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Overview of endonasal corridors to intracranial targets
Operative Techniques in Otolaryngology (2011) 22, 194-199
Overview of endonasal corridors to intracranial targets Tiffiny Ainsworth, MD, Belachew Tessema, MD, Seth M. Brown, MD, MBA From the University of Connecticut Health Center, Division of Otolaryngology Head and Neck Surgery, Farmington, Connecticut. KEYWORDS Skull base; Endoscopic surgery; Transphenoid; Transnasal; Transethmoid; Transpterygoid
Intracranial targets for lesions or disease processes of the skull base are increasingly approached through endoscopic endonasal surgical approaches. The endonasal approach to the skull base can be divided into the nasal or sinus corridor traversed to reach an intracranial target. The transnasal, transethmoid, transphenoid, and transpterygoid approaches are discussed to provide a framework on how to approach various intracranial targets and diseases of the skull base. While endoscopic skull base surgery is minimal access surgery it is maximally invasive. The most common complication is a cerebrospinal fluid leak. © 2011 Elsevier Inc. All rights reserved.
Intracranial targets of the anterior, middle, and posterior skull base have been traditionally approached via transfacial and transcranial open surgeries. The surgeries are invasive, with long recovery periods and with risk of significant complications. The emphasis on less-invasive surgical procedures led to the development of endonasal approaches to the skull base. As technology improved, particularly with development of the Hopkins rod lens system in the 1960s, the endoscope was increasingly used to access the skull base endonasally (Figure 1). Purely endoscopic endonasal approaches to intracranial targets, without the combined access of transfacial or transcranial approaches, became popular for select pathology as early as the 1990s. Since then, the limits of the intracranial targets that are accessible continue to be expanded.1
Indications The indications for endonasal endoscopic skull base surgery are extensive. The endoscopic approach is not a surgery but a vehicle to access a variety of regions and an even greater variety of pathologies. Each of the various pathologies has
Address reprint requests and correspondence: Tiffiny Ainsworth, MD, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06119. E-mail address: [email protected]. 1043-1810/$ -see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.otot.2011.08.001
Figure 1 The endoscope allows access to the skull base through the nose and sinuses. This cut-away figure of the skull demonstrates the anatomical relationship between the sinuses and the skull base. (Reprinted with permission.2) (Color version of figure is available online.)
its own indications, goals, and outcome measures. The keys to performing endoscopic skull base surgery include the skill set of the surgical team; possessing adequate skull base
Ainsworth, Tessema, and Brown
Overview of Endonasal Corridors to Intracranial Targets
195
Figure 2 Transnasal or trans-sinus approaches are used to access a variety of intracranial targets. Depicted are the various intracranial targets that can be accessed via a given transnasal or trans-sinus approach. (Reprinted with permission.2) (Color version of figure is available online.)
instrumentation (including visualization, surgical navigation, and instruments for control of the vasculature); having adequate pre-, peri-, and postoperative care; and choosing the proper pathology on which to use this approach. We present a method of breaking down endoscopic skull base surgery by the approach used to assist in surgical planning as well as resection on the basis of the system created by Schwartz et al.2
Technique The endoscopic endonasal approaches to the skull base can be divided into 2 general anatomic concepts; the corridor
that is taken to approach the skull base and the target area that is operated on. Although not all surgeries will fall into one category, generally there is one primary corridor that is used to reach the target area. On occasion, multiple corridors are combined to perform surgery. The ability to divide the surgery into corridor and target region allows the surgical team to plan appropriately to have the necessary instrumentation, the proper surgical team members available for the surgery, and to facilitate a worthwhile preoperative surgical discussion.2,3 Other groups have presented similar systems, most notable the Pittsburgh group, which divides the corridors into 2 general areas: the sagittal plane (between the carotid arteries) and the coronal plane (lateral to the carotid arter-
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Operative Techniques in Otolaryngology, Vol 22, No 3, September 2011
Figure 3 Depicted are the variety of intracranial targets that are accessible via endoscopic transnasal or trans-sinus approaches. (Reprinted with permission.2) (Color version of figure is available online.)
