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Auditory and vestibular disorders
Korean Journal of Audiology 2011;15(2):76-80.
What Causes Incomplete Facial Function Recovery in Patients with Immediate Facial Paralysis Following Vestibular Schwannoma Surgery?.
Joo Hyun Kim, Jin Kim, See Young Park, Hyo Jin Chung, Won Sang Lee
1Department of Otorhinolaryngology, Inje University College of Medicine, Goyang, Korea. jinsound@gmail.com
2Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Korea.
Abstract
BACKGROUND AND OBJECTIVES
Preservation of facial nerve function in vestibular schwannoma (VS) surgery is still a significant operative challenge. Several prognostic factors correlate with postoperative facial nerve function. Most partial facial nerve damage can recover completely without functional defect. However, recovery of the facial nerve in some patients is either incomplete or non-existent. To evaluate the cause of incomplete facial function recovery at long term follow-up (> or =1 year), we analyzed the factors that influenced facial function recovery in a consecutive series of patients that had immediate post-operative, partial paralysis after VS surgery with preservation of neural integrity.
MATERIALS AND METHODS
We conducted a retrospective review of 143 cases of VS surgery that occurred between January 1994 and December 2008. Twenty-seven patients that had immediate, postoperative partial facial paralysis and normal preoperative facial function with intact nerve after tumor excision were analyzed with regards to age, sex, tumor size, tumor location, internal auditory canal (IAC) widening, duration of surgical procedure, postoperative complication, and facial function after a postoperative follow-up period of > or =1 year by the House-Brackmann (HB) grading system.
RESULTS
Of the 143 patients that underwent VS surgery, 27 (18.8%) patients had immediate, postoperative partial facial paralysis. At long-term follow-up, there were 11 (7.6%) patients with incomplete facial recovery. Facial function recovery after facial nerve injury did not show a significant difference in tumor size, surgical approach, or tumor location. However, preoperative IAC widening and the duration of the procedure were related to facial restoration after surgery.
CONCLUSIONS
The injured facial nerve during VS surgery showed incomplete recovery in many cases. Chronic compression of the facial nerve, together with IAC widening preoperatively, led to incomplete restoration of injured facial nerves.
Keywords: Facial paralysis;Vestibular schwannoma;Surgery

Address for correspondence : Jin Kim, MD, PhD, Department of Otolaryngology, Inje University College of Medicine, 2240 Daehwa-dong, Ilsanseo-gu, Goyang 411-706, Korea
Tel : +82-31-910-7114, Fax : +82-31-910-7518, E-mail : jinsound@gmail.com

Introduction


Facial nerve paralysis is a significant morbidity in patients that undergo vestibular schwannoma (VS) surgery. With the advent of the operative microscope in 1960, mortality and morbidity rates in the surgical excision of VS have declined and consequently the preservation of the facial nerve has become an essential aspect of VS surgery. Although facial nerve outcomes are now excellent in over 90% of patients in virtually all reports,1) and anatomical and functional preservation of the facial nerve has become routine with experienced physicians,2) facial paralysis always remains a major concern, and preservation of the facial nerve can still be challenging.
Several prognostic factors have been known to correlate well with postoperative facial nerve function. One such prognostic factor is the intracranial tumor size.3,4) It has been postulated that patients with cystic VS have poorer facial nerve outcomes compared with noncystic tumors.5) Patients with VS as a result of neurofibromatosis type 2 also have poorer facial nerve outcome.6)
Although most studies have reported on the long-term outcomes of facial nerve function related to prognostic factor, there are only a few reports on immediate postoperative facial nerve paralysis. Immediate postoperative facial nerve paralysis after VS surgery could be an important prognostic factor of final facial function and analyzing it can elucidate the cause of nerve damage during surgical manipulation of the facial nerve without delay. Even if a surgeon can confirm nerve integrity during surgical manipulation, immediate postoperative facial nerve paralysis indicates surgical neural injury and just neural patency cannot guarantee complete restoration of facial function. 
In this study, to evaluate the cause of incomplete facial function recovery at long-term follow up, we analyzed factors that influence facial function recovery in a consecutive series of patients that had immediate post-operative, partial paralysis after VS surgery with preservation of neural integrity.

