Perspectives Commentary on: Surgical Microanatomy of the Anterior Clinoid Process for Paraclinoid Aneurysm Surgery and Efficient Modification of Extradural Anterior Clinoidectomy by Ota et al. World Neurosurg 83:635-643, 2015
Respecting the Clinoid: An Application of Preoperative Computed Tomography Angiography H. Hunt Batjer and Babu G. Welch
S
urgical management of paraclinoid aneurysm is a practice in flux. As a larger proportion of these lesions are treated by endovascular techniques, it is not unreasonable to expect the level of surgical unfamiliarity with the anatomy of this region to increase. The article by Ota et al. provides a timely discussion of the use of computed tomography (CT) angiography preoperatively to evaluate anatomic variations of the anterior clinoid process (ACP). The authors suggest modifications to standard anterior clinoidectomy be based on observations from CT angiography to improve the surgical access.
anatomy but also the presence of calcification of the aneurysm neck because this may adversely affect surgical clipping. Even when preoperative magnetic resonance angiography is available, we believe that CT angiography allows an improved approximation of the relationship between the aneurysm and skull base. This understanding allows the surgeon to plan better for modes of proximal control via endovascular or cervical carotid exposure. Occasionally, we have also found evaluation of the ACP to be useful in approaches to laterally directed aneurysms of the posterior carotid wall. This nuance is well illustrated in an analysis by Park et al. (2).
The study by Ota et al. comprises 144 sides in 72 cases of paraclinoid aneurysms treated by extradural anterior clinoidectomy (EAC). All cases were analyzed preoperatively using multidetector-row CT. Particular consideration was given to the presence of the caroticoclinoid foramen and the interosseous bridge and the presence and routes of pneumatization of the clinoid process. Each of these variances has the potential to limit complete resection of the ACP via the authors’ chosen extradural approach or produce the complication of cerebrospinal fluid rhinorrhea. We provide a skull base image because we think that the operative anatomy provided by the authors may be difficult to interpret (Figure 1).
The influence of CT angiography on modern cerebrovascular neurosurgery is such that any practitioner in the field should develop facility with the software necessary to manipulate the data. Each surgeon should incorporate into his or her preoperative routine the use of software to extract the benefits of axial and reconstructed CT images of the cranial base. These images are invaluable as teaching tools when trainees are asked to prepare them before a case and in their application in the operative theater. Advanced use of CT angiography not only provides structural anatomy but also can provide measurements crucial to harvesting of potential bypass conduits (e.g., radial artery) (1).
The article by Ota et al. discusses the impact of CT angiography in the management of paraclinoid (or transitional) aneurysms and nuances of extradural versus intradural clinoidectomy. Similar to the authors, we routinely use CTA to evaluate not only clinoid
When variances in the anatomy of the ACP are identified, the authors encourage a “felicitous modification” to achieve a safe and effective approach to the lesion in question. The authors use the term “felicitous” not to emphasize their joy of surgery but to
Key words Anatomic variation of the anterior clinoid process - Caroticoclinoid foramen - Extradural anterior clinoidectomy - Interclinoid osseous bridge - Paraclinoid aneurysms - Pneumatization of the anterior clinoid process -
1022
Abbreviations and Acronyms ACP: Anterior clinoid process CT: Computed tomography EAC: Extradural anterior clinoidectomy
www.SCIENCEDIRECT.com
The University of Texas Southwestern Medical Center, Dallas, Texas, USA To whom correspondence should be addressed: H. Hunt Batjer, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2015) 83, 6:1022-1023. http://dx.doi.org/10.1016/j.wneu.2015.01.032
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2015.01.032
PERSPECTIVES
on CT angiography, the surgeon should modify his or her approach to include an intradural component to the clinoidectomy. Two observations are important here: 1) a completely intradural procedure might be more efficient, and 2) the increase in drilling necessary to treat many of the aneurysms should prompt a discussion of endovascular techniques. In suggesting a modified approach, the authors accentuate some of the benefits of intradural clinoidectomy, not the least of which is better access to variant anatomy. Although we agree that EAC is very useful, the lack of access to the vasculature at the time of a hemorrhagic complication needs to be emphasized and appreciated. Another, less appreciated, nuance is the tailoring of bone removal that is more likely to occur with intradural clinoidectomy. It is natural to maximize bone removal with EAC “in case you need it,” whereas bone removal with intradural clinoidectomy is performed “because you need it.” In an era where endovascular procedures provide effective alternatives for aneurysms in this region, it is prudent that the modern cerebrovascular surgeon be very clear about the benefits of surgery over endovascular therapy when making a surgical recommendation. A thorough understanding of the individual anatomy is crucial to this suggestion. When arriving at a decision to treat, patient-specific variables may influence the mode of therapy. In our practice, endovascular management (e.g., flow diversion, coil embolization) is considered for patients who have larger lesions (>10 mm) without cranial neuropathy, proximal vascular access, and tolerance to antiplatelet agents. Such an approach has led to improved outcomes in surgical and endovascular groups in multidisciplinary cerebrovascular treatment. Figure 1. Skull base image demonstrating the remnants of the interosseous bridge connecting the anterior and posterior clinoid processes. A spike of bone off of the distal lateral clivus (arrow) approximates the caroticoclinoid foramen. Coloring clarifies the relationship of the carotid artery to these structures.
