Manual of Surgery Volume II Part 33

[Ill.u.s.tration: FIG. 177.--Multiple Wens.

(Photograph lent by Sir George T. Beatson.)]

_Serous cysts_ are occasionally found in the occipital region, and are believed to be meningoceles that have become shut off from the interior of the skull before birth.

_Adenomas_ originating in the sebaceous or sweat glands are sometimes multiple, of a purplish colour, and the skin covering them is thin and glistening. They show a tendency to ulcerate and fungate, giving rise to a ftid discharge, and may be mistaken for epithelioma; they are also liable to become the seat of epithelioma. They are treated by excision.

Large, flat _papillomas_ or warts may be single or multiple; they are of slow growth, and as they may also become the starting-point of epithelioma, they should be removed.

[Ill.u.s.tration: FIG. 178.--Adenoma of Scalp.]

The _plexiform neuroma_ forms a loose soft tumour situated in the course of one or more branches of the trigeminal nerve, especially the supra-orbital branch. In its most aggravated form the tumour hangs over the face or neck in large pendulous ma.s.ses, and is described as a _pachydermatocele_ (V. Mott).

A _sarcoma_ usually has its origin in the bones of the skull, and only implicates the scalp secondarily.

_Epithelioma_ of the scalp may originate in relation to a wart, an ulcerated wen or sebaceous adenoma, or the cicatrix of a burn. It may affect comparatively young persons, may spread over a wide area, or pa.s.s deeply and involve the bone. Free and early removal is indicated.

_Rodent cancer_ may originate on the scalp, but usually spreads thither from the face.

In operating for extensive tumours of the scalp the haemorrhage is sometimes formidable. It may be controlled by an elastic tourniquet applied horizontally round the head, or if, on account of the position of the tumour or from other causes, this is not practicable, by ligation or temporary clamping of the external carotid on one or on both sides.

#Air-containing Swellings#--_Pneumatocele Capitis._--Cases have been recorded in which, as a result of pathological or traumatic perforations of the mastoid, and less frequently of the frontal cells, air has pa.s.sed under the pericranium and given rise to a tense rounded tumour, resonant on percussion, and capable of being emptied by firm pressure. Such swellings exhibit neither pulsation nor fluctuation; and as they are painless, and give rise to almost no inconvenience, they do not call for treatment.

_Emphysema of the scalp_ may follow fractures implicating any of the air sinuses of the skull, the air infiltrating the loose cellular tissue between the pericranium and the aponeurosis, and on palpation yielding a characteristic crepitation. It usually disappears in a few days.

#Vascular Tumours.#--_Naevi_ on the scalp present the same features as elsewhere. If placed over one of the fontanelles, a naevus may derive pulsation from the brain, and so simulate a meningocele.

_Cirsoid aneurysm_ is usually met with in the course of the temporal artery, and may involve the greater part of the scalp. Large, distended, tortuous, bluish vessels pulsating synchronously with the heart are seen and felt. They can be emptied by pressure, but fill up again at once on removal of the pressure. The patient complains of dizziness, headache, and a persistent rus.h.i.+ng sound in the head.

Ulceration of the skin over the dilated vessels, leading to fatal haemorrhage, may take place.

They may be treated by excision, after division and ligation of the larger vessels entering the swelling; or the dilated vessels may be cut across at several points and both ends ligated. Krogius recommends the introduction of a series of subcutaneous ligatures so as to surround the whole periphery of the pulsating tumour, and interrupt the blood flow. Ligation of the main afferent vessels, or of the external or common carotid, has been followed by recurrence, owing to the free anastomatic circulation in the scalp. In some cases electrolysis has yielded good results.

_Traumatic aneurysm_ of the temporal artery was comparatively common in the days when the practice of bleeding from this vessel was in vogue, but it is seldom met with now.

_Arterio-venous aneurysm_ may also occur in the course of the temporal artery, as a result of injury, and is best treated by complete extirpation of the segments of the vessels implicated.

CHAPTER XII

THE CRANIUM AND ITS CONTENTS

Anatomy and physiology--Cerebral localisation--Lumbar puncture. HEAD INJURIES--Concussion--Cerebral irritation--Compression--Contusion and laceration of the brain, and traumatic intra-cranial haemorrhage: _Middle meningeal haemorrhage_; _Haemorrhage from internal carotid and venous sinuses_--Intra-cranial haemorrhage of the newly born. Cerebral dema--Wounds of brain--After-effects of head injuries--Traumatic epilepsy and insanity--Infective complications.

#Anatomy and Physiology.#--The _Cranium_ is irregularly ovoid in shape, and its floor is broken up by various projections to form three separate fossae--anterior, middle, and posterior--in which rest respectively the frontal, the temporal, and the occipital lobes of the brain; the cerebellum, pons, and medulla oblongata also occupy the posterior fossa.

