Endoscopic techniques have influenced almost all of the surgical specialties. From open procedures to minimally invasive approaches, the endoscope and its ability to reach areas within the human body has gained popularity among specialists, creating a revolution in some fields. Two of the fields in which endoscopes provided a true revolution are otolaryngology and neurosurgery. The authors discuss some important factors for the evolution of endoscopic skull base surgery and expanded endonasal approaches, highlighting historical landmarks but also addressing the current concepts, complications, and the future of this promising field for clinical research and surgical techniques and technology.
Endoscopic techniques have influenced almost all of the surgical specialties. From open procedures to minimally invasive approaches, the endoscope, and its ability to reach areas within the human body, has gained popularity among specialists, creating a revolution in some fields. Two of the fields in which endoscopes provided a true revolution are otolaryngology and neurosurgery.
Endoscopic skull base (ESB) surgery is now a rapid growing field for otolaryngologists and neurosurgeons. Of course, to perform safe and effective ESB procedures, a multidisciplinary team is paramount and this team should include an anesthesiologist, endocrinologist, pathologist, radiologist, intensive care unit specialists, and specialized paramedical staff.
The current limits for endoscope-assisted skull base procedures are constantly changing. In the past decades we moved from endoscopic closure of cerebrospinal fluid (CSF) leaks, to a myriad of lesions extending from the cribriform plate to the craniocervical junction and laterally to the infratemporal fossa and petrous apex. These recent advances are termed “expanded endonasal approaches” (EEA) and they provide access to the anterior, middle, and posterior cranial fossae.
However, all of these advances were dependent on several technical and technological components, which included high endoscopic anatomic knowledge, advanced endoscopic surgical techniques and skills, crystal clear endoscopes and cameras, CT and MRI, specially designed instruments, powered instrumentation, and more recently, image guidance systems. However, even with all the evolution in this field, complications still occur.
Objectives
In this content the authors discuss some important factors for the evolution of ESB surgery and EEA, highlighting historical landmarks but also addressing the current concepts, complications, and the future of this promising field for clinical research and surgical techniques and technology.
Brief history
Although the history of skull base surgery is intrinsically linked with the evolution of pituitary surgery, the history of ESB surgery starts with the capability to close small dural defects through the nose.
With the evolution of endoscopic sino-nasal procedures for inflammatory diseases since the 1980s, purely endoscopic approaches for the evaluation and treatment of CSF rhinorrhea were also developed. These endoscopic approaches allowed the complete closure of CSF leaks through a minimally invasive perspective, but with safety and good results. The use of free grafts and other types of materials allowed surgeons to close small defects, traumatic, spontaneous, and iatrogenic CSF leaks from the 1990s to 2000s.
However, the paucity of good closure results with large (>2 cm) dural defects was still a limiting factor for the EEA. Problems, such as infections, meningitis, and ventriculitis, were serious complications. Also, the location of the pathology relative to important neural and vascular structures was another important limiting factor, but for many tumors the endonasal corridor provided the most direct access with the least manipulation of neural and vascular structures.
This important anatomic consideration drove surgeons to other ESB applications, such as pituitary adenomas. Since the 1990s, several surgeons published reports with good results that popularized the use of endoscopes in this area. The functional and endocrinologic results were better when compared with open microscopic approaches, but tumors with suprasellar or lateral (into cavernous sinus) invasion were still a challenge, mainly because of a lack of specialized instruments and an inability to control vascular lesions and to close large dural defects with assistance of endoscopes.
The works of several important authors allowed the evolution regarding these limiting factors. The limitations in technology and instrumentation were overcome. However, the real revolution occurred in 2004 when doctors from Argentina designed and used pediculated nasoseptal flaps for the closure of big CSF defects. At first the doctors were discredited, but the good results obtained with those pediculated, robust, reconstructive tissues forced the endoscopic surgeons to use it.
Although this evolution (ie, the ability to safely remove large tumors endoscopically) did not change the philosophy of tumor removal, it closed the large, created dural defects with good success rates, which was the last limiting factor for the EEA. Since 2006 several other types of pediculated flaps were designed and developed, such as inferior and medium turbinates flaps, pericranial flaps, and palatal flaps, among others. Along with the flaps, several endoscopic approaches were described and the authors are going to discuss them.
Brief history
Although the history of skull base surgery is intrinsically linked with the evolution of pituitary surgery, the history of ESB surgery starts with the capability to close small dural defects through the nose.
With the evolution of endoscopic sino-nasal procedures for inflammatory diseases since the 1980s, purely endoscopic approaches for the evaluation and treatment of CSF rhinorrhea were also developed. These endoscopic approaches allowed the complete closure of CSF leaks through a minimally invasive perspective, but with safety and good results. The use of free grafts and other types of materials allowed surgeons to close small defects, traumatic, spontaneous, and iatrogenic CSF leaks from the 1990s to 2000s.
