Surgical management of large lower cranial nerves schwannomas: long term results of a less aggressive resection strategy

doi:10.21203/rs.3.rs-3879358/v1

Background

In an effort to reduce the high morbidity and life-threatening complications after radical resection in large schwannoma surgery, alternative strategies of nontotal resections have emerged.

Objectives

To evaluate the long term clinical and oncological outcome after lower cranial nerves (LCN) schwannoma surgery operated on with a cranial nerve-sparing technique.

Methods

Single center retrospective cohort study of 8 consecutive patients harboring LCN schwannomas operated on between March 2005 and October 2021.

Results

The mean LCN schwannoma diameter was 33mm (range 26–51). Seven patients (87,5%) underwent a modified retrosigmoid approach. Three patients underwent gross total resection (37,5%), 3 had received neartotal resection (mean tumor residue 0,25cc) and subtotal resection in 2 patients who presented with an extracranial extension of the tumor (mean tumor residue 2,44cc). Both patients had received upfront additional GKRS. The three patients who presented with preoperative CN IX & X injuries recovered within 6 months after surgery. All of the five patients freed from any preoperative CNs IX & X symptoms experienced transient (80%) or definitive (one patient) disturbances after surgery. They all improved within 6 months but one who required long term gastrostomy feeding tube. This patient harbored a schwannoma originating from the glossopharyngeal nerve, which could not be anatomically preserved during surgery. Tumor control was achieved in 100% of cases with a mean follow-up of 91 months.

Conclusion

LCN schwannomas could be surgically removed through a less aggressive non-radical resection strategy with acceptable functional results and excellent tumor control.

Hypoglossal nerve schwannoma

lower cranial nerves schwannoma

Gamma Knife Radiosurgery

nontotal resection

tumor residue

Intracranial schwannomas represent 7 to 10% of primary intracranial tumors [10, 12]. They are divided into vestibular and non-vestibular schwannomas, which represent only 0.8–8% of all intracranial schwannomas [10, 11, 13–15]. Lower cranial nerves (LCN) schwannomas are rare pathological entities that can affect CN IX, X, XI (also called jugular foramen schwannomas) or CN XII. They can develop from the cervical region, jugular foramen, and hypoglossal canal. These tumors mostly develop in the parapharyngeal space (31%) and the cervical region (23%) [7]. Intracranial location only represents 19% of cases [7].

LCN schwannomas surgery, if carried out in a traditional radical way, usually requires sacrificing the nerve of tumor origin, which could lead to permanent life-threatening LCN deficit.⁷ In an effort to reduce the incidence of postoperative cranial nerve disturbances, alternative strategies of nontotal resections have emerged in schwannoma surgery [17, 18]. The “Functional Sparing Surgery” policy for large schwannomas consists in performing an optimal tumor resection while reducing the risk for the CN, underlying the possibility of leaving a tumor remnant. To emphasize the rational of this option, we retrospectively analyzed our series of consecutive patients operated on for large LCN schwannomas, assessing long term clinical outcome and tumor growth control.

Study design:

All patients who underwent surgical resection of a LCN Schwannoma between June 2006 and October 2021 in our institution were enrolled in this retrospective cohort study. During this period a total of 270 patients diagnosed with Schwannomas were operated on in our institution, of which 250 were vestibular schwannomas, 8 were LCN schwannomas, 8 were CN V schwannomas, 2 were facial nerve schwannomas and 2 originated from oculomotor nerves (see Fig. 1 – Flowchart).

The diagnosis of LCN schwannoma was radiologically, operatively and histologically confirmed in all cases. Informed consent of all patients was obtained, and our institutional local ethical committee approved this study (Aix-Marseille University Ethics Committee - Authorization number: 2018-24-01-003).

Patient characteristics:

Clinical features such as LCN (CN IX, X, XI, XII) examination, FN function (scored according to the House & Brackmann Classification (HB)) [5], cochleo-vestibular symptoms including Gardner-Robertson Hearing Scale (G&R) [3], and radiological examinations (including volumetric measurements performed pre- and postoperatively on axial Gadolinium-enhanced T1 weighted MR images– iPlan 3.0 Cranial Brainlab, Munich, Germany) [19] were recorded at presentation and during follow-up. Surgical findings such as extent of resection and anatomical and functional preservation of the nerves were registered.

