occurs after a latent period; the nystagmus is directional* according to the
head position; and the nystagmus is fatiguable. Reassurance is required,
and the patients learn to avoid the position which stimulates the vertigo.
The central type, which is sometimes called malign or malignant, may occur
hi association with tumours, either primary or secondary, in the posterior
cranial fossa, with disseminated sclerosis or with vascular lesions. There is
no latent period before nystagmus appears, the direction varies and the
nystagmus persists and is not fatiguable.
Vertebrobasilar Artery Ischaemia. This may produce vertigo as the main
symptom, and is associated with black-outs. The vertebrobasilar artery is
compressed by a lesion in the cervical spine, notably spondylosis, and
vertigo results from movement of the head, either rotation or extension.
Treatment is that of the cause, and the wearing of a cervical collar often
Posterior Inferior Cerebellar Artery Thrombosis. The onset of this condi-
tion is associated with severe vertigo having features suggestive of laby-
rinthine origin. The development of ipsilateral cerebellar signs and a Homer's
syndrome, together with a contralateral hemi-analgesia, indicates the true
nature of the condition. Deafness may or may not be found.