The overall prognosis for survival and intact neurologic function for patients with sporadic schwannomas is relatively good. In most cases, these are benign, slow-growing, encapsulated tumors with a limited capacity for infiltration and destruction of surrounding tissues. Studies evaluating the natural history and growth rates of vestibular schwannomas support this viewpoint. Approximately 40% to 60% of tumors treated conservatively do not enlarge during the period of observation (Wazen et al 1985; Thomsen and Tos 1990; Bederson et al 1991; Nedzelski et al 1992; Macfarlane and King 1995; Rosenberg 2000; Swan 2000; Nutik and Babb 2001; Al Sanosi et al 2006). Of those tumors that do enlarge, 75% to 80% grow at a rate of 0.9 mm to 2 mm per year (Rosenberg 2000). The growth rate may be even slower in elderly patients. In addition, there is a small subgroup of patients (4% to 12%) wherein the tumor will spontaneously involute during long term follow-up (Luetje 2000). When an operation is required for a vestibular schwannoma, a complete resection is considered curative (Jackler and Pitts 1990; Macfarlane and King 1995). The recurrence rate after gross total removal is only 1% to 2% in most large series. Complications of surgery include perioperative mortality (0.5% to 7%), general neurologic sequelae (0.6% to 1.3%), and gait imbalance (up to 9% at 1 year) (Swan 2000). If the resection is incomplete, the residual tumor may have a slower growth rate than the preoperative mass (Wazen et al 1985). Although, in up to 44% of cases, tumor will recur within 7 years, often requiring further surgery or other treatment modalities (El-Kashlan et al 2000). Further growth was persistent once the incompletely resected tumors showed evidence of development. After treatment for a vestibular schwannoma, 70% of patients are able to return to work within 4 months, with another 25% eventually returning at a later date (Jackler and Pitts 1990). However, other authors feel the percentages are lower, with a range of 9% to 38% of all operated patients unable to return to work (Swan 2000). Recent data have demonstrated that the length of the tumor-cochlear nerve contact is an accurate predictor of hearing outcome (p = 0.0365). Large tumors had longer lengths of contact, resulting in more stretch and extension of the nerve, and a greater chance of hearing loss. This parameter correlated more closely to hearing outcome than tumor diameter (Yong et al 2008).
A recent study evaluated the quality of life in patients with vestibular schwannomas treated with surgical resection or radiotherapy, or followed by observation (Di Maio and Akagami 2009). Patients treated with radiotherapy or followed by observation did not have any significant changes in quality of life throughout the follow-up period. There were some mild trends for improvement in quality of life for the surgical cohort with tumors less than or equal to 3 cm in size, out to 24 months.
The prognosis for trigeminal schwannomas, as well as those of other cranial nerves, is not as favorable. It is more difficult to achieve a complete resection of these tumors, due to problems such as inadequate surgical exposure, involvement of the cavernous sinus, encasement of blood vessels, and adherence to the brainstem (Miller 1988; Pollack et al 1989; Samii et al 1995; Strauss and Post 1995; Bulsara et al 2008). For trigeminal tumors, the complete resection rate is 70% to 80% in modern series. Recurrence is rare after total extirpation. However, in cases with residual tumor, progression usually occurs within 3 years.
The prognosis for spinal schwannomas is excellent in most cases. The complete resection rate is 85% to 90% in modern series (Seppala et al 1995b; Safavi-Abbasi et al 2008). Recurrence is extremely uncommon after complete resection. Following subtotal removal, recurrence develops in 50% to 55% of patients, often after several years. Reoperation is clinically indicated in only 18% of patients with recurrent tumor (Seppala et al 1995b). The survival of patients with spinal schwannomas is similar to the general population.
For patients with sporadic spinal neurofibromas, the prognosis is also excellent, with a complete resection rate of 90% or better (Seppala et al 1995a). Recurrence is rare after gross extirpation. However, the survival of these patients is reduced compared to that of the general population.
