LESIONS OF INTERNAL CAPSULE. 163 EFFECTS OF LESIONS OF THE INTERNAL CAPSULE. The situation of this bundle of nerve-fibers renders it liable to become directly involved when hæmorrhage, softening, or tumors of the central portions of the hemisphere exist; or, indirectly, when these conditions affect the caudate nucleus, the lenticular nucleus, or the optic thalamus. The most frequent seat of cerebral apoplexy is the corpus striatum; because that ganglion is extremely friable and very vascular. The optic thalamus probably ranks next in the order of comparative frequency. The blood-vessels which enter these bodies' through the anterior and posterior perforated spaces at the base of the cerebrum seem to be frequently affected with atheromatous degeneration and miliary aneurysms,' ‚' and are often ruptured when subjected to any unnatural strain. Nature has given to the carotid and the vertebral arteries a remarkable tortuosity before their entrance into the cavity of the cranium, in order, as it were, to diminish the liability to rupture of blood-vessels by decreasing the velocity of the flow when the heart's action is excessive; but even this mechanical safeguard is not always sufficient to protect the intracranial vessels from rupture when extensively diseased. Again, the condition of softening may result from embolic obstruction to some branches of the carotid (usually of the left side), because the nutrition of the parts supplied by the 3 'The motor regions of the cortex are supplied by the middle cerebral artery; the nucleus caudatus by branches of the anterior cerebral and anterior communicating arteries; the lenticular nucleus by the middle cerebral; and the optic thalamus by branches of the middle and posterior cerebral vessels. The vessels most frequently affected with aneurysmal dilatations are the internal carotid, basilar, and middle cerebral. Within the cavernous sinus large aneurysmal tumors are not uncommon. It must not be supposed, however, that the smaller vessels of the brain are exempt. Miliary aneurysms, which give to an artery and its branches an appearance resembling a bunch of grapes, frequently affect the vessels that form the circle of Willis, and even those of the pia mater within the substance of the brain and in the ventricles. The small vessels which nourish the corpora striata and the optic thalami are sometimes affected. Miliary aneurysms frequently coexist with aneurysmal tumors outside of the cranium, but they seem to exhibit an independence of atheroma which is quite remarkable. 3 The reasons for this fact can be found mentioned in a late work by the author"Practical Medical Anatomy." William Wood & Co., 1882. occluded vessel is thus arrested either entirely or in part. The same result may also follow an attack of cerebritis or a previous extravasation of blood into the substance of the brain, both of which tend often to create impairment of the blood-supply to adjacent regions. FIG. 41.-Miliary aneurysms of a cerebral artery. (After Hammond.) Finally, tumors sometimes develop within the cerebral hemispheres, and create pressure upon, as well as destruction of, important nerve-tracts. Time will not permit us to enter into detail respecting all the diagnostic points by which the existence of each of these conditions may be recognized during life. I direct your attention, therefore, only to such points as are of importance in the diagnosis of disturbance of the supposed functions of the internal capsule. It may be stated with some degree of positiveness that, if the anterior part of the "thalamo-lenticular" division of the internal capsule (Fig. 38) be affected, a hemiplegia of the opposite side is developed.' This is more or less complete, according to the seat and extent of the lesion which causes it. The exciting cause may possibly be situated within the anterior or middle portions of the white center of the cerebral 1 Exceptions to this rule are occasionally observed. The hemiplegia, in rare cases, exists on the same side as the lesion. The explanation of this fact has been shown, by the researches of Flechsig, to lie in the varying proportions of the direct and decussating fibers which pass from the cerebrum to the spinal cord. LESIONS OF INTERNAL CAPSULE. 165 hemisphere, above the level of the basal ganglia, in which case it will interfere with the normal action of certain bundles of the internal capsule which spring from the motor convolutions of the cortex previously enumerated. Again, it may be situated within the constricted portion (the capsule proper), in which case bundles of nerve-fibers, functionally associated with widely diffused areas of the cortex, may be affected by a lesion of small size. Finally, it may be apparently confined to the substance of one of the two nuclei of the corpus striatum (Fig. 40), or the optic thalamus, and still exert sufficient pressure upon the constricted part of the internal capsule to produce more or less extensive and complete paralysis— chiefly of the opposite lateral half of the body. The hemiplegia of intra-cerebral lesions forms, as a rule, a striking contrast with the various types of monoplegia (p. 85), which are produced by circumscribed lesions of the cortex. The latter are often of the greatest aid to the neurologist in localizing the seat of the exciting cause.' They