suggest that approaches other than a pure EAC may be better suited to the variant anatomy observed. Simply put, when caroticoclinoid foramen or interosseous bridge variations are noted
REFERENCES 1. Markham JC, Eddleman CS, Uhrbrock D, Welch BG: Bending the curve: preoperative determination of bypass graft length and trajectory using curved-planar reformatted CT angiography: technical note. Neurosurgery 70(2 Suppl Operative): 327-331, 2012.
Diverse terminology has been applied to the paraclinoid region (e.g., paraophthalmic, proximal carotid, transitional). An aneurysm that is intimately related to the ACP should be respected. Such respect is a manifestation of understanding and admiration of the intricate anatomy of the region. Innovations in preoperative imaging and treatment technology have improved the therapies we can offer patients with this lesion. We appreciate the analysis of Ota et al. and encourage all cerebrovascular surgeons to take time to understand this useful addition to the literature.
2. Park SK, Shin YS, Lim YC, Chun J: Preoperative predictive value of the necessity for anterior clinoidectomy in posterior communicating artery aneurysm clipping. Neurosurgery 65:281-286; discussion 285-286 2009.
Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2015 Published by Elsevier Inc.
Citation: World Neurosurg. (2015) 83, 6:1022-1023. http://dx.doi.org/10.1016/j.wneu.2015.01.032
WORLD NEUROSURGERY 83 [6]: 1022-1023, JUNE 2015
www.WORLDNEUROSURGERY.org
1023
Respecting the Clinoid: An Application of Preoperative Computed Tomography Angiography H. Hunt Batjer and Babu G. Welch
S
urgical management of paraclinoid aneurysm is a practice in flux. As a larger proportion of these lesions are treated by endovascular techniques, it is not unreasonable to expect the level of surgical unfamiliarity with the anatomy of this region to increase. The article by Ota et al. provides a timely discussion of the use of computed tomography (CT) angiography preoperatively to evaluate anatomic variations of the anterior clinoid process (ACP). The authors suggest modifications to standard anterior clinoidectomy be based on observations from CT angiography to improve the surgical access.
anatomy but also the presence of calcification of the aneurysm neck because this may adversely affect surgical clipping. Even when preoperative magnetic resonance angiography is available, we believe that CT angiography allows an improved approximation of the relationship between the aneurysm and skull base. This understanding allows the surgeon to plan better for modes of proximal control via endovascular or cervical carotid exposure. Occasionally, we have also found evaluation of the ACP to be useful in approaches to laterally directed aneurysms of the posterior carotid wall. This nuance is well illustrated in an analysis by Park et al. (2).
The study by Ota et al. comprises 144 sides in 72 cases of paraclinoid aneurysms treated by extradural anterior clinoidectomy (EAC). All cases were analyzed preoperatively using multidetector-row CT. Particular consideration was given to the presence of the caroticoclinoid foramen and the interosseous bridge and the presence and routes of pneumatization of the clinoid process. Each of these variances has the potential to limit complete resection of the ACP via the authors’ chosen extradural approach or produce the complication of cerebrospinal fluid rhinorrhea. We provide a skull base image because we think that the operative anatomy provided by the authors may be difficult to interpret (Figure 1).
The influence of CT angiography on modern cerebrovascular neurosurgery is such that any practitioner in the field should develop facility with the software necessary to manipulate the data. Each surgeon should incorporate into his or her preoperative routine the use of software to extract the benefits of axial and reconstructed CT images of the cranial base. These images are invaluable as teaching tools when trainees are asked to prepare them before a case and in their application in the operative theater. Advanced use of CT angiography not only provides structural anatomy but also can provide measurements crucial to harvesting of potential bypass conduits (e.g., radial artery) (1).