The prognosis is significantly less favorable for patients with malignant schwannomas (Sordillo et al 1981; Ducatman et al 1986; Cashen et al 2004; Gupta and Maniker 2007). These tumors grow more rapidly and are less amenable to complete resection than typical schwannomas, due to an increased capacity for infiltration of surrounding tissues. In a series of 165 patients with malignant schwannomas of various sites, 60% had no evidence of neurofibromatosis type 1 (Sordillo et al 1981). After radical surgery, 58% of the nonneurofibromatosis type 1 group had local recurrence of disease. Of those patients with recurrent tumors, 52% developed distant metastases, mainly to lung, liver, and bone. The 5-year survival rate for the cohort was 47%. In a study of patients with malignant peripheral nerve sheath tumors, 9% of the nonneurofibromatosis type 1 cohort developed distant metastases, and had a 5-year survival rate of 53% (Ducatman et al 1986). In a more recent report of 80 patients with malignant schwannomas of the peripheral nerves, the functional outcome and survival were similar between patients with neurofibromatosis type 1 and those with nonneurofibromatosis type 1-related tumors (Cashen et al 2004). After aggressive treatment with maximal surgical resection, radiotherapy, and chemotherapy, the survival at 11 years was 85%. A more recent series of 205 patients with malignant peripheral nerve sheath tumors from a single institution had a disease-specific morality rate of 43% at 10 years (Anghileri et al 2006). Higher grade tumors were more likely to have distant metastases, but not a significantly worse survival rate.
Complications of schwannomas vary depending on the location and size of the tumor. In general, the most frequent complications are permanent deficits of the parent nerve and surrounding cranial or spinal nerves, as well as symptoms and signs caused by brainstem or spinal cord compression. The vast majority of patients with vestibular schwannomas are left with some degree of hearing loss in the involved ear as a result of damage from the tumor and treatment (Jackler and Pitts 1990; Glasscock et al 1993; Macfarlane and King 1995; Sanna et al 1995; Samii and Matthies 1997a; Battista 2009). Overall, less than 10% of patients have functional hearing after surgical resection. The most significant prognostic factor for preservation of hearing may be the presence or absence of severe adhesions at the interface between the cochlear nerve and the tumor (Moriyama et al 2002). Another factor that appears to impact on hearing preservation is tumor size (Jacob et al 2007). Tumors less than 1 cm in diameter had the best chance of hearing preservation. However, a recent review from Duke suggests that with meticulous technique, even large tumors (diameter of 2.1 cm to greater than 4.1 cm) can be completely or near-completely resected, with some degree of hearing preservation (Wanibuchi et al 2009). In their series of 54 patients, 41 patients underwent complete resection (75.9%), with an overall hearing preservation rate of 53.7%.
Although the facial nerve is anatomically intact after surgery in 90% of large tumors and almost 100% of small tumors (ie, intracanalicular and small cisternal), many patients have facial weakness (Jackler and Pitts 1990; Moulin et al 1995; Taha et al 1995; Samii and Matthies 1997b). The degree of facial weakness can vary; 70% of patients with large tumors, 50% of those with medium tumors, and 30% of those with small tumors have neuropraxia of the facial nerve after resection. The weakness is permanent in 30% of cases involving large tumors and 10% of cases involving small and medium-sized tumors. However, more recent series suggest a larger percentage of patients with large tumors can have preserved facial nerve function (75% to 80%) after a retrosigmoid exposure, alone or in combination with a translabyrinthine approach (Anderson et al 2005). More recent reports are in agreement that the retrosigmoid approach is excellent for preservation of hearing and facial nerve function (Samii et al 2006). Some authors recommend aggressive, early nerve reconstruction in patients with facial nerve discontinuity (Samii and Matthies 1997b). Using various methods of reconstruction of the severed nerve, more than 70% of patients can achieve satisfactory results (Samii and Matthies 1997b). Vertigo is a common problem postoperatively, but is usually transient; persistent vertigo is rare. Vertigo occurs more often with small tumors and typically resolves after several weeks to months. On occasion, patients have persistent cerebellar dysmetria as a result of tumor compression of the brainstem or cerebellar retraction during surgery. Impairment of the trigeminal nerve or nerves of the jugular complex (IX, X, XI) can rarely be persistent after treatment of large tumors. Other uncommon complications of schwannomas include hydrocephalus, intratumoral hemorrhage, subarachnoid hemorrhage, rapid cyst expansion, and malignant degeneration (Miller 1988; Jackler and Pitts 1990; Macfarlane and King 1995; Strauss and Post 1995; Pirouzmand et al 2001). Hydrocephalus usually occurs with tumors greater than 3 cm in size and may be present at diagnosis or postoperatively. Permanent shunting should be considered for patients with persistent, symptomatic, postoperative hydrocephalus (Pirouzmand et al 2001). Most patients with preoperative hydrocephalus (78%) will not require a permanent shunt after aggressive resection). It is extremely rare for a sporadic schwannoma to degenerate into a malignant tumor. This complication usually occurs with tumors from patients with neurofibromatosis type 1 or 2. Malignant peripheral nerve sheath tumors can result in distant metastases, including deposits in the lungs and brain (Park et al 2007).