Hemianæsthesia involving the organs of special sense, unilateral amblyopia, and color-blindness is supposed to be connected with a lesion of the posterior third of the internal capsule, or the thalamus in its immediate vicinity, sometimes also with a lesion of the pons. Bilateral hemiopia—blindness of the corresponding sides of both eyes—is apt to be connected with a lesion of the occipital lobe of the opposite side. Rendu and Gombault remark that hemianæsthesia of the limbs and face may be met with in certain lesions of the cerebral peduncles, but in this case the higher special senses (sight, smell) remain unaltered. Hemichorea points to the same localization as the more complete hemianæsthesia.
Alternate hemiplegia is due to a lesion of the pons upon the side of the facial paralysis, and opposed to the paralysis of the limbs and in the posterior or lower half. Care should be taken not to confound this with the accidental addition of a facial paralysis to a hemiplegia of the other side.
Irregular ocular paralyses are very likely to be due to lesion of the same region. In some of these forms an investigation of the electrical condition with reference to the presence of the degeneration reaction may be of great assistance.
With extensive lesions profound coma and relaxation without distinct hemiplegia are likely to be due to injury of the pons. A thrombus of the basilar artery may lead not only to rapid, but even to sudden, death. A phthisical patient died suddenly while eating his supper, and a thrombosis of the basilar artery, with softening of the pons, was found. Of course the lesion must have been of older date.50 Bright51 thought that when symptoms pointing to disease of the intracranial vessels were present the diagnosis was confirmed, and the location of the lesion in the vertebral arteries rendered highly probable, by a persistent occipital pain. In the upper part of one side of the pons the hemiplegia is not alternate, but of the ordinary form.
50 Bull. de Société anatomique, 1875.
51 Guy's Hospital Reports, 1836.
Any extensive lesion of the medulla must cause death so rapidly as almost to defy diagnosis, but such rarely occurs. The very rapid termination of certain cases of hemorrhage into the pons and cerebellum is due to the escape of blood into the fourth ventricle and consequent compression of the medulla.
Lesions of the lower and inner part of the crus are indicated by paralysis of the third nerve of the same, and hemiplegia of the opposite side of the body.
Obstinate vomiting, severe occipital headache, and vertigo, with or without a distinct paralysis, render a cerebellar hemorrhage probable, though no one of these symptoms is necessarily present or pathognomonic. Vomiting is very much more common with cerebellar hemorrhage than with cerebral. Ocular symptoms, like nystagmus and strabismus, accompany cerebellar lesions.
A difference in the temperature of the paralyzed and non-paralyzed sides, when amounting to one and a half to two degrees and lasting for a long time, is thought by Bastian to indicate a lesion of the optic thalamus.