14.1 Introduction

Sandifort was the first to describe a vestibular schwannoma (VS) in 1777 following a postmortem autopsy. Since the first attempts at surgical tumor removal at the end of the 19th century, it was assumed for almost a century that, if left untreated, these tumors would invariably continue to grow over time. Upon diagnosis, surgical treatment was therefore considered mandatory for decades, irrespective of tumor size. Approaching the end of the 20th century, some patients were, however, treated conservatively and observed for tumor growth by interval imaging, as surgery was considered too risky due to severe patient comorbidities and/or advanced age. In 1985, Silverstein et al were among the first to report on conservative managements. Literatur and since then, a number of studies have documented that tumor growth following diagnosis was not inevitable and that some tumors do not grow for extended periods of time.

A large cerebellopontine angle tumor may be associated with serious complications and become life threatening due to brainstem compression. Thus, surgery is definitively advocated in patients with large VS. In patients with small- or medium-sized tumors, however, there are currently three management options: observation with interval imaging, surgery, or radiotherapy. Success of treatment is usually perceived to be control of tumor growth. Preservation of serviceable hearing in patients presenting with socially useful speech discrimination scores together with no or minimal treatment side effects are also regarded as important secondary outcomes. In order to justify invasive treatment by either surgery or radiotherapy for small- to medium-sized tumors, the outcome should be superior to that resulting from the natural history of the disease and should also be balanced against the need for intervention in order to avoid or minimize subsequent problems. Only a detailed knowledge of the natural history of these tumors will allow valid, evidence-based comparison of the outcome of observational management compared with active treatment. Accordingly, this chapter reviews the existing evidence on the natural history of tumor growth in patients observed with small- or medium-sized unilateral sporadic VS, whereas the natural history of hearing and vestibular function is addressed in Chapter 51 These issues are increasingly relevant for the patients and clinicians involved, as a steadily increasing number of patients are diagnosed with small- and medium-sized tumors, as reported in Chapter 3 on the epidemiology of VS.

14.2 Measurement of Tumor Size and Determination of Tumor Growth

According to the international consensus meeting in Japan in 2003,s. Literatur a tumor should be defined as either intrameatal or extrameatal, the latter designating a tumor with growth into the cerebellopontine angle. The size of a tumor with cerebellopontine angle extension should be determined by measuring the largest extrameatal tumor diameter, excluding the intrameatal portion.

It should be emphasized that determined tumor size and growth rate may depend on the diagnostic tool (computed tomography [CT] vs. magnetic resonance imaging [MRI]), the method of measurement (e.g., plane of dimensions assessed), and the definition of growth (e.g., number of millimeter enlargement). The largest diameter measurement is considered adequate when merely questioning absolute growth,s. Literatur which is the parameter relevant for clinical assessment and decision making, as it is the absolute size that determines the risk of brainstem or adjacent cranial nerve compression. Using contemporary MRI, diameter measurement error is up to 2 mm.s. Literatur Thus, tumor growth should be defined as an increase of 2 mm or more when measuring any diameter.

14.3 Natural History of Vestibular Schwannoma Growth

The evidence for the natural history of VS growth presented in this chapter is based on a review of the literature using the databases PubMed and Embase, including studies published during the period 1984 to 2014. Clinical articles reporting original data (thus excluding reviews and meta-analyses) from observational studies based on case series/cohorts and with more than 30 patients were considered. In total, there were 53 studies identified in the VS literature that reported on sporadic unilateral VS growth using serial predominantly MR imaging, which offered a definition of tumor growth (directly or indirectly) and reported mean/median follow-up. Collectively, these 53 studies contain data on tumor growth from almost 6,000 patientss. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur (Table 14‑1 ).

Weighted calculation based on the number of included patients in each publication produces an overall mean follow-up of 3.3 years, ranging from 0.5 to 10 years. Only three papers, representing 170 patients, have a mean follow-up of more than 5 years (5.5, 6.7, and 10 years, respectively).s. Literatur ^,​ s. Literatur ^,​ s. Literatur Weighted calculation on the occurrence of growth showed that a mean of 33% of tumors grow within a mean observation period of 3.3 years (Table 14‑1 ). Growth after diagnosis is unpredictable in rate and time and does not appear to be related to age, sex, tumor size at diagnosis, symptoms, or any other recognized factor of relevance, although cystic tumors may display sudden and dramatic growth.s. Literatur In addition, the risk of growth appears to be higher for tumors with extrameatal extension at diagnosis compared with tumors located exclusively within the internal auditory canal, although this may depend on the definition of growth (see later).

Although long-term data are scarce, it appears that tumor growth occurs almost exclusively within 5 years of diagnosis, and only rarely at a later stage. Growth may be continuous, but may also occur after a dormant period.s. Literatur Similarly, approximately 20% of tumors stop growing following a period of growth demonstrable on MRI.s. Literatur Notably, tumor shrinkage is also seen in approximately 5% of patients.s. Literatur For those tumors that demonstrate growth, the growth rate varies from 2 to 16 mm per annum with a mean annual growth rate varying between 1.6 and 4.7 mm.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur