Evaluation And Management

Otolaryngol Clin N Am 40 (2007) 463–478

Evaluation and Management of Endolymphatic Sac and Duct Tumors Cliff A. Megerian, MD*, Maroun T. Semaan, MD Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, University Hospitals-Case Medical Center, 11100 Euclid Avenue, Cleveland, OH 44106, USA

Endolymphatic sac tumor (ELST) is a slow-growing, locally aggressive neoplasm that originates from the epithelium of the endolymphatic sac and duct. It demonstrates the histologic appearance of a papillary adenomatous lesion, and before its acceptance as a disease entity, its destructive behavior within the temporal bone was attributed in some cases to a metastatic renal cell carcinoma variant [1,2]. By virtue of ELST-related obstruction of the vestibular aqueduct, patients often develop symptoms of endolymphatic hydrops [3], and this pathologic finding recently was confirmed histologically [4]. The earliest manifestations of ELSTs are often hearing loss and vertigo that initially may lead to a misdiagnosis of Meniere’s disease. Disease progression can lead to profound sensorineural hearing loss, posterior fossa invasion, brainstem compression, drop metastasis, and eventual death. Although ELSTs are known to occur more frequently in patients with von Hippel-Lindau disease (VHL), a diagnosis of VHL is not a prerequisite, because these tumors also appear sporadically in patients who do not have VHL. Early diagnosis and surgical attention are the primary objectives in the management of patients who have ELST because recent studies have shown the potential for hearing preservation when small tumors are removed successfully. Historical background ELST is a recently recognized neurotologic disease entity characterized by the presence of a destructive papillary cystic adenomatous tumor of the temporal bone. Its roots and evidence for its existence date to early in * Corresponding author. E-mail address: [email protected] (C.A. Megerian). 0030-6665/07/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.otc.2007.03.002

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the last century in a report that described a destructive lesion of the temporal bone in a patient who had VHL that was ascribed to metastatic renal cell carcinoma in the absence of a primary kidney tumor [1]. Throughout the ensuing years it became clear that an aggressive papillary tumor could arise primarily within the temporal bone; however, the site of epithelial origin remained an area of conjecture. This uncertainty was partly caused by the fact that many of these cases occurred in patients with an intact tympanic membrane and normal external auditory canal, so the glandular epithelial tissue of the external auditory canal was excluded as the site of origin. In 1989, Heffner [5] studied 20 such large papillary cystic tumors of the temporal bone and concluded that the endolymphatic sac epithelium represented the most likely area at which these lesions initially grow. This finding was corroborated by an earlier study in 1984 by Hassard and colleagues [6], who described a papillary cystic lesion filling the endolymphatic sac that was encountered during decompression surgery for presumed Meniere’s disease and likely represented the first clinical confirmation of the validity of the ELST designation. In 1993, Li and colleagues [7] formally proposed that the designation for aggressive papillary tumors of the temporal bone be changed to ELST. In 1995, Megerian and colleagues [3] provided temporal bone histologic evidence of a de novo ELST tumor in a patient who had VHL (Fig. 1) and died of complications related to a massive ELST of the contralateral ear. Included in that study were seven additional clinical cases that revealed that most of the patients had Meniere’s-like symptoms years before the diagnosis of ELST, which raised the possibility that early manifestations of tumor growth included perturbations of vestibular aqueduct function and the development of endolymphatic hydrops-related symptomatology. Poe and colleagues [8] and later Manski and colleagues [9] studied ELST in patients who had VHL, and the latter group documented the fact that at least 13% of

Fig. 1. Histologic section through the right temporal bone of 48-year-old patient with VHL who died of large intracranial ELST of left posterior fossa. Arrow points to de novo ELST within endolymphatic sac and duct of left ear.

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patients who had VHL harbored ELST tumors. They suggested that patients who had VHL should undergo regular surveillance, because undetected growth was shown to result in deafness that sometimes was bilateral. By 1997, screening for ELST using MRI became standard for patients who had VHL, whereas before that time annual MRI evaluations of the head focused mainly on detection of VHL-related cerebellar hemangioblastomas. These practices, coupled with an increased number of reports in the literature of sporadic ELSTs, led to the evolution of surgical alternatives for tumor removal. In 2002, Megerian and colleagues [10] described techniques for tumor removal in small ELSTs that afforded hearing preservation. Subsequent reports by Hansen and Luxford in [11] 2004 and Kim and colleagues [12] in 2005 confirmed the clear role for hearing preservation surgery using the retrolabyrinthine approach for small tumors and more aggressive skull base extirpations for larger lesions.

