Extended Transbasal Approach to Skull Base Tumors
Extended Transbasal Approach to Skull Base Tumors
Drs. Chandler and Silva do a good job describing the bifrontal biorbital sphenoethmoidal approach to the skull base. This approach allows full access to the anterior skull base, the paranasal sinuses between the medial thirds of the maxillary sinuses, and the entire clivus medial to the carotid arteries and the hypoglossal nerves and below the pituitary gland. It should be recognized that the full extent of the approach is not always necessary, and a good degree of tailoring is possible. Specifically, I have not found it necessary to perform orbital osteotomies for access to the paranasal sinuses or for cribriform plate resection. A small midline frontal craniotomy with an inferior extension to the level of the frontonasal suture is usually sufficient. One of Many Options
The main indications for this approach are large intracranial anterior skull base tumors such as olfactory groove meningiomas and clival tumors without extension lateral to the carotids. I agree that most ethmoid sinus tumors located medial to the medial third of the maxillary sinuses can be resected via a transcranial approach without the need for facial incisions. This technique for paranasal sinus malignancy was initially described by Blacklock et al and subsequently further validated by McCutcheon et al. When managing malignancy of the skull base, the surgical approach detailed by Chandler and Silva represents one of many varied approaches that should be available to the surgical team. Which surgical approach is ultimately chosen depends upon the location and extension of the malignancy and its pathology. Surgery itself also represents one of several management options and should only be employed as part of a management plan carefully constructed by a multidisciplinary team of experts in the evaluation, diagnosis, and treatment of malignancies of the skull base. Assessment Tools
Evaluation of these patients involves a thorough examination of the head and neck, including an endoscopic evaluation of the sinonasal region. The cranial nerves must be evaluated, and patients should have a baseline neuro-opthalmologic review. Computed tomography (CT) and magnetic resonance imaging (MRI) are complementary studies and the radiologic methods of choice for assessing these tumors. CT is particularly useful in assessing bony changes, especially erosion. Direct coronal CT provides the best images for assessing the integrity of the anterior skull base, including the orbital roof, cribriform plate, and planum sphenoidale. The extent of tumor is best seen with MRI, which also is able to differentiate tumor from inflamed mucosa, blood, or inspissated mucus in most cases. Signal voids within the tumor identified by MRI or proximity of the neoplasm to the internal carotid artery may be an indication for preoperative angiography to assess tumor vascularity and plan surgical treatment. Preoperative tumor embolization may be necessary. The key to diagnosis and management is biopsy. Flexible endoscopes permit access for biopsy to most tumors of the paranasal sinuses. In the case of deep-seated lesions, a CTguided needle biopsy may be performed. Evaluation of the biopsy specimen by an experienced pathologist cannot be overemphasized. Tumor pathology and extent, the availability and potential success rates of adjuvant therapies, as well as the potential for functional impairment and esthetic deformity are all important parameters to consider when planning the best management options for a patient with a paranasal sinus tumor. In most cases, surgery and radiation are employed as a combined treatment modality, but other adjuvant therapies such as radiosurgery and chemotherapy may be indicated. Management paradigms for certain malignancies are listed in Table 1. Management Paradigms
Using management paradigms, such as the ones listed in Table 1, several large modern surgical series currently report survival rates of approximately 50% to 70% at 5 years and 40% to 50% at 10 years.[5-12] Quality of life (QOL) studies have shown maintenance of high levels of independence and excellent self-reported QOL scores when brain and head and neck-specific questionnaires are used. QOL scores on general questionnaires are generally depressed, indicating the difficulties patients experience with the psychosocial adjustment to illness. Similar diseasespecific outcomes have been reported in the elderly population. Great strides have been made in the management of skull base malignancies, especially in our ability to resect these tumors safely and with adequate margins. The surgical technique described by Chandler and Silva in this issue is a prime example of such advancement. Ideally, however, improvements in the chemotherapeutic management of these tumors would lessen the need for extensive extirpative surgeries. Improved radiotherapeutic targeting is reducing the morbidities associated with radiation and will likely become even more refined. The careful selection and implementation of these emerging techniques and technologies will continue to improve the outcome of patients with malignancy of the skull base.
The author has no significant financial interest or other relationship with the manufacturers of any products or providers of any service mentioned in this article.
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