75 Management of Sporadic Vestibular Schwannoma in the Only Hearing Ear

10.1055/b-0039-169229

75 Management of Sporadic Vestibular Schwannoma in the Only Hearing Ear

Neil S. Patel and Colin L. W. Driscoll

75.1 Introduction

When determining optimal management of vestibular schwannoma (VS), the hearing status of both ears must be considered. While unilateral deafness impairs sound localization and speech understanding in noise, many patients with good hearing in the contralateral ear eventually accommodate to these changes and do not seek aural rehabilitation. This is in sharp contrast to patients with acquired severe-to-profound bilateral sensorineural hearing loss, where the disability of deafness is usually devastating.

Fortunately, the vast majority of sporadic VSs are diagnosed in patients with normal or serviceable hearing in the contralateral ear. The clinical scenario of VS in an only hearing ear is distressing for patients and surgeons alike. In these cases, the standard treatment paradigm for VS is disrupted and the goals of hearing preservation and aural rehabilitation come to the forefront of the discussion. A standard algorithm cannot be applied and the path forward is influenced by auditory and vestibular function of the ipsilateral and contralateral ear, tumor size, growth rate, patient health, and preferences. All patients need support and guidance as they adapt and accept the diagnosis and implications. A successful treatment plan addresses their fears and anxiety, engages them in decision making, and sets realistic expectations.

The primary objectives of the current chapter are to (1) identify the key steps in assessing the contralateral (deaf) ear for hearing restoration potential; (2) discuss management of tumors of varying sizes and pretreatment hearing status; (3) comment on hearing rehabilitation options in the ipsilateral tumor ear; (4) evaluate the modern experience with cochlear implantation (CI) following stereotactic radiosurgery (SRS) and microsurgery; and (5) highlight important patient factors that drive decision making in this challenging situation.

75.2 Auditory Rehabilitation of the Contralateral Ear

The first practical step is to sort out rehabilitative options for the contralateral ear. What was long thought to be a “useless” ear may now become valuable. If there is residual hearing, a hearing aid trial can be initiated. If the ear has not been used for many years, it may take some time before the patient maximizes performance with the aid. Even poor hearing in the contralateral ear may be reassuring for the patient, as they consider treatment options for their tumor, as well as for the surgeon, as this assures an intact auditory pathway for potential treatment options such as CI.

The modern CI has revolutionized management of sensorineural hearing loss. If the patient performs very poorly with a conventional hearing aid or lacks any hearing, a standard CI evaluation is initiated. If hearing in the tumor ear is significantly compromised already or if the tumor is large and hearing preservation with treatment is unlikely, this evaluation may be started early. In the case of a small tumor and good hearing, a CI evaluation for the contralateral ear may be either postponed or pursued upfront. With the latter option, the benefits of implantation will gradually increase, as hearing loss in the tumor ear inevitably declines either from treatment or the natural history of disease.

In addition to audiometric testing, CI candidacy workup should include magnetic resonance (MR) imaging with appropriate T2-weighted sequences to evaluate cochlear patency plus parasagittal reconstructions of the internal auditory canal establish presence of the cochlear nerve in cases of congenital deafness. If there is concern for ossification of the cochlea, a CT will be beneficial for surgical planning. The role of electrical promontory stimulation testing (EPST) in determining CI candidacy remains controversial and will be discussed later in this chapter.

Unfortunately, it is common that the diagnosis of VS in an only hearing ear occurs in patients with long-standing and even congenital contralateral hearing loss.s. Literatur We would normally consider these patients to be poor candidates for CI, as the results are often suboptimal by standard outcome criteria; however, in this setting, there is little to lose. It is possible the patient will still gain open-set speech understanding; however, even access to environmental sound, enhanced lip-reading, and voice modulation may be valuable to the patient over time.

If a patient is a CI candidate, the sequence of tumor treatment and implantation must be considered. If the patient is considering radiation therapy for a growing tumor, it is preferable to perform radiosurgery first as MRI-based lesion targeting becomes increasingly complex in the presence of device or magnet artifact and hearing loss from radiosurgery generally occurs in a protracted manner. If surgery or observation is being contemplated, it is preferable in most cases to proceed with implantation first as the outcome of the CI in this context has a direct influence on the approach to the tumor. Hearing preservation may not be prioritized as highly as in the tumor ear if the patient has enjoyed a good result with their CI. In contrast, a patient with a poor result may favor a more conservative approach or cochlear nerve-sparing surgery that may permit a CI in the ear affected should serviceable hearing be lost.