Etiology As recently as 2004, Bambakidis and colleagues [13] reported that most ELSTs described in the literature have occurred sporadically in patients who do not have VHL compared with patients who do (103 versus 46). Much information that has been learned recently regarding the genesis of these lesions has been via an understanding of the genetics and molecular biology that result from a mutation in the VHL tumor suppressor gene. VHL is an autosomal dominant multisystemic disorder characterized by cerebellar hemangioblastomas, retinal angiomas, and renal cysts, clear cell renal carcinomas, and other visceral tumors. In the late 1990s, ELST became a recognized part of the disease spectrum because it was associated with online Mendelian inheritance in man VHL disease (No. 193300) [9]. VHL has a prevalence of 1 in 39,000 people [14] and is caused by a germline mutation in the VHL gene on chromosome 3 (3p25-26) [15]. The VHL gene product is a tumor suppressor that when lost or mutated results in a loss of inhibition to cell growth and can lead to neoplasms such as ELST. The VHL gene product protein is important in the regulation of hypoxia inducible factor–1a, which controls angiogenesis and cell metabolism [16]. In normal situations, patients have two copies of the wild-type (normal) VHL gene allele. The disease develops in people who have VHL and have a spontaneous ‘‘loss of heterozygosity,’’ that is, a mutation of the normal copy of the VHL gene, which leaves only the mutated copy of the VHL gene [17]. This mutation leads to tumorigenesis and the development of the highly vascular ELST in vulnerable tissue, such as the epithelium of the vestibular aqueduct. Recent studies of clinically tumor-free endolymphatic duct and sac tissue of patients who have VHL revealed VHL gene– deficient microscopic abnormalities with morphologic similarities to ELST

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not only within the sac epithelium but also within the duct [18]. The implications of this finding are important, because it confirms prior histologic observations regarding a de novo ELST reported in 1995, which showed a tumor filling not only the proximal sac but also the intraosseous duct, and it underscores the need for surgery to include removal of the duct for long-term cure [3,12]. The propensity for microscopic tumor foci along the duct also may explain the observation that as many as 65% of patients who have VHL demonstrate an audiologic disturbance despite only 6% of those patients showing MRI evidence of a tumor [9]. It is likely that these tumors remain radiologically undetectable for some time, causing hearing and balance disturbance with an average delay of 15 years before tumor is detected [9]. It follows that patients who do not have VHL who develop ELST likely have suffered a ‘‘two-hit’’ injury to the VHL locus and have lost function of both copies of the wild-type VHL tumor suppressor allele.

Pathophysiology Whether an ELST develops in a patient who has VHL or sporadically in a patient without it, the pathologic sequence of growth seems to advance slowly, over the course of years. Initially, a small tumor within the confines of the endolymphatic sac and duct (usually the distal duct and proximal sac) causes audiovestibular dysfunction that can take one of two courses. One such course is an acute significant hearing loss, which may be irreversible and has been shown to likely be secondary to intralabyrinthine hemorrhage followed by inflammation and neural degeneration [12]. More commonly, symptoms of endolymphatic hydrops develop, which result in low frequency hearing loss, tinnitus, fullness, and vertigo [3,10]. This development is likely caused by blockage of endolymphatic fluid resorption or even excess fluid production that results in classic endolymphatic hydrops and frequent early diagnosis of Meniere’s disease [3,4]. As the tumor grows, it takes on the appearance of an infiltrative, poorly circumscribed neoplasm composed of cuboidal to low-columnar epithelial cells disposed in a fibrous stroma and arranged either in papillary patterns (Fig. 2) or cystic spaces that contain proteinaceous material reminiscent of thyroid follicles [3–5]. The epithelial cells are often clear and are sometimes arranged in follicular configurations; however, thyroglobulin stains are negative [3]. By this time, an enlarging tumor typically has eroded the osseous vestibular aqueduct and proceeds to grow along four potential vectors of extension from the endolymphatic sac [3]. In order of frequency, ELSTs progress posteriorly to the cerebellopontine angle through the posterior fossa dura, laterally via the mastoid air cell tracts to the middle and external ear (often with facial paralysis), superiorly toward and into the middle cranial fossa (usually with destruction of semicircular canals) (Fig. 3), and

