Abstract
Facial nerve schwannoma (FNS) is an extremely rare benign tumour that may arise anywhere along the course of the facial nerve; the standard treatment is total removal via microsurgery. Stereotactic radiotherapy has been shown to be effective in the treatment of skull base tumours, in particular for acoustic neuromas; it is interesting to notice that also the few data existing in literature about the use of radiotherapy for non acoustic schwannomas show an excellent local control rate and few adverse effects. Here we report a case of facial nerve neuroma, involving the nerve sheath from the geniculate ganglion to the parotid gland, treated with fractionated stereotactic radiotherapy after debulking surgery.
1
Introduction
Facial nerve schwannomas (FNSs) are extremely rare benign tumours that may arise anywhere along the course of the facial nerve, from the cerebello-pontine angle to the neuro-muscular junction, but there is a predilection for involvement of the geniculate ganglion (65.8%) ; from the geniculate ganglion an FNS may extend to involve the tympanic and/or labyrinthine portions of the facial nerve resulting in a variety of clinical symptoms and surgical challenges. Uncommonly FNSs involve the middle cranial fossa by means of direct upward spread through the roof of the temporal bone, or may have an anterior spread through the facial hiatus .
The standard treatment for non acoustic intracranial neuromas is total removal via microsurgery; despite advances in skull base surgical techniques the resection is frequently associated with development of new neurological deficits and complete removal is often impossible . Stereotactic radiotherapy has been shown to be effective in the treatment of acoustic neuromas but not many data exist in literature about the use of radiotherapy for non acoustic schwannomas.
Here we report a case of facial nerve neuroma, involving the nerve sheath from the geniculate ganglion to the parotid gland, treated with fractionated stereotactic radiotherapy after debulking surgery.
2
Case report
In November 2009 a 48 years old woman was referred to our Department for a right facial nerve neuroma diagnosed 5 months before: after the onset of right eye lacrimation and a painful mass on the right parotid gland an MRI showed a soft tissue lesion, with avid contrast enhancement, on the cranial portion of the parotid gland extending trough the stylomastoid foramen into the intra-temporal segment of the facial nerve. A neurological examination revealed a partial facial palsy (House–Brackmann grade III). Pure-tone audiometry indicated slight bilateral neuro-sensorial hearing loss.
In June 2009 the patient underwent a superficial parotidectomy with extratemporal tumour debulking with histological diagnosis of schwannoma.
A post-operative MRI showed the T1 gadolinium-enhanced residual tumour extending from the stylomastoid foramen to the geniculate ganglion ( Fig. 1 ) and the patient accepted to undergo a fractionated stereotactic radiotherapy (FSRT) course for the residual mass. The patient was immobilized with a combination of a thermoplastic mask (Head Mask R-PRT3, Klarity) and a bite-block (3DLine®) fixed to a stereotactic frame support (Head Frame, 3DLine®); the frame for stereotactic coordinate generation (Multimodality Localizer CT/MRI, 3DLine®) was applied over the mask. For planning purposes a contrast-enhanced CT scan (GE LightSpeed® Scanner; GE Healthcare Diagnostic Imaging, Slough, UK) with a 1.25 mm slice thickness was obtained in axial mode; the post-operative MRI study was used for image registration with the planning CT; CT images were transferred to the Ergo stereotactic treatment planning system (Elekta 3DLine® Medical System PMM Vers. 1.6.3.1.) in order to contour the gross tumour volume (GTV), consisting of the intra-temporal disease from the cranial portion of the parotid gland across the stylomastoid foramen up to the intratympanic portion of the nerve, and to stereotactically localize the isocenter. CT images with a marker point (isocenter) and GTV contours were transferred from Ergo to Pinnacle (Philips Medical System, Andover, MA); CT and MRI images were automatically registered on Syntegra software (Pinnacle, Philips Medical System, Andover, MA). The CT-contoured GTV was corrected on CT–MRI registration; planning target volume (PTV) and organs at risk (OARs) were delineated. The PTV was defined as the GTV plus a 3 mm isotropic margin; eyes, lens, optic nerves and parotid glands on both sides, pituitary gland, brainstem and cord were delineated.