ies).4 The 2 planes are then subdivided on the basis of the target region into various modules.4 The corridors we have chosen are determined on the basis of the sinus that needs to be transversed to reach the target area. The Schwartz/Anand classification developed at Cornell2 divides the corridors into 4 areas: transnasal, transethmoidal, transsphenoidal, and transpterygoidal (Figures 2 and 3). The transnasal corridor is unique in that no sinus is transversed to reach the skull base (Figure 4). The transnasal approach can either be anterior (medial to the middle turbinate) or inferior (the nasopharynx). The anterior transnasal approach allows access to the anterior cranial fossa through the cribriform plate. This would most commonly be performed for a small meningoencephalocele. The inferior transnasal approach allows access into the nasopharynx and upper oropharynx. This allows resection of pathologies of the lower clivus, the vertebrobasilar junction, craniovertebral junction and the odontoid process. The transethmoidal corridor, particularly when opened bilaterally and combined with the transnasal transcribriform approach, allows access from orbit to orbit, from frontal sinus to sphenoid sinus (Figure 5). This traditionally is for pathologies of the fovea ethmoidalis (ie, cerebral spinal fluid leaks) but also allows access to the orbital apex and the frontal fossa. Pathologies that can often be approached through this corridor include orbital apex hemanogiomas,
hemangiopericytomas, esthesioneuroblastomas, meningoencephaloceles, and olfactory groove meningiomas. The transsphenoidal corridor is the most versatile of the approaches (Figure 6). It is also perhaps the least controversial because endonasal approaches to the sella have been in existence for many years. Although mostly used for pituitary tumors, it can be expanded to access a multitude of target areas, including the orbital apex, the suprasellar cistern, the cavernous sinus, the upper portion of the clivus, and the petrous apex. Pathologies approached within these target areas are numerous but include petroclival and planum meningiomas, all sellar pathology, suprasellar extent of pituitary tumors, craniopharyngiomas, and clival tumors in the superior portion of the clivus. Even giant pituitary tumors extending into the lateral ventricle can be approached from below.5 The transpterygoidal corridor involves removal of the back wall of the maxillary sinus to reach the skull base (Figure 7). This is often a unilateral approach that facilitates access to the cavernous sinus, the upper and lateral portions of the clivus, the petrous apex, and the infratemporal fossa. In addition to biopsying lesions in the infratemporal fossa, it is commonly used for meningoencephaloceles that are in lateral aspect of a pneumatized sphenoid sinus, also known as a Sternberg’s canal encephalocele.6
Ainsworth, Tessema, and Brown
Overview of Endonasal Corridors to Intracranial Targets
197
Figure 4 The transnasal corridor provides access to the anterior cranial fossa, medial cribiform plate, lower clivus, basilar artery, and odontoid process. (Reprinted with permission.2) (Color version of figure is available online.)
Figure 5 The transethmoidal corridor provides access to the anterior cranial fossa, orbital apex, and suprasellar cistern. (Reprinted with permission.2) (Color version of figure is available online.)
Figure 6 The transsphenoidal corridor provides access to the pituitary, orbital apex, suprasellar cistern, cavernous sinus, upper clivus, and petrous apex. (Reprinted with permission.2) (Color version of figure is available online.)
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Operative Techniques in Otolaryngology, Vol 22, No 3, September 2011
Figure 7 The transpterygoidal corridor provides access to the cavernous sinus, petrous apex, infratemporal fossa, and the upper and lateral portions of the clivus. (Reprinted with permission.2) (Color version of figure is available online.)
Complications The complications for the surgery will depend on approach used and the extent of surgery. It is important to note that although endoscopic skull base surgery is minimal access, it is maximally invasive. This means that despite not having skin incisions, the risks of the surgery are similar to open approaches. Depending on the anatomical approach used, the complications from endoscopic endonasal skull base surgery include but are not limited to cerebrospinal fluid leak, infections, bleeding, cranial nerve palsies, anosmia, septal perforation, atrophic rhinitis, iatrogenic created sinusitis (particularly from turbinate resection), pituitary dysfunction, vision loss, diabetes insipidus, stroke, and death.7 The most common complication is a cerebrospinal fluid leak, with a reported incidence of 5%.4 This incidence has decreased significantly with use of the pedicled nasal septal flap.8 Considering that endonasal approaches have the potential to expose nasal and pharyngeal pathogens intracranially, the risk of meningitis is low at only 2%.4 It is also reported that extended
broad-spectrum antibiotics are not necessary to prevent infection as is popular with open skull base approaches, although their use may be prudent.9,10
Discussion The division of the skull base into corridors and targets allows surgeons to effectively communicate about the surgery that is being performed. This has become more important as more surgeons have adopted the endoscopic approach into their surgical repertoire. Furthermore, as the limits of endoscopic surgery are expanded, a common language allows for more understanding in the literature as well as at meetings. As we move forward with endoscopic approaches we must continue to choose the pathologies that are most appropriately removed with this technology and continue to adhere to the principles of surgical oncology.4 We should never let a minimal-access surgery limit our ability to adequately treat the pathology we set out to resect.
