73 Management of Small Vestibular Schwannoma in Patients with Minimal Symptoms

10.1055/b-0039-169227

73 Management of Small Vestibular Schwannoma in Patients with Minimal Symptoms

Erling Myrseth, Morten Lund-Johansen, and Øystein V. Tveiten

73.1 Introduction

Treatment of small, slow-growing, benign tumors may be challenging as the treatment should not increase the patient’s symptoms or complaints. Treatment of small vestibular schwannomas (VSs) is no exception. More recently, in the past one to two decades, there has been an increase in the detection of small VS, especially in the elderly population and those with minimal symptoms. The most plausible explanation for the observed increase in incidence is greater access to magnetic resonance imaging (MRI).s. Literatur A thorough knowledge of the natural course of growth and symptomatology is mandatory so that the best treatment option can be chosen, and the patient can be convinced and reconciled that the right decision has been made.

The management of small VSs in patients with minimal complaints is a matter of debate, and currently there is no consensus on initial treatment strategy. The chosen treatment is strongly influenced by the physicians’ and patients’ preference. The goal of this chapter is to review the latest evidence regarding treatment outcomes for patients with small, asymptomatic, incidentally discovered, or minimally symptomatic VS.

73.2 Definition of Small Vestibular Schwannoma

In this context, small VSs are defined as tumors according to Koos grades I and IIA: grade I tumors are purely intracanalicular, and grade IIA tumors are protruding not more than 10 mm into the cerebellopontine angle (CPA) measured from the lip of the porus acusticus, and not in contact with the brain stem (Fig. 73‑1 ).s. Literatur

**Fig. 73.1** Koos stages 1 to 4 tumor staging system for vestibular schwannoma.

73.3 The Natural History of Vestibular Schwannoma

Vestibular schwannoma usually grows slowly, but the growth pattern is heterogeneous. The typical growth rate for a growing tumor is 1 to 2 mm/year. However, some may enlarge much more rapidly, and yet others may actually involute. Growth patterns may be characterized by saltatory growth, linear growth, exponential growth, stable size, and decreasing size. There is a common belief that after growth is witnessed, most tumors will continue to grow indefinitely. However, this notion is easily discredited by the simple observation that many tumors do not grow for extended periods following diagnosis, but of course, the tumor must have grown at some point to reach its current size. Especially intrameatal tumors often do not grow for years.s. Literatur Risk of growth and growth rates are shown in Table 73‑1 and further summarized in Chapter 14. Not surprisingly, the proportion of growing tumors seems to increase with longer follow-up.s. Literatur No strong predictor of tumor growth has been detected, except for cystic tumors which tend to have a higher growth rate than completely solid tumors.s. Literatur

Table 73.1 Natural growth rate in vestibular schwannoma
Author (year)	Follow-up period	Percentage of growth (range)	Growth rate (mean)
Nikolopoulos et al (2010)	NR	NR (7-73)	1–2 mm/y
Yoshimoto (2005)	38 mo	46 (15–85)	1.2 mm/y
Thakur et al (2012)	3 y	44 (29–54)	NR
Whitehouse et al (2010)	3.65 y	51.1	1.24 mm/y
Hajioff et al (2008)	10 y	78	1.0 mm/y
Abbreviations: NR=not reported

Gradual hearing deterioration is common in untreated VS patients, even in the absence of tumor growth. Overall, a hearing preservation rate of approximately 50% during a mean follow-up period ranging from 2 to 5 years is to be expected.s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur In one series, 100% speech discrimination at diagnosis was a positive prognostic factor for maintaining long-term useful hearing with conservative treatment.s. Literatur Sudden sensorineural hearing loss (SSNHL), defined as 30 dB or greater hearing loss over less than 72 hours, in VS patients occurs in approximately 10 to 20% of cases.s. Literatur ^, s. Literatur Contrary to what might be expected, tumor size was significantly smaller in VS with SSNHL compared to other VSs.s. Literatur

In small- and medium-sized VS, the difference in long-term quality of life (QoL) between treatment strategies when evaluated by disease-specific questionnaires is small and not necessarily clinically significant.s. Literatur ^, s. Literatur

