Ve s t i b u l a r schwannomas are benign tumors that. Sporadic unilateral vestibular schwannoma in the pediatric population.

Transcription

1 J Neurosurg Pediatrics 4: , 4: , 2009 Sporadic unilateral vestibular schwannoma in the pediatric population Clinical article Br i a n P. Wa l c o t t, M.D., 1,2 Ga n e s h Si va r a ja n, B.S., 3,4 Br o n i s l ava Ba s h i n s k aya, 2 Do u g l a s E. And e r s o n, M.D., 3,4 Jo h n P. Le o n e t t i, M.D., 3,5 a n d Th o m a s C. Or i g i ta n o, M.D., Ph.D. 3,4 1 Neurosurgical Service, Massachusetts General Hospital, Boston; 2 Department of Neurosurgery, Harvard Medical School, Boston, Massachusetts; and 3 Stritch School of Medicine, 4 Department of Neurological Surgery, and 5 Department of Otolaryngology-Head and Neck Surgery, Loyola Center for Cranial Base Surgery, Loyola University Chicago, Loyola University Medical Center, Maywood, Illinois Object. Vestibular schwannomas (VSs) are rare in the pediatric population. Most often, these lesions manifest as a bilateral disease process in the setting of neurofibromatosis Type 2. Even in the absence of additional clinical diagnostic criteria, the presentation of a unilateral VS in a young patient may be a harbinger of future penetrance for this hereditary tumor syndrome. Methods. The authors retrospectively reviewed the charts of a cohort of 7 patients who presented with apparently sporadic, unilateral VSs. These patients had previously undergone surgery via translabyrinthine, retrosigmoid, or combined approaches. Clinical outcomes were reviewed with emphasis on facial nerve function and follow-up for signs and symptoms of a heritable disorder. Results. All patients underwent microsurgical resection in a multidisciplinary effort by the senior authors. The average tumor size was 4.57 cm, with an average duration of symptoms prior to definitive diagnosis of 31.2 months. The tumor size at the time of presentation followed a trend different from reports in adults, while the duration of symptoms did not. At a follow-up average of 6.3 years (range 1 12 years), 100% of patients demonstrated good facial function (House-Brackmann Grade I or II). No patient in this cohort demonstrated symptoms, objective signs, or genetic analysis indicating the presence of neurofibromatosis Type 2. Conclusions. Diagnosis and management of sporadic, unilateral VSs in children is complicated by clinical presentations and surgical challenges unique from their adult counterparts. Careful consideration should be given to a heritable genetic basis for sporadic unilateral VS in the pediatric population. Results of genetic testing do not preclude the necessity for long-term follow-up and systemic investigation. In patients who present with large tumors, preliminary experience leads the authors to suggest that a combined retrosigmoid-translabyrinthine approach offers the greatest opportunity for preservation of facial nerve function. (DOI: / PEDS08434) Ke y Wo r d s facial nerve neurofibromatosis pediatric neurosurgery retrosigmoid approach translabyrinthine approach vestibular schwannoma Ve s t i b u l a r schwannomas are benign tumors that arise from the superior portion of the vestibulocochlear nerve. The earliest report of successful resection for this lesion was by Sir Charles Balance in Shortly thereafter, major developments in the surgical technique were made by Cushing 7 and Dandy. 8 Technological advances such as the application of the operating microscope 23,42 and utilization of intraoperative Abbreviations used in this paper: GTR = gross-total resection; IAM = internal auditory meatus; NF2 = neurofibromatosis Type 2; VS = vestibular schwannoma. electrophysiological monitoring of the facial nerve 10 complemented the development of the retrosigmoid, 32 middle fossa, 18 translabyrinthine, 5,22 and combined retrosigmoid-translabyrinthine surgical approaches. 3 In addition, the introduction of stereotactic radiosurgery 24 and stereotactic radiotherapy 41 have increased the treatment options, intricacies, and expectations for patients harboring these tumors. Overall, the majority of VSs (> 95%) are sporadic and unilateral, often presenting in the 4th and 5th decades of life. 30,39 Although the development of a bilateral VS is the most frequent presentation of the inherited au- 125

