Microsurgery of a rare case of abducens schwannoma: surgical techniques

Introduction

Non-vestibular schwannomas are very rare cases in the clinical context, among which trigeminal and jugular foramen schwannomas are the most common types. Abducens schwannoma is relatively very rare, and accounts for only about 1% of all intracranial schwannomas (1,2). Abducens schwannoma may originate from any part of the abducens nerve (VI), and is divided into cisternal, cavernous (3), or intraconal subtype. Sometimes the tumor may invade an extended area, for instance, Shibao et al. reported a case of dumbbell-shaped abducens schwannoma invading both cavernous sinus and cerebellopontine angle (CPA) via Dorello’s canal (4). Current treatments of abducens schwannoma include microsurgery (5) or stereotactic radiosurgery (SRS) (6). Imran Zaidi et al. reported resection of an abducens schwannoma using a trans-endonasal approach (7). Here, we introduced a case of abducens schwannoma removed by using the classic retro-sigmoid approach. We present this article in accordance with the SUPER reporting checklist (available at https://cco.amegroups.com/article/view/10.21037/cco-2025-aw-126/rc).

Preoperative preparations and requirements

This was a 54-year-old female patient who presented with headache and dizziness at admission. Upon physical examination, we found the patient had no eye movement deficits, and facial & auditory nerves function were normal, but showed slight unsteady walking and a positive Romberg sign. Magnetic resonance imaging (MRI) scan of the brain revealed a mass located at the right CPA, compressing brain stem (Figure 1), and the tumor was partially enhanced after contrast MRI scan (Figure 2). Thus, schwannoma is suspected before surgery, but it’s difficult to identify its origin by MRI images. Considering tumor compression to brain stem and available microsurgical techniques nowadays, we selected craniotomy surgery for the patient, and classic retro-sigmoid approach was recommended, which is a safe and commonly used surgical approach.

Figure 1 T2-weighted brain MRI scan showed a lesion located at right CPA, with partial hyperintense signal inside the tumor. CPA, cerebellopontine angle; MRI, magnetic resonance imaging.

Figure 2 Contrast brain MRI scan showed the lesion was partially enhanced, schwannoma is suspected, and the brain stem was compressed by the tumor. MRI, magnetic resonance imaging.

Step-by-step description

During the surgery (Video 1), the patient was fixed on lateral position after general anesthesia, and electrophysiological monitor electrodes were placed on the patient. After craniotomy by retro-sigmoid approach, we first isolated the trigeminal, facial and auditory nerves from the tumor surface. Then we separated the posterior group of cranial nerves and the anterior inferior cerebellar artery (AICA) from the tumor, and cut the supply artery from the AICA. Tumor debulk was performed subsequently to decrease the tumor volume. After sufficient decompression of the tumor, there was space to identify the tumor-bearing nerve, which was found to arise from the brain stem end of the abducens nerve. Finally, a total resection of the tumor was achieved after careful detachment of the tumor from the brain stem, and protection of the vertebral artery (VA) should also be verified. During operation, we also performed an electrophysiological monitor for the facial nerve (0.03 mA stimulation) and the auditory nerve [brainstem auditory evoked potential (BAEP)] (Figure 3), both of which were preserved well.

Figure 3 During operation, electrophysiological monitor was performed for facial nerve (0.03 mA stimulation, left picture) and auditory nerve (BAEP, right picture) function, both of which were preserved well. BAEP, brainstem auditory evoked potential.

All procedures performed in this study were in accordance with the ethical standards of the Huashan Hospital research committee and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article, accompanying images and the video. A copy of the written consent is available for review by the editorial office of this journal.

Postoperative considerations and tasks

The patient tolerated the surgery very well, but had transient abducens paralysis and ataxia after surgery, which gradually improved in 3 months after rehabilitation training. There were no other new neural deficits for the patient, such as facial paralysis, dysphagia or hoarseness. The histologic feature was typical of a schwannoma (Figure 4). The follow-up brain MRI scan 3 months after surgery indicated no residual or relapse of the tumor (Figure 5).

Figure 4 Pathological analysis showed typical of schwannoma (×200). (A) H&E; immunohistochemical staining for (B) S-100, (C) Vimentin, and (D) SOX-10. H&E, hematoxylin and eosin.

Figure 5 Follow-up brain MRI images indicated no residual or relapse of the schwannoma. (A) T2 scan; (B) contrast scan. MRI, magnetic resonance imaging.

Tips and pearls

For this rare case of abducens schwannoma, some points need to be noticed during the whole therapy process. First, pre-operative diagnosis of abducens schwannoma is always difficult from the clinical manifestation and radiological features. In our case, it’s mainly evaluated by intra-operative findings, because there was no obvious eye movement problem at admission; Second, if there is no enlargement of internal auditory canal (IAC) or no dysfunction of posterior group of cranial nerves, schwannoma located at CPA should be sometimes taken into account as abducens schwannoma; Third, classic retro-sigmoid approach is sufficient to exposure the tumor and achieve total resection of the tumor.

Discussion

Intracranial schwannomas usually arise from sensory nerves, most frequently from the vestibular nerve (VIII). But motor nerves are rarely affected, for instance, abducens schwannoma is an extremely rare case, which was first reported by Chen in 1981 (8). Diagnosis of abducens schwannoma is always difficult from the clinical manifestation and radiological features before surgery. In our case, it’s mainly evaluated by surgical findings. Surgical approaches to abducens schwannoma depend on the location of the tumor. In our case, the classic retro-sigmoid approach is sufficient to expose and resect the tumor. During the surgery, protection of the trigeminal, facial & auditory nerves, and the posterior group of cranial nerves was very important, using intra-operative electrophysiological monitoring. Then the key step was to identify the tumor-bearing nerve. In our case, it’s proved to be cisternal-segment abducens schwannoma. In addition, isolating AICA and VA during tumor resection is necessary to decrease post-operative complications. After sufficient tumor decompression, separation of the tumor-bearing tumor from the brain stem and a total resection of the schwannoma was finally achieved.

The patient tolerated the surgery well but suffered from transient abducens paralysis and ataxia after surgery, which gradually improved in 3 months. Nakamizo et al. reported a case of abducens nerve schwannoma in which the course of the abducens nerve was intraoperatively unclear but complete recovery was achieved, and suggested that subcapsular dissection may help functional recovery (9). Current treatments of abducens schwannoma include microsurgery (5) or SRS (6,10). Langlois et al. proposed that SRS for schwannomas originating from oculomotor, trochlear, and abducens nerves is effective and could provide tumor control rates similar to those for other cranial nerve schwannomas. SRS allows improvement of diplopia in the majority of patients. However, in our case, the surgical resection is the first option because of the tumor compression to the brain stem.

Conclusions

Here, we report a rare case of cisternal-segment abducens schwannoma in a female patient. Classic retro-sigmoid craniotomy was recommended for tumor resection. During the surgery, the tumor was found to arise from the abducens nerve, and a total resection of the schwannoma was finally achieved. The patient had transient abducens paralysis and ataxia after surgery, but gradually improved in 3 months. The follow-up brain MRI images 3 months after surgery indicated no residual or relapse of the tumor.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the SUPER reporting checklist. Available at https://cco.amegroups.com/article/view/10.21037/cco-2025-aw-126/rc

Peer Review File: Available at https://cco.amegroups.com/article/view/10.21037/cco-2025-aw-126/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://cco.amegroups.com/article/view/10.21037/cco-2025-aw-126/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the Huashan Hospital research committee and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article, accompanying images and the video. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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