In the vast majority of cases the lesion is situated upon the side of the brain opposite to the paralysis, except in some instances of cerebellar lesion, while in the peculiar form known as alternate paralysis due to lesion of the pons it is on the opposite side to the paralysis of the limbs and on the same side with the facial. It should be distinctly stated, however, that there are exceptions which are inexplicable on the present basis of cerebral anatomy. It is well known that only a part of the motor tracts cross to the other side of the cord at the decussation, and also that the proportion between the fibres which do and those which do not cross is a variable one. It has been suggested, in some cases of the kind mentioned, that all the motor fibres, instead of only a minority, as is usual, pass down on the same side of the cord as their origin. This has not been demonstrated. The number of such cases are so small that it need not be taken into account in diagnosis, and if the practitioner should make a mistake on this basis, he will have the recompense of knowing that he has assisted in a very rare case, in which it was next to impossible for him to be right. This condition is said to be found more frequently when the brain lesion and paralysis are on the right side.
Severe pain in the head, followed by gradually but rapidly deepening coma and paralysis of one side, becoming more and more complete, probably means a hemorrhage into or just outside of the great ganglia and involving a large extent of one of the hemispheres.
If there have been moderate loss of power or complete paralysis lasting some hours, with, afterward, sudden loss of consciousness and general muscular relaxation, with sudden fall, soon followed by rapid rise, of temperature, it is very probable that a hemorrhage has broken through into the ventricles or beneath the membranes, and is still going on.
Rapidly-deepening unconsciousness, with general muscular relaxation and gradual manifestations of more paralysis on one side than the other, may come from meningeal hemorrhage.
Very sudden and complete hemiplegia without prodromata, with deep unconsciousness coming on rapidly or suddenly, but a little after the paralysis, is likely to denote the occlusion of the middle (and perhaps anterior cerebral) artery of the opposite side at a point sufficiently low down to produce extensive anæmia of the motor centres along the fissure of Rolando as well as the underlying great ganglia.
Aphasia with hemiplegia, often without the slightest disturbance of consciousness, is in a considerable proportion of cases connected with a lesion of the third left frontal convolution, and in a somewhat larger proportion with the frontal lobes in general and the island of Reil. This lesion is in a great majority of cases occlusion of the artery. Difficulty of speech, connected with difficulty of swallowing and associated with a certain amount of amnesic aphasia, has been found with lesions of the pons. As aphasia, however, may occur without any fatal lesions at all, it is not certain in all these cases that the obvious lesion of the pons is a direct cause of all the symptoms.
Word-blindness is associated, according to a case reported by Skworzoff and a few others,49 with a lesion of the angular gyrus, pli courbe (P2 of Ecker), and word-deafness with a lesion of the first temporal (T1). These localizations agree with those experimentally determined.
49 West, Brit. Med. Journ., June 20, 1885.
Conjugate deviation is of importance as a localizing symptom, chiefly because it may be manifest when other signs of hemiplegia are difficult to elicit. I do not find it mentioned in twenty-seven cases of cerebellar hemorrhage not included in the table of Hillairet, but it is not infrequent with lesions of the pons; and when the lesion is in the lower third, it is in the opposite direction to that described as usual with lesions of the hemispheres.