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Fig. 2. ELSTs are grossly described as highly vascular, polypoid lesions with common cystic areas. ELSTs demonstrate a papillary growth pattern with extensive soft tissue and bony destruction. (From Bambakidis NC, Megerian CA, Ratcheson RA. Differential grading of endolymphatic sac tumor extension by virtue of von Hippel-Lindau disease status. Otol Neurotol 2004;25:777; with permission.)

finally along the petrous ridge to the clivus and cavernous and sphenoid sinuses. Before recognition of the ELST entity, the finding of these lesions in the temporal bone and cerebellopontine angle was thought by some to be the result of ectopic choroid plexus papillomas because of the similar appearance of aggressive papillary tumors (later believed to be ELSTs) of the temporal bone and tumors of the choroids plexus. The ELSTs were shown to lack reliable immunohistochemical staining for transthyretin,

Fig. 3. Grade I ELST in a 15-year-old patient with VHL who first developed facial paralysis 1 year before presentation. Severe vertigo and sudden sensorineural deafness on the right side resulted in referral when MRI showed enhancing lesion of the temporal bone. CT scan reveals ELST tumor extending superiorly with destruction of the lateral and superior semicircular canals. Resection via a translabrinthine approach ensued. No evidence of contralateral ELST has developed on serial MRI.

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however, which is an important marker for choroid plexus and is readily expressed in choroid plexus papillomas [19]. Nearly all ELSTs express cytokeratin, vimentin, and epithelial membrane antigen, and most stain positive for S-100 and neuron-specific enolase [19].

Clinical features When considering the sequence of symptoms and signs that develop in a patient affected by an ELST, patients who have VHL and patients who do not proceed along a similar pathway of clinical problems; however, their age of presentation and rate of disease progression may vary. Much can be learned from careful study of the VHL patient group, however, because by virtue of yearly MRI screening these patients are often found to have small tumors or even present to VHL clinics with only hearing loss (the earliest sign of ELST) and are believed to harbor radiographically nondetectible ELST. In one series of VHL patients with MRI evidence of ELST, more than 90% had hearing loss and tinnitus, whereas 62% had vertigo and 29% reported aural fullness, with 8% having facial paralysis [9,20]. Hearing loss may be sudden but is usually slowly progressive, especially in patients who do not have VHL and often may have been misdiagnosed earlier with Meniere’s disease. Hearing loss in patients who have VHL occurs early in life and is not reversible, with a mean age at onset of 22 years [9]. As tumors enlarge, a patient may experience tumor presentation in the external auditory canal, which appears as a polypoid mass. Usually by this time, facial paralysis and deafness have become apparent and the patient experiences symptoms of cerebellopontine angle extension, including headache secondary to brain compression. Mukherji and colleagues [21] provided the first comprehensive radiologic study of ELST in 20 patients. CT of ELSTs demonstrated destruction centered at the posterior petrous surface, often with calcifications centered at the retrolabyrinthine region. MRI studies of 15 preoperative lesions revealed that 80% have increased signal intensity on unenhanced T1-weighted images and 20% were isointense to cerebellar white matter [21]. All tumors enhanced with gadolinium on T1-weighted images and similarly showed increased signal intensity relative to cerebellar white matter on T2 weighting. The T2 increased signal was heterogeneous in 9 of 14 lesions, whereas 5 were homogeneously increased [21]. MRI often reveals that these tumors have a fairly large cystic component. Tumors O2 cm showed flow voids in some cases [21]. They were found to be vascular tumors, and the blood supply arose predominantly from the external carotid (Fig. 4), whereas larger tumors developed additional supply from the internal carotid and posterior circulation [21]. Patel and colleagues [22] recently confirmed these findings in a study of 31 patients and showed that 100% had central calcific spiculation and posterior rim calcification on CT.

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Fig. 4. (Left) MRI reveals hyperintense cystic or hemorrhagic areas on T1- and T2-weighted sequences. There may be hypointense tumor centers as a result of necrosis, calcifications, or bony trabeculae. Heterogeneous enhancement is common, and flow voids may be seen on T2-weighted images. (Right) Angiographic evaluation typically demonstrates the hypervascular nature of ELSTs, and feeding vessels usually involve branches of the ascending pharyngeal artery or occipital artery or both. Unlike paragangliomas of the temporal bone, which demonstrate a discrete tumor capsule, angiographic borders of ELSTs are usually irregular and ill defined as a result of their invasive nature. Preoperative embolization is helpful in reducing blood flow through the tumor during resection.

