Letter: Petroclival Synchondrosis and Its Relevance to Operative Feel
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.
E474 | VOLUME 78 | NUMBER 3 | MARCH 2016
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:
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
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
The authors have no personal, financial, or institutional interest in any of the
drugs, materials, or devices described in this article.
Industry Sponsorship of Spine Device Trials Is the Norm
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 .
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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 .