Nerve crush but not displacement-induced stretch of the intra-arachnoidal facial nerve promotes facial palsy after cerebellopontine angle surgery.
Little is known about the reasons for occurrence of facial nerve palsy after removal of cerebellopontine angle tumors. Since the intra-arachnoidal portion of the facial nerve is considered to be so vulnerable that even the slightest tension or pinch may result in ruptured axons, we tested whether a graded stretch or controlled crush would affect the postoperative motor performance of the facial (vibrissal) muscle in rats. Thirty Wistar rats, divided into five groups (one with intact controls and four with facial nerve lesions), were used. Under inhalation anesthesia, the occipital squama was opened, the cerebellum gently retracted to the left, and the intra-arachnoidal segment of the right facial nerve exposed. A mechanical displacement of the brainstem with 1 or 3 mm toward the midline or an electromagnet-controlled crush of the facial nerve with a tweezers at a closure velocity of 50 and 100 mm/s was applied. On the next day, whisking motor performance was determined by video-based motion analysis. Even the larger (with 3 mm) mechanical displacement of the brainstem had no harmful effect: The amplitude of the vibrissal whisks was in the normal range of 50°-60°. On the other hand, even the light nerve crush (50 mm/s) injured the facial nerve and resulted in paralyzed vibrissal muscles (amplitude of 10°-15°). We conclude that, contrary to the generally acknowledged assumptions, it is the nerve crush but not the displacement-induced stretching of the intra-arachnoidal facial trunk that promotes facial palsy after cerebellopontine angle surgery in rats.
Department of Neurosurgery, Hospital Merheim, University of Witten-Herdecke, Cologne, Germany.|Department of Anatomy I, University Hospital of Cologne, Joseph-Stelzmann-Strasse 9, 50924, Cologne, Germany.
Habib
H
Bendella
House Clinic, 2100 West 3rd St, Suite 111, Los Angeles, CA, 90057, USA.
Derald E
DE
Brackmann
Department of Neurosurgery, University of Cologne, Cologne, 50924, Germany.
Roland
R
Goldbrunner
Department of Anatomy I, University Hospital of Cologne, Joseph-Stelzmann-Strasse 9, 50924, Cologne, Germany. angelov.anatomie@uni-koeln.de.
Doychin N
DN
Angelov
D000818:Animals; D002530:Cerebellopontine Angle / Q000601:surgery*; D004195:Disease Models, Animal; D005154:Facial Nerve / Q000473:pathology*; D005158:Facial Paralysis / Q000209:etiology* / Q000601:surgery*; D005260:Female; D007839:Functional Laterality; D009068:Movement / Q000502:physiology; D009409:Nerve Crush / Q000009:adverse effects*; D051381:Rats; D017208:Rats, Wistar; D020127:Recovery of Function / Q000502:physiology; D014404:Tubulin / Q000378:metabolism; D014738:Vibrissae / Q000294:innervation
D014404:Tubulin
Acoustic neuroma; Axonal stretching; Crush lesion; Facial nerve; Rat; Whisking function