2 B. P. Walcott et al. tosomal dominant condition NF2, 14 a retrospective analysis indicates that 10 25% of VSs are initially unilateral at presentation. 13 From an alternative vantage point, the risk of NF2 in patients with an apparently sporadic unilateral VS is extremely small except for those in the pediatric age group. 15 The possibility of NF2 must therefore be taken into consideration in the evaluation and treatment of unilateral tumors in children, as the chance that a contralateral tumor could develop may influence the management of the primary side. 12,16 In the present study, we reviewed the presentation, surgical approach, and outcome in a consecutive series of pediatric patients harboring apparently sporadic, unilateral VSs. Special attention was given to analysis of facial nerve preservation in addition to follow-up for signs and symptoms of NF2. Methods Patient Population and Symptoms Of all the cranial base operations performed by the senior authors at Loyola University Medical Center between April 1996 and May 2007, 7 children were identified with apparently sporadic, unilateral VSs. Five patients were girls and 2 were boys. The mean age of the patients was 15.1 years, ranging from 9 to 18 years. The average duration of symptoms was 31.2 months. The most common presenting symptom was hearing loss, which was reported in all but 1 patient. Six patients (86%) presented with balance or gait instability, and 3 (43%) presented with tinnitus. Facial numbness and paresthesias were noted in 2 patients (29%). Nausea and vomiting occurred in only 1 patient. Of the 7 patients, 1 reported overt difficulty swallowing and abnormal phonation, indicative of lower cranial nerve dysfunction. Objective presenting signs included papilledema, nystagmus, partial abducens nerve palsy, abnormal corneal reflex, facial weakness, and cerebellar ataxia. Magnetic resonance imaging provided for preoperative determination of tumor dimensions and impingement on surrounding cranial structures (Fig. 1). Maximal tumor diameter ranged in size from 1 to 7 cm, with a mean size of 4.57 cm. Six of the 7 tumor measurements were > 4 cm. Five patients in this group were identified with preoperative radiographic evidence of hydrocephalus. Fig. 1. Representative preoperative axial (left) and coronal (right) T1- weighted contrast-enhanced MR images demonstrating a massive cerebellopontine angle lesion. Determination of Surgical Approach Three different surgical techniques were used for tumor resection: the translabyrinthine, the retrosigmoid, and the combined retrosigmoid-translabyrinthine approach. The selection criteria used to determine the surgical approach was based on several anatomical factors including the size of the tumor, extension of the tumor into the IAM, and the distance between the jugular bulb and the superior petrosal sinus. Additionally, the surgical plan was influenced by preoperative hearing functionality as assessed with audiometric studies. In patients with smaller tumors extending into the fundus of the IAM or if the patient had a wide-angled petrous apex (a normal or enlarged space between the jugular bulb and the superior petrosal sinus), a translabyrinthine approach was considered. A purely retrosigmoid approach was considered for medially based tumors. For the majority of the patients in this cohort, it was recognized that very large tumor sizes (most commonly > 4 cm) necessitated a combined approach to overcome the inherent individual limitations of each. 17,23,28 Surgical Technique One translabyrinthine, 1 retrosigmoid, and 5 combined translabyrinthine-retrosigmoid approaches were used in the surgical management of 8 tumors in the same number of children. The multidisciplinary cranial base team composed of a pediatric neurosurgeon, a neurotologist, a neuroanesthesiologist, and intraoperative electrophysiological monitoring personnel was assembled in much the same fashion as for the adult skull base tumors routinely treated at this tertiary care academic medical center. The combined translabyrinthine-retrosigmoid approach, uniquely developed by the lead authors, 3 seeks to incorporate the strengths of the 2 separate approaches to maximize the likelihood of facial nerve preservation when performing gross-total removal of very large tumors. The bonework was completed first, allowing for both aspects of the 2 individual approaches. Sequentially, the translabyrinthine isolation of the IAM and the lateral