Definition.—Clotting of blood in the cerebral arteries, veins, or sinuses.
Etiology.—-This is most frequently due to disease of the walls of the blood-vessels, whereby their surface is roughened, favoring the deposit of fibrin. This may arise from endarteritis, atheroma, or syphilitic endarteritis, or from weakening of the circulation from diphtheria, typhoid fever, tuberculosis, cancer, and such diseases as impair the integrity of the blood. It may result from aneurisms, and it has followed the ligation of the carotid artery. In fact any condition that affects the vessel wall, or obstructs the blood-current, or increases its coagulability, is a possible cause of thrombosis. The thrombosis occurs most frequently in the middle cerebral and in the basilar arteries.
Pathology.—Taylor thus describes the anatomical changes: "Embolism and thrombosis, by obstructing" the circulation of the blood, alike lead to softening of the districts of the brain to which the vessels correspond, unless the vascular supply is maintained by means of anastomoses. These are not abundant in the case of the cerebral vessels, and, indeed, the vessels going to the central ganglia are really terminal vessels, while those going to the cortex of the brain do anastomose more or less. At least, this is true of the distribution of the middle cerebral artery—the vessel most often obstructed. A part of the brain in which softening has taken place has generally lost the smooth, glistening surface of a normal brain-section, is more opaque, or gray, or speckled; it breaks down readily under a stream of water; or it is milky, or diffluent. It shows under the microscope drops of myelin, portions of nerve-fibers, granule-corpuscles, and free fat-globules. It sometimes has a yellowish or brownish color from blood-pigment; or minute extravasations may be present in cases of sudden obstruction, and a form of red softening results. In cases of rapid death after embolism, the brain substance may look perfectly healthy, as there has not been time for any changes visible to the naked eye to take place. Occasionally an embolus sets up inflammatory changes in its neighborhood; sometimes it leads to aneurism and cerebral hemorrhage. Rarely actual infarcts are formed. The later stages of softening consist in the absorption of the disintegrated tissue, and the formation of a cyst; or, if the softening is small, a cicatrix may be produced.
"Embolic lesions, involving the motor tract, are followed by the same secondary changes (descending sclerosis) as are hemorrhagic lesions. A persistent lesion of the brain, whether embolic or hemorrhagic, causing hemiplegia in infancy or early childhood, has the remarkable effect of checking the growth of one-half of the brain, or it may be of other parts of the central organs, so that years after it is smaller than the other half, and is described as atrophied (cerebral hemiatrophy, unilateral atrophy). If the lesion is in the motor cortex, the hemisphere is atrophied on that side, and there is sclerosis of the pyramidal tract; if it is in the basal ganglia, there is in addition atrophy of the middle fillet in the pons medulla, and of the antero-lateral region of the spinal cord on the same side; and atrophy of the cerebellum, superior cerebellar peduncle and dentate nucleus on the opposite side (Mott and Tredgold)."
Symptoms.—Naturally, the symptoms will depend upon the location and extent of the lesion. They may be so slight as to escape detection, and only be discovered during- an autopsy, or they may be so severe as to destroy life in a few hours. The shock from cerebral embolism may be so similar to cerebral hemorrhage as to be almost indistinguishable.
A very important factor in determining the symptoms is whether the embolism be in a small artery or in a large one, and if it be located in the hemispheres or toward the base of the brain.
In embolism, the onset is almost invariably sudden, there being no premonitory symptoms, the patient suddenly losing consciousness. Usually this is not so severe as in cerebral hemorrhage, and the patient soon regains consciousness, though, when very severe, coma becomes pronounced, and the case terminates fatally. Convulsions may occur when the motor regions are involved.
If the anterior cerebral is the vessel involved, the symptoms are often negative, since branches of the middle cerebral will supply about the same area. Apathy and dullness are sometimes present.
When the middle cerebral is involved, the one most frequently affected, hemiplegia follows, and is permanent or transient according to the location of the plug. Thus if the vessel be blocked before the central arteries are given off, it is permanent, while if beyond this point, the arm and face suffer, but it is generally temporary.
If the left side be involved, there is aphasia. If the trunk be spared and the branches are involved, the symptoms will vary according to the part affected. These branches supply the inferior frontal, the anterior and posterior central gyri, the supramarginal, angular, and temporal gyri.
The different types of aphasia are thus explained: Motor or ataxic aphasia, when the patient remembers the words, but can not articulate them: here the lesion is in the third left frontal convolution. Sensory aphasia, where the patient fails to comprehend the meaning of spoken words (word-deafness), is due to lesions of the first and second temporo-sphenoidal convolutions. If the angular gyrus be involved, word-blindness follows.
The posterior cerebral vessels supply the occipital and temporo-sphenoidal lobes, and when involved—a rare case—there is hemianesthesia due to softening of the internal capsule, and hemianopsia due to softening of the cuneus. Sometimes there is complete loss of sight, though, generally, but temporary.
Involvement of ihe Internal Carotid.—If the circulation be by the communicating vessels of the circle of Willis, there will be an absence of symptoms; but if these vessels are small or absent, the circulation is arrested, and permanent paraplegia and death are apt to follow in a few days.
Basilar Artery.—Where this is occluded, bilateral paralysis, from involvement of both motor tracts, is apt to follow. In these cases the temperature rapidly rises to 107°, 108° or 109°, or even higher, the pulse is rapid and irregular, and convulsions may occur. Bulbar symptoms are frequently present.
Vertebral Artery.—The left is the more frequently involved, and usually in connection with the basilar. The nuclei in the medulla are affected, and attended by symptoms of acute bulbar paralysis.
Cerebellar Arteries.—Incoordinations of movement have been recorded as a result of cerebellar softening, though the lesion is rare.
Thrombosis, though not so rapid in its development, is followed by the same results, apoplexy and hemiplegia. The disease comes on more gradually; there is frequent and persistent headache, more or less dizziness, a gradual loss of the mental powers, and a perverted sensibility manifested by a numb, tingling, or creeping sensation in arm or leg. These symptoms, especially in elderly people, gradually increase till the mental faculties are destroyed, and we have the "softening of the brain" of old people.
Diagnosis.—It is sometimes almost impossible to differentiate between embolism and cerebral hemorrhage during the first few days; generally, however, they can be recognized by the following conditions: A history of rheumatism or endocarditis usually precedes embolism. Unconsciousness is not so prolonged nor coma so marked. The face is pale, not flushed, nor is there stertorous breathing.
Thrombosis comes on gradually, preceded by dizziness, headache, and perverted sensibility.
Prognosis.—The prognosis from embolism is slightly more favorable than from hemorrhage; the location is also a determining factor in the recovery. Paralysis is more apt to be permanent in embolism. In thrombosis, cerebral softening frequently follows, the prognosis in such cases being unfavorable.
Treatment.—In the administration of remedies we will be guided entirely by the conditions present. The immediate treatment will be rest in bed, and, if shock be present, stimulants administered. Later, in those cases where irritation occurs, sedative agents will be used. The antisyphilitics will be used where the lesion has been preceded by syphilis.
In cerebral softening, but little can be done save improving the general health. Hygienic and dietetic measures will be an important part of the treatment.