In nearly one third (30.2%) of patients who have VHL-related ELSTs, bilateral tumors can develop (Fig. 5) [9,10]. This fact poses a significant risk for the possibility of bilateral profound sensorineural hearing loss if tumor growth continues. Early diagnosis and treatment with hearing preservation surgery is the most reasonable course of action when small tumors are detected. To standardize tumor size and reporting, a grading system was devised [13]. This system was used to create a surgical treatment algorithm for this report (Table 1) [13]. In 2004, Bambakidis and colleagues [13] combined data from a new group of patients who had ELST and a detailed study of all known reports to date of ELSTs. They subjected each case to a radiographically based grading system (Figs. 6–9) and correlated tumor size and symptomatology with VHL status. The mean age of tumor presentation in patients who did not have VHL was 52.5 years, whereas the group of patients who had VHL was much youngerd31.3 years. The ratio of female/ male patients who had ELST and VHL was 2:1, whereas the ratio for patients who did not have VHL was 1:1. Patients who had VHL had a mean duration of hearing loss before tumor diagnosis of 10 years, whereas the duration among patients who did not have VHL was 7.8 years. These findings, coupled with a lower incidence

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Fig. 5. Bilateral grade I ELST in a 36-year-old patient with VHL. Note larger left ELST, which resulted in Meniere’s-like symptoms and low-frequency hearing loss. Removal resulted in return of hearing for 1 year and then hearing began to fluctuate. Note small contralateral ELST associated with normal hearing upon presentation. (From Megerian CA, Haynes DS, Poe DS, et al. Hearing preservation surgery for small endolymphatic sac tumors in patients with von HippelLindau syndrome. Otol Neurotol 2002;23:380; with permission.)

of facial paralysis in patients who had VHL compared with patients who did not, suggest that ELSTs may grow more slowly in the patients who have VHL. ELSTs in patients who had VHL were significantly more likely to be a lower grade than tumors in patients without it (grade I, 40% versus 25%; grade II, 50% versus 58%; grade III 8% versus 14%; grade IV, 2% versus 4%; P ! .05). The study also showed that because the routine use of intracranial imaging became commonplace after 1988, sporadic ELSTs have been diagnosed at a lower grade. The advantage of removing tumors at grade I size is not only the potential for hearing preservation and cure but also prevention of disease entrance into the posterior fossa and admixture with the subarachnoid space. Although distant hematogenous metastasis of this tumor has not been described, the potential for ‘‘drop metastasis’’ to the spinal column causing lower extremity paralysis was reported recently [23].

Medical and surgical treatment Most patients who have an ELST suffer from unilateral progressive sensorineural hearing loss and vertigo for months to years before diagnosis. Initially the diagnosis of ELST is suspected after obtaining an MRI that

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Table 1 Grading and treatment system for endolymphatic sac tumors Grade

Tumor extent

Surgical options

I

Confined to temporal bone, middle ear cavity, and/or external auditory canal Extension into posterior fossa

Hearing preservation with retrolabyrinthine transdural approach Extended retrolabyrinthine transdural approach, approach with labyrinthectomy if hearing poora Subtemporal craniotomy with petrosectomya Staged anterior and posterior fossa techniquesa

II

III IV

Extension in posterior fossa and middle cranial fossa Extension to clivus and/or sphenoid wing

a Preoperative embolization for grades II–IV and postoperative stereotactic radiosurgery for postoperative residual disease may be adjunctive. Adapted from Bambakidis NC, Megerian CA, Ratcheson RA. Differential grading of endolymphatic sac tumor extension by virtue of von Hippel-Lindau disease status. Otol Neurotol 2004;25:773–81; with permission.

