FACIAL PARALYSIS 347
3. If severe muscle atrophy has occurred muscle grafts or strips of fascia
lata may be employed as a sling to elevate the sagging corner of the mouth.
This is usually carried out by the plastic surgeon.
4. The facial nerve may be re-routed with an end-to-end anastomosis.
FACIAL PARALYSIS IN SKULL FRACTURES
The facial nerve is more commonly injured in fractures of the skull than
any other cranial nerve except the olfactory nerve. It may be damaged in
fractures of the base of the skull either at the internal auditory meatus or
in its canal. Diagnosis of the exact site is always difficult. The paresis may
be immediate or delayed, and may be complete or partial in either event.
Immediate paralysis is due to laceration or bruising of the nerve with intra-
neural haemorrhage. Delayed paralysis follows pressure on the nerve from
bleeding inside its canal, and, whether partial or complete, it usually clears
up completely and rapidly. Immediate paralysis is less certain of recovery
on account of degeneration. There may be slow, but often incomplete,
return of function, and the prognosis is worse if infection of the middle
ear occurs during healing. Treatment is primarily concerned with care of
the facial muscles, and operative interference is not justified within 6 months
after the onset. The progress is assessed by the electrical tests, and the site
of the injury is located by hearing and vestibular tests and topognostic
facial nerve investigations.
Schirmer's blotting paper test, a quantitative method for measuring
lacrimation, is sometimes of value in determining damage situated proximal
to the geniculate ganglion and the greater superficial petrosal nerve. Loss
of taste in the anterior two-thirds of the tongue in a lower motor neuron
paralysis is suggestive of damage proximal to the chorda tympani nerve.
Impairment of taste may be mentioned by the patient or may be detected
by testing and comparing sensation on both sides of the anterior two-thirds
of the tongue, using salt and sugar. Electrogustometry can be used to assess
progress as studies have shown that recovery of taste within the first 10
days is a good indication of eventual complete recovery. The anterior part
of the tongue is stimulated electrically on each side to determine the smallest
direct current in microamps which will evoke a distinct acidic or metallic
taste. When a definite increase of threshold is found in the affected side a
lesion involving the chorda tympani or more central fibres within the facial
nerve may be deduced. A difference in threshold between the two sides
suggests that denervation is likely to occur.
Involvement of the nerve to the stapedius tendon may be determined by
measurement of acoustic impedance. If the evidence points to damage
within the facial nerve canal it should be explored. If the lesion is in the
internal acoustic meatus, facio-hypoglossal anastomosis may be indicated,
and possibly some subsequent plastic procedure. In many lesions direct repair
of the defect may be possible.