However, the paucity of good closure results with large (>2 cm) dural defects was still a limiting factor for the EEA. Problems, such as infections, meningitis, and ventriculitis, were serious complications. Also, the location of the pathology relative to important neural and vascular structures was another important limiting factor, but for many tumors the endonasal corridor provided the most direct access with the least manipulation of neural and vascular structures.
This important anatomic consideration drove surgeons to other ESB applications, such as pituitary adenomas. Since the 1990s, several surgeons published reports with good results that popularized the use of endoscopes in this area. The functional and endocrinologic results were better when compared with open microscopic approaches, but tumors with suprasellar or lateral (into cavernous sinus) invasion were still a challenge, mainly because of a lack of specialized instruments and an inability to control vascular lesions and to close large dural defects with assistance of endoscopes.
The works of several important authors allowed the evolution regarding these limiting factors. The limitations in technology and instrumentation were overcome. However, the real revolution occurred in 2004 when doctors from Argentina designed and used pediculated nasoseptal flaps for the closure of big CSF defects. At first the doctors were discredited, but the good results obtained with those pediculated, robust, reconstructive tissues forced the endoscopic surgeons to use it.
Although this evolution (ie, the ability to safely remove large tumors endoscopically) did not change the philosophy of tumor removal, it closed the large, created dural defects with good success rates, which was the last limiting factor for the EEA. Since 2006 several other types of pediculated flaps were designed and developed, such as inferior and medium turbinates flaps, pericranial flaps, and palatal flaps, among others. Along with the flaps, several endoscopic approaches were described and the authors are going to discuss them.
Current concepts
Several endoscopic approaches, following the endonasal corridor, exist according to the size and location of the tumor. However, in some cases of large tumors, combined procedures may still be required.
The choice of a surgical approach depends on patient comorbidities, tumor characteristics (location, proximity to important neurovascular structures), and the skills and comfort level of the surgeons. If nerves or vessels need to be mobilized to reach the tumor, then an alternative microscopic approach should be considered. Relative contraindications to an endonasal approach include tumor involvement of superficial tissues, the need for vascular reconstruction, and the duration of surgery.
Potential current advantages of ESB surgery include the lack of external incision, decreased trauma to normal soft tissue and bone, improved visualization, increased access, improved outcomes, fewer complications, rapid recovery, decreased hospitalization, and cost. Disadvantages include unfamiliar anatomy, physiologic sinonasal alterations with potential postoperative complications, a long learning curve, and still some technological limitations.
The current concepts of EEA rely on endoscopes to provide a better field of image with angulated views when compared with microscopes. However, because we use rigid instruments, this capability is only achieved if the endoscopes reach the surgical field.
The nose and paranasal sinuses have several important anatomic landmarks and potential natural barriers to the skull base, such as the nasal septum, turbinates, and sphenoid rostrum, among others.
To access important skull base structures through the nose you have to create a pathway for instruments and the surgeons. The current concept of a multidisciplinary team is important and EEA should always be done with the presence of two or more surgeons.
The current ESB pathways from anterior to posterior are transfrontal, transcribriform, transplanum, trans-sellar, transclival, and transodontoid/craniocervical junction ( Fig. 1 ). Also, there are the ESB lateral approaches, which include all orbital, transpterygoid, and infratemporal accesses. Each one of these approaches has its own applications, important landmarks, and pitfalls. A brief discussion of these approaches follows.
The transfrontal approach provides access to the floor and posterior wall of the frontal sinus. Examples of lesions found in this area include inflammatory sinus disease, erosive mucocoeles, and frontal osteomas, among others. The transfrontal approach is the anterior limit of an endonasal craniofacial resection for malignant sinonasal neoplasms and for these approaches a Draf III procedure and complete ethmoidectomy is common practice. To close defects in this area, a nasal septal flap can be used, although the use of free grafts is also successful according to the size of the dural defect.
The trans-cribriform access extends from the crista galli to the planum sphenoidal and across the roof of the ethmoid sinuses (fovea ethmoidalis) to the orbital roof. This module is most often used for sino-nasal malignancies and esthesioneuroblastomas and olfactory groove meningiomas.
Often, a Draf III procedure and complete ethmoidectomy is necessary. Sometimes, in cases of malignances, a nasal septal flap cannot be used because the surgeon may suspect compromised margins. In these cases, to close the dural defect, a turbinate, palatal, or even pericranium flap may be used ( Figs. 2 and 3 ).
The transplanum module provides access to suprasellar lesions, such as pituitary tumors with extra-sellar extension, meningiomas, and craniopharyngiomas. It is limited anteriorly by the posterior ethmoidal artery and posteriorly by the optic canals.
To allow good transplanum access, a complete ethmoidectomy, wide opening of the sphenoid sinus, and occasionally middle turbinate removal, are performed. An example of a meningioma requiring a transplanum approach is depicted in Figs. 4 and 5 . The use of a nasal septal flap, pediculated at the sphenopalatine artery, is possible for the closure of the dural-created defects. Sometimes, according to the size of the defect, two nasal septal flaps are required.
