Histological study of the facial nerve obtained during hypoglossal-facial nerve anastomosis from patients with acoustic neurinoma

Abstract

The histological features of the facial nerve removed in patients with facial palsy after removal ofacoustic neurinoma, and the relationship of histological findings with the clinical data were investigated inorder to clarify the pathology of facial palsy and the indications for hypoglossal-facial nerve anastomosis.Facial nerve specimens were obtained near the stylomastoid foramen during hypoglossal-facial nerveanastomosis from9patients. The interval between the tumor removal and the anastomosis ranged from 3 weeks to V23 months in 7 patients who were followed up for 10 months or more after anastomosis. Theintervals in the other 2 patients who were followed up for less than 10 months after anastomosis were 3 weeks and48months. The nerve specimens were examined by light and electron microscopy, and thefindings obtained were compared with the clinical data prior to tumor removal and the improvement offacial palsy after anastomosis. Facial nerve specimens obtained from patients with facial palsy prior totumor removal showed a smaller diameter of the endoneurial space than those obtained from patientswithout prior palsy. As the interval between tumor removal and anastomosis increased, the density ofregenerating myelinated and unmyelinated nerve fibers became greater. However, the diameter of theregenerating myelinated nerve fibers was smaller than that of normal nerve fibers. Because theelectromyographic findings and the facial palsy scores prior to anastomosis indicated the severe dysfunctionin all of the patients, the regenerating nerve fibers histologically observed in this study were regarded asessentially nonfunctional. Facial nerve palsy improved after the anastomosis in seven patients, except fortwo who were followed up for a short period of time postoperatively, regardless of the difference ofhistological findings of the facial nerves. Accordingly, the following conclusion was drawn from thisresult. Anastomosis is recommended even in the patients who show a poor recovery of facial palsy thatmight be due to the facial nerve atrophy or proliferation of collagen fibers, when the interval between tumorremoval and surgical anastomosis is shorter than at least 23 months.