Nerve sheath tumors are tumors arising from the nerve itself or from the surrounding structures, such as the Schwann cells. They can be classified into benign nerve sheath tumors, the most common being schwannomas and neurofibromas and malignant nerve sheath tumors known as malignant peripheral nerve sheath tumors (MPNSTs). Nerve sheath tumors can be associated with inherited syndromes such as neurofibromatosis (type 1 and type 2) and schwannomatosis or can be sporadic.
How Do You Treat A Nerve Sheath Tumor?
The treatment of nerve sheath tumor involves surgery, radiation therapy, chemotherapy and/or combination of either or all of them depending on the type of tumor, whether benign or malignant; extent; location; clinical presentation and spread of the tumor.
Surgery: Surgical resection is the gold-standard for the treatment of nerve sheath tumors. The goal of the treatment is to completely excise the nerve sheath tumor with the preservation of the associated nerve and surrounding healthy tissues. This provides best treatment outcomes in terms of both local recurrences and distant metastases. The surgery of a schwannoma poses less difficulty as the tumor originates from Schwann cells, which surround the axons and these tumors can be extirpated from the surface of the nerve without causing any damage to the nerve itself. On the other hand, the surgery of a neurofibroma or malignant nerve sheath tumor is more complicated as these tumors arise from the nerve itself and complete removal of the nerve sheath tumor may cause permanent damage to the nerve, complete removal of the affected nerve or limb amputation.
The prognosis for malignant nerve sheath tumor is also poor due to increased chances of recurrence and metastases.
Radiation Therapy: It is now an important component of nerve sheath tumor treatment, in addition to surgery. This is especially true for the treatment of malignant peripheral nerve sheath tumors. Radiation therapy can be either done pre-operatively, intra-operatively and post-operatively. High-dose radiation therapy is also employed in the setting of peripheral nerve tumors or tumors found in or around the brain that helps in destroying the tumor without the need of surgery.
Pre-operative radiation therapy helps with planning of accurate radiation, localization of nerve sheath tumor, smaller requirement of dose and volume of treatment.
However, it causes delay in wound healing and delay in surgery. Radiation therapy post-operatively is beneficial for prompt surgery, lesser complications related to wound healing along with providing larger specimen for tissue diagnosis. However, it requires larger volumes of treatment, higher requirement of dose and seeding surgical bed/scar with possible nerve sheath tumor.
Radiation therapy can also be administered via catheters, embedding in the surgical bed during resection or loading radioactive material during peri-operative period. This kind of radiation therapy is known as brachytherapy. These methods provide concentrated treatment in a focal area in addition to very little damage to the surrounding tissues, and smaller quantity of doses, overall. However, they may pose problems with wound healing.
Chemotherapy: Chemotherapy is useful in the setting of systemic disease in which the tumor is too small or too diffuse and where there are greater chances of metastatic disease. The use of chemotherapy may require weighing pros and cons as some of its side-effects may be irreversible.
Chemotherapy can be administered either pre-operatively or post-operatively. Pre-operative chemotherapy provides immediate treatment of micrometastatic disease and the potential for tumor shrinkage in certain tumors that are sensitive to chemotherapy. Chemotherapy also helps radiosensitize some tumors, making both combined chemotherapy and radiation therapy synergistically advantageous, which further helps with limb-salvage surgery.
Chemotherapy is not indicated in smaller nerve sheath tumors <5-8 cm and also avoided in cases where the tumor is localized to local cutaneous or subcutaneous tissues. It is indicated for patients under the age of 65 years with limited medical comorbidities and good cardiac function. Tumors that are high grade, large and deep are typically treated with chemotherapy.
Prognosis Of Nerve Sheath Tumor
Good outcome depends on early detection and treatment of the tumor. Malignant nerve sheath tumor has greater chances of recurrence and metastases, thus poorer prognosis. Benign nerve sheath tumor has lesser chances of recurrence with no metastases, thus a better prognosis.