Surgical protocol (modified retrosigmoid approach) [16]: (Figs. 2&3)

The patient is installed in a lateral position toward the opposite side. The head is fixed in a Mayfield 3-pin holder, the mastoid tip at the highest point. The ipsilateral shoulder is distracted inferiorly to increase the working space. Intraoperative facial nerve monitoring system is compulsory (NIM-Response® 3.0 Medtronic Xomed, Jacksonville, FL).

A straight retromastoid incision is carried out, starting above the pinna and ending-up at the level of the mastoid tip inferiorly. The occipital squama, from the asterion to the digastric groove, and the mastoid process anteriorly are exposed.

One burr hole is done under and below the asterion, which exposes the dura of the sigmoid sinus. The dura is detached from inner table of the bone. A 3 cm bone flap is cut while the mastoid air cells covering the posterior third of the sigmoid sinus are shaved (using a 6-mm cutting burr). A thin shell of compact bone is left and subsequently elevated with a sharp dissector to avoid tearing of the SS.

A curved dural opening is carried-out and reflected against the mastoid process using tacked up sutures placed adjacent to the SS to optimize exposure. The cerebellar hemisphere is protected with a piece of oxycellulose and cottonoids. The first intradural step is to open the cerebellomedullary cistern under the microscope to obtain optimal CSF depletion and get enough brain relaxation. The operative window is focused on the posterior pole of the tumor and the lower CNs. There is an attempt to identify the acoustic-facial bundle before starting the resection. The tumor capsule is then opened and extensive intracapsular debulking is carried-out using an ultrasonic aspirator. A maximum safe resection is carried out while preserving the CNs. The intraoperative decision to interrupt the resection is driven by the evidence of critical adhesion of the tumor capsule to a cranial nerve. There is no attempt to enter into the Jugular foramen neither to remove the extracranial part of the tumor.

At the end of the procedure, the dura usually cannot be closed in a watertight way. Interrupted sutures are done using a 5/0 prolen thread, while the defects are plugged using stripes of sub-occipital muscle with fibrin glue. The mastoid air cells are carefully sealed using bone wax to prevent CSF leak. The bone flap is putted back and maintained with titanium plates.

Postoperative Outcome:

Clinico-radiological follow-up was planned at 6 and 12 months after resection, and subsequently at 2, 3, 5, 7 & 10 years after surgery, and then once every 3 years thereafter. The postoperative tumor residue was assessed by a Gadolinium-enhanced MRI 6 months after surgery. Extent of resection was assessed by the volume of residue on the first postoperative MRI as gross total resection (GTR) (100% tumor clearance), near total resection (NTR) (tumor remnant < 5%), subtotal resection (tumor remnant between 5 and 10%), or partial resection (tumor remnant > 10%). The patients could then allocated into a Wait-&-reScan policy (small tumor residues) or upfront adjunctive GKRS treatment (large residues or extracranial component of the tumor). If radiological progression was demonstrated, a salvage radiosurgical GK treatment of the tumor residue was proposed.

Radiosurgical protocol:

Treatment was delivered using a Leksell Gamma Knife (Elekta Instrument AB, Stockholm, Sweden). The median dose directed at the tumor margin was 12 Gy, and the median isodose to the margin was 50%.

Population Study

(Table 1)

Table 1

Population study characteristics.
Characteristic	Nb
M/F (%)	5 (62.5) / 3 (37.5)
Mean age in years (range)	60 (44–69)
Hist. of prev. MS (delay in months)	1 (42)
Hist. of prev. GKRS	0
NF2 (%)	1 (12.5)
Clinical features (%) balanced instability cerebellar ataxia headaches hydrocephalus Trigeminal hypoesthesia diplopia (CN VI) Facial weakness hearing loss (CN VIII) LCN (dysphagia & dysphonia) Hypoglossal (tongue paralysis)	3 (37.5) 2 (25) 4 (50) 0 3 (37.5) 1 (12.5) 2 (25) 4 (50) 3 (37.5) 2 (25)
Radiological features Mean diameter in mm (range) / median Mean volume in cc (range) / median	33 (26–51) / 29 10 (4–25) / 7
Surgical Approach (%) TL RS	1 (12.5) 7 (87.5)
Extent of Resection (%) GTR NTR PR	3 (37.5) 3 (37.5) 2 (25)
Postop vol Residue in cc NTR group PR group	0.25 2.42
Mean Follow-Up in months / median	91 (25–170) / 89
M: male. F: female. GTR: gross total resection. MS: microsurgery. NTR: near total resection. PR: partial resection. RS: retrosigmoid approach. TL: translabyrinthine approach.

