In general, these tumors are slow-growing, benign neoplasms that have an indolent evolution. In 75% to 80% of cases, the growth rate is estimated to be 1 to 2 mm per year (Wazen et al 1985; Thomsen and Tos 1990; Bederson et al 1991; Nedzelski et al 1992). The rate of growth may be slower in older patients. Tumor growth is rarely predictable. Charabi and colleagues followed 127 tumors with serial neuroimaging studies over several years (Charabi et al 1998). They noted some growth in over 80% of tumors, although growth patterns were varied and changing for individual tumors. Clinical deterioration is to be expected in vestibular schwannomas that are symptomatic and growing.