Ainsworth, Tessema, and Brown
Overview of Endonasal Corridors to Intracranial Targets
References 1. Solares CA, Ong YK, Snydreman CH: Transnasal endoscopic skull base surgery: what are the limits? Curr Opin Otolaryngol Head Neck Surg 18:1-7, 2010 2. Schwartz TH, Fraser JF, Brown S, et al: Endoscopic cranial base surgery: Classification of operative approaches. Neurosurgery 62:991-1005, 2008 3. Anand VK, Schwartz TH (eds): Practical Endoscopic Skull Base Surgery. Oxford, Plural Publishing, 2007 4. Snyderman CH, Carrau RL, Kassam AB, et al: Endoscopic skull base surgery: Principles of endonasal oncological surgery. J Surg Oncol 97:658-664, 2008 5. Greenfield JP, Leng LZ, Chaudhry U, et al: Combined simultaneous endoscopic transsphenoidal and endoscopic transventricular resection of a giant pituitary macroadenoma. Minim Invasive Neurosurg 51:306-309, 2008
199
6. Tabaee A, Anand VK, Cappabianca P, et al: Endoscopic management of spontaneous meningoencephalocele of the lateral sphenoid sinus. J Neurosurg 112:1070-1077, 2010 7. Nyquist GG, Anand VK, Brown S, et al: Middle turbinate preservation in endoscopic transsphenoidal surgery of the anterior skull base. Skull Base 20:343-347, 2010 8. Kassam AB, Thomas A, Carrau RL, et al: Endoscopic reconstruction of the cranial base using a pedicled nasoseptal flap. Neurosurgery 63(suppl 1):ONS44-ONS53, 2008 9. Brown SM, Anand VK, Tabaee A, et al: Role of perioperative antibiotics in endoscopic skull base surgery. Laryngoscope 117:15281532, 2007 10. Kraus DH, Gonen M, Mener D, et al: A standardized regimen of antibiotics prevents infectious complications in skull base surgery. Laryngoscope 115:1347-1357, 2005
Overview of endonasal corridors to intracranial targets Tiffiny Ainsworth, MD, Belachew Tessema, MD, Seth M. Brown, MD, MBA From the University of Connecticut Health Center, Division of Otolaryngology Head and Neck Surgery, Farmington, Connecticut. KEYWORDS Skull base; Endoscopic surgery; Transphenoid; Transnasal; Transethmoid; Transpterygoid
Intracranial targets for lesions or disease processes of the skull base are increasingly approached through endoscopic endonasal surgical approaches. The endonasal approach to the skull base can be divided into the nasal or sinus corridor traversed to reach an intracranial target. The transnasal, transethmoid, transphenoid, and transpterygoid approaches are discussed to provide a framework on how to approach various intracranial targets and diseases of the skull base. While endoscopic skull base surgery is minimal access surgery it is maximally invasive. The most common complication is a cerebrospinal fluid leak. © 2011 Elsevier Inc. All rights reserved.
Intracranial targets of the anterior, middle, and posterior skull base have been traditionally approached via transfacial and transcranial open surgeries. The surgeries are invasive, with long recovery periods and with risk of significant complications. The emphasis on less-invasive surgical procedures led to the development of endonasal approaches to the skull base. As technology improved, particularly with development of the Hopkins rod lens system in the 1960s, the endoscope was increasingly used to access the skull base endonasally (Figure 1). Purely endoscopic endonasal approaches to intracranial targets, without the combined access of transfacial or transcranial approaches, became popular for select pathology as early as the 1990s. Since then, the limits of the intracranial targets that are accessible continue to be expanded.1
Indications The indications for endonasal endoscopic skull base surgery are extensive. The endoscopic approach is not a surgery but a vehicle to access a variety of regions and an even greater variety of pathologies. Each of the various pathologies has
Address reprint requests and correspondence: Tiffiny Ainsworth, MD, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06119. E-mail address: [email protected]. 1043-1810/$ -see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.otot.2011.08.001
Figure 1 The endoscope allows access to the skull base through the nose and sinuses. This cut-away figure of the skull demonstrates the anatomical relationship between the sinuses and the skull base. (Reprinted with permission.2) (Color version of figure is available online.)
