2. FOCAL LESIONS OF THE CEREBELLUM.—(a) Lesions strictly limited to one lateral lobe or hemisphere of this organ do not give rise to any characteristic symptoms—in some cases, indeed, to no symptoms at all. When the lesion tends basad, irritating and compressing the subjacent pons and oblongata on one side, incomplete paralysis appears in the limbs opposite the lesion, the face usually remaining normal. Occipital headache, attacks of vomiting, opisthotonos, or intense subjective stiffness of the back of the neck, with neuro-retinitis, would strengthen the diagnosis. If the lesion extend laterad, so as to involve the processus ad pontem (lateral peduncle), a tendency to rotate while lying or to deviate in walking toward the side of the lesion may be added.
(b) Lesions of the middle lobe, or vermis superior in particular, may be positively recognized during life. Besides the above-mentioned general symptoms of cerebellar and bulbar irritation and compression—viz. occipital headache, cervical stiffness, attacks of vomiting, neuro-retinitis, and atrophy of the optic nerve—there is a very characteristic, almost pathognomonic, symptom. This is cerebellar titubation, miscalled cerebellar ataxia. The patient, whose equilibrium may be perfect while lying or sitting, upon rising and attempting to walk does so somewhat like an intoxicated person: the head and body are bent forward; the arms and hands held out and moved as balancing weights; the feet are widely separated, the toes clutching the floor or carpet; the body oscillating somewhat over its base of support. There are not the wide excursions of the entire body, the zigzagging, of alcoholic intoxication, nor is there any of the stamping or jerky step of locomotor ataxia. If the patient be tested lying or sitting, it is found that neither in the hands nor in the legs is there a trace of ataxia: muscular strength and sensibility are long preserved, and the patellar reflex is exaggerated.
3. FOCAL LESIONS OF THE BASE OF THE BRAIN, either within the nervous substance or springing from the dura, and acting by irritation and pressure upon various parts of the basal aspect of the encephalic mass.
(a) Diffused bilateral lesions of this class situated frontad of the crura give rise to more or less distinct symptoms, and a diagnosis is sometimes possible. (1) Lesions in the vicinity of the sella turcica and optic chiasm produce symptoms in the optic apparatus very early, and these remain prominent throughout the illness. These symptoms are, irregular (at least not lateral) hemianopsia, neuro-retinitis followed by atrophy of the optic nerve, temporary or permanent paralysis of one or several ocular nerves. If these exist without symptoms of lesion of other parts of the brain (reasoning by the process of exclusion), we may strongly suspect the seat of the lesion to be in the region named. Other symptoms are paroxysmal headache and occasional vomiting, epileptiform convulsions (never Jacksonian in distribution), partial hemiplegia, or general muscular weakness. By such data we were recently led to the correct localization of a tumor. (2) If the lesion be farther frontad—i.e. strictly in the orbital areas of the basis cerebri—anosmia, uni- or bilateral, usually with hallucinations of smell, will be an early symptom, along with neuro-retinitis and obscure motor and sensory symptoms (headache and convulsions more especially).
(b) Lesions situated caudad of the infundibulum. (1) Bilateral lesions give rise to symptoms which are the symmetrical duplication on either side of the face and body of those to be next described as characteristic of—
(2) Unilateral focal lesions of the base of the encephalon from the crura caudad to the pyramidal decussation.
In a general way, the symptoms of these lesions are designated as varieties of crossed paralysis.
Clinically, a crossed paralysis is one in which one or several cranial nerves show symptoms of irritation or destruction on one side of the median line, while body symptoms are present on the opposite side.
Physiologically and anatomically, a crossed paralysis is one in which the lesion is so placed as to affect a cranial nerve (or more than one) at a point caudad (below) of the decussation of the fibres which connect its nucleus with the cerebral cortex, or at its nucleus of origin, or so as to injure the nerve-trunk itself; while at the same time the lesion affects the main fasciculus of the pyramidal tract frontad (above) of its decussation, in the crus, pons, or oblongata.