Syringing with hot water causes a nystagmus directed towards the ear syringed; syringing with cold water, away from the ear.
(b) If there be a localized labyrinthine lesion, and the function of the labyrinth is still maintained, the same results will be obtained on syringing. Care, however, must be taken that the syringing is not forcible, otherwise the caloric tests will be unreliable, as in these cases nystagmus may be produced on even slight increase of pressure within the external auditory canal, and with this there may be a sensation of giddiness and nausea.
Spontaneous nystagmus, however, will probably be present, and will be directed towards the affected side. This spontaneous nystagmus is greatly modified by the caloric tests, being strongly exaggerated on syringing with hot water, and weakened or arrested on syringing with cold water.
(c) If the function of the labyrinth be destroyed, as in suppurative labyrinthitis, nystagmus will not be produced as a result of the caloric tests, but the spontaneous nystagmus, if present, will be directed towards the opposite, the normal side.
These various tests must be taken in combination with the symptoms, and frequently are of extreme value in deciding whether operation is indicated or not.
The chief difficulty is to exclude the possible existence of a cerebellar abscess (see [p. 460]). In favour of labyrinthine inflammation is complete internal-ear deafness, although this in itself does not exclude an accompanying intracranial lesion.
1. Immediate exploration of the labyrinth is indicated (provided there is internal-ear deafness):—
(a) If symptoms of acute labyrinthine suppuration occur in the course of a middle-ear suppuration, even although at the time of opening of the mastoid no definite fistula of the labyrinthine wall can be discovered.
(b) If symptoms of involvement of the labyrinth be present and a definite fistula is found on operation.
(c) If symptoms of a cerebellar abscess or of meningeal irritation be present in addition to those suggestive of a labyrinthine affection.