have been discussed in preceding pages. The second symptom which may indicate a lesion of the internal capsule is hemi-anasthesia. By this, I mean a loss of sensation, more or less complete, which is confined to the lateral half of the body. It exists (save in rare instances) on the side opposite to the seat of the lesion. This may occur when fibers of the sensory tract of the internal capsule (Fig. 39) are destroyed or impaired by diseased conditions directly affecting them, as noted by Charcot, Raymond, Rendu, Ferrier, and others, or by the pressure exerted by lesions situated in parts adjacent to them. It is usually accompanied with a slight form of motor paralysis; probably because a few of the motor fibers of the internal capsule are, as a rule, simultaneously interfered with. The tests by which this condition may be recognized are, doubtless, familiar to you all. No examination of a patient afflicted with paralysis is ever complete unless sensation, as well 1 The term covers many forms of paralysis where special groups of muscles are alone affected. as muscular power, is carefully tested, before a diagnosis is made. A third symptom of lesions of the internal capsule includes a variety of manifestations of impairment of the special senses. In connection with the discussion of the optic thalamus, you will recall the views advanced respecting the possibility of existence of special centers of smell, sight, hearing, and sensation within the substance of that ganglion. Clinical facts point strongly also to a relationship between nerve fibers related to certain special-sense perceptions and the internal capsule. We are forced to admit that some of the fibers of the posterior part of the internal capsule probably have a direct or an indirect association with smell, sight, hearing, sensation, and perhaps of taste also. In a subsequent section, many interesting facts in physiology, which show the value of abnormal phenomena in smell, sight, speech, hearing, taste, etc., upon the diagnosis of intra-cranial lesions, will be given. Many of these might be mentioned here with advantage, if space would permit. Charcot has endeavored to explain a statement, that has until lately been accepted, viz., that hemianopsia' seldom (?) occurs in connection with lesions of the internal capsule, but an amblyopia is developed on the same side as the cutaneous anææsthesia, with a remarkable contraction of the field of vision and difficulty in discrimination of color. The explanation which this author made of this statement is, that a second decussation of the fibers of the optic nerve takes place somewhere between the optic chiasm and the internal capsule, probably in the tubercula quadrigemina. Some late discoveries of Munk and Wernicke (coupled with a collection of autopsies bearing upon the subject) have caused this author to modify his views. It is now considered as questionable if many cases, reported as exhibiting amblyopia during life, were not affected with hemianopsia. This subject will be discussed in connection with the corpora quadrigemina. The term "hemiopia" signifies half sight; hemianopsia means a blindness of one half of the retina. The latter is, therefore, the preferable term in this connection. LESIONS OF INTERNAL CAPSULE. 167 When the radiating fibers of the internal capsule are involved in a lesion which creates a gradually increasing pressure (as in the case of tumors which grow slowly) the fundus of the eye exhibits morbid changes in the region of entrance of the optic nerve which are of value in diagnosis. The condition so produced is commonly known as the "choked disk." It is nearly always bilateral, but often most marked in one eye. It may be considered as one of the most positive signs of an extensive intra-cerebral lesion, and especially of tumors of the brain. When such an eye is examined with an ophthalmoscope, the condition found is characterized by a swollen appearance of the optic nerves, which project appreciably above the level of the surrounding retina; the margin of the disk is either obscured or entirely lost; the arteries appear small, and the veins large and tortuous; finally, small hemorrhagic spots may often be detected in the retina near the margins of the disk. In spite of this condition, the power of vision may be little impaired; so that the existence of "choked disk" may be unsuspected unless the ophthalmoscope be used before the diagnosis is considered final. After a number of weeks, and very much longer if a tumor is the exciting cause of the condition, the appearance of the disk changes. An unnatural bluish-white color, which denotes atrophic changes, develops; the outline of the disk becomes sharply defined; the retinal vessels become small; and vision becomes markedly interfered with. In exceptional cases of destruction of the internal capsule, the sense of smell has been abolished on the side opposite to the seat of the lesion. This fact requires special consideration, as it has been shown that the center proper for olfactory perceptions seems to be in the hemisphere of the same side. Meynert and Gudden claim, however, to have demonstrated the existence of an olfactory chiasm in the region of the anterior commissure, in animals where the bulbs are largely developed; and fibers have been traced in the region of the ་ |