75.3 Tumor Management

While hearing preservation and rehabilitation are tenable goals when evaluating any patient with a VS, the order of priorities shifts dramatically when a tumor is diagnosed in an only hearing ear. Given the remarkable variability in treatment approaches for small- and medium-sized tumors in the setting of normal hearing in the contralateral ear, the present discussion focuses on situations where a change in approach can be attributed to deafness in the contralateral ear, rather than attempting to reestablish treatment paradigms for all scenarios.

75.3.1 The Small Tumor

In patients with unilateral functional hearing, even minor auditory symptoms are typically noticed and reported promptly. Thus, most tumors in this population are identified at a small size when hearing is often still serviceable. Following diagnosis, a period of radiologic surveillance is almost always the initial course of action. Intuitively, the best scenario for the patient is for the tumor to remain stable. Recent epidemiologic studies have substantially increased our understanding of growth and preservation of long-term serviceable hearing among small tumors. In line with the authors’ experience, less than 30% of purely intracanalicular tumors exhibit growth into the cerebellopontine angle (CPA) over long-term follow-up.s. Literatur Tumors that extend into the CPA may exhibit slightly higher growth rates. The interested reader may refer to Chapters 14 and 51 for an in-depth review of the natural history of VS growth and hearing decline. Unfortunately, hearing can progressively deteriorate even when a tumor remains radiographically stable. Sudden changes or fluctuating hearing loss may respond favorably to a course of steroids. If the tumor remains stable but the patient no longer benefits from a conventional hearing aid, then CI should be pursued with or without treating the tumor. This strategy is discussed in greater depth later in the chapter.

Surgical intervention is generally considered only after there has been definite radiological evidence of tumor growth. The couple of exceptions to this rule may be in the setting of a very small tumor that is favorably located from a hearing preservation standpoint or a nongrowing (or slowly growing) tumor with progressive audiometric decline. A small tumor originating from the superior vestibular nerve medially in the internal auditory canal can be removed with a low risk of hearing loss by an experienced surgeon (Fig. 75‑1 ). In the case of a stable tumor with progressive hearing loss, internal auditory canal decompression via middle cranial fossa may prolong serviceable hearing in select cases.s. Literatur However, even in this setting, it is our general practice to advocate observation. If a small tumor follows a typical slow-growing course, the decision to undertake surgery requires thoughtful and honest assessment of hearing preservation outcome. In the setting of an only hearing ear, one must take into account tumor and patient characteristics and select for surgery-only tumors with the highest likelihood of successful hearing preservation. Patients with good preoperative word recognition score, superior vestibular nerve tumors,s. Literatur ^, s. Literatur and those with evidence of fundal fluid on T2-weighted MRI sequencess. Literatur may enjoy an increased likelihood of hearing preservation. Consistent with our experience, the realistic likelihood of hearing preservation for a small favorably located tumor based on early postoperative audiometry is in the range of 50 to 80% range, with estimates varying substantially in the literature.s. Literatur A small tumor that extends to the fundus, under the transverse crest and into the base of the modiolus, is much more difficult to remove successfully. If the surgeon is not highly confident that a complete removal can be obtained with hearing preservation, strong consideration needs to be given to continued observation or SRS. Patient preference also has a large role in this decision. When hearing is successfully preserved with surgery, it is felt to be durable in most cases. Estimates of long-term serviceable hearing following microsurgical resection demonstrate hearing preservation rates from 65 to 89%; however, a large subset of patients in these studies were lost to follow-up.s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur

**Fig. 75.1** Example of small right-sided vestibular schwannoma of superior vestibular nerve origin, located in the midportion of the internal auditory canal.

If the tumor is not favorable for microsurgical removal or the patient declines surgery, then SRS is a viable alternative. Even in the presence of slow growth, it may be beneficial to delay treatment, as radiosurgery will most likely accelerate hearing loss. Treating upfront or the so-called proactive treatment to protect hearing is controversial and not our practice. An in-depth understanding of the factors that determine hearing preservation following SRS is needed to decide when to intervene (see Chapter 52).

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