The _outer_ table is the most elastic layer of the calvarium, and it varies greatly in thickness in different skulls and in different parts of the same skull. It is nourished chiefly from the pericranium which is firmly bound down along the lines of the sutures. The _inner_ or vibreous table is thin and fragile, and its smooth internal surface is grooved by the middle meningeal and other arteries of the dura mater, and by the large venous sinuses. The intermediate layer--the _diploe_--is highly vascular, branches of the meningeal vessels anastomosing freely in its open porous substance with branches derived from the pericranial vessels. Some of its veins open into the external veins, and others into the intra-cranial sinuses, and they communicate with the emissary veins as these pa.s.s through the bone, which explains the spread of infective processes from the structures outside the skull to those within. The possibility of withdrawing blood from the interior of the skull by leeching, bleeding, or cupping depends on the existence of the emissary veins.

_The Membranes of the Brain._--The _dura mater_ is a fibro-serous membrane, the outer, fibrous layer const.i.tuting the endosteum of the skull, the inner, serous layer forming one of the coverings of the brain. Between the fibrous layer and the bone the meningeal vessels ramify; and along certain lines the two layers split to form channels in which run the cranial venous sinuses. Inside the dura, and separated from it by a narrow s.p.a.ce--the _sub-dural s.p.a.ce_--lies the _arachno-pial membrane_, consisting of an outer (_arachnoid_) layer which envelops the brain but does not pa.s.s into the sulci, and a highly vascular inner layer--the _pia mater_--which closely invests the brain and lines its entire surface.

The s.p.a.ce between these layers--the _sub-arachnoid s.p.a.ce_--is traversed by a network of fine fibrous strands, in the meshes of which the cerebro-spinal fluid circulates. Each nerve-trunk as it leaves the skull or spinal ca.n.a.l carries with it a prolongation of each of these membranes and their intervening s.p.a.ces. The membranes gradually become lost in the fibrous sheaths of the nerves, and the sub-dural and sub-arachnoid s.p.a.ces become continuous with the lymph s.p.a.ces of the nerves.

The _cerebro-spinal fluid_ is secreted by the choroid plexuses and fills the cerebral ventricles, the central ca.n.a.l of the cord, the sub-dural and sub-arachnoid s.p.a.ces, and the sheaths of the intra-cerebral blood vessels. At the base of the brain, particularly in the posterior fossa, the sub-arachnoid s.p.a.ce is wider than elsewhere, forming "cisterns" filled with cerebro-spinal fluid which supports the cerebral structures. Through the foramen of Magendie in the roof of the fourth ventricle the sub-arachnoid fluid of the cranial cavity communicates with that of the vertebral ca.n.a.l.

Although it differs in its chemical const.i.tution from true lymph, the cerebro-spinal fluid seems to functionate as lymph, in addition to acting as a lubricating agent, and playing a part in regulating the vascular supply of the brain. In cases of cerebral haemorrhage, abscess, tumour, or depressed fracture, room is made up to a certain point for the extraneous matter by displacement of cerebro-spinal fluid.

_Vascular supply._--The free anastomosis between the vessels entering into the formation of the circulus arteriosus (circle of Willis) ensures an abundant supply of blood to the brain. The larger arteries run in the sub-arachnoid s.p.a.ce and give off branches which ramify in the pia mater before entering the cerebral substance. Within the brain, each artery being more or less terminal, there is no free anastomosis between adjacent vessels, with the result that if any individual artery is obstructed the vitality of the area supplied by it is seriously impaired. The venous arrangements are also peculiar in that the veins are thin-walled and valveless, and open into the rigid, incompressible sinuses which run between the layers of the dura mater.

Most of the blood pa.s.ses to the internal jugular vein, and any increase in the pressure of this vessel is immediately transmitted back to the cerebral veins. As the blood vessels project into a rigid case filled with incompressible material, and as the total _volume_ of blood in the brain is constant (Munro and Kelly), any alteration in the supply of blood to the cerebral tissue must be due to an increased _velocity_ of flow, and this in turn depends upon changes in the aortic and vena cava pressure. Thus, if the aortic pressure rises, more blood will enter the cerebral vessels and will move along more rapidly; while if the pressure in the vena cava rises there is obstruction to the pa.s.sage of blood in the arteries and diminished velocity of flow. The ebb and flow of cerebro-spinal fluid in and out of the spinal ca.n.a.l may also help to control the pressure.

#Nerve Elements.#--The nervous system is composed of a mult.i.tude of units, called _neurones_, each neurone consisting of a nucleated cell, with branching protoplasmic processes or _dendrites_ and one _axis-cylinder_ or _axon_. The nutrition of an axis cylinder depends on its continuity with a living cell. If the cell dies, the axis cylinder degenerates. If the axis cylinder is severed at any point, it degenerates beyond that point, and the nucleus of the nerve-cell disintegrates--chromatolysis.

The axis cylinder of one cell ends in a number of fine filaments which arborise around another nerve-cell, thus bringing it into physiological, if not anatomical, relations.h.i.+p with the first cell.

The termination is called a cell-station or _synapsis_. In this way the various sections of the nervous system are kept in a.s.sociation with one another and with the rest of the body.

