Schwannomas are most effectively treated by surgical excision; however, these benign tumors of minimal malignant potential grow in a manner that usually, but not always, permits separation and preservation of their nerve of origin. Therefore, considerations of surgical morbidity should be included when selecting a treatment modality.
Although clinical and radiographic information may suggest the diagnosis of a schwannoma, the precise nerve of origin may not be apparent until the tumor is surgically exposed. Consequently, the potential for postoperative nerve dysfunction resulting in vocal cord paralysis, Horner's syndrome, shoulder dysfunction, or other deficits must always be considered.17
Surgical exposure of the tumor and the presumed nerve of origin is usually obtained via a mid-neck horizontal incision with every attempt made to preserve the anatomic integrity of nerve branches that can be identified and separated from the tumor. The surgeon must be aware of the fact that, with some schwannomas that have attained a significant size, the chances
Figure 16-17. A, Plexiform neurofibromat. B and C, MRI of plexiform neurofibromat.
of compromise of adjacent neurovascular structures secondary to the surgical procedure (in addition to the nerve of origin) can add an additional element of potential morbidity to the operative procedure.
In the case of schwannomas arising from the cervical roots, a portion of the tumor may extend into the lateral neck while another component may pass within the intravertebral foramen. These tumors may thus adopt a dumbbell type configuration (Figure 16-16).74 Such tumors may be optimally resected through neu-rosurgical/head and neck surgical collaboration. When a peripheral nerve sheath tumor is suspected of arising from any of the roots of the brachial plexus, the use of preoperative EMG for the assessment of subtle muscle dysfunction as well as the intraoperative use of nerve monitoring may be helpful.8081
As previously noted, schwannomas are slow-growing tumors with approximate growth rates of 1 mm/year. Consequently, unless there is rapid recent growth suggestive of malignant transformation, careful clinical observation of a tumor whose surgical removal might result in significant morbidity has been advocated. Such a strategy of observation is most frequently advocated in the management of schwannomas in the elderly or patients who are poor surgical candidates. However, it must be recognized that the morbidity of surgical resection and the potential for incomplete tumor excision will likely increase with increased tumor size, therefore early intervention is preferable in most situations.
In addition to surgical excision and careful observation, there is a growing body of evidence (particularly with respect to schwannomas arising from the eighth cranial nerve), for the use of external beam radiotherapy (so-called stereotactic radiosurgery or the "gamma knife") for the treatment of schwannomas. Recently, the long-term results of the treatment of schwannomas of the eighth cranial nerve with radiosurgery have demonstrated excellent rates of tumor control with preservation of nerve function and minimal treatment-related morbidity (hearing loss).82
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