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Cavernous Sinus Tumors and Aneurysms

The cavernous sinus is a small blood-filled space on either side of the base of the skull located behind the eyes. Each cavernous sinus contains the carotid artery, the nerves that go to the muscles that move the eye, and part of the nerve that provides sensation to the eye and face. Various disorders may affect the cavernous sinus such as meningiomas, schwannomas, aneurysms, invasive pituitary tumors, chordomas and infections that extend from the face and eyes.

Modern skull base surgery provides better exposure of deep-seated cranial base lesions with less cerebral retraction by combining the removal of noncritical osseous structures with specialized operative maneuvers. Because of the complexity in anatomical structures, the cavernous sinus (parasellar) and the petroclival areas are the most frequently discussed territory for the management of the skull base tumors. With the introduction of these techniques, most skull base tumors can be safely approached, and many are radically resected. Many cavernous sinus and petroclival tumors that were previously thought to be inoperable have been successfully removed.

Chordomas are benign, slow-growing, rare tumors that are usually seen in patients 50 to 60 years old. Their most common locations are the base of the skull and the lower portion of the spine. Although these tumors are benign, they tend to invade the adjacent bone and put pressure on nearby neural tissue.

Symptoms

For patients with tumors involving the skull, the most common symptoms are headache and double vision. Symptoms of cavernous sinus tumors vary based on the extent of the tumor but can include seizures, symptoms of brain compression and, occasionally, brain ischemia.

Diagnosis

While the history and physical examination are always important, the diagnosis of these tumors depends on good imaging studies. The best test is an MRI performed both without and with intravenous contrast material. CT scanning can also show these tumors, but MRI is more sensitive.

Diagnostic studies for skull base tumors include magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), computed tomography (CT) scans, bone window and three-dimensional (3-D) CT scans, and angiography. MRI is currently an essential test to show the nature and extent of the tumor. Bone window and 3-D CT scans are useful in determining surgical approaches and in deciding what areas of the cranium should be drilled to best expose the tumor. Angiography is being replaced with MRA and the 3-D CT to show the major arterial anatomy. However, angiograms are still superior in revealing the venous anatomy and blood supply to the tumor, which often influence the surgical and treatment approach. A balloon occlusion test is essential when the sacrifice of a major cerebral artery is anticipated during surgery.

Treatment

When possible, the best treatment for chordomas is complete surgical resection. Unfortunately, complete resection is not always possible. Interventional radiological techniques (eg, selective embolization of tumor arterial supply) are useful in reducing blood loss in the removal of vascular tumors. It has also shown effectiveness in delivering chemotherapeutic agents directly to the tumor. Post-operative radiation therapy is sometimes recommended, as is stereotactic radiosurgery. These decisions are usually made by the neurosurgeon in consultation with a radiation oncologist.

Because of the vital importance of the cavernous sinus structures, the surgical approach to this area is technically demanding, and surgical complications are relatively frequent. Major complications such as intracranial hematomas can include worsening cranial neuropathy and leakage of cerebrospinal fluid . These risks are higher with a history of previous surgery and radiotherapy. However, most of these complications are temporary, and many can be treated successfully. Complete surgical removal often can be achieved and recurrence after a complete resection is less than 9% with a follow-up period of one to 12 years. The sacrifice of the oculomotor nerve and the trigeminal nerve can rarely be achieved without significant postoperative deficit. Therefore, the preservation of these nerves is important during surgery.

The development of focused stereotactic radiotherapy has provided another useful tool to control tumor growth with minimal complications. It rarely shrinks the tumor to a significant degree and does not reduce the mass effect. Due to the dangers of precipitating neurologic compromise or collapse by radiation-induced swelling in larger tumors, the size of treatable tumors should be less than 2.5 cm. This size limitation restricts a radiosurgical treatment approach to approximately one half of the patients in our surgical series, since the mean diameter of tumors in the majority of the surgical series is approximately 3.5 cm. The follow-up period for most gamma knife series is less than five years, an insufficient length to discuss the long-term benefits. Microsurgery and the combination of microsurgery and radiosurgery are offered to selected patients with cavernous sinus tumors on the basis of tumor characteristics, patient age, occupation, and goals.

Conventional radiotherapy has been used primarily for some malignant skull base tumors and radiosensitive tumors. Radiation therapy also reduces the growth and recurrence rates of some of the benign tumors. Heavy particle beam focused radiotherapy has been advocated for tumors such as chordomas and chondrosarcomas, which are known to be radioresistant, but long-term follow-up in a large number of patients is lacking. High-intensity, focused radiotherapy (gamma knife or linear accelerator radiosurgery) is effective in reducing the growth rate of benign or intermediate malignant tumors. Experience with this modality is rapidly accumulating, but definite limitations exist with this therapy, and the relationship of tumor size, configuration, and long-term efficacy remain to be defined. Although complications of radiotherapy are often reported as minimal, delayed complications can occur such as parenchymal injury, pituitary dysfunction, visual changes, and/or radiation-induced tumors treated with radiotherapy for benign intracranial tumors. Therefore, careful long-term follow-up of irradiated patients is necessary.

Chemotherapy is indicated in specific malignant tumors. Cisplatin is effective in treating epithelial carcinomas and has been associated with significantly improved clinical outcomes. Other chemotherapeutic agents such as cyclophosphamide, vincristine, and doxorubicin have been administered to treat a variety of cranial base malignancies. Bromocriptine is effective in treating prolactinoma, often with dramatic reductions in tumor size and in improved long-term control. Hormonal therapy for meningiomas and juvenile angiofibromas, which often carry a hormonal receptor, is still in the investigative stage. Interferon, somatostatin analogues, monoclonal antibodies, and gene therapies are likewise considered experimental.

Combining Therapies

To obtain the maximum effect of treatments, various combined treatment regimens are indicated for the management of certain skull base tumors. For incompletely resected meningiomas, radiotherapy is effective in delaying the rate of growth and symptomatic recurrences. In esthesioneuroblastoma, there is evidence that patients benefit from a combination of preoperative or postoperative chemotherapy and radiation therapy. A combination of chemotherapy, radiotherapy, and en bloc surgical resection has been advocated for nasopharyngeal carcinomas. Improved outcomes for cranial base sarcomas have been achieved with a combination of radiotherapy and chemotherapy. A multidisciplinary skull base tumor team should consider all treatment alternatives for patients with cranial base tumors, and the therapeutic regimen should be tailored to each individual case. The final therapeutic decision must take into account the patient?s condition, the natural history of the tumor, and the risks and benefit of each treatment option.

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