The article by Ota et al. discusses the impact of CT angiography in the management of paraclinoid (or transitional) aneurysms and nuances of extradural versus intradural clinoidectomy. Similar to the authors, we routinely use CTA to evaluate not only clinoid
When variances in the anatomy of the ACP are identified, the authors encourage a “felicitous modification” to achieve a safe and effective approach to the lesion in question. The authors use the term “felicitous” not to emphasize their joy of surgery but to
Key words Anatomic variation of the anterior clinoid process - Caroticoclinoid foramen - Extradural anterior clinoidectomy - Interclinoid osseous bridge - Paraclinoid aneurysms - Pneumatization of the anterior clinoid process -
1022
Abbreviations and Acronyms ACP: Anterior clinoid process CT: Computed tomography EAC: Extradural anterior clinoidectomy
www.SCIENCEDIRECT.com
The University of Texas Southwestern Medical Center, Dallas, Texas, USA To whom correspondence should be addressed: H. Hunt Batjer, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2015) 83, 6:1022-1023. http://dx.doi.org/10.1016/j.wneu.2015.01.032
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2015.01.032
PERSPECTIVES
on CT angiography, the surgeon should modify his or her approach to include an intradural component to the clinoidectomy. Two observations are important here: 1) a completely intradural procedure might be more efficient, and 2) the increase in drilling necessary to treat many of the aneurysms should prompt a discussion of endovascular techniques. In suggesting a modified approach, the authors accentuate some of the benefits of intradural clinoidectomy, not the least of which is better access to variant anatomy. Although we agree that EAC is very useful, the lack of access to the vasculature at the time of a hemorrhagic complication needs to be emphasized and appreciated. Another, less appreciated, nuance is the tailoring of bone removal that is more likely to occur with intradural clinoidectomy. It is natural to maximize bone removal with EAC “in case you need it,” whereas bone removal with intradural clinoidectomy is performed “because you need it.” In an era where endovascular procedures provide effective alternatives for aneurysms in this region, it is prudent that the modern cerebrovascular surgeon be very clear about the benefits of surgery over endovascular therapy when making a surgical recommendation. A thorough understanding of the individual anatomy is crucial to this suggestion. When arriving at a decision to treat, patient-specific variables may influence the mode of therapy. In our practice, endovascular management (e.g., flow diversion, coil embolization) is considered for patients who have larger lesions (>10 mm) without cranial neuropathy, proximal vascular access, and tolerance to antiplatelet agents. Such an approach has led to improved outcomes in surgical and endovascular groups in multidisciplinary cerebrovascular treatment. Figure 1. Skull base image demonstrating the remnants of the interosseous bridge connecting the anterior and posterior clinoid processes. A spike of bone off of the distal lateral clivus (arrow) approximates the caroticoclinoid foramen. Coloring clarifies the relationship of the carotid artery to these structures.
suggest that approaches other than a pure EAC may be better suited to the variant anatomy observed. Simply put, when caroticoclinoid foramen or interosseous bridge variations are noted
REFERENCES 1. Markham JC, Eddleman CS, Uhrbrock D, Welch BG: Bending the curve: preoperative determination of bypass graft length and trajectory using curved-planar reformatted CT angiography: technical note. Neurosurgery 70(2 Suppl Operative): 327-331, 2012.
Diverse terminology has been applied to the paraclinoid region (e.g., paraophthalmic, proximal carotid, transitional). An aneurysm that is intimately related to the ACP should be respected. Such respect is a manifestation of understanding and admiration of the intricate anatomy of the region. Innovations in preoperative imaging and treatment technology have improved the therapies we can offer patients with this lesion. We appreciate the analysis of Ota et al. and encourage all cerebrovascular surgeons to take time to understand this useful addition to the literature.
2. Park SK, Shin YS, Lim YC, Chun J: Preoperative predictive value of the necessity for anterior clinoidectomy in posterior communicating artery aneurysm clipping. Neurosurgery 65:281-286; discussion 285-286 2009.
Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2015 Published by Elsevier Inc.
Citation: World Neurosurg. (2015) 83, 6:1022-1023. http://dx.doi.org/10.1016/j.wneu.2015.01.032
WORLD NEUROSURGERY 83 [6]: 1022-1023, JUNE 2015
www.WORLDNEUROSURGERY.org
1023
