Pediatric vestibular schwannoma with or without neurofibromatosis: Characteristic features and operative nuances

Pallav Garg; Sanjay Behari; Shishir Jaiswal; Awadesh Jaiswal; Vijendra K Jain; Ashok K Mahapatra

doi:10.4103/1817-1745.36764

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ORIGINAL ARTICLE

Year : 2007 \| Volume : 2 \| Issue : 2 \| Page : 58-66

Pediatric vestibular schwannoma with or without neurofibromatosis: Characteristic features and operative nuances

Pallav Garg, Sanjay Behari, Shishir Jaiswal, Awadesh Jaiswal, Vijendra K Jain, Ashok K Mahapatra
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow - 226 014, India

Correspondence Address:
Sanjay Behari
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Rae Bareli Road, Lucknow - 226 014, UP
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/1817-1745.36764

Abstract

Vestibular schwannomas (VSs) are rarer in children than in adults and are often associated with neurofibromatosis 2 (NF2). We focus on characteristic presentations of VSs in children (< 16 years old) both with and without NF2 and illustrate essential surgical steps using the retromastoid suboccipital approach. Materials and Methods: Three patients had unilateral tumors and five had bilateral tumors with associated NF2. On computed tomography (CT)/ magnetic resonance (MR) imaging, tumor diameters were measured parallel and perpendicular to the petrous ridge and vertically in coronal slices. The size of the VS was taken as the largest diameter in any one axis. Tumors were categorized as: Small: < 1 cm in size; Medium: 1-2.5 cm; Large: 2.5-4 cm and Giant: > 4 cm. Surgery was done in the park-bench position using the suboccipital retromastoid approach. Results: Raised intracranial pressure (ICP), often with visual deterioration, was the most commonly found presentation. Preoperative VIIth nerve involvement was grade IV in three, III in two and II in two patients. One of the patients with NF2 with proptosis did not have any VIIth nerve deficit. None of the patients had any functionally useful hearing on the side of larger tumor. Tumors were giant in six and large in two patients. In NF2 patients, two patients had large, two had medium-sized and one patient had a small contralateral tumor. Seven patients had significant hydrocephalus out of which three underwent ventriculoperitoneal shunt. Total excision of the larger lesion was performed in six patients. A small tumor remnant was left adherent to the preserved VIIth nerve in one patient. A patient with NF2 underwent excision of orbital neurofibroma and is awaiting surgery for VS. Two patients underwent bilateral VS excision. Anatomical preservation of the VIIth nerve was possible in six out of seven patients who underwent tumor excision. Postoperatively, symptoms of raised intracranial pressure and ataxia improved; visual deficits continued to deteriorate in two and VIIth nerve function deteriorated from grade III to V. Conclusions: In children, only a high degree of awareness facilitates early diagnosis of VS; otherwise, initial complaints may be neglected and the underlying tumor detected only after incapacitating raised ICP features appear. The retromastoid suboccipital approach is an effective approach for safe removal of large to giant-sized tumors.

Keywords: Facial nerve, neurofibromatosis type 2, pediatric patients, retromastoid suboccipital approach, vestibular schwannoma

How to cite this article:
Garg P, Behari S, Jaiswal S, Jaiswal A, Jain VK, Mahapatra AK. Pediatric vestibular schwannoma with or without neurofibromatosis: Characteristic features and operative nuances. J Pediatr Neurosci 2007;2:58-66

How to cite this URL:
Garg P, Behari S, Jaiswal S, Jaiswal A, Jain VK, Mahapatra AK. Pediatric vestibular schwannoma with or without neurofibromatosis: Characteristic features and operative nuances. J Pediatr Neurosci [serial online] 2007 [cited 2023 Dec 5];2:58-66. Available from: https://www.pediatricneurosciences.com/text.asp?2007/2/2/58/36764

Introduction

Vestibular schwannomas (VSs) are less frequent in the pediatric (≤ 16 years) age group than the adult population.^{[1],[2],[3],[4],[5],[6]} In children, they are often associated with neurofibromatosis 2 (NF2).^{[1],[4],[5],[6],[7]} The surgical techniques for VSs have undergone tremendous refinement to shift the aim of the surgery from prolongation of life to preservation of cranial nerve function.^{[3],[6],[8],[9],[10],[11],[12],[13]} This article attempts to focus on the characteristic presentations of VSs in the pediatric population both with and without NF2 and illustrates the essential surgical steps of tumor excision using the retromastoid suboccipital approach.