The study group was composed of 8 patients of which 5 were women (62.5%) and 3 men (37.5%). Median age at time of surgery was 60 years old (range 44–69).

One patient (12.5%) had been previously operated on in another center through an enlarged translabyrinthine approach (see Fig. 2). She had received a partial resection with a voluminous tumor residue. The sequential MR images showed evidence of progressive tumor growth with significant mass effect on the brainstem. She underwent salvage tumor resection 42 months after the first surgery.

One patient had clinical presentation highly suggestive of schwannomatosis. He harbored a LCN schwannoma in association with multiple schwannomas of the cauda equina. One patient had a confirmed medical history of neurofibromatosis type 2 (NF2). One other patient presented a contralateral vestibular schwannoma, but did not meet the Manchester’s criteria to conclude to NF2.

Presenting symptoms

(Table 1)

Four patients (50%) suffered from headache, but none presented symptoms related to hydrocephalus. Three (37.5%) patients reported balanced instability, 2 (25%) presented with cerebellar ataxia.

Only three patients (37.5%) presented with preoperative lower cranial nerves disturbances, clinically resulting in dysphagia and dysphonia in all of them (CN IX & X) in association with tongue paralysis (CN XII) in two patient.

Two patients (25%) reported facial hypoesthesia (CN V). Diplopia due to CN VI palsy was observed in one patient (12.5%). Two patients showed facial weakness (HB Grades 3 & 4) associated with intermedius nerve disturbances. One had been previously operated on in another center and the other one was the NF2 patient. These patients and two others (4 patients – 50%) showed preoperative non-serviceable hearing.

Radiological Features

(Table 1)

The mean largest cross sectional tumor diameter was 33mm (range 26–51/ median 29 mm); the mean tumor volume was 10 cc (range 4–25 / median 7 cc). The tumor appeared as a well-defined lesion homogeneously enhanced by Gadolinium in T1 weighted MRI in most patient. The MRI study showed evidence of jugular foramen involvement in five patients (62.5%) including two with a voluminous extracranial component, while the 3 others harbored LCN schwannomas which strictly developed in the CPA. One tumor presented a cystic component. No patient presented with radiological hydrocephalus. According to the Pellet et al. grading system [9], all 6 patients who presented with mixt nerves schwannomas harbored type A tumors (primilarly intracranial, with minimal extension to the JF). The two patients who harbored hypoglossal schwannomas presented with dumbbell-shaped tumors (with intra & extracranial extension).

Surgical Features

(Figs. 3&4 - Table 1)

Seven patients were operated on through a modified retrosigmoid approach (87.5%). The last patient had been previously operated on through an enlarged translabyrinthine approach.

The schwannoma originated from the glossopharyngeal nerve in 2 (25%), the vagus nerve in 4 (50%) and the hypoglossal nerve in 2 (25%) patients. Gross total resection (GTR) could be safely achieved in three patients (37.5%). Three patients underwent a near total resection. In those configurations, the tumor arose from CN IX & X. The glossopharyngeal nerve, of which the schwannoma was originating, could not be anatomically preserved during surgery in one case. A small tumor residue (0.16cc) was left against the choroid plexus in that case. In another case, a little tumor remnant (0.07cc) was left against CN IX because of strong adherences. A tumor remnant was left into the Jugular foramen in the last case (0.52cc). The mean postoperative tumor residue volume in the NTR group was 0.25 cc (0.07–0.52 cc). The two patients who harbored a schwannoma with a voluminous extracranial component underwent a partial tumor resection (25%). Both originated from CN XII. There was no attempt to enter into the hypoglossal canal neither to remove the extracranial part of the tumor (extracranial tumor residues: 2.18 & 2.69 cc).

Complications:

The mean length of hospital stay was 8 days (range 5–14). Three patients (37.5%) required postoperative total parental nutrition, with gradual resumption of oral feeding within a week. No postoperative hematoma, CSF leak, meningitis, or hydrocephalus occurred. The NF2 patient died seven years after surgery. Death was caused by respiratory distress syndrome related to a thoracic tumor.

Cranial Nerve Preservation: (Table 2)

Table 2: Individual patient clinical presentation and cranial nerve outcome.

