For more than 1 hundred years, lesions and disorders of the skull base have provided significant challenges to neurosurgeons, otolaryngologists, and craniofacial surgeons for many reasons. Lesions of the skull base are seated deep in the skull, are often midline, and usually have multiple delicate critical neurovascular structures intermingled between the pathology and the route required to access the lesion. Injuries to any of these structures could result in significant permanent morbidity and even mortality to patients requiring treatment of a skull base lesion. If patients were to survive these risks, postoperative recovery is also fraught with potential problems including cerebrospinal fluid (CSF) leaks, meningitis, swallowing dysfunction requiring tracheostomy or gastrostomy tube placement, and corneal anesthesia resulting in infection or potential visual loss. In the past 20 years, significant advancements in technology and techniques in neurosurgery, otolaryngology, and craniofacial surgery have allowed for a revolution in skull base surgery with the introduction of minimal access endoscopic approaches.
Endoscopic skull base surgery is an extension of endoscopic sinus surgery pioneered by the work of Messerklinger, Stammberger, and Kennedy during the 1970s and 1980s. Their advent and refinement of rod lens endoscopy overcame the limitations of visualization and illumination encountered previously with microscopic endonasal approaches, allowing for less invasive approaches via an endoscopic endonasal route to the paranasal sinuses. As collaborative efforts between neurosurgery and otolaryngology improved outcomes with open skull base approaches, neurosurgeons began to work with sinus otolaryngologists to address pathology of the parasellar regions via a totally endoscopic transnasal approach.
When it became evident that endoscopes allowed better illumination and visualization than microscopic approaches, neurosurgical otolaryngologic teams began to approach pathologies outside the sella. These early attempts of endoscopic skull base surgery, however, were very challenging and resulted in unacceptably high complication rates for many reasons. Pioneers of endoscopic skull base surgery including Sethi, Jho and Carrau, Cappabianca and de Devitiis, Frank and Pasquini, Kassam and Snyderman, and Schwartz and Anand methodically addressed each of these obstacles:
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Infection
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Imaging
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Neurophysiologic monitoring
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Dural reconstruction
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Radiation therapies/radiosurgery
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Operative visualization/magnification
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Instrumentation
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Neuronavigation
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Hormonal management
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Hemostatic management
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Neuroanesthesia
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Operative illumination.
The development of safe surgical corridors based on anatomic cadaveric endoscopic work in combination with the integration of improved imaging and image-guided stereotactic systems gave the skull base endoscopic surgeon confidence when manipulating pertinent anatomy relative to the location along the approach. The development of endoscopic endonasal coagulation devices and hemostatic materials to manage bleeding as safely as open approaches allowed for more aggressive sharp dissection in the skull base, and allowed the surgeon to extend beyond structures of the skull base that were previously forbidden to operate around because of bleeding concerns, such as the intercavernous sinuses, the medial cavernous sinus, the petrous carotid artery, the basilar plexus, and the anterior cranial fossa. The development of endoscopic vascularized autologous flaps, reconstructive allografts such as DuraGen (Integra Lifescience Corporation, Plainsboro, NJ, USA) and AlloDerm (Lifecell Corporation, Branchburg, NJ, USA), dural sealants such as DuraSeal (Confluent Surgical, Inc, Waltham, MA, USA) and fibrin glue, and techniques to keep reconstructions in place have significantly decreased the CSF leak rates and infection rates to acceptable levels allowing for the expansion of endoscopic endonasal skull base surgery far beyond the sella.
Although advancements in techniques and technologies allowed for expansion in where the endoscopic skull base surgeon could operate, Kassam and colleagues developed what is now called the expanded endonasal approach to access the entire ventral skull base. They divided the approach into units or modules based on its anatomic orientation in the skull base ( Box 1 ). This approach has now become the workhorse for endoscopic skull base surgery from which multiple centers have made slight modifications based on their individual experiences, comfort levels, training, and pathologies treated. Fig. 1 shows a diagrammatic comparison of transsphenoidal microscopic surgery of the sellar region to the expanded endonasal approach to the ventral skull base.
