In some cases the hernia is accompanied by intra-cranial suppuration; the prognosis is then very hopeless. The surface of the hernia should be removed in the manner described above, and sinus forceps should be introduced into the brain beneath the hernia, and their blades expanded so as to ascertain if any pus is present. If an abscess is found, the cavity should be dealt with as described on p. 402.

SINUS THROMBOSIS.

The venous sinuses in the skull are probably more predisposed to the occurrence of thrombosis than most other veins, owing to their anatomical characters and the peculiarities of the circulation through

them. Two forms of thrombosis are met with, namely, non-infective or marasmic thrombosis, and the infective form. Of these the latter is the more common, and is in fact the only one for which active treatment can be employed.

The marasmic form chiefly occurs in the longitudinal sinus and affects weakly people, especially children or old subjects, after prolonged and debilitating illnesses. In children, exhausting diarrhoea is one of the most common causes, and the thrombosis generally appears during convalescence, the result being cerebral congestion and oedema. In bad cases the ventricles may be distended with serous fluid, and there may be subsequent cerebral softening.

The symptoms are generally somewhat indefinite, but in young children thrombosis may be suspected if convulsions occur after exhausting illnesses, and more especially if the symptoms are unilateral and accompanied by muscular rigidity, or strabismus.

Treatment. There is little to be done beyond ensuring absolute rest and administering nutriment in the most concentrated and easily assimilated form. Citric acid or citrate of potash may be given in large doses to check the spread of the thrombosis, but these drugs have no action on clot which has already formed. Any symptoms which arise should be appropriately treated, but there seems to be no scope for surgical intervention.

The infective form. This condition is usually met with in the basal sinuses, especially in young adults. It is always secondary to some external lesion, and generally occurs at the point nearest to the source of infection. Among the causes which give rise to it are septic compound fractures, and infective processes such as erysipelas, diffuse cellulitis, carbuncle about the face or scalp, and middle-ear disease. The condition has already been described in connection with thrombosis of the lateral sinus occurring after disease of the ear (see p. 390). Among the other sinuses which may be affected are the cavernous and the transverse sinuses.

Symptoms. When the cavernous sinus is involved there are disturbances in the eye on the affected side, such as congestion of the veins, compression of the oculo-motor nerves, pain, small pupils, cloudy corneæ, ædematous eyelids and exophthalmos. Later on, the pupil becomes dilated, and optic atrophy and corneal ulceration may result. There is pain in the supra-orbital and frontal regions, which is increased on pressure. When the tranverse sinus is involved the symptoms are chiefly connected with the vagus which is irritated at first and subsequently paralysed.

Treatment. The principles of treatment have been discussed in connection with the lateral sinus (see p. 399). Unfortunately these principles cannot be fully carried out, either in the case of the cavernous or the transverse sinus, but they should be borne in mind in case it may be possible to carry them into effect.

TUBERCULOUS MENINGITIS.

In this condition there is a deposit of tubercles in the pia mater. especially about the vessels at the base of the brain. The result is inflammation and effusion, acute distension of the ventricles with fluid, and increased intra-cranial pressure. For the condition of the cerebro-spinal fluid, the reader should consult the section by Dr. Emery, (see p. 442).

TREATMENT.-Attempts have been made to relieve the intracranial pressure by draining the ventricles, or by inserting a drain through the condyloid foramen, but, although the immediate symptoms are often relieved by the drainage of the cerebro-spinal fluid, no permanent good can be expected from this procedure. One or two cases have certainly recovered after drainage, but it is doubtful whether the condition in them was tuberculous or merely a simple meningitis. Repeated lumbar puncture is probably quite as efficacious as direct drainage of the cranial cavity, and is a much less severe procedure.

The following is the best method of draining the posterior part of the cranial cavity (see Fig. 172). The head is shaved, purified in the usual manner (see p. 328), and placed on a suitable head-rest (see Fig. 155). A semilunar incision with its convexity upwards is made over the side selected for drainage. The incision should begin at the middle line well below the external occipital protuberance-which is often very slightly marked in young children-and reach as high as the superior curved line. The flap thus marked out is retracted, the inner portion of the complexus either cut through or detached from the occipital bone, and the inferior curved line exposed. The rectus capitis posticus major muscle is stripped from its attachment by a rugine, and the skull is then opened by a trephine or a gouge, just below the inferior curved line and to one side of the middle line so as to avoid the sinus. This exposes the dura mater which generally bulges into the opening and does not pulsate. The dura mater is opened at the lowest possible point by a mere nick of the knife, and then a fine blunt spatula such as the dura mater separator (see Fig. 171) is passed beneath the lower edge of the cerebellum and the latter lifted gently up. The result generally is a free gush of fluid, which continues to flow and to pulsate in the opening. The greatest gentleness must be observed in lifting up the cerebellum, and the spatula must not be thrust in too deeply lest the important structures in the floor of the fourth ventricle be damaged.

Drainage is effected by passing an india-rubber tube (No. 6) through the opening in the dura and beneath the cerebellum, and a hole is made for it in the centre of the scalp flap, which is then sewn up with a continuous suture and the usual dressings applied.

The drainage of the cerebro-spinal fluid for the first two or three days.