aspect of the facial nerve were performed prior to durotomy for the continuation of the retrosigmoid portion of the exposure. Ultrasonic aspiration and debulking of the tumor mass were performed, initially defining and later maintaining the surgical plane between the tumor and the cerebellum. Perseverance eventually led to the establishment of a similar plane between the lesion and both the brainstem and cranial nerves. Paramount to the success of the dissection was the early identification of the facial nerve medially to facilitate a medial to lateral dissection of the tumor away from the facial nerve and other neural structures. After tumor removal, attention was solely focused on the facial nerve, which was stimulated at the most proximal region of the brainstem root exit zone. Anatomical preservation of the facial nerve was achieved in all cases and further documented by a response to this stimulus. If no response was initially obtained, the current was increased in 0.1-mA increments until a response was achieved. Finally, the wound closure was performed in the usual, routine fashion. 126

3 Pediatric vestibular schwannoma Outcome and Follow-Up Several end points were observed with an emphasis on facial nerve function in addition to long-term follow-up for signs and symptoms of a heritable disorder. Relating to this, the completeness of tumor resection, intraoperative electrophysiological facial nerve activity, facial nerve response at the finale of the procedure, clinical facial nerve function using the House-Brackmann facial nerve grading scale (Table 1), 19 complications, and genetic studies were reviewed. Additionally, review of a routine postoperative questionnaire was used to help summarize patient perception of facial function and long-term outcome. Uniform follow-up averaged 6.3 years, ranging from 1 to 12 years. Results Operative Procedure The average duration of the procedure was 12.5 hours, ranging from 4 to 17 hours. In 4 patients (57%) CSF diversion procedures were necessary prior to definitive resection. Gross-total resection was achieved in all patients as determined on postoperative MR imaging studies (Fig. 2). In 1 patient, apparent tumor recurrence was treated with stereotactic radiosurgery; this patient is currently undergoing follow-up with serial imaging. Pathological analysis revealed the diagnosis of schwannoma and the absence of atypia in all specimens. The average duration of hospital stay was 7 days, with a range of 4 20 days. The longest hospital stay reflected the complexity associated with a 2-stage operation performed over the interval of 1 week. There were no operative deaths in this cohort of patients. TABLE 1: Facial nerve grading system based on the House-Brackmann scale Grade Description Measurement* % Function Observation I normal 8/8 100 normal II slight 7/ normal at rest, slight synkinesis III moderate 5 6/ normal at rest, moderate synkinesis IV moderately severe 3 4/ normal at rest, obvious facial weakness w/ movement, impaired eye closure V severe 1 2/ asymmetric at rest, no movement of forehead, impaired eye closure VI total 0/8 0 no facial nerve function * Measurement is determined by measuring the superior movement of the eyebrow and the lateral movement of the oral commissure. One point is assigned for each 0.25 cm of motion in each direction up to 1 cm, allowing for a maximum of 8 points when added together. Fig. 2. Representative postoperative axial (left) and coronal (right) T1-weighted contrast-enhanced MR images demonstrating GTR of the previously demonstrated massive VS. Facial Nerve In 2 patients, facial nerve weakness was noted preoperatively (House-Brackmann Grade III and VI). These patients were assumed to have had the deficit due to the direct effect of the tumor on the nerve. Routine follow-up included objective assessment in the immediate postoperative period, with questionnaire forms, and at routine clinic visits. Ultimately, all 7 patients (100%) achieved good facial function over time (House-Brackmann Grade I or II). Postoperative Complications There was no incidence of CSF leaks, wound infections, or hematomas in our patients, which are the common perioperative complications associated with this procedure. 9 Two patients experienced brief postoperative episodes of psychosis attributed to corticosteroid therapy, a known adverse effect that has been demonstrated to be more variable in children. 