its own indications, goals, and outcome measures. The keys to performing endoscopic skull base surgery include the skill set of the surgical team; possessing adequate skull base
Ainsworth, Tessema, and Brown
Overview of Endonasal Corridors to Intracranial Targets
195
Figure 2 Transnasal or trans-sinus approaches are used to access a variety of intracranial targets. Depicted are the various intracranial targets that can be accessed via a given transnasal or trans-sinus approach. (Reprinted with permission.2) (Color version of figure is available online.)
instrumentation (including visualization, surgical navigation, and instruments for control of the vasculature); having adequate pre-, peri-, and postoperative care; and choosing the proper pathology on which to use this approach. We present a method of breaking down endoscopic skull base surgery by the approach used to assist in surgical planning as well as resection on the basis of the system created by Schwartz et al.2
Technique The endoscopic endonasal approaches to the skull base can be divided into 2 general anatomic concepts; the corridor
that is taken to approach the skull base and the target area that is operated on. Although not all surgeries will fall into one category, generally there is one primary corridor that is used to reach the target area. On occasion, multiple corridors are combined to perform surgery. The ability to divide the surgery into corridor and target region allows the surgical team to plan appropriately to have the necessary instrumentation, the proper surgical team members available for the surgery, and to facilitate a worthwhile preoperative surgical discussion.2,3 Other groups have presented similar systems, most notable the Pittsburgh group, which divides the corridors into 2 general areas: the sagittal plane (between the carotid arteries) and the coronal plane (lateral to the carotid arter-
196
Operative Techniques in Otolaryngology, Vol 22, No 3, September 2011
Figure 3 Depicted are the variety of intracranial targets that are accessible via endoscopic transnasal or trans-sinus approaches. (Reprinted with permission.2) (Color version of figure is available online.)
ies).4 The 2 planes are then subdivided on the basis of the target region into various modules.4 The corridors we have chosen are determined on the basis of the sinus that needs to be transversed to reach the target area. The Schwartz/Anand classification developed at Cornell2 divides the corridors into 4 areas: transnasal, transethmoidal, transsphenoidal, and transpterygoidal (Figures 2 and 3). The transnasal corridor is unique in that no sinus is transversed to reach the skull base (Figure 4). The transnasal approach can either be anterior (medial to the middle turbinate) or inferior (the nasopharynx). The anterior transnasal approach allows access to the anterior cranial fossa through the cribriform plate. This would most commonly be performed for a small meningoencephalocele. The inferior transnasal approach allows access into the nasopharynx and upper oropharynx. This allows resection of pathologies of the lower clivus, the vertebrobasilar junction, craniovertebral junction and the odontoid process. The transethmoidal corridor, particularly when opened bilaterally and combined with the transnasal transcribriform approach, allows access from orbit to orbit, from frontal sinus to sphenoid sinus (Figure 5). This traditionally is for pathologies of the fovea ethmoidalis (ie, cerebral spinal fluid leaks) but also allows access to the orbital apex and the frontal fossa. Pathologies that can often be approached through this corridor include orbital apex hemanogiomas,
hemangiopericytomas, esthesioneuroblastomas, meningoencephaloceles, and olfactory groove meningiomas. The transsphenoidal corridor is the most versatile of the approaches (Figure 6). It is also perhaps the least controversial because endonasal approaches to the sella have been in existence for many years. Although mostly used for pituitary tumors, it can be expanded to access a multitude of target areas, including the orbital apex, the suprasellar cistern, the cavernous sinus, the upper portion of the clivus, and the petrous apex. Pathologies approached within these target areas are numerous but include petroclival and planum meningiomas, all sellar pathology, suprasellar extent of pituitary tumors, craniopharyngiomas, and clival tumors in the superior portion of the clivus. Even giant pituitary tumors extending into the lateral ventricle can be approached from below.5 The transpterygoidal corridor involves removal of the back wall of the maxillary sinus to reach the skull base (Figure 7). This is often a unilateral approach that facilitates access to the cavernous sinus, the upper and lateral portions of the clivus, the petrous apex, and the infratemporal fossa. In addition to biopsying lesions in the infratemporal fossa, it is commonly used for meningoencephaloceles that are in lateral aspect of a pneumatized sphenoid sinus, also known as a Sternberg’s canal encephalocele.6
Ainsworth, Tessema, and Brown
Overview of Endonasal Corridors to Intracranial Targets
197
Figure 4 The transnasal corridor provides access to the anterior cranial fossa, medial cribiform plate, lower clivus, basilar artery, and odontoid process. (Reprinted with permission.2) (Color version of figure is available online.)