Materials and Methods

Eight pediatric patients (≤ 16 years) with VS were included in this series. Three of them presented with unilateral tumors without neurofibromatosis [Figure - 1]a-d while five others had bilateral tumors with associated NF2. Their clinicoradiological presentations and management outcomes are given in [Table - 1]. Their preoperative facial nerve function was graded according to the House-Brackmann [HB] score.^[7],[14] Their hearing assessment was carried out using pure tone audiometry. The criterion for impairment of useful hearing was a hearing loss greater than 60 decibels (according to the classical Norstadt Classification for audiometric hearing).^[3] The speech discrimination test was not performed. Radiological assessment included bilateral tumor measurement in the three axes, i.e. , diameter measurements parallel to the petrous ridge, perpendicular to the petrous ridge and the vertical diameter in coronal slices. The size of the VS was taken as the largest diameter in any one of these three axes. The tumors were then categorized according to the classification proposed by Jackler et al. as: 1) Small: < 1 cm in size, 2) Medium: 1-2.5 cm, 3) Large: 2.5-4 cm and 4) Giant: > 4 cm in size.^[9]

All patients were operated in the park-bench position using the suboccipital retromastoid approach.^{[2],[9],[10],[11],[12],[13]} The steps of surgery are illustrated in [Figure - 3]a-k.

Results

The mean age in the series was 15.5 years [Table - 1]. There was no significant difference in age in the patients with and without NF2. Raised pressure often with significant visual deterioration (due to secondary optic atrophy) was the most common presentation followed by hearing loss, ataxia and cerebellar signs. Preoperative VII^th nerve involvement was of House-Brackmann grade IV in three, grade III in two and grade II in two patients. One of the patients with NF2 with proptosis (due to orbital schwannoma) and multiple neurofibromas did not have any VII^th nerve deficit (Patient 5). One of the patients with bilateral VS had bilateral VII^th nerve paresis (Patient 2). None of the patients had any functionally useful hearing on the side of the larger tumor so postoperative hearing preservation was not a consideration in these tumors. None of them had any family history of NF2.

The five patients with NF2 in the current series had characteristic features (Patients 1-5). Bilateral hearing loss was present in four of them. Of these, three had no useful hearing on either side. Two of these patients had multiple neurofibromas all over the body. One of them also had an orbital neurofibroma (which was excised-Patient 5; [Figure - 3]a and b) while the other also had an intradural, extramedullary neurofibroma (that is being managed conservatively-Patient 1).

The tumors were of giant size in six out of the eight patients and large in the other two. Among the five patients with NF2, two patients had large, two had medium-sized and one had a small tumor on the contralateral side. Seven out of the eight patients had significant hydrocephalus. Three of them underwent a ventriculoperitoneal shunt. One of them was in a poor functional status while the other had rapidly deteriorating vision. Both these patients underwent a preoperative cerebrospinal fluid (CSF) diversion. The third patient with a giant VS on one side and a large VS on the other, underwent a ventriculoperitoneal shunt at follow-up after excision of the giant VS (Patient 3). This was on account of persistent pseudomeningocele formation that did not respond to serial lumbar punctures and acetazolamide administration.^[15] Total excision of the larger lesion was performed in six patients. In one patient, a small tumor remnant was left adherent to the preserved VII^th nerve. One of the patients with NF2 and bilateral VSs, who initially underwent excision of the orbital neurofibroma is awaiting surgery for the larger VS. Two patients with NF2 underwent bilateral tumor excision (Patients 2 and 4). Both patients presented with severe headache, rapidly deteriorating vision and no useful bilateral hearing. Despite the excision of the larger tumor, they had persisting and disabling cerebellar signs, which necessitated contralateral tumor excision. One of the patients underwent a staged excision of his tumor due to the tumor being extremely vascular (Patient 6). The C6-7 neurofibroma has not been excised in the patient in whom it was present.

Anatomical preservation of the VII^th nerve was possible in six out of the seven patients who underwent tumor excision. Following surgery, the symptoms of raised intracranial pressure and ataxia improved in all patients. The visual deficit continued to deteriorate in two of the patients due to progressive secondary optic atrophy. The postoperative VII^th nerve function deteriorated from grade III to V in patients in whom its anatomical preservation was possible.

Discussion

The most commonly found manifestations in this series of pediatric patients with VSs were symptoms of raised intracranial pressure and visual compromise. Hearing loss and ataxia were subsequently noticed. The tumors were often large or giant-sized before these patients underwent surgery. In seven out of the eight cases, there was significant hydrocephalus due to cerebrospinal fluid pathway block by the large size of the tumor. Thus, in children, the initial complaints may often be neglected and the underlying tumor investigated only after gross and incapacitating manifestations appear. Due to the large size of the tumor, hearing preservation was not an issue in these patients. Despite the large size of the tumor, the preoperative VII^th nerve function was reasonably preserved in most of the patients but often deteriorated after tumor excision.

