The more typical localizing symptoms are as follows:—
Vertigo is a prominent symptom, most evident on sudden alteration of position on the part of the patient. He complains, for instance, of great giddiness on sitting up in bed. The sensation of movement may be of self or of objects.
Fig. 77. A Cerebellar Abscess.
When standing, he tends, when unsupported, to fall or lurch in some particular direction, more commonly, in my experience, towards that side on which the abscess is situated. On this point, however, there is some difference of opinion and, by itself, it cannot be accepted as having any great localizing value.
In some rare cases Dana’s symptom may be noticed—a sudden unexpected attack of vertigo, roaring in the head, relaxation of limbs, and falling to the ground in an unconscious state. This symptom is said to be almost pathognomonic of an abscess (or tumour) situated in the region of the cerebello-pontine angle.
The cerebellar gait can of course only be demonstrated when the patient is in a fit condition to walk. He shows, by the position of the feet, a desire to obtain a wide base of support and staggers on, in his desire to carry out his instructions, usually inclining towards the side on which the lesion is situated. This inclination is probably dependent on the weakness of the muscles of the ipso-lateral side (see [below]). Another important feature may be observed in the tendency on the part of the patient to turn the head in such a way that he faces somewhat in the opposite direction, the chin being directed towards the opposite shoulder.
Disturbances of co-ordination may be demonstrated by telling the patient to touch the tip of his nose with his finger, or to strike at an object held a foot or two in front of him. Such attempts are characterized by uncertainty and irregularity of movement, accompanied by considerable tremor.
Paresis or paralysis of the limbs on the ipso-lateral side. The abscess usually occupies the antero-external aspect of the lateral lobe of the cerebellum, and is so situated that no direct pressure is exercised on the pyramidal fibres. Some weakness—perhaps paralysis—of the muscles of the extremities on the same side as the lesion can, however, usually be demonstrated. According to Luciani, this is explained in the following manner:—between the cortex of the one side and the cerebellum of the other there are certain ‘associated’ fibres, the strength of the impulses sent out from the cortex depending in part on the integrity of these reinforcing cerebellar fibres. In cases of cerebellar abscess these reinforcements are cut off with consequent paresis, or even paralysis, of the muscles of the face, arm, and leg on the same side as the lesion. Associated with this muscular weakness there is usually some increase in the deep reflexes. Some of the pyramidal fibres do not decussate, and, consequently, an ipso-lateral paralysis may be associated with a contra-lateral paresis.
The same lessening of cortical impulses accounts for a weakening in the external rectus of the same side, which muscle, acting with the internal rectus of the sound side, allows of a conjugate deviation of the eyes towards the opposite side, with well-marked nystagmus—of a coarse type—on attempting to correct this deviation.