37 One patient experienced postoperative cerebellar and brainstem swelling, resulting in a transient ipsilateral palsy of cranial nerve IX and X. These symptoms resolved by the time of discharge and were attributed to venous congestion. Genetic Analysis One patient underwent a full genetic evaluation at the time of admission in light of the highest concern for NF2 in this cohort given a familial history of hearing loss and a personal history of congenital cataracts. Molecular analysis including single-strand conformation polymorphism studies and fluorescence in situ hybridization with probes directed at the 22q11 region failed to reveal any abnormality. Discussion The risk of unilateral tumors presenting as the first manifestation of NF2 is related to the age of the patient. It has been determined that individuals < 30 years of age are at the highest risk of developing a contralateral tumor, 15 and thereby fulfilling the diagnostic criteria necessary for NF2. 1 According to the NIH consensus statement, 1 these criteria are as follows: 1) the presence of a bilateral cranial nerve VIII mass visible on Gd-enhanced MR images; or 2) a first-degree relative with NF2 and either a unilateral cranial nerve VIII mass or 2 of the following: neuro- 127

4 B. P. Walcott et al. fibroma, meningioma, glioma, schwannoma, or posterior capsular cataract or opacity at a young age. Evans et al. 15 also reported that ~ 6% of all individuals with an apparently isolated VS are mosaic for an NF2 gene mutation, and may therefore go on to develop of various features of NF2 despite an initial negative genetic analysis. The dilemmas inherent to the treatment of VSs in patients with NF2 are well-known and are highlighted by facial nerve paralysis, in addition to a multitude of other tumors and complications. 11,26 These considerations are magnified in children and can be extrapolated to the apparently sporadic VS patient population given the implications for impairment of childhood development and lifelong disability in the setting of possible future contralateral tumors. Clinical management, including the selection of operative approach and execution of surgical technique, must be aimed at minimization and deferment of these complications, as in all patients. 34 Although significant controversy remains regarding the optimal treatment, timing, and selection of a surgical approach, tumor size and the presence of serviceable hearing remain important, common, and consistent factors in this decision process. 5,6,20 By exposing the areas both anterior and posterior to the sigmoid sinus, a prominent vertical and lateral exposure of the tumor is established. It was found that the retrosigmoid portion of the exposure was particularly helpful in instances of a high jugular bulb, as a solely translabyrinthine approach limits vertical exposure. 38 In conjunction, the translabyrinthine approach allowed for early identification of the facial nerve distally, enabling its visualization at the porous acousticus and within the posterior fossa. The translabyrinthine approach also allows the most lateral portion of very large tumors to be reached, maximizing the potential for GTR. The results of facial nerve preservation may be related to the combined approach that allows for early identification of the facial nerve proximally, facilitating its immediate and frequent monitoring. Preservation of facial nerve function is paramount, especially in children, as it is often regarded as the single most important determinant of quality of life in the postoperative setting. 31 A combined translabyrinthine-retrosigmoid approach was most advantageous for tumors that extended to the fundus of the IAM and were very large, as was almost universally found in our cohort of pediatric patients with apparently sporadic unilateral VSs. In a meta-analysis of 1345 adult patients, the average size of adult VS was reported as 11.8 mm. 36 In our cohort, the average size tumor size was 4.57 cm, substantially larger than that reported in the adult literature. A similar finding has been observed comparing the size of pediatric and adult meningiomas. 2,25 In this series, the duration of symptoms prior to definitive diagnosis, 31.2 months, was consistent with that typically reported in tumors in adults. 