NF2 is diagnosed by the criteria proposed by the National Institutes of Health (NIH) in 1988.^[7],[16] These include bilateral VSs or a family history of NF2 plus a unilateral VS or at least two NF2-related abnormalities. Patients commonly develop multiple schwannomas of the cranial, spinal and peripheral nerves; optic nerve gliomas; meningiomas; ependymomas and posterior subcapsular lenticular opacities. Patients with NF2 have VSs at a much earlier age than patients without NF2.^[1],[5],[6] In concordance with this observation, five out of our eight pediatric patients with VS had NF2 with the presence of bilateral VS. Although increased intracranial pressure was commonly found in all these patients, a high index of suspicion regarding the presence of the underlying NF2 was established based upon the characteristic features of bilateral hearing loss; multiple neurofibromas all over the body; the presence of an orbital neurofibroma causing proptosis; and the presence of an intradural extramedullary neurofibroma causing myelopathic features.

Bilateral VSs as a part of NF2 may manifest as three distinct phenotypes:

i) The Wishart type has an early onset rapid course with other coexisting multiple tumors in addition to bilateral VS.

ii) The Gardener type on the other hand has a late onset, a more benign clinical course and usually has solely bilateral VS.

iii) The Le-Abbott type has a variable age of presentation and is characterized by the association of multiple, generalized meningiomatosis with NF2.^[16]

Thus, three patients with bilateral VSs were of the Wishart type with other coexisting tumors and two were of the Gardner's type. None of our pediatric patients had multiple meningiomatosis. In the three patients with unilateral tumors without NF2, the tumors were giant-sized and much larger than the size attained by the larger tumor in patients with NF2. All of them had hydrocephalus with periventricular lucency. Thus, pediatric patients with NF2 were identified earlier than those with unilateral VS because of the characteristic manifestations of NF2 and perhaps, because of the earlier mass effect exerted by the combined size of the bilateral VS.

Two of our patients required an urgent preoperative ventriculoperitoneal shunt as one of them was in a moribund state with severe headache, recurrent vomiting and the other had rapidly deteriorating vision. The third required a postoperative ventriculoperitoneal shunt due to persistent pseudomeningocoele formation at the operative site with persistent hydrocephalus. A cerebrospinal fluid diversion and subsequent shunt-related complications may usually be avoided by direct excision of the tumor and reestablishing the cerebrospinal fluid pathway.

Two of our patients with bilateral VSs underwent a staged bilateral tumor excision. In both these patients, hearing was severely compromised bilaterally. In others, the disabling symptoms of raised intracranial pressure and unsteady gait were alleviated by excision of the larger tumor. The smaller tumor on the opposite side was not removed and the patients are on a regular follow-up with emphasis on their developing lipreading skills before progressive hearing loss on that side. Although subcapsular dissection and gamma knife therapy may prevent the progression of the smaller tumor,^{[3],[4],[9],[12],[13],[17]} the definite risk of compromised hearing prevented us from undertaking either of these procedures on the side of the smaller tumor with preserved hearing.

In 2005, Cunnigham et al .^[1] reported on neurotologic skull base surgery in pediatric patients. The majority of tumors in this series were VS and 65 patients were diagnosed with NF2. The surgical approaches used included middle fossa, translabyrinthine, transcochlear, infratemporal fossa and retrosigmoid craniotomy resulting in excellent hearing and VII^th nerve preservation rates. Slattery et al . reviewed 35 children with NF2 who had undergone middle fossa resection.^[6] Following surgery, facial nerve function was good (House-Brackmann grades I or II) in 81% of the patients and in 55% of surgeries, hearing ≤ 70 decibels (dB) using pure tone average was maintained postoperatively. However, their mean tumor size was 1.1 + 0.63 cm. The Middle fossa approach is more frequently undertaken in an attempt to preserve hearing when resecting VSs ≤ 2 cm in maximum dimension.^[6],[18] The spectrum of patients seen in these studies, however, completely differs from that seen in our patients and therefore the surgical considerations and outcome are entirely different. In our experience, the retrosigmoid suboccipital approach provides adequate exposure for total excision of our large to giant-sized tumors with reasonable VII^th nerve preservation rates. A study by Nunes et al .^[5] on 12 pediatric patients with NF2, reported surgical removal of VS being performed in 58% patients; none had full preservation of hearing postsurgery. Functionally, 75% of children had hearing loss, 83% had visual impairment, 25% had abnormal ambulation and 25% were performing below grade level. In our patients also, hearing deficit, visual impairment and mild ataxia often persisted following surgery.

Conclusions

In pediatric (≤ 16 years) patients, VSs may occur with or without associated NF2. In children, especially those with neurofibromatosis, unless a high index of awareness is maintained and screening using pure tone audiogram is carried out, initial complaints may often be neglected. Thus, the underlying tumor would be detected only after gross and incapacitating manifestations of raised intracranial pressure and visual deterioration appear. The retromastoid suboccipital approach is an effective approach for the safe removal of large to giant-sized tumors seen in this study.

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