Treatment plan was produced on Pinnacle3 version 8.0 m (Philips Medical System, Andover, MA); GTV and PTV were respectively of 1.79 ml and 7.97 ml; 7 no-coplanar beams (6 MV photons) were used to perform the treatment plan ( Fig. 1 ). The PTV was enclosed within the 95% isodose; the total dose of 54 Gy (2 Gy per fraction, 5 days a week) was prescribed to the 95% isodose.
The patient was treated with Linac Elekta Synergy® S (Elekta Oncology Systems, Crawley, UK) equipped with Beam Modulator TM (leaf width of 0.4 cm at the isocenter) and a kilovolt (kV) cone-beam computed tomography (CBCT). During the first week of treatment a daily CBCT was acquired before each treatment session to verify set-up errors ; after the second week of radiotherapy the set-up alignment was verified weekly with a CBCT and daily with portal images.
The patient was monitored during the treatment and then periodically by neurologic examination and tests (electroneurography, audiometry and impedance test). Follow-up images (MRI) were obtained at 6 month intervals during the first year after FSRT, to assess local tumour control, then annually.
After a follow-up period of 30.2 months the patient has no new cranial nerve deficit and no adverse effects have been diagnosed. A recent MRI showed that the tumour size was slightly reduced, from 1.79 ml to 0.96 ml, with an evident decreased gadolinium enhancement; the patient experienced an improvement in control of her right eyelid without facial palsy modification (House–Brackmann grade III).
2
Case report
In November 2009 a 48 years old woman was referred to our Department for a right facial nerve neuroma diagnosed 5 months before: after the onset of right eye lacrimation and a painful mass on the right parotid gland an MRI showed a soft tissue lesion, with avid contrast enhancement, on the cranial portion of the parotid gland extending trough the stylomastoid foramen into the intra-temporal segment of the facial nerve. A neurological examination revealed a partial facial palsy (House–Brackmann grade III). Pure-tone audiometry indicated slight bilateral neuro-sensorial hearing loss.
In June 2009 the patient underwent a superficial parotidectomy with extratemporal tumour debulking with histological diagnosis of schwannoma.
A post-operative MRI showed the T1 gadolinium-enhanced residual tumour extending from the stylomastoid foramen to the geniculate ganglion ( Fig. 1 ) and the patient accepted to undergo a fractionated stereotactic radiotherapy (FSRT) course for the residual mass. The patient was immobilized with a combination of a thermoplastic mask (Head Mask R-PRT3, Klarity) and a bite-block (3DLine®) fixed to a stereotactic frame support (Head Frame, 3DLine®); the frame for stereotactic coordinate generation (Multimodality Localizer CT/MRI, 3DLine®) was applied over the mask. For planning purposes a contrast-enhanced CT scan (GE LightSpeed® Scanner; GE Healthcare Diagnostic Imaging, Slough, UK) with a 1.25 mm slice thickness was obtained in axial mode; the post-operative MRI study was used for image registration with the planning CT; CT images were transferred to the Ergo stereotactic treatment planning system (Elekta 3DLine® Medical System PMM Vers. 1.6.3.1.) in order to contour the gross tumour volume (GTV), consisting of the intra-temporal disease from the cranial portion of the parotid gland across the stylomastoid foramen up to the intratympanic portion of the nerve, and to stereotactically localize the isocenter. CT images with a marker point (isocenter) and GTV contours were transferred from Ergo to Pinnacle (Philips Medical System, Andover, MA); CT and MRI images were automatically registered on Syntegra software (Pinnacle, Philips Medical System, Andover, MA). The CT-contoured GTV was corrected on CT–MRI registration; planning target volume (PTV) and organs at risk (OARs) were delineated. The PTV was defined as the GTV plus a 3 mm isotropic margin; eyes, lens, optic nerves and parotid glands on both sides, pituitary gland, brainstem and cord were delineated.