27 Overall, these findings summate in a typically larger tumor at the time of diagnosis in this group of pediatric patients given the same duration of symptoms. These attributes may be a consequence of biologically unique tumor characteristics from their adult counterparts. Also plausible is that a younger patient population is unable to articulate the severity or characteristics of their symptoms in the same fashion as adults, resulting in a delay in diagnosis. For example, 1 patient in our series presented only after prolonged deterioration of academic performance in grade school related to a profound, unrecognized hearing impairment. Recurrence of VS after GTR is rare. 21,35 However, a single patient in our study was found to have a 1-cm recurrence at the time of a routine, 6-month postoperative surveillance MR imaging study. She then underwent stereotactic radiosurgery. Currently, attainment of tumor control in this patient remains to be elucidated given the short interval since the time of her treatment. The clinical behavior of recurrent VSs, such as in this child, remains unclear. Microscopic fragments of the tumor may remain viable after GTR, and if given proper vascularization, propagate. 35 The role of stereotactic radiosurgery after microsurgery has been explored and shown to be an effective measure in the treatment of both tumor regrowth and for use after subtotal resections. 29,33,40 Although the goal of microsurgery is ultimately total tumor removal, the benefit of stereotactic radiosurgery in children with very large tumors may rest in the planned combination of dual modality treatment. Conclusions Although children typically present with larger VSs than adults, it is possible to preserve good long-term facial nerve function. A combined translabyrinthine-retrosigmoid approach provides excellent results in terms of GTR and ability to meticulously preserve the facial nerve. Follow-up for a heritable genetic basis should be undertaken in all cases of apparently sporadic unilateral VS in the pediatric population. Disclaimer The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. References 1. Acoustic neuroma. NIH Consensus Statement 9:1 24, Amirjamshidi A, Mehrazin M, Abbassioun K: Meningiomas of the central nervous system occurring below the age of 17: report of 24 cases not associated with neurofibromatosis and review of the literature. Childs Nerv Syst 16: , Anderson DE, Leonetti J, Wind JJ, Cribari D, Fahey K: Resection of large vestibular schwannomas: facial nerve preservation in the context of surgical approach and patient-assessed outcome. J Neurosurg 102: , Ballance CA: Some Points in the Surgery of the Brain and its Membranes. London: Macmillan, 1908, pp Bennett M, Haynes D: Surgical approaches and complications in the removal of vestibular schwannomas. Neurosurg Clin N Am 19: , Briggs RJ, Luxford WM, Atkins JS Jr, Hitselberger WE: Translabyrinthine removal of large acoustic neuromas. Neurosurgery 34: , Cushing H: Tumors of the Nervus Acusticus and the Syndrome of the Cerebellopontine Angle. Philadelphia: Saunders, Dandy WE: Results of removal of acoustic tumors by the unilateral approach. AMA Arch Surg 42: ,

5 Pediatric vestibular schwannoma 9. Darrouzet V, Martel J, Enee V, Bebear J, Guerin J: Vestibular schwannoma surgery outcomes: our multidisciplinary experience in 400 cases over 17 years. Laryngoscope 114: , Delgado TE, Bucheit WA, Rosenholtz HR, Chrissian S: Intraoperative monitoring of facial muscle evoked responses obtained by intracranial stimulation of the facial nerve: a more accurate technique for facial nerve dissection. Neurosurgery 4: , Evans DG, Huson SM, Donnai D, Neary W, Blair V, Newton V, et al: A clinical study of type 2 neurofibromatosis. Q J Med 84: , Evans DG, Huson SM, Donnai D, Neary W, Blair V, Newton V, et al: A genetic study of type 2 neurofibromatosis in the United Kingdom. II. Guidelines for genetic counseling. J Med Genet 29: , Evans DG, Lye R, Neary W, Black G, Strachan T, Wallace A, et al: The probability of bilateral disease in individuals presenting with a unilateral vestibular schwannoma. J Neurol Neurosurg Psychiatry 66: , Evans DG, Moran A, King A, Saeed S, Gurusinghe N, Ramsden R: Incidence of vestibular schwannoma and neurofibromatosis 2 in the North West of England over a 10 year period: higher incidence than previously thought. Otol Neurotol 26: 93 97, Evans DG, Ramsden RT, Gokhale C, Bowers N, Huson SM, Wallace