Figure 5 The transethmoidal corridor provides access to the anterior cranial fossa, orbital apex, and suprasellar cistern. (Reprinted with permission.2) (Color version of figure is available online.)
Figure 6 The transsphenoidal corridor provides access to the pituitary, orbital apex, suprasellar cistern, cavernous sinus, upper clivus, and petrous apex. (Reprinted with permission.2) (Color version of figure is available online.)
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Figure 7 The transpterygoidal corridor provides access to the cavernous sinus, petrous apex, infratemporal fossa, and the upper and lateral portions of the clivus. (Reprinted with permission.2) (Color version of figure is available online.)
Complications The complications for the surgery will depend on approach used and the extent of surgery. It is important to note that although endoscopic skull base surgery is minimal access, it is maximally invasive. This means that despite not having skin incisions, the risks of the surgery are similar to open approaches. Depending on the anatomical approach used, the complications from endoscopic endonasal skull base surgery include but are not limited to cerebrospinal fluid leak, infections, bleeding, cranial nerve palsies, anosmia, septal perforation, atrophic rhinitis, iatrogenic created sinusitis (particularly from turbinate resection), pituitary dysfunction, vision loss, diabetes insipidus, stroke, and death.7 The most common complication is a cerebrospinal fluid leak, with a reported incidence of 5%.4 This incidence has decreased significantly with use of the pedicled nasal septal flap.8 Considering that endonasal approaches have the potential to expose nasal and pharyngeal pathogens intracranially, the risk of meningitis is low at only 2%.4 It is also reported that extended
broad-spectrum antibiotics are not necessary to prevent infection as is popular with open skull base approaches, although their use may be prudent.9,10
Discussion The division of the skull base into corridors and targets allows surgeons to effectively communicate about the surgery that is being performed. This has become more important as more surgeons have adopted the endoscopic approach into their surgical repertoire. Furthermore, as the limits of endoscopic surgery are expanded, a common language allows for more understanding in the literature as well as at meetings. As we move forward with endoscopic approaches we must continue to choose the pathologies that are most appropriately removed with this technology and continue to adhere to the principles of surgical oncology.4 We should never let a minimal-access surgery limit our ability to adequately treat the pathology we set out to resect.
Ainsworth, Tessema, and Brown
Overview of Endonasal Corridors to Intracranial Targets
References 1. Solares CA, Ong YK, Snydreman CH: Transnasal endoscopic skull base surgery: what are the limits? Curr Opin Otolaryngol Head Neck Surg 18:1-7, 2010 2. Schwartz TH, Fraser JF, Brown S, et al: Endoscopic cranial base surgery: Classification of operative approaches. Neurosurgery 62:991-1005, 2008 3. Anand VK, Schwartz TH (eds): Practical Endoscopic Skull Base Surgery. Oxford, Plural Publishing, 2007 4. Snyderman CH, Carrau RL, Kassam AB, et al: Endoscopic skull base surgery: Principles of endonasal oncological surgery. J Surg Oncol 97:658-664, 2008 5. Greenfield JP, Leng LZ, Chaudhry U, et al: Combined simultaneous endoscopic transsphenoidal and endoscopic transventricular resection of a giant pituitary macroadenoma. Minim Invasive Neurosurg 51:306-309, 2008
199
6. Tabaee A, Anand VK, Cappabianca P, et al: Endoscopic management of spontaneous meningoencephalocele of the lateral sphenoid sinus. J Neurosurg 112:1070-1077, 2010 7. Nyquist GG, Anand VK, Brown S, et al: Middle turbinate preservation in endoscopic transsphenoidal surgery of the anterior skull base. Skull Base 20:343-347, 2010 8. Kassam AB, Thomas A, Carrau RL, et al: Endoscopic reconstruction of the cranial base using a pedicled nasoseptal flap. Neurosurgery 63(suppl 1):ONS44-ONS53, 2008 9. Brown SM, Anand VK, Tabaee A, et al: Role of perioperative antibiotics in endoscopic skull base surgery. Laryngoscope 117:15281532, 2007 10. Kraus DH, Gonen M, Mener D, et al: A standardized regimen of antibiotics prevents infectious complications in skull base surgery. Laryngoscope 115:1347-1357, 2005