Letter: Petroclival Synchondrosis and Its Relevance to Operative Feel

Neurosurgery, Mar 2016

Balasubramanian, Chandramouli

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Letter: Petroclival Synchondrosis and Its Relevance to Operative Feel

Accessed October 0 Chandramouli Balasubramanian, MS, MRCS Queen Elizabeth Hospital NHS - University of Birmingham Birmingham , United Kingdom 1 Pathology University of Washington Seattle , Washington , USA 2 Laligam N. Sekhar, MD , USA 3 Neurological Surgery To the Editor: We read with great interest the brilliant article by Sekhar et al1 in the August issue of Clinical Neurosurgery. Various modules such as petrous drilling, internal carotid artery safety, and the contemporary concept of aggressive resection are highly commendable. We can only add this letter as one of the challenges during resection, namely drilling of the petroclival synchondrosis. On the other hand, Almefty et al,2 in one of the largest series of petroclival meningioma, made a clear inclusion of only “true” petroclival cases and not sphenoclival or midclival meningiomas. Xu et al3 also echo their comments about the confusion in the terminologies used with special reference to petrosectomy and petroclival area. With larger tumors and those medial to the internal auditory canal, combined transpetrosal approaches remain an important tool, as quoted: in these tumors, petrosectomy is prerequisite “bone work.” The captured concept in this letter would be tactile feedback (the consistency of bone and cartilage) while drilling this area, which is not discussed in many articles. In the pediatric and young adult population, there can be cartilaginous parts around this area. In this letter, we endeavor to elaborate on this. For example, the youngest patient in the series by Almefty et al2 is 30 years old. Some of these tumors are noted to be firm, which can only add to the confusion in the differentiation between tumor bone interface in the young. THE JOINT AND THE BONES FORMING IT Petroclival synchondrosis is the joint commonly referred to as petroclival fissure or petroclival area.4 As in most other parts of the skull base, the junction is an immovable joint (synarthrosis). Histologically, fissure (a fibrous joint) is different from synchondrosis (a cartilaginous joint). Both fissure and synchondrosis come under synarthrosis. In the petroclival area within pediatric and young adults, the cartilaginous parts occur in the following areas: 1) Petroclival synchondrosis: In adults aged .25, it is usually seen only at the petro-clival junction. 2) Occipital bone (between 2 or more ossification centers within the occipital bone itself): In a child ,6 years there can be synchondrosis in the clival portion of the occipital bone because most of the base of the skull develops from endochondral ossification5 and complete fusion of the chondral subcomponents occurs around 6 years. 3) Clivus bone (formed from part of sphenoid and occipital bone): In a young adult ,25 years the cartilage part can occur in the spheno-basi-occiput joint. The synchondrosis in this For the purpose of discussion, we could imagine a small cube comprising of bone and cartilage sitting in this area.6 Figuratively, after the bone work via endoscopic route, one should be able to visualize the dura. This bone work involves drilling a cube of bone in order to get to the petroclival window. The part of the cube facing the petrous bone will have a petrosal face and that facing the clivus will have a clival face. ICA would be just anterolateral to this cube. The synchondrosis will be within it. In a cranial microsurgical approach to the petroclival area, such as the anterior petrosectomy, the initial drilling occurs on the superior part of the cube.7 Hence, the tactile feedback during drilling these areas creeps into importance. Another example is the lateral approaches to pontomesencephalic junction; an anterior tentorial cut is used after anterior petrosectomy. This is usually performed when the petrous apex has been removed and after the superior petrosal sinus has been divided.8 Intraoperative tumor and vital structure navigation will guide surgeons as to how much bone and cartilage needs to be drilled. Professor Rhoton7 points out that there are venous plexuses both in the intracranial (inferior petrosal vein) and extracranial locations of this petroclival junction, which might be considered to be the limits of drilling of petrous bone. These veins can be considered to be on the anterior and posterior face of the cube. All contribute to the important look-listen-feel of drilling. The author has no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES E474 | VOLUME 78 | NUMBER 3 | MARCH 2016 10.1227/NEU.0000000000001148 In Reply: Petroclival Synchondrosis and Its Relevance to Operative Feel This is in response to the letter to the editor by Dr Balasubramanian regarding the petroclival synchondrosis and its relevance to operative