A: Should NF2 mutation screening be undertaken in patients with an apparently isolated vestibular schwannoma? Clin Genet 71: , Evans DG, Ramsden RT, Huson SM, Harris R, Lye R, King TT: Type 2 neurofibromatosis: the need for supraregional care. J Laryngol Otol 107: , Haberkamp TJ, Meyer GA, Fox M: Surgical exposure of the fundus of the internal auditory canal: anatomic limits of the middle fossa versus the retrosigmoid transcanal approach. Laryngoscope 108: , House WF: Surgical exposure of the internal auditory canal and its contents through the middle, cranial fossa. Laryngoscope 71: , House JW, Brackmann DE: Facial nerve grading system. Otolaryngol Head Neck Surg 93: , Jung S, Kang SS, Kim TS, Kim HJ, Jeong SK, Kim SC, et al: Current surgical results of retrosigmoid approach in extralarge vestibular schwannomas. Surg Neurol 53: , Kemink JL, Langman AW, Niparko JK, Graham MD: Operative management of acoustic neuromas: the priority of neurologic function over complete resection. Otolaryngol Head Neck Surg 104:96 99, King TT, Morrison AW: The translabyrinthine operation for the removal of acoustic nerve tumors, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques: Indications, Methods, and Results, ed 2. Philadelphia: WB Saunders, 1988, pp Kriss TC, Kriss VM: History of the operating microscope: from magnifying glass to microneurosurgery. Neurosurgery 42: , Leksell L: A note on the treatment of acoustic tumors. Acta Chir Scand 137: , Liu Y, Li F, Zhu S, Liu M, Wu C: Clinical features and treatment of meningiomas in children: report of 12 cases and literature review. Pediatr Neurosurg 44: , Martuza RL, Eldridge R: Neurofibromatosis 2 (bilateral acoustic neurofibromatosis). N Engl J Med 318: , Matthies C, Samii M: Management of 1000 vestibular schwannomas (acoustic neuromas): clinical presentation. Neurosurgery 40:1 9, McElveen JT Jr: The translabyrinthine approach to cerebellopontine angle tumors, in Wilkins RH, Rengachary SS (eds): Neurosurgery Update I: Diagnosis, Operative Technique and Neuro-Oncology. New York: McGraw-Hill, 1990, pp Pollock BE, Lunsford LD, Flickinger JC, Clyde BL, Kondziolka D: Vestibular schwannoma management. Part I. Failed microsurgery and the role of delayed stereotactic radiosurgery. J Neurosurg 89: , Pool JL, Pava AA, Greenfield EC: Acoustic Nerve Tumors: Early Diagnosis and Treatment, ed 2. Springfield, IL: Charles C Thomas, 1970, p Prasad D, Steiner M, Steiner L: Vestibular schwannoma. Crit Rev Neurosurg 9: , Rand RW, Kurze T: Preservation of vestibular, cochlear, and facial nerves during microsurgical removal of acoustic tumors. Report of two cases. J Neurosurg 28: , Roche PH, Robitail S, Delsanti C, Marouf R, Pellet W, Régis J: Radiosurgery of vestibular schwannomas after microsurgery and combined radio-microsurgery. Neurochirurgie 50: , Samii M, Matthies C, Tatagiba M: Management of vestibular schwannomas (acoustic neuromas): auditory and facial nerve function after resection of 120 vestibular schwannomas in patients with neurofibromatosis 2. Neurosurgery 40: , Schmerber S, Palombi O, Boubagra K, Charchon R, Chirossel J, Gay E: Long-term control of vestibular schwannoma after a translabyrinthine complete removal. Neurosurgery 57: , Smouha EE, Yoo M, Mohr K, Davis RP: Conservative management of acoustic neuroma: a meta-analysis and proposed treatment algorithm. Laryngoscope 115: , Stuart FA, Segal TY, Keady S: Adverse psychological effects of corticosteroids in children and adolescents. Arch Dis Child 90: , Symon L: Surgical management of high jugular bulb in acoustic neurinoma via retrosigmoid approach. Neurosurgery 33: 533, Tos M, Charabi S, Thomsen J: Incidence of vestibular schwannomas. Laryngoscope 109: , Unger F, Walch C, Papaefthymiou G, Feichtinger K, Trummer M, Pendl G: Radiosurgery of residual and recurrent vestibular schwannomas. Acta Neurochir (Wien) 144: , Varlotto JM, Shrieve DC, Alexander E III, Kooy HM, Black PM, Loeffler JS: Fractionated stereotactic radiotherapy for the treatment of acoustic neuromas: preliminary results. Int J Radiat Oncol Biol Phys 36: , Yaşargil MG, Fox JL: The microsurgical approach to acoustic neurinomas. Surg Neurol 2: , 1974 Manuscript submitted October 4, Accepted March 9, Address correspondence to: Douglas E. Anderson, M.D., Neuro surgical Surgery, Loyola University Medical Center, 2160 South First Avenue, Maywood, Illinois dander1@lumc.edu. 129