ACCREDITED CPD - SURGERY
Nerves Which are Affected by Otitis Media
Dr Liesel van der Merwe BVSc (Hons) MMedVet (Med)
Small Animals.
There are several important nerves which run through
and immediately adjacent to the middle and inner
ears. These structures are affected with progressive
otitis and can also be damaged during surgery.
The middle ear lies beyond the tympanic membrane
and consists of the mucosa lined bulla which contains the three auditory ossicles which transmit sound
from the external ear to the inner ear. The auditory
(eustachian) tube connects the nasopharynx to the
middle ear.
The facial nerve and the sympathetic supply to the
eye are closely associated with the cavity of the middle ear. Deficits may include facial paralysis, horners
syndrome or pain on opening the mouth.
The bony cochlea together with the vestibule and
semicircular canals is situated within the petroustemporal bone and comprises the inner ear. Inflammation of this area will result in peripheral vestibular
disease. The facial nerve runs, along with and just
above, the vestibuloc ochlear nerve (CNVIII) through
the petrosal bone and emerges from the skull through
the stylomastoid foramen.
Chronic ear infection can result in pyogranulomatous otitis media - interna with the development of
osteomyelitis of the tympanic bulla. This will generally
result in peripheral or central vestibular disease - often without any of the other intracranial neurological
deficits expected with space occupying lesion:head/
neck pain, lethargy, seizures.
Horners syndrome:
The sympathetic supply to the eye originates in the
hypothalamus descends through the brain stem
and spinal cord to T1-T3 where it synapses and exits through the brachial plexus nerve roots and travels
rostrally again within the vagosympathetic trunk, synapsing on the cranial cervical ganglion. The axons
finally travel through the middle ear along the floor of
the skull and exit via the orbital fissure to innervate the
smooth muscles of the eye.
Miosis: Ipsilateral. Best seen when lights are dimmed
and failure to dilate is noted. With aniscoria it is always
important to decide which pupil is actually affected
- the small pupil or the dilated pupil – and this interpretation will depend on levels of light and stress.
Ptosis: Ipsilateral loss of tone to the eyelid causes
them to droop - narrowing the palpebral opening.
Enopthalmosis: Ipsilateral loss of sympathetic tone
to the smooth muscles of the orbit resulting in the
retractor bulbi muscles pulling the eyes, to sink further
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