Fig. 6. Grade I ELST tumor in an 85-year-old woman (without VHL) with complaints of unilateral progressive hearing decline over a 5-year period. She was initially diagnosed with Meniere’s disease. After 3 months of progressive vertigo followed by left facial weakness, intracranial imaging demonstrated a destructive lesion of the petrous ridge with involvement of the labyrinth and compression of the internal auditory canal without extension into the posterior fossa. An audiogram demonstrated profound deafness in the left ear. The patient subsequently underwent tumor resection through a transmastoid approach and facial nerve decompression. The dura was not violated during the procedure. Facial nerve function returned to normal, and Gamma knife therapy to residual posterior fossa tumor bed was performed. Four-year follow-up revealed no disease progression. (Left) Axial CT scan demonstrates lesion within the left temporal bone with extensive destruction and trabeculation (arrow). (Right) Noncontrast T1-weighted MRI of hyperintense lesion confined to the temporal bone without extension into the posterior fossa. (From Bambakidis NC, Megerian CA, Ratcheson RA. Differential grading of endolymphatic sac tumor extension by virtue of von Hippel-Lindau disease status. Otol Neurotol 2004;25:776; with permission.)

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Fig. 7. Grade II ELST in a 40-year-old man with no past medical history of VHL who presented with increased headache and ataxia with episodic vertigo. He had lost his hearing in his right ear 15 years earlier from a presumed sudden hearing loss. His evaluation for headache and ataxia included an MRI, which demonstrated a lesion filling the petrous portion of the right temporal bone with destruction of labyrinthine structures and extension into the posterior fossa with a significant cystic component. He was approached surgically in a staged fashion. He initially underwent a posterior fossa craniotomy with complete excision of tumor to the level of the petrous ridge and endolymphatic sac region. This region was then lined by bovine pericardium, leaving tumor along the petrous bone lateral to the pericardium. Three weeks later, a translabyrinthine approach allowed for removal of the tumor from the temporal bone, leaving the pericardium as a dural repair. He fared well postoperatively without experiencing any complications. Contrasted T1- (left) and T2-weighted (right) MRI of a right cerebellopontine angle demonstrates heterogeneously enhancing ELST with a large cystic component extending into the posterior fossa and compressing the fourth ventricle. (From Bambakidis NC, Megerian CA, Ratcheson RA. Differential grading of endolymphatic sac tumor extension by virtue of von Hippel-Lindau disease status. Otol Neurotol 2004;25:777; with permission.)

reveals a gadolinium-enhancing mass epicentered at the posterior petrous ridge. The presence of calcifications along the posterior rim on CT with encroachment or invasion of the posterior fossa raises the highest levels of suspicion preoperatively for the diagnosis of ELST. In the absence of a personal history of VHL-related lesions, once must obtain a detailed history of first-degree relatives for problems such as retinal angiomas, renal or pancreatic cysts, pheochromocytomas, or other manifestations of VHL. If VHL is suspected, co-management of the patient with an oncologist who is familiar with treating VHL is recommended, and genetic testing and counseling of the patient and family are in order. A known VHL patient typically presents with a small grade I tumor after having been referred to an otolaryngologist for hearing loss and vertigo with subsequent imaging or comes directly from a VHL clinic, where a tumor was detected in an asymptomatic ear. Patients who do not have VHL typically are older (fourth decade or older) but present with similar audiovestibular complaints and usually more advanced tumors. The goal in these scenarios should be total tumor eradication with a goal of hearing preservation in grade I and possibly grade II tumors. Achieving this goal may require

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Fig. 8. Grade III ELST demonstrates pitfalls of incomplete resection in Fig. 9. The patient is a 55-year-old woman who initially was diagnosed with a left-sided ELST in 1994 after progressive hearing loss of several years’ duration. She had undergone multiple subtotal resections of the tumor, which originally involved the posterior and middle cranial fossas consistent with a grade III case. (From Bambakidis NC, Megerian CA, Ratcheson RA. Differential grading of endolymphatic sac tumor extension by virtue of von Hippel-Lindau disease status. Otol Neurotol 2004;25:778; with permission.)

discussions with a patient about the need for removing these tumors from an otherwise normal hearing ear before the onset of severe audiovestibular symptoms. The evolution of surgical approaches for the small ELST has paralleled the accumulation of knowledge regarding the behavior and position of this tumor within the endolymphatic sac and substantial portions of the osseous endolymphatic duct. The most effective method that allows for removal of both sides of the dural sleeves that surround the endolymphatic sac has been called the retrolabyrinthine-transdural approach [10] or the retrolabyrinthine posterior petrosectomy approach [12]. The patient is placed supine and positioned with head turned away from the surgeon. Hair is shaved, but head pins are not necessary. A facial nerve monitor is used. Using an extended postauricular incision, a mastoidectomy is performed with identification of the horizontal semicircular canal and facial nerve. The jugular bulb is skeletonized, as is the tegmental dura and the sinodural angle. After identifying and skeletonizing the posterior semicircular canal, the outline of a bulging tumor-filled endolymphatic sac is often seen (Figs. 10–14). The endolymphatic duct is then followed with a diamond