Materials and Methods

Patients with immediate, postoperative facial paralysis that underwent VS surgery between January 1994 and December 2008 were included in this study. A retrospective chart review of the patients was performed and the following information relevant to the study was recorded: patient age, gender, initial signs, tumor size, tumor shape, neurological status at presentation, surgical approach, duration of surgical procedure, postoperative complications, and facial function after the patient recovered from anesthesia at discharge and 1 year postoperatively by House-Brackmann (HB) grading system. Patients with preoperative facial paralysis were excluded.
The mean age of the 143 patients was 48.5 years (range 11-73), and this set of patients consisted of 43 men and 100 women. The left side was involved in 81 cases whereas the right side was involved in 62. Diagnosis was confirmed by magnetic resonance imaging (MRI) in most cases. The sizes of tumors ranged from 6 mm to 60 mm, with a mean of 19.38±11.01 mm [standard deviation (SD)]. 
The surgical approach was selected on the basis of the location and size of the tumor and the presence or absence of serviceable hearing. Other factors, such as age, anatomy, and contralateral hearing levels, were also taken into consideration. If hearing preservation was not a goal, a translabyrinthine approach was typically used. The middle cranial fossa approach was selected in the case of laterally-located, small tumors, with serviceable hearing levels. However, for the final surgical approach, serviceable hearing was decided by the patient after careful counseling by a neuro-otologist.
The translabyrinthine and middle cranial fossa procedures were performed in an identical fashion. Facial nerve monitoring (NIM-Response 2.0 Nerve Integrity Monitoring System, Medtronic Xomed Surgical Products) was used to identify and confirm the function of the facial nerve intraoperatively.
The tumor was completely removed in all cases except two. CT with a bony window was performed within 1 day of the operation. Completeness of tumor resection, facial nerve function, including sign and symptoms, audiograms, if needed, and imaging materials were used to evaluate the patient's post-operative condition. Two patients were treated with staged operations, due to the large size of their tumors. Two patients had undergone radiosurgical treatment previously.
Univariate analysis was performed if the outcome (presence or absence of facial recovery) was associated with age, sex, tumor size, tumor origin, tumor location, IAC widening, duration for surgical procedure, and postoperative complication. Tumor location was divided according to fundus involvement or fundus intact, and brainstem indentation or brainstem intact. IAC widening was evaluated by calculating porus-width of internal auditory canal of tumor located side subtracted from that of the normal side. Continuous variable predictors (age, tumor size, IAC widening, duration for surgical procedure) were evaluated with the Kruskal-Wallis test, whereas categorical variables (sex, tumor origin, tumor location, postoperative complication) were analyzed with Fisher exact test. 

Results

Patients with immediate, postoperative facial paralysis 
   Twenty-seven patients had immediate, postoperative and partial facial paralysis after tumor excision out of the 143 consecutive patients that underwent surgical removal of VS. The mean age of the 27 patients was 48.1 years (range 14-70), and this set of patients consisted of 12 men and 15 women. The left side was involved in 18 cases whereas the right side was involved in 9. The sizes of tumors ranged from 6 mm to 60 mm, with a mean of 25.6±13.4 mm (SD).
Average surgical timing from skin incision to skin closure was 8.14 hours with a range of 6.1 to 12.9 hours. Sixteen patients had IAC widening following MRI findings. Twenty-two patients underwent VS surgery via the translabyrinthine approach and 5 patients underwent it via the middle cranial fossa approach. Post-operative complications were found in 7 patients including cerebrospinal fluid (CSF) leakage in 5 patients and intracranial hemorrhage in 2 patients.
Of the patients who had post-operative, immediate facial paralysis with preserved integrity of facial nerve, 7 patients had facial function of HB grade II, 8 patients had HB grade III, 7 patients had grade IV, and 5 patients had grade V. With respect to HB grades, 8 patients improved by one grade, 9 patients by two grades, 3 patients by three grades and 7 patients had no change of facial function after VS surgery. The mean HB grade evaluated postoperative immediately, at discharge, and 1 year later was 3.4±1.1, 3.5±0.9, and 2.3±1.0, respectively (Arabic numerals used to allow decimals)(Fig. 1).

Patients with incomplete facial recovery (HB grade≥III)
The facial recovery after neural injury was influenced by tumor size, but this finding was not statistically significant in our study (p>0.05). In immediate postoperative partial facial paralysis patients, facial recovery was much less in patients with large tumors 1 year later and this was not significantly different compared with small tumors. However, the incidence of postoperative facial paralysis in patients with large tumors increased with tumor size statistically (p<0.05). 
The tumor origin which had been confirmed at surgical field and preoperative MRI findings did not influence postoperative facial recovery. An unknown origin tumor that could not be confirmed at the surgical field due to a large size or severe adhesion did not show a significant difference in restoration compared with a tumor of different origin.
There was no significant difference in facial recovery between the translabyrinthine approach and middle cranial fossa approach. Since the surgical approach was determined by tumor size and hearing level, there was a difference in the tumor size between the two groups. The tumor size of patients treated by the translabyrinthine approach was 28.0±13.3 (mean± SD) and 14.2±7.12 in patients treated with the middle cranial approach. 
A 17% frequency of CSF leak represented the most common complication. Two patients experienced cerebral hemorrhage. The average change of facial function in patients with surgical complication was 3.8, 3.2 and 2.5 immediately postoperative, at discharge and 1 year postoperative, respectively, but these findings were not statistically different.
The tumor location in IAC and cerebellar pontine angle was divided according to tumor involvement of the fundus and brainstem. Preoperative fundus or brainstem involvement on MRI was not related to facial recovery after VS surgery. 
The facial recovery after injury of facial nerve was much affected by preoperative IAC widening on MRI findings. Although the IAC widening was related to tumor size and its presence did not always have a linear correlation with tumor size (average tumor size in patients with IAC widening was 28.8 mm and 21.1 mm in patients without widening, no statistical significance in t-test). Facial restoration in patients with preoperative IAC widening on MRI was low after 1 year follow-up. Four patients improved by one grade, 4 patients by two grades, and 8 patients had no change of facial function after VS surgery. Two patients had increased facial nerve deficit in the interval between hospital discharge and follow-up examinations performed at 1 year. At the final follow-up, 8 patients had facial function of HB grade II, 5 patients had HB grade III, 2 patients had grade IV, and 1 patient had grade V. The mean HB grade evaluated postoperative immediately, at discharge, and 1 year later was 3.2±1.20, 3.0±0.96, and 2.64± 0.99, respectively. 
The duration of the procedure highly correlated to facial restoration after surgery. The duration of VS surgery was prolonged in patients with large schwannoma, severe adhesion and anatomical variation of the facial nerve. The time required for the procedure decreased as the experience of the surgical team increased (Table 1).

Discussion

Permanent facial paralysis as a consequence of incomplete recovery after a facial nerve injury poses a grave social and emotional challenge to the health of VS patients. In some patients, psychological distress may become an even more significant problem than the functional loss. In our study, the incidence of immediate, postoperative and partial facial paralysis associated with VS surgery was estimated to be 18.8% (27/143) and long-term follow-up revealed partial facial paralysis to be 11.1% (16/143)(partial facial paralysis included near normal facial function or HB grade≤2). Following an insult to the facial nerve without nerve discontinuity, what causes differences in the functional restoration of facial nerves? 
Published reports show that approximately 90% of VS patients have normal or near normal post-operative facial function.1,2) However, these previous studies reported on the end result of facial function including the reconstruction technique of the facial nerve due to loss of integrity of neural patency. In postoperative observation of VS surgery, we frequently encounter patients with postoperative partial paralysis due to iatrogenic neural damage while preserving the facial nerve. 
Following VS surgery, facial paralysis may present with an immediate postoperation or develop with delayed onset. In general, when the paralysis is incomplete immediately after the operation, a "wait-and-see" policy is indicated, because most partial facial nerve damage recovers completely without functional defects. 
Based on this, what causes the partial sequelae of facial function in some patients with VS surgery? Recovery of the facial nerve in some patients is either incomplete or non-existent. The unexpected and incomplete recovery of several cases involving facial nerves is not yet explained.
Tumor size, patient age, previous treatment, intraoperative monitoring of facial nerve and surgical approach have all been implicated as prognostic factors of facial function.7,8) In our study, preoperative widening of the IAC on MRI is associated with poorer postoperative facial function 1 year after the development of facial paralysis.
The widening of the IAC is clinically significant for the diagnosis of VS, but its mechanism remain unclear. As a tumor grows, the wall of IAC will be compressed and such pressure will increase osteoclast activity.9,10,11) This may explain the enlargement of the IAC. One of the mechanisms of facial nerve damage is compression of the nerve fiber in the IAC.12,13) Even though the facial nerve does not lose function preoperatively, it is thought that the vulnerability of the facial nerve can increase as the IAC pressure increases after manipulation of tumor resection by mechanical and chemical activity. However, it is reported that the degree of expansion of the IAC would not correspond to the deterioration in neural function.14) 
The average duration for the procedure was 8.1 hours. The time required for the procedure decreased with the increased experience of the surgical team. In the surgical procedure, finding the course of the facial nerve buried in the tumor as well as tumor removal without facial nerve damage can effect the duration of the procedure. A long procedure can lead to frequent surgical injuries of the facial nerve. In our series, there were significant differences of facial recovery in the duration of the procedures. However, the duration cannot directly predict postoperative facial function at the 1 year follow-up. Because duration is related to tumor size, the adhesiveness of the facial nerve and location of the tumor is relevant. It is considered that the size and location of tumor is related to facial recovery after VS surgery, but in our study there was no significant difference observed. 
Preoperative blink reflex and electroneurography can yield important information about postoperative facial function. However, most patients with acoustic schwannoma have normal facial function preoperatively, so we do not examine blink reflex or electroneurography routinely, and this was found to be one limitation of our study, due to retrospective data collection.
In conclusion, an injured facial nerve recovers incompletely in many cases during and after VS surgery. Chronic compression of the facial nerve together with IAC widening preoperatively can lead to incomplete restoration of the injured facial nerve.


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