Patient	Age	Medical History	CN Origin	Clinical Presentation	Early postoperative new CN deficit	6 months postoperative CN outcome
1	44	NF2	X	CN V, VII (Grade 4), VIIbis, VIII, Cereb ataxia	CN X (dysphagia/dysphonia)	Total recovery CN V, CN X Persistant CN VII, VIIbis, VIII
2	60		XII	CN V, VI, VIII, IX, X, XII, Cereb ataxia	CN VII (Grade 5)	Total recovery CN VI, IX, X Persistant CN V, VIII, XII
3	61	VS Koos 3 (contralateral)	IX	Headaches	CN X (dysphagia)	Total recovery CN X
4	55		X	CN IX, X	Worsening CN X (dysphagia/dysphonia)	Total recovery CN IX, X
5	56	Surgery 2011	XII	CN VII (Grade 3), VIIbis, VIII, X, XII		Improvement CN X, Persistant CN VII, VIIbis, XII
6	68		X	Cereb ataxia	CN VIII, CN X (dysphagia/dysphonia)	Persistant CN X (slight dysphagia with solids)
7	69		IX	CN VIII, Cereb ataxia	CN X (dysphagia/dysphonia)	Persistant CN VIII, CN X (gastrostomy)
8	68	Schwannomatosis	X	Asymptomatic	CN X (dysphonia)	Total recovery CN X

Cereb: cerebellar. CN: cranial nerve. VS: vestibular schwannoma.

Table 3: Individual patient surgical findings and tumor control outcome.

Patient	Age	Medical History	Tumor diameter (in mm)	Surgical Approach	CN Origin	Extent of Resection	Tumor Residue (volume)	Adjuvant Treatment	Follow-up (months)	Tumor Residue Last FU
1	44	NF2	28	RS	X	NTR	0,075		84	0,059
2	60		40	RS	XII	PR	2,808	GKRS	170	2,690
3	61	VS Koos 3	26	RS	IX	GTR	0		131	0
4	55		30	RS	X	GTR	0		140	0
5	56	Surgery 2011	51	TL	XII	PR	2,136	GKRS	94	1,593
6	68		27	RS	X	GTR	0		34	0
7	69		35	RS	IX	NTR	0,518		32	0,449
8	68	Schwannomatosis	28	RS	X	NTR	0,161		14	0,136

CN: cranial nerve. GTR: gross total resection. NTR: near total resection. PR: partial resection.

Lower cranial nerves:

Of the three patients who presented with preoperative CN IX & X injuries, one totally recovered in the early postoperative period, while the 2 others experienced transient worsening of the symptoms in the early postoperative period. Both recovered within 6 months after surgery.

All of the five patients freed from any preoperative CNs IX & X symptoms experienced transient (80%) or definitive (one patient − 20%) disturbances after surgery. They all improved within 3 to 6 months but one who retained long term laryngeal and pharyngeal paralysis in association with hypertonia of the upper esophageal sphincter. This patient harbored a schwannoma originating from the glossopharyngeal nerve, which could not be anatomically preserved during surgery. He required long term gastrostomy feeding tube.

The two patients who presented with preoperative hypoglossal nerve palsy harbored schwannomas originating from CN XII. The anatomical preservation of the nerve could not be achieved during surgery. They retained hemi-tongue paralysis. No patient experienced new postoperative hypoglossal palsy.

Cochlear nerve:

One patient experienced postoperative cophosis. None of the 4 patients who presented with hearing loss recovered serviceable hearing after surgery. As a reminder, one had been previously operated through an enlarged translabyrinthine approach, and one other was a NF2 patient.

Facial nerve:

Immediately after surgery, among the 6 patients with normal preoperative FN function, 5 (83%) retained a HB Grade I FN function, while 1 patient (16%) harbored a severe HB Grade V postoperative FN palsy. At last follow-up examination, he retained long-term intermediate HB Grade III FN function and developed a crocodile tears syndrome.

None of the 2 patients who presented with preoperative FN palsy recovered after surgery. One of these patients developed postoperative hemifacial spasm that required specialized treatment with botulinum toxin.

Other cranial nerves:

The patient suffering from preoperative diplopia due to CN VI palsy was released from this symptom 6 months after surgery. Of the two patients who reported facial hypoesthesia, one recovered while the other one improved after surgery. None of the patients freed from this symptom before surgery have developed a postoperative facial hypoesthesia.