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Fig. 9. Grade IV ELST in patient from Fig. 8 in 2002 after having been lost to follow-up. She demonstrated multiple cranial nerve palsies, including bilateral vocal cord paralysis, and tumor had progressed to involve the clivus, cavernous sinus, and sphenoid sinus via the anterior cranial fossa. (From Bambakidis NC, Megerian CA, Ratcheson RA. Differential grading of endolymphatic sac tumor extension by virtue of von Hippel-Lindau disease status. Otol Neurotol 2004;25:779; with permission.)

drill behind the posterior semicircular canal toward the vestibule and tumor is carefully removed. If the posterior semicircular canal is violated, it can be sealed quickly with bone wax. A margin of at least 0.5 cm around the sac on healthy posterior fossa dura is obtained as the sac and duct are removed en bloc. This procedure is performed after removing tumor-laden bone from the posterior dural surface using the high-speed drill. The antrum is then

Fig. 10. Drawing of a right mastoid cavity demonstrates the endolymphatic sac (ELS), endolymphatic sac tumor (ELST), jugular bulb (JB), posterior fossa dura (PFD), and sigmoid sinus (SS). The dotted lines correspond to Donaldson’s lines and the usual location of the ELS.

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Fig. 11. Drawing demonstrates the removal of the ELST via a retrolabyrinthine-transdural approach, with elevation of posterior fossa dura (PFD). CNs VII and VIII are seen in the cerebellopontine cistern. The semicircular canals are preserved. SSC, superior semicircular canal; SS, sigmoid sinus; ELS, endolymphatic sac.

sealed with bone wax; abdominal fat is used to seal the dura, often with the aid of a tissue sealant to prevent cerebrospinal fluid leaks. A transmastoid approach, which carries the shortcoming of leaving the posterior sleeve of dura intact and potentially providing a site for tumor recurrence, has been described [10]. Similarly, a posterior fossa approach

Fig. 12. After resection of grade I ELST, the mastoid cavity is obliterated with abdominal fat. LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal; SS, sigmoid sinus; VII, vertical portion of facial nerve.

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Fig. 13. Drawing illustrates the transmastoid removal of an ELST from the right ear. The endolymphatic sac (ELS) has been elevated and retracted superiorly, exposing the ELST and preserving the posterior fossa dura (PFD). Excision of the lesion can be performed without violating the dura. ELD, endolymphatic duct; SS, sigmoid sinus.

leaves the anterior dural sleeve and does not afford visualization of the posterior semicircular canal during dissection of the endolymphatic duct [10,12]. Patients with poor or unserviceable hearing should have a similar approach to the retrolabyrinthine approach, but often these patients have labyrinthine invasion, and a concomitant translabyrinthine approach is required. Because of their vascularity and posterior fossa invasion, larger grade II lesions are complicated, usually by a significant amount of bleeding. For these lesions, preoperative embolization is advised. Based on the size of the lesion and middle fossa extension, a subtemporal transpetrous approach may be required. The freedom from tumor recurrence using these approaches is excellent. Two studies (a total of nine patients) that used techniques for grade I tumors uniformly allowed for hearing preservation and freedom from tumor, with follow-ups ranging from 6 months to 8 years [10,12]. Using microsurgical techniques, a large study from the House Ear Institute of 14 patients with larger tumors showed that only 2 patients had persistent disease after an average follow-up of 59.6 months [11]. For patients with unresectable disease or patients not deemed surgical candidates, stereotactic radiotherapy using the Gamma knife seems to be useful in arresting tumor growth. In rare cases of bilateral deafness after resection

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Fig. 14. Drawing demonstrates the cerebellopontine angle as seen during a retrosigmoid craniotomy for removal of ELST. The cerebellum is retracted medially. The endolymphatic sac (ELS) is seen halfway between the sigmoid sinus (SS) and internal auditory canal. The endolymphatic sac tumor (ELST) is seen bulging into the posterior fossa. Once dura over the ELST has been opened and retracted, the tumor can be dissected from the sac and duct. This approach preserves hearing only if the contents of the labyrinth are not violated. PFD, posterior fossa dura.

in patients who have VHL, cochlear implantation remains a viable option for hearing rehabilitation.

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