|Year : 2012 | Volume
| Issue : 6 | Page : 567--569
Choosing a surgical corridor for skull base chordoma
Department of Neurosurgery, Madurai Medical College, Madurai, India
Muruganagam, 138, Anna Nagar, Madurai - 625 020, Tamil Nadu
|How to cite this article:|
Muthukumar N. Choosing a surgical corridor for skull base chordoma.Neurol India 2012;60:567-569
|How to cite this URL:|
Muthukumar N. Choosing a surgical corridor for skull base chordoma. Neurol India [serial online] 2012 [cited 2021 Jan 16 ];60:567-569
Available from: https://www.neurologyindia.com/text.asp?2012/60/6/567/105187
"It is our choices …. that show what we truly are, far more than our abililities" J.K. Rowling
Choosing the most effective surgical corridor to a deep seated and difficult lesion is crucial to improve the surgical outcome. In this issue, Hagihara and colleagues  present a novel approach to a giant multi-compartmental pediatric chordoma. This index case highlights several important issues as noted below.
Chordoma is histologically a benign tumor but locally aggressive. These tumors have a bleak long-term outcome as shown by the most comprehensive survival analysis involving more than 400 cases,  which showed a median survival of 6.29 years. The issues that adversely affect the long-term outcome of these tumors include: the often large tumor burden at the time of diagnosis, spread along critical bony structures, encasement of important neurovascular structures, and poor margination all of which make both radical surgical resection and radiation therapy challenging. 
Chordomas are rare tumors and they are rarer in the pediatric age group.  Less than 5% of all chordomas occur in children and adolescents. , Even in the pediatric age group, there is an age-dependent variation in the outcome.  Children less than 5 years of age have higher incidence of atypical histological findings and higher incidence of metastases than those less than 5 years of age. 
Local recurrence is the most important predictor of mortality in chordomas and the extent of resection is the most important predictor of tumor control.  Overall, the long-term outcome of chordoma depends upon the maximum reduction of the tumor burden by adopting a safe, maximally cytoreductive surgery.  However, large series by experienced skull base surgeons have achieved only 40-58% radical resection rate. ,, In all the reported series, surgeons were able to achieve more radical resections and with less morbidity only in primary surgical interventions with the significant decrease in the extent of resection as well as an increase in the complication rates in redo surgical excisions. Keeping this in mind, surgeons who embark on the removal of these lesions should aim for safe, maximal cