Extended Transbasal Approach to Skull Base Tumors

Drs. Chandler and Silva provide an excellent review of the technical aspects of tumor extirpation in their article, "Extended Transbasal Approach to Skull Base Tumors." The authors describe the subtleties of the approach in a clear and concise manner. As they note, the extended transbasal approach allows for excellent access, which can be modified to meet the specific surgical need. Skull Base Team
In terms of the preoperative assessment, radiologic studies such as computed tomography (CT), magnetic resonance imaging (MRI), and, if necessary, angiography rely on the expertise of neuroradiology and interventional radiology colleagues. In a comparable fashion, I have included a battery of neuropsychological tests as part of our comprehensive approach. This testing is not conducted by all skull base teams performing cranial base surgery, but I believe it is extremely important to determine if any neuropsychological deficits are present preoperatively and, if so, whether these deficits are improved or worsened by surgical intervention. It is equally important to understand whether a surgical procedure creates additional deficits. Once identified, these deficits can be addressed and managed. Often, radiation and chemotherapy are part of the treatment regimen of patients with malignant skull base tumors. Consequently, an additional component of the skull base team includes the radiation oncologist and medical oncologist. A comprehensive team approach should not be undervalued. This is a vital component of the transbasal approach and, indeed, crucial for successful treatment of patients. Surgical Advances
Cranial base surgery continues to advance as a result of burgeoning new technology and a team approach to surgical resection. The transbasal approach, as described, has been shown to have a low incidence of complications. Intraoperatively, this procedure eliminates facial incisions and minimizes the need for retraction of the brain. Studies have also indicated that such treatment results in low morbidity and mortality. A movement is afoot to increasingly perform minimally invasive cranial base surgery endoscopically or to use endoscope-assisted procedures.[1-4] The use of endoscopes allows superior panoramic imaging and can lead to improved surgical access compared to the tunnel view sometimes found at the depths of a surgical field or when using a standard operating microscope. While select cases can be performed entirely by the endoscopic method, it is important to remember that endoscopes are part of our surgical armamentarium and can be utilized in conjunction with myriad procedures such as the transbasal approach. Olfactory Preservation
Drs. Chandler and Silva skillfully describe the extended transbasal approach, which allows the neurosurgeon and the otolaryngologist to unite their individual skills. The beauty of the procedure is its versatility and the resultant ability to modify the surgical extent based on tumor anatomy. Consequently, preservation of olfactory fibers is possible if the tumor allows. Many patients do not have any significant sense of smell prior to surgery. In some cases, this is a consequence of the physical obstruction created by the tumor mass and not necessarily due to involvement of both cranial nerves with tumor. A considerable portion of taste is aided by the sense of smell.[5,6] Sense of smell is also a protective mechanism allowing a per- son to detect hazardous situations. Preservation of the olfactory nerve in selected cases enables the patient not only to enjoy smells and foods, but also to fully enjoy daily life experiences. Thus, if the olfactory nerve can be preserved unilaterally, it greatly enhances the patient's quality of life. Consider also that chemosensory decrements can lead to food poisoning or overexposure to environmentally hazardous chemicals that are otherwise detectable by taste and smell. This can be a significant limitation. Granted, this is a deficiency that can often be overcome by lifestyle modifications, but again, if it does not compromise the surgical integrity of the procedure, then the olfactory nerve is best left intact. Procedural Variations
Additional versatility is attained with this procedure if a mass involves the anterior cranial fossa, including the orbitonasal and paranasal sinuses. For this approach, Drs. Chandler and Silva discuss performing an osteotomy "across the superior aspect of the nasion just adjacent to the frontonasa suture in an anterior-to-posterior direction." In cases where the paranasal sinuses are involved, an additional modification includes an osteotomy initiated from just anterior to the anterior lacrimal crest, which can then be extended onto the nasal process of the maxilla. This is continued with a transnasal osteotomy ensuring that a 2- to 3-mm segment of nasal bone is left in place and attached to the upper lateral cartilages to prevent valvular collapse. This creates a larger window for surgical removal. Conclusions
As noted, the extended transbasal approach can be modified to meet the need of the tumor extent. It can be combined with other approaches such as a midface degloving, the transfacial approach, or the subtemporal approach. In a comprehensive team fashion, utilizing all the skills and techniques acquired from our colleagues, lesions that were previously considered to be inoperable can be treated with low complication rates and low morbidity and mortality.

Disclosures:

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.

References:

1. Jho HD, Ha HG: Endoscopic endonasal skull base surgery: Part 3-The clivus and posterior fossa. Minim Invas Neurosurg 47:16-23, 2004.
2. Jho HD, Ha HG: Endoscopic endonasal skull base surgery: Part 1-The midline anterior fossa skull base. Minim Invas Neurosurg 47:1-8, 2004.
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5. Linderman B: Receptors and transduction in taste. Nature 413:219-225, 2001.
6. Sullivan SL: Mammalian chemosensory receptors. Neuroreport 13:A9-17, 2002.