_Motor Functions and Mechanism._--The nerve centres, which together make up the motor area, and govern the voluntary muscular movements of the body, are situated in the grey matter of the praecentral or ascending frontal gyrus, and of the frontal aspect of the central sulcus (fissure of Rolando). The upper limit of the motor area reaches on to the mesial aspect of the paracentral lobule, and the lower limit stops short of the lateral cerebral fissure (fissure of Sylvius) (Fig.

179).

[Ill.u.s.tration: FIG. 179.--Relations of the Motor and Sensory Areas to the Convolutions and to Chiene's Lines.

(After Cunningham.)]

Each group of muscles has its own regulating centre, the size of the area representing any group depending upon the character and complexity of the movements performed by the muscles, rather than upon the amount of muscular tissue that is governed by the centre--for example, the centre for the mouth, tongue, and vocal cords is larger than that for the muscles of the trunk.

The motor centres have been localised on the surface of the brain with approximate accuracy. For example, above the superior genu of the praecentral gyrus, the centres governing the hip, knee, and toes are grouped; opposite the genu are the centres for the movements of the trunk; between the superior and middle genua lie the centres for the upper extremity; opposite the middle genu, those for the neck, and below it, those for the face, jaws, and tongue, pharynx and larynx.

#The Motor Tracts.#--It is now generally accepted that there are two paths by which motor impulses pa.s.s from the brain: one--the _rubro-spinal tract_--which controls the more elemental movements of the body, such as standing, walking, breathing, etc.; the other--the _pyramidal tract_--developed later in the evolution of the nervous system, and concerned with the finer and more skilled movements.

The pyramidal tract is the more important clinically. From the pyramidal cells in the cortex of the Rolandic area, the axis cylinders pa.s.s through the centrum ovale towards the base of the brain. They converge at the internal capsule, and pa.s.s through the anterior two-thirds of its posterior limb (Figs. 180 and 195). The fibres for the eyes, face, and tongue lie farthest forward, and next in order from before backward, those for the arm and the leg.

From the internal capsule, the motor fibres pa.s.s as the _pyramidal tract_ through the crusta of each crus cerebri, the pons and the medulla oblongata. Throughout this part of its course, numerous axons leave the tract, and enter the mid-brain, pons, and medulla in which lie the nuclei of the motor cranial nerves.

At the _decussation of the pyramids_ in the lower third of the medulla, the main ma.s.s of the motor fibres crosses the middle line, and enters the lateral column of the spinal cord as the _crossed pyramidal tract_. The remaining fibres pa.s.s down as the _direct pyramidal tract_, and decussate in the cord near their termination.

The fibres forming the second path pa.s.s through the red nucleus in the cerebral peduncle (crus cerebri) and thence by way of the rubro-spinal tract in the lateral column of the cord.

The existence of this double motor path explains how after a hemiplegic stroke in which the pyramidal tract is destroyed while the rubro-spinal tract escapes, the patient is able to perform such primitive movements as are involved in walking or standing, while he is unable to carry out finer movements that require higher education.

The pyramidal and rubro-spinal tracts, in addition to conveying motor impulses, convey impulses that influence muscle tonus and the deep reflexes. The pyramidal tract conveys impulses that inhibit muscle tonus, while the rubro-spinal tract is the path by which excitatory impulses travel. When the inhibitory influences are cut off, as in a lesion of the internal capsule, the paralysed muscles become spastic, and the deep reflexes are exaggerated. When the excitatory impulses are also lost, as in a total transverse lesion of the cord, the paralysed muscles are flaccid and the deep reflexes disappear. In destructive lesions of the lower neurones, the muscles are always flaccid.

The axons pa.s.sing from the cerebral cortex terminate at different levels in the cord by breaking up into dendrites which arborise around the cells on the grey matter of the posterior horns--this system of cells, axons, and dendritic processes forming an _upper neurone_. From this synapsis the _lower neurone_ proceeds, its axons travelling to the anterior horn and arborising around the motor cells. The axis cylinders pa.s.s out in the anterior nerve roots to the spinal nerves and are continued in them to their distribution in voluntary muscles.

If the continuity of any group of these lower neurones is interrupted, not only do the nerve fibres degenerate, but the nutrition of the muscles supplied by them is interfered with and they rapidly degenerate and waste, and after an interval show the reaction of degeneration. In addition, the reflex arc is disturbed, and reflexes are lost. As these changes do not occur in lesions of the upper neurones, an appreciation of the differences enables us to distinguish between lesions implicating the upper and the lower neurones.

#Sensory Functions and Mechanism.#--Three kinds of sensory impulses pa.s.s from the periphery to the brain; (1) deep, or muscular sensibility, (2) protopathic sensibility, and (3) epicritic sensibility.

_Deep sensibility_ includes the recognition of (_a_) deep pressure, say by the blunt end of a pencil; (_b_) the position of a joint on pa.s.sive movement (joint sense); (_c_) active muscular contraction (kinesthetic sense). The fibres that convey these impulses to the spinal cord pa.s.s in the afferent nerves from the muscles, tendons, and bones, and so long as these nerves are intact these sensations are retained, even if the surface of the skin is quite anaesthetic.