feel. The comments are directed towards our article in Clinical Neurosurgery titled “Skull Base Meningiomas: Aggressive Resection.”1 In discussing petrosectomy or clivectomy, one must make a distinction between a predominantly intradural tumor such as meningioma and predominantly extradural tumors such as chordoma or chondrosarcoma. In our article, we were only discussing meningioma, which is quite rare in children. Occasionally, we see aggressive meningiomas in children, which may require the same approaches as in adults (transpetrosal, extreme lateral partial transcondylar, or endoscopic/Le Fort 1 maxillotomy transclival). In such cases, we may encounter the petroclival or petro-occipital synchondrosis during the drilling, but generally the interaction is limited because usually our goal is to get just enough exposure of the lesion without brain retraction. We may also use similar approaches to intradural vascular lesions such as a brain stem cavernoma.2,3 For extradural lesions, we are more likely to be drilling the petrous apex and the clivus in approaches such as the petrous apicectomy (Kawase approach), subtemporal-infratemporal approach, extreme lateral transcondylar approach, or endoscopic or Le Fort 1 maxillotomy endonasal approach. Here of course, the tactile feel during the removal of a tumor becomes important, but the visualization of the margin is even more important because we are trying to get a tumor-free margin in the infiltrated bone or cartilage at the end of the operation. We try to use both the intradural visual and tactile impressions during the surgery, as well as the information from the navigational magnetic resonance imaging scans. Because these tumors are already cartilaginous, or mixed bone and cartilage during the surgery, the goal is to get to healthy bone beyond the margins of the tumor. In such circumstances, the anatomical feel of the synchondrosis is less important. We still do not have a good way to know the intraoperative margins of the tumor, similar to fluorescence imaging for brain tumors. If available and reliable this will be a good way to achieve a more complete resection because complete resection correlates best with long-term outcome of chordomas.4 At present, in most patients, surgical resection is followed by irradiation of the tumor margins by proton beam therapy to kill tumor cells in the resection margins. The idea of performing frozen sections to evaluate the margins intraoperatively is not practical in these tumors. The author of the letter has drawn attention to tactile feedback during surgery, which is very important, not only during tumor surgery, but also during other microsurgical and endoscopic operations, including vascular surgery. In designing robots to perform surgical operations (master-slave robots), the tactile feedback is called “haptic sensation.” This will be a feature of the newer-generation of surgical robots, and such inventions will also help surgeons to quantify the feel and use it with standard surgical instruments in the future.5 Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 10.1227/NEU.0000000000001149 Industry Sponsorship of Spine Device Trials Is the Norm NEUROSURGERY VOLUME 78 | NUMBER 3 | MARCH 2016 | E475 6. Simal-Julián JA , Miranda-Lloret P , Botella-Asunción C , Kassam A. Full endoscopic endonasal expanded approach to the petroclival region: optimizing the carotid-clival window . Acta Neurochir (Wien) . 2014 ; 156 ( 8 ): 1627 - 1629 . 7. Rhoton AL Jr. Cavernous Sinus and Middle Fossa-Part 2 of 2 . AANS Neurosurgery, October 26 , 2011 . Available at: https://www.youtube.com/watch?v¼9tX4HK9TTi8. Accessed October 1 , 2015 . 8. Jittapiromsak P , Wu A , Nakaji P , Spetzler RF , Preul MC . The challenge of access to the pontomesencephalic junction: an anatomical study of lateral approach and exposure . Skull Base . 2010 ; 20 ( 5 ): 311 - 320 . 1. Sekhar LN , Juric-Sekhar G , Brito da Silva H , Pridgeon JS . Skull base meningiomas: aggressive resection . Neurosurgery . 2015 ; 62 ( suppl 1 ): 30 - 49 . 2. Mai JC , Ramanathan D , Kim LJ , Sekhar LN . Surgical resection of cavernous malformations of the brainstem: evolution of a minimally invasive technique . World Neurosurg . 2013 ; 79 ( 5 /6): 691 - 703 . 3. Sekhar LN , Mantovani A . Surgical approaches to brain stem cavernous hemangiomas . World Neurosurg . 2014 ; 82 ( 6 ): 1028 - 1029 . 4. Di Maio S , Temkin N , Ramanathan D , Sekhar LN . Current comprehensive management of cranial base chordomas: 10-year meta-analysis of observational studies . J Neurosurg . 2011 ; 115 ( 6 ): 1094 - 1105 . 5. Sekhar LN , Tariq F , Kim LJ , Pridgeon J , Hannaford B . Commentary: virtual reality and robotics in neurosurgery . Neurosurgery . 2013 ; 72 ( suppl 1 ): 1 - 6 .

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Balasubramanian, Chandramouli. Letter: Petroclival Synchondrosis and Its Relevance to Operative Feel, Neurosurgery, 2016, E474-E475, DOI: 10.1227/NEU.0000000000001148