43. Positional Vertigo Test
- Patients with limitations of horizontal or vertical gaze. Testing the vestibulo-ocular reflex can help localize the lesion (see Chapter 13 in Neuroanatomy Through Clinical Cases 3e). The vestibulo-ocular reflex can be tested either using the oculocephalic maneuver, in which the eyes are held open and the head is turned rapidly either from side to side or up and down, or by using caloric testing, in which cold or warm water is instilled into one ear, producing asymmetrical stimulation of the semicircular canals. See the section “Coma Exam” in Chapter 3 in Neuroanatomy Through Clinical Cases 3e for further details of these tests and their significance; see also KCC 12.6.
- Patients in coma. The vestibulo-ocular reflex is often the only way to test eye movements in these patients (see the discussion of comatose patients in Chapter 3 in Neuroanatomy Through Clinical Cases 3e).
What is Being Tested?
Hearing loss can be caused by lesions in the acoustic and mechanical elements of the ear, the neural elements of the cochlea, or the acoustic nerve (CN VIII) (see Figure 12.5 in Neuroanatomy Through Clinical Cases 3e). After the hearing pathways enter the brainstem, they cross over at multiple levels and ascend bilaterally to the thalamus and auditory cortex (see Figure 12.16 in Neuroanatomy Through Clinical Cases 3e). Therefore, clinically significant unilateral hearing loss is invariably caused by peripheral neural or mechanical lesions.
Abnormalities in vestibular testing can be associated with lesions in the vestibular apparatus of the inner ear (see Figure 12.15 in Neuroanatomy Through Clinical Cases 3e), the vestibular portion of CN VIII, the vestibular nuclei in the brainstem, the cerebellum, or pathways in the brainstem (such as the medial longitudinal fasciculus) that connect the vestibular and oculomotor systems (see Figure 12.19 in Neuroanatomy Through Clinical Cases 3e). Further details are provided in Chapter 12 and in the section “Coma Exam” in Chapter 3 in Neuroanatomy Through Clinical Cases 3e.