CLINICAL ARTICLE

Image-guided drainage of cystic vestibular schwannomata

Chris Barrett & K. S. Manjunath Prasad & John Hill &Ian Johnson & Judith M. Heaton & John E. Crossman &

Alexander D. Mendelow

Received: 9 September 2008 /Accepted: 5 August 2009 /Published online: 20 August 2009# Springer-Verlag 2009

Abstract The management of vestibular schwannomata iscontroversial. Surveillance remains an acceptable option forelderly patients or those with small lesions. Stereoradiosur-gery is also an option, while surgery is often preferred inyounger patients with larger lesions. In elderly patients withlesions causing brainstem compression, craniotomy is amajor undertaking. We report two cases of cystic cerebel-lopontine angle tumours in patients with co-morbidity, whowere managed successfully with image-guided insertion ofa cystoperitoneal shunt.

Keywords Vestibular schwannoma . Acoustic neuroma .

Cystic . Elderly . Image guidance . Cystoperitoneal shunt .

CSF diversion

Introduction

Vestibular schwannomas are said to account for up to 10%of intracranial neoplasms and 80% of cerebellopontineangle lesions. They occur due to loss of a tumour

suppressor gene on chromosome 22. They can be the resultof a sporadic mutation, but are also associated withneurofibromatosis type 2. Bilateral acoustic neuromas arepathognomic for this condition.

They arise from the Schwann cells surrounding thevestibular component of the cranial nerve VIII. They occurat the junction between the glia of the central and peripheralnervous system, known as the Obersteiner–Redlich zone.Histologically, they have two classic appearances which areAntoni types A and B. In the former, the nuclei are morenumerous and are arranged in palisades and whorls. In thelatter, the appearances are less regular with fewer nuclei anda looser stroma.

Clinically, patients most often present with unilateralsensorineural hearing loss and tinnitus but other featuresinclude ataxia/imbalance, headache, facial numbness orweakness, otalgia, and altered gustation. Assessment isusually first by the otologists and includes audiometry andcranial imaging.

Management can be surveillance only or may involveradiotherapy or surgery, depending on the clinical circum-stances. Expectant management requires regular clinicalreview and interval imaging. Radiation treatment can be inthe form of external beam radiotherapy or stereotacticradiosurgery and can be combined with surgery.

Three classical surgical approaches are described. Theretrosigmoid or sub-occipital approach is commonly used(especially if hearing is partially preserved) and is thepreference in our unit. The translabyrinthine approach,which by definition involves destruction of the inner earstructures, is used if ipsilateral hearing is significantlyimpaired or absent and avoids retraction of the brainstemand cerebellum. Finally, a sub-temporal or middle fossaapproach can be used for attempted hearing preservation in apatient with a small intracanalicular vestibular schwannoma.

C. Barrett (*) :K. S. M. Prasad : J. E. Crossman :A. D. MendelowDepartment of Neurosurgery, Regional Neurosciences Centres,Newcastle General Hospital,Newcastle Upon Tyne, UKe-mail: chris.barrett@nuth.nhs.uk

J. Hill : I. JohnsonDepartment of Otolaryngology, Freeman Hospital,Newcastle Upon Tyne, UK

J. M. HeatonDepartment of Otolaryngology, Sunderland Royal Hospital,Sunderland, UK

Acta Neurochir (2010) 152:177–180DOI 10.1007/s00701-009-0493-0

In the two following cases, we describe a further strategywhich can be added to the surgeon’s armamentarium whenapproaching a specific subgroup of these tumours. Cysticvestibular schwannoma, in cases in which it would beconsidered a high risk for traditional surgical approaches,can be managed with insertion of a cystoperitoneal shunt.

Case 1

A 76-year-old lady had originally presented to the Otologydepartment some 4 years previously with a left sensorineu-ral deafness and imaging which revealed a left cerebello-pontine angle tumour. A surveillance strategy was adopted,but this was reconsidered when the patient developedheadache, left facial sensory disturbance, left facial weak-ness, and ataxia. On examination, she was found to have aHouse–Brackmann grade 3 weakness with an absentcorneal reflex. Repeat magnetic resonance imaging (MRI)scans (Fig. 1a) showed a significant increase in the sizeof the tumour, which now contained a large cyst, withassociated brainstem compression, effacement of the fourthventricle, and early hydrocephalus.

On a semi-urgent basis, surgery was undertaken. Usingthe Brainlab image guidance system (frameless stereotaxy),the patient was positioned supine with the head rotated to theopposite side and facial surface marking registration wasperformed in the usual manner. A left retromastoid burr holewas then made, and a ventricular catheter was placed in thecystic portion of the tumour (if so desired the catheter canitself be registered to increase the accuracy of cystcannulation). Fluid was aspirated for histology, and thecatheter was then connected to a reservoir.

Nearly 2 weeks after surgery, a further aspiration of thereservoir was required due to clinical and radiological

evidence of cyst re-accumulation. A second re-aspirationwas required one week later. Finally at one month afterthe initial operation, a distal catheter was connected to thereservoir allowing drainage of the cyst fluid to theperitoneum.

At 1 month after the second operation, the patient hadmade an excellent recovery, with complete resolution ofboth the facial weakness and the ataxia. Magnetic reso-nance imaging scans at 12 and 24 months (Fig. 1b) did notshow any cyst, with no significant mass effect from theresidual solid tumour. Similarly, there had been norecurrence of symptoms on clinical evaluation.

Case 2

A 73-year-old lady presented with symptoms of right-sidedfacial pain, headaches, and diminished right-sided hearing.She had a significant past medical history of temporalarteritis (with associated left-sided visual loss), hyperten-sion, and duodenal ulceration. On examination, she wasfound to have a sensorineural hearing loss on the right withaltered sensation in the second and third divisions of theright trigeminal nerve.

Assessment included audiometry, which revealed bilat-eral high-frequency sensorineural hearing loss, more pro-nounced on the right. An MRI brain demonstrated a rightvestibular schwannoma with a large cystic component(Fig. 2a).

Patient co-morbidity precluded craniotomy. Using Brain-lab image guidance (frameless stereotaxy) the cyst wascannulated via a right retromastoid burr hole. The catheterwas connected to a valveless reservoir, and a distal catheterwas tunnelled to the peritoneal cavity. There were no peri-operative complications.

Fig. 1 a Axial T1 weightedMRI post-gadoliniumdemonstrating the cysticvestibular neuroma. b Axial T1weighted MRI post-gadoliniumat 24 months; Solid tumour onlywith no residual cyst

178 C. Barrett et al.

On follow-up, the patient complained of some ipsilateralfacial numbness but had no other significant symptoms. Acomputed tomography (CT) scan at 6 months demonstratedthat the cyst was smaller; an MRI scan at 24 months did notshow any residual cyst.

Discussion

Cystic vestibular schwannomata are a well-described sub-group of tumours. The reported incidence varies in theliterature, from as high as 13.5% in a study of 104patients [10] to 5.7% in the largest series that specificallyalludes to the cystic sub-type of vestibular schwannoma(773 patients) [8].

The pathogenesis of the cyst is thought to be explained byrepeated micro-haemorrhage into the initially solid tumour[11]. The cystic variety tends to be larger than the solid type,with less severe hearing loss. The postulated mechanism ofrepeated micro-haemorrhage is supported by histologicalevidence of haemosiderin deposition, phagocyte infiltration,and telangiectasis [1]. One other possible explanation isinfarction and subsequent necrosis of tumour tissue.

There also appears to be clinical and radiologicalcorrelation with the histology. In a study of 30 patients[9], 13 were found to have small homogeneous tumours withAntoni type Amicroscopic appearances. Twelve patients hadheterogeneous tumours, which were larger and had relativelymore Antoni type B features. Finally, the largest tumours ofall were cystic, with mainly Antoni type B histology and thegreatest deposits of haemosiderin. These findings wouldseem to support the hypothesis that repeated haemorrhage

into small solid tumours leads to heterogeneity, an increasein size, and, finally, cyst formation.

Since the mechanism of cyst formation appears to behaemorrhage, these tumours are felt to be at risk of suddenexpansion, and in theory, an associated clinical deteriora-tion from hydrocephalus [4]. This weighs against a purelyconservative strategy in the management of these lesions.

Various studies have analysed the outcome followingsurgery in the cystic sub-group. In general, the results appearto be poorer when compared with solid tumours with the samesize [6, 14]. Although solid tumours are often more adherentto the facial nerve, nevertheless, functional preservationappears to be greater for solid than for cystic tumours [8].This also is apparently true for translabyrinthine resection inaddition to the more common retrosigmoid approach [5].

There are also a number of reports regarding the efficacy ofradiosurgery [3, 7, 12, 13]. There may be an initial risk ofcyst enlargement with corresponding clinical deterioration.In some cases, the cyst may rupture post-radiotherapy [2].In the long term, cystic tumours show reduction in size aftergamma knife treatment. However, there is concern over theuse of radiotherapy in patients with large symptomatic cystsdue to this risk of expansion in the early period.

In summary, although the pathogenesis, histology, andradiological features of cystic vestibular schwannomata arewell-described, there remain some controversies regardingtreatment. The surgical outcome would appear to be worseand there are also some concerns with regards to the role ofradiotherapy in schwannomas with cystic change. We proposethat image-guided cystoperitoneal shunting is a usefuladditional option to consider when there is a significant cysticcomponent to vestibular schwannomata.

Fig. 2 a Axial T1 weightedMRI post-gadolinium,demonstrating the acousticneuroma with the prominentcystic component. b Axial T1MRI post-gadolinium at24 months; shunt catheter insitu, no residual cyst

Image-guided drainage of cystic vestibular schwannomata 179

Conclusion

The diagnosis, investigation, and management of vestibularschwannomata remain controversial. Traditional therapiesinclude surgical resection and radiotherapy (external beam orstereotactic). In the two cases discussed above, we demon-strate the effective management of a known sub-group whichis the cystic vestibular schwannoma. Both patients wererelatively elderly with co-morbidity and significant symp-toms related to large cerebellopontine angle tumours. Aresectional procedure would have carried significant risksand radiotherapy may not have ameliorated the symptoms ina reasonable timescale. There are several notable advantagesof shunt insertion in managing these cystic tumours: it is asimple with a straightforward procedure that utilises techni-ques well-known to every neurosurgeon, image guidance,and cerebrospinal fluid (CSF) diversion. There are consider-able savings with regards to theatre time and cost and the in-tensity of post-operative care required. Neither does efficacyappear to be sacrificed; both patients had good surgicaloutcomes, although, they were elderly and had co-morbidity.

Acknowledgement The Brainlab image guidance system waspurchased with a grant from the Northern Brainwave Appeal.

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