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.