73.4 Treatment Options

There are three main treatment options for VS: (1) conservative management with observation/serial radiological follow-up, (2) radiation, and (3) surgery. This results in five possible treatment strategies: (1) observation, (2) observation followed by radiosurgery if tumor growth, (3) observation followed by microsurgery if tumor growth, (4) immediate radiosurgery, and (5) immediate microsurgery. Each modality has pros and cons, and several factors have to be taken into account when advising patients about treatment options. Usually, the tumor size is the most important determining factor, but age, medical condition, hearing level as well as other complaints, and patients’ preferences also have to be considered.

For patients with small tumors and mild or no symptoms, the controversy is especially pointed. According to the Hippocratic Oath, treatment should not cause more morbidity to the patient than the natural course of the disease, neither in the short or long term. Therefore, it is most important to have a thorough knowledge about the natural course of the disease, both regarding tumor growth, QoL, and symptom development. Unnecessary treatment should be avoided. The dilemma in patients with small tumors and good ipsilateral hearing is to evaluate the treatment choice regarding chance of hearing preservation and tumor control, both immediately and in the long term.

73.4.1 Conservative Treatment

Conservative treatment, also called “wait-and-see” or “wait-and-scan,” implies clinical and MRI follow-up at regular intervals. There are different follow-up algorithms regarding imaging intervals and duration of follow-up needed. Most authors recommend the first scan 6 months after the initial scan to identify rapid growing tumors. In case of no growth, further MRI scans should be taken annually for at least 5 years. Stangerup et al suggested further MRI scans at 7, 9, and 14 years after the initial MRI scan.s. Literatur Martin et al recommended follow-up scans every 5 years for the rest of the patient’s life.s. Literatur Smouha et al recommended continuation of annual MRI scans.s. Literatur

For small tumors with minimal symptoms, the “wait-and-scan” treatment strategy hopes to prolong the period of minimal complaints, avoiding the risk of new symptoms or complications related to the treatment. Several authors recommended conservative treatment, or no treatment, for most small tumors with minor or no complaints.s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur One objection against this strategy is the risk of early progressive or SSNHL. This risk needs to be compared with the likelihood of preserving hearing if the tumor is treated by surgery or radiosurgery.

Tveiten et al analyzed the hearing status in small- and medium-sized VS at a mean time of almost 8 years after initial treatment, and found that treatment modality was an independent risk factor for hearing deterioration; patients treated by observation had the best prognosis.s. Literatur Among ears with serviceable hearing at baseline, functional hearing was maintained in 68% of observed patients, 40% of those receiving Gamma Knife radiosurgery (GKRS; Elekta AB, Stockholm, Sweden), and 14% treated with surgery (p < 0.005). These results may be biased by the fact that observed tumors were not growing and that larger tumors tended to receive microsurgical resection.

Jeyakumar et al suggested that small incidentally discovered VSs tend to follow a more benign course requiring intervention less frequently than symptomatic larger lesions (47 vs. 76%, respectively).s. Literatur However, other studies have found that the biological behavior and eventual need for treatment of an asymptomatic tumor is no different than one causing hearing loss or other symptoms when comparing VS of equal size.s. Literatur

Failure of conservative management is most often due to tumor growth and rarely due to symptom progression. Tumor growth is usually defined as linear increase or tumor volume doubling time, but growth of intrameatal tumors to extrameatal extension is also used.s. Literatur This variation, as well as length of follow-up period, might obviously influence the reported growth rate results and treatment failure rates.

The efficacy of conservative treatment, as defined as freedom from active treatment, is reported in several studies. Breivik et al studied a cohort of 193 consecutive VS patients prospectively for a minimum of 24 months (median: 43 months), and found that 74 patients (38%) underwent active treatment (microsurgery or radiosurgery) during the period of observation, 37 patients (19%) before 3 years.s. Literatur This result is comparable with other series.s. Literatur ^, s. Literatur However, the need for active treatment is reported in the range of 18 to 49%.s. Literatur ^, s. Literatur ^, s. Literatur