Injury of the lacrimal component of the nervus intermedius function after radiosurgery versus microsurgery

Due to the synergetic role of the facial nerve and the nervus intermedius in the mechanical protection of the eye, vestibular schwannomas (VS) and/or their treatment are dangerous for the visual function. Our goal was to evaluate and compare the impact of the tumor itself, and the microsurgery (MS) or radiosurgery (RS).

A functional questionnaire evaluating among other items the patient's complaints related to the eye was addressed to a series of 100 patients, 3 years after GKS of a previously unresected unilateral VS. Answers were compared with those of a group of 100 patients operated microsurgically. A Shirmer test was additionally performed before radiosurgery, and more than 2 years after radiosurgery in 46 patients.

The risk of dry eye and burning eye was much higher in patients operated by MS compared to patients operated by GKS due to the high incidence of facial palsy in the former (57/99) and the its absence in the later (0/80). In the population operated microsurgically, the presence of a permanent facial palsy (57 patients among 99 responding to the questionnaire) was, of course, associated with a high rate of complaints about burning eye (n=18) and crying eye (n=23). Among patients from the two arms with no facial palsy, a dry eye was reported by 8/64 after GKS and 7/42 after MS (NS) and a burning eye by 9/64 after GKS and 9/42 after MS (NS). Thus patients with no clinical signs of impairement of the VII motor nerve accounted for 14% of the cases signs indicating injury of the intermedius nerve with the same probability whatever the kind of surgery. When no permanent facial palsy was observed a crocodile tear syndrome was more frequently observed after MS (4/42 versus 1/64, p=0.07). This suggests an early lesion of the VII motor and intermedius, and a subsequent abnormal regrowth. The only patient reporting a crocodile tear syndrome after GKS turned out to have presented transiently a discret deficit of orbicular muscle signaling transient partial facial nerve injury. In absence of facial palsy, a "crying eye" was reported more frequently after MS (16/42 versus 9/64, p=0.01), leading us to suspect frequent infraclinical VII nerve injury in patients with no obvious facial palsy operated by MS. Patients tested with Shirmer test, before and more than 2 Years after, were improved in 28.3%, stable in 56.5%, and worse in 15.2%.

This study is the first demonstrating that radiosurgery can induce nervus intermedius injury in a small percentage of cases (14%). These patients had been treated 11 years ago with what we can consider as "archeoGKS technology" compared to today's refinements. The impact of modern GKS on the nervus intermedius is currently under evaluation in our group. However, symptoms related to the eye either due to the injury of the nervus intermedius or of the VII motor or both are much more frequent after MS than after RS.