Tumor Control: (Table 3)

The mean duration of radiological follow-up was 91 months (range 25–170 / median 89 months). Of the three patients who had received GTR, none showed evidence of tumor recurrence after surgery. The 3 patients who underwent NTR had been allocated into a Wait-&-rescan policy. Two patients had received additional GKRS of the extracranial part of the tumor residue (respectively 2.14 and 2.69cc) 6 months after surgery. Both experienced tumor volume decreasing after GKRS. Tumor control was achieved in 100% of cases. No patient presented evidence of regrowth of the tumor residue during the follow-up period.

LCN schwannomas are rare pathological entities. During the study period, 270 patients underwent a surgical resection of an intracranial schwannoma, of which only 8 (3%) were LCN schwannomas. Because of the life-threatening complications in lower cranial nerves schwannomas surgery, patients harboring small tumors are preferentially oriented toward GKRS, with satisfying functional outcome and tumor control reported in the literature [4, 6, 8, 21]. Anyway, large LCN schwannomas must be surgically resected. In an effort to reduce postoperative CN deficits in CPA tumors surgery, alternative non-radical resection strategies have emerged within the past decades. We report our experience of this “fonctionnal sparing surgery” policy. We believe that patients harboring voluminous LCN schwannomas can be operated on through a less dilapidating surgical approach and a less aggressive strategy regarding to tumor resection, with satisfying functional and oncological long-term outcome.

Surgical approach & strategy:

Total removal of LCN tumors usually requires the sacrifice of some nerve's rootlets. In order to preserve the LCN anatomy and function, we moved to a less aggressive strategy of optimal tumor resection, leaving a tumor residue in case of strong adherence to any neurovascular structure. In doing so, only three patients underwent a gross total resection (37,5%). In our study, an anatomical preservation of CN IX, of which the tumor arose, could not be achieved in one case (12,5%). This patient retained long term laryngeal and pharyngeal paralysis and required long term gastrostomy feeding tube. This illustrates how crucial it is to preserve those CNs function. However, in all cases where CN preservation could be anatomically performed, patients experienced postoperative transient worsening of the LCN function which recovered within 6 months after surgery. Thus it is necessary to inform the patient before surgery, and work in strong collaboration with the otorhinolaryngology department. Even the patients presenting with preoperative CN IX & X injuries totally recovered or improved within 6 months after surgery. They only retained long term occasional difficulties swallowing solid foods. Thus, preoperative dysfunction of the LCN may be reversible, which justifies trying to anatomically preserve the nerve of tumor origin. Wilson & al [20] reported 50% new LCN palsy after GTR of jugular foramen schwannomas, related to the sacrifice of the nerve of tumor origin. Furthermore, none of the two patients presenting with preoperative LCN deficit recovered after surgery. In total, 83% of the patients in this study (five other six) retained long term LCN deficits. Similar results are reported in other studies about radical resection of LCN schwannomas through skull base approaches [2, 12].

Our policy is to deliberately no attempt to resect the extracranial part of the tumor, which would be subsequently addressed toward GKRS. Thus, we opted for a no time-consuming and less agressive cisternal approach, that could be performed by a regular neurosurgeon (easy to go & easy to leave). The modified RS approach [16] focuses on the LCN nerves. It offers a sufficient operative window to address LCN schwannomas, while avoiding in the meantime manipulating the cerebellum due to the CSF depletion obtained by opening the cerebello-medullary cistern. Traditional extra-intracranial techniques are cumbersome and laborious procedures, which can result in inherent complications of the technique [1, 2, 12, 20]. Through this approach, a GTR of the intracranial part of the tumor could be achieved in 62,5% of cases, while a NTR was done in the other 37,5%. The mean length of hospital stay was 8 days (range 5–14). No patient experienced postoperative hematoma, CSF leak, meningitis, or hydrocephalus. Moreover, both patients who harbored an extracranial tumor residue treated with adjunctive GKRS experienced decreasing of the tumor volume with tumor control 94 & 170 months after surgery.

Other CNs preservation:

As slow growing tumors, symptoms related to LCN schwannomas usually do not manifest until the tumor reaches a large size. Intracranial and foraminal tumors have the longer duration as opposed to extracranial tumors, because of their slow insidious growth pattern [11]. Therefore, it is not surprising that patients harboring LCN schwannomas presented with symptoms related to acoustic-facial bundle, CN V, CN VI or cerebellar disturbances, as described in the literature [1, 2, 7, 11, 12, 15, 20]. Thus, the most common presenting clinical symptoms reported by Bakar in a review paper about surgical series of jugular foramen schwannomas (192 patients) were hearing loss (48.2%), tinnitus (24.9%); dysphagia (23.4%); ataxia (23.4%); and hoarseness (21.2%) [1].

Although no postoperative worsening of CN V or VI occurred, it is important to inform the patient of the potential deterioration of hearing or FN function (one patient in our study, who harbored a voluminous tumor extending from LCN to the Meckel’s cave; he retained long term HB Grade III FN function and cophosis). A postoperative FN palsy is reported in 13–50% of cases in the literature [2, 12, 20]. Interestingly, none of the patients who presented with hearing loss recovered after surgery, while a conservative cisternal approach had been performed.

Tumor control

Although none of the 3 patients who had received GTR showed evidence of tumor recurrence, it is also important to notice that none of those who had received nontotal resection experienced tumor regrowth after 91 months follow-up (range 14–170 / median 89 months). Two of them harbored an extracranial tumor residue, subsequently treated with GKRS. Both experienced tumor volume decreasing. The 3 patients who underwent NTR had been allocated into a Wait-&-rescan policy of the intracranial tumor remnant. Due to the small volume of tumor left and the sequential radiological monitoring, we reserve the right to offer them salvage GKRS in case of evidence of tumor regrowth in the future. These reassuring data support the idea of performing nontotal tumor resection in case of surgical difficulties, in order to preserve functionality as much as possible. Moreover, it has been previously described cases of tumor reappearance after GTR. Indeed, Bakar reported in his review paper 159 patients who had received GTR, of which 14 showed unexpected evidence of tumor recurrence (8,8% of cases) in a mean delay of 59,6 months [1].

Limitations:

There are several limitations inherent to the retrospective design of the study. The small number of subjects included in the population study precludes making a general conclusion. The quality of life has not been evaluated in this series.

Because of the high morbidity and life-threatening complications after radical resection in lower cranial nerves schwannoma surgery, patients harboring small tumors should be addressed toward GKRS. When necessary, LCN schwannomas could be surgically removed through a less aggressive non-radical resection strategy with acceptable functional results and excellent tumor control. Tumor residues could be allocated into a Wait-&-reScan policy or upfront adjunctive GKRS treatment.

Cerebro-spinal fluid (CSF), Cranial Nerve (CN), Facial nerve (FN), Gamma-Knife radiosurgery (GKRS), Gardner & Robertson (G&R), Gross total resection (GTR), House & Brackmann (HB), Lower Cranial Nerves (LCN), Near total resection (NTR).

Conflict of interest: None of the authors disclose any conflict of interest in relation with this study.

Disclosure of Funding: None of the authors disclose any financial disclosure in relation with this study.

Availability of data and material: My manuscript has data included as electronic supplementary material.

Code availability: Not applicable

Ethics approval: Comité d’Ethique de l’Université d’Aix-Marseille (Authorization number: 2018-24-01-003).

Consent to participate: Informed consent was obtained from all patients

Consent for publication: All patients agreed for publication

Submission Statement: This manuscript has not been previously published in whole or in part or submitted elsewhere for review.

Author contributions: All authors have made substantial contributions so as to qualify for authorship, and have read and approved the final version of this manuscript.

LT, JR, PHR: conception and design of the study
LT, YEA, AB, GB: acquisition of data & drafting the Article
LT, YEA, GB: analysis and interpretation of data
JR, PHR: critically revising the Article

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Surgical management of large lower cranial nerves schwannomas: long term results of a less aggressive resection strategy

Status:

Journal Publication

Version 1

Abstract

Background

Objectives

Methods

Results

Conclusion

Figures

INTRODUCTION

METHODS

Study design:

Patient characteristics:

Postoperative Outcome:

Radiosurgical protocol:

RESULTS

Complications:

Cranial Nerve Preservation: (Table 2)

Lower cranial nerves:

Cochlear nerve:

Facial nerve:

Other cranial nerves:

Tumor Control: (Table 3)

DISCUSSION

Surgical approach & strategy:

Other CNs preservation:

Tumor control

Limitations:

CONCLUSIONS

Abbreviations

Declarations

References

Supplementary Material

Additional Declarations

Status:

Journal Publication

Version 1