gms | German Medical Science

However anatomic preservation of the facial nerve is achieved in about 90% of patients reported in large series after vestibular schwannoma surgery paresis or even paralysis of facial nerve early after operation of CPA tumor is still common [Ref. 1], [Ref. 2], [Ref. 3]. Later on in postoperative course, when anatomical continuity of facial nerve is preserved its recovery is characterized by slight deterioration, in the immediate postoperative period, and frequently improvement in the long-term follow-up [Ref. 2], [Ref. 4]. Application of intraoperative monitoring, precise instruments, microscope, endoscope etc. during excision of CPA tumors has remarkable improved anatomic and physiologic preservation of the facial nerve [Ref. 1], [Ref. 2], [Ref. 5], [Ref. 6], [Ref. 7]. On the other hand successful removal of vestibular schwannomas and results of surgery, especially facial nerve outcome is strongly depended on experience of operating team [Ref. 1], [Ref. 8]. The objective of this study was to analyse time and dynamics of facial nerve recovery after operation. We tried to assess of possible factors influencing period of facial status stabilisation and possible degree of facial improvement.

We analysed group of 226 patients operated via retrosigmoid approach. There were 146 vestibular schwannomas, 27 meningiomas, 25 epidermoid cysts, and 28 other tumors (8 astrocytomas, 4 arachnoid cysts, 4 hemangioblastomas 3 metastases, 2 lipomas and one papilloma, lymphoma, abscessus, sarcoma, teratoma cavernous angioma. We introduced monitoring of neurophysiological functions of central and peripheral nervous system as a routine in CPA surgery in 1998. Since that year the patients underwent the surgery having neurophysiological functions monitored in a continuous mode using four channel units Nicolet Viking IV D equipped in intraoperative software. Somatosensory evoked potentials, auditory evoked potentials and function of V, VII and IX cranial nerves were registered simultaneously. In selected cases intraoperative monitoring of cochlear function was also conducted using distortion product otoacoustic emissions. Details of our methods of multimodal monitoring have been published [Ref. 7], [Ref. 9], [Ref. 10], [Ref. 11]. All the patients were operated on under general anaesthesia in a sitting position by the same team of surgeons via retrosigmoid craniotomy or craniectomy. In 120 cases we were able to completely documented facial nerve recovery month by month up to 18 month after surgery. Out of them were 74 vestibular schwannomas, 17 meningiomas, 12 epidermoid cysts, and 17 other tumors. There were 49 male (41%) and 71 female (59%) in the age between 12–77 years old (mean=45±14). Tumor size was defined as largest diameter measured from MR or CT scans, and ranged from 5 to 70 mm (mediana=24, mean=27±15). Facial nerve according to HB scale was assessed immediately after operation (at discharge from hospital, and up to 18 months after surgery. When direct assessment was impossible, patients responded to questionnaire regarding facial function.

In patients followed VS excision FN function in long-term observation persists as follows: HB I – 33%, HB II – 16%, HB III – 16%, HB IV – 9%, V – 16% and HB VI 11%. Results are definitively better wen we consider only patients operated with intraoperative multimodal neurophysiological monitoring (HB I – 32%, HB II – 23%, HB III – 19%, HB IV 11%, HB V – 8%, HB VI – 7%). We should consider that in 49% of VS patients we excised large tumors (more than 3 cm in diameter). Late outcome of FN function in patients after CPA meningioma excision persists as follows: HB I – 58%, HB II – 12%, HB III – 8%, HB IV 23%, HB V – 0%, HB VI – 0%. Comparison of late facial function in correlation to age, sex, intraoperative monitoring, size of VS and tumor histology as well as extension of resection are presented in four upper parts of Table 1 [Tab. 1].

Age above 60 years is negative prognostic factor of postoperative FN function in present series (47% of them are in V or VI HB grade). Considering all of CPA tumor patients it is clear that FN status is relatively better in 18^th month comparing to function directly after surgery (at discharge from hospital). 64% of patients directly in II HB grade finally came back to normal facial function. 56% of III HB grade patients improved to II grade and 11% to I HB grade. None of patients who were directly assessed as IV HB remained stabile. 85% of them improves (46% in to III grade, 39 in to II grade) but 15% (two patients) get worsted in to V or VI grade. 66% of patients improved from V HB grade into II HB (22%), III HB (22%) or IV HB (22%). Reminded 34% of patients are still in V HB grade. Only 20% of patients with facial palsy directly after operation improved (every in to III HB grade). One of the goals of present paper is to estimate dynamics of facial function recovery. 72 out of 120 patients were in I HB grade at discharge from hospital. Their status unchanged during 18 months observation period. In most of patients (75%) demonstrated II H-B grades (n=12) directly after operation facial status stabilised until 4^th month after surgery however two of them stabilised in 11^th or 12^th month. On the basis of Gaussian frequency curve we can conclude that expected facial status stabilisation period (EFSSP) is 4 months. In 67% of patients assessed as III H-B grade (n=9) directly FN status stabilised also until 4^th month but in one case for FN status stabilisation we have to wait until 15^th month. We estimate EFSSP in III HB grade patients group as 5 months. In IV HB grade patients group (n=13) FN function stabilised between 3^rd and 12^th month after surgery. Estimated, on the basis of Gaussian curve EFSSP in this group is 9 months. Only one case from V HB patients group (n=9) stabilised before 8^th month. In 89% of patients FN function stabilised in period between 8^th and 18^th month after surgery (44% after one year). EFSSP in this group is 10 months. One patient assessed as VI HB grade immediately after surgery stabilised in 6th month, second one in 16^th month.

In recent studies authors are quite agree in question of predictive factors for postoperative nerve function. Fenton et al. [Ref. 4], using multivariate logistic regression model, have found that independent predictors of a favourable initial facial status outcome are tumor size and the minimum intensity required to provoke a stimulus threshold event stimulating medially to the tumor. Other authors advocate as predictors: preoperative EnoG [Ref. 12], intraoperative burst or train response [Ref. 13], intraoperative four-channel responses monitoring [Ref. 14], immediate post-op facial function in context to late outcome [Ref. 2], [Ref. 4] and tumor histology in non-vestibular schwannoma CPA tumors [Ref. 15]. However excellent results in facial nerve preservation after CPA tumor excision dominant in recent reported series pure outcome (V^th or VI^th HB grade) is still noticed [Ref. 1], [Ref. 2], [Ref. 3], [Ref. 7], [Ref. 8], [Ref. 10], [Ref. 11], [Ref. 13], [Ref. 14], [Ref. 16]. In present series range of facial palsy is quite similar than in others but we encountered improvement to HB grade II even when grade V function was present directly after surgery. Commonly patients with HB grade V or VI are qualified for reconstructive or plastic procedures [Ref. 1], [Ref. 3], [Ref. 16], [Ref. 17]. The final assessment of their facial status finished at 12^th month after surgery [Ref. 1], [Ref. 17], [Ref. 18] (the “cut-off point in achieving a good postoperative recovery”) and the support for decision of reconstruction made is fact that that good facial outcome (HB grade I or II) from an immediate postoperative palsy is extremely rare [Ref. 19]. In our material we observed possibility of facial nerve function improvement even after 18 months of severe paresis (44% of immediate V or VI HB grade improved after one year). We advocate that qualifying patients with severe facial paresis for reconstructive or plastic procedures we should considered stabilization period of facial nerve function even 18 months after surgery.

Recovery of facial nerve clinical function after surgery for cerebellopontine angle tumor may prolong up to 18 months. During that period we should strongly considered any reconstructive or plastic interventions.