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THE LABYRINTH AND THE EIGHTH NERVE
TRAUMATIC AFFECTIONS OF THE AUDITORY NERVE
Direct Injury. The labyrinth may be affected as the result of direct injuries
by missiles or by the passage of a sharp implement, such as a knitting-needle,
through the external auditory meatus and the oval window, into the inner
ear. Deafness, giddiness and nausea supervene at once, facial paralysis is
also met with, and acute labyrinth suppuration may result. The local treat-
ment is the same as in the case of injuries to the middle ear. Rest in bed is
indicated as long as the giddiness lasts and antibiotics should be given hi
Indirect Injury. Labyrinthine concussion followed by sensorineural deafness
can be caused either by transmission of the effect of a blow* on the head
or by the sudden alteration in atmospheric pressure from an explosion.
Disturbance of vestibular function may also result from such injuries (see
'Explosion* Deafness, p. 386). Examination of temporal bones from soldiers
who died after exposure to severe concussion shows rupture of the tympanic
membranes and haemorrhage into the middle ear, with slight haemorrhages
into the scala tympani in the region of the round window and basal coil of
the cochlea; also haemorrhage at the fundus of the internal auditory meatus.
The nervous elements of the cochlea show degenerative changes and Corti's
organ has a ghost-like appearance (Fig. 199).
Fractures of the base of the skull involving the temporal bone are followed
by deafness which may be permanent.
Dislocation of the incus or malleus, resulting in the interruption of the
ossicular chain, may be the essential cause of such deafness. The middle
fossa is most frequently involved in fractures of the base of the skull and
this is due to the line of weakness which exists by the union of the basi-
occipital and basisphenoid from the petrotympa.nic fissure to the foramen
lacerum. The Eustachian tube, canal for tensor tympani, tympanum, and
tympanic antrum are intimately connected with this line.
Fractures of the temporal bone are divided into two main groups, longi-
tudinal and transverse, while in severe injuries a combination of these may
occur. The longitudinal fracture is the more common. The fracture line
runs either from the squamous portion medially, involving the roof of the
external auditory meatus, the tympanic ring and tegmen tympani; or from
the parietal bone across the upper part of the mastoid process to the tegmen.
From the tegmen the line follows the anterior aspect of the petrous pyramid
and ends in one of the foramina of the middle cranial fossa. The tympanic
membrane is generally torn and there is bleeding from the ear. The internal