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|LETTER TO EDITOR
|Year : 2021 | Volume
| Issue : 4 | Page : 1087-1088
Potential Utility of Sodium Fluorescein can Distinguish Tumor from Cranial Nerves in Vestibular Schwannoma Surgery
Basant K Misra, Ashish K Jha
Department of Neurosurgery, Hinduja National Hospital and MRC, Mahim, Mumbai, Maharashtra, India
|Date of Submission||08-Oct-2020|
|Date of Decision||17-Jan-2021|
|Date of Acceptance||29-Mar-2021|
|Date of Web Publication||2-Sep-2021|
Basant K Misra
Department of Neurosurgery, 2nd Floor, OPD Block, Hinduja National Hospital and MRC, Mahim West, Mumbai - 400 016, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Misra BK, Jha AK. Potential Utility of Sodium Fluorescein can Distinguish Tumor from Cranial Nerves in Vestibular Schwannoma Surgery. Neurol India 2021;69:1087-8
Small vestibular schwannomas can be managed by observation, radiosurgery, or microsurgery. There is no Level I evidence regarding the superiority of any particular option. Small tumors may cause facial nerve weakness and progressive hearing loss., Microsurgery for a small tumor is justified only when it does not produce any additional morbidity. However, there is a learning curve among the young neurosurgeons for this kind of surgery, and all adjuncts helping in identification of facial and cochlear nerves would be useful., We demonstrate for the first time the usefulness of sodium fluorescein (SF) in differentiating tumor from the cranial nerves at risk.
A 57-year-old gentleman presented with complaints of gradual decrease in hearing in the right ear over 9 months, with occasional episodes of giddiness. Magnetic resonance imaging (MRI) showed a small right cerebellopontine angle tumor (1.8 cm) with extension into the internal auditory meatus suggestive of a vestibular schwannoma [Figure 1]. Audiometry showed mild sensorineural hearing loss in the right ear. BERA (brainstem-evoked response audiometry) was negative. During the outpatient visit, the patient was presented with the pros and cons of the different options of management: observation, radiosurgery, and microsurgery. An initial period of observation showed increase in the tumor size, and the patient opted for microsurgery. During the preoperative counseling, the patient was informed about the use of SF during the surgery.
|Figure 1: Pre-op images of the case. (a and b) T2-weighted and postcontrast axial images, respectively. There is a mass lesion in the right cerebellopontine angle extending into the internal auditory meatus suggestive of vestibular schwannoma|
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The patient was operated in a lateral position with monitoring of facial nerve by electromyography (EMG). Because the BERA was negative preoperatively, intraoperative monitoring of hearing was not done. A standard retrosigmoid approach was undertaken with internal auditory meatus (IAM) drilling. Intravenous SF was injected at the beginning of craniotomy (5 mg/kg). Intraoperatively, the operative field was evaluated under the yellow filter multiple times: before the start of the tumor decompression, when the nerves were identified along the anteroinferior border of cisternal part of the tumor under the white light, when the nerves were identified at the level of the entry into the IAM, and eventually after total excision of the tumor [Figure 2].
|Figure 2: (a and b); first view of the tumor; (a) under white light and (b) under yellow filter. It shows the tumor is brilliantly enhanced under the yellow filter. The adjacent dural enhancement can also be appreciated. (c) first view of the cochlear nerve at the inferior border of the tumor. (d) the same field under yellow filter, which shows that the nerve is not enhanced but the tumor is enhanced. (e) first view of the facial nerve. The dissector is on the nerve. The integrity of the nerve was ascertained by the stimulation obtained using a stimulator dissector. (f) the same view under yellow filter, which shows the nerve is not enhanced|
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The facial nerve was confirmed with the response obtained when stimulated with the stimulator dissector at the anterosuperior border of the tumor. Under the yellow filter, the tumor was enhanced until it was completely excised, whereas the cranial nerves showed no enhancement at all. A small piece of the tumor attached to the posterior part of the facial nerve at its root exit zone, indistinguishable from the nerve under white light, could be distinguished from the facial nerves under the yellow filter because of their differential enhancement and could be totally excised. Opened air cells in the IAM were waxed and packed with fat and fibrin glue. The dura was closed watertight and mastoid air cells were obliterated with bone wax, fat, and glue. The bone flap was replaced and secured with plates and screws. The wound was closed in layers. Postoperatively, the patient had a normal facial function, and the postoperative MRI suggested complete excision [Figure 3].
|Figure 3: (a and b) Post-operative T2 and T1 postcontrast fat-sat images showing complete resection of the tumor|
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Functional preservation is of primary importance in the surgery of vestibular schwannoma. Although the risk of facial paresis might be very low in small and medium tumors, it is not nonexistent.,, Moreover, anatomical preservation of cochlear nerve, even in the absence of functional hearing, is desirable as the patient can be helped with cochlear implant. Hence, all adjuncts in differentiating the tumor from the thin strands of compressed nerves are desirable. The use of SF in vestibular schwannoma surgery is just an outreach of its already established use in gliomas. SF, the sodium salt of fluorescein, is a fluorescent dye that is excited by a light wavelength of 475 to 490 nm and emits radiation in the wavelength range of 510 to 520 nm. The use of SF in brain tumors was first described by Moore in 1947. Its use in skull base tumors and vascular neurosurgery have also been reported in the literature., We present a case, the first such report in the literature, of the use of SF to effectively distinguish the facial and cochlear nerves from the tumor because of their differential enhancement thus facilitating total excision of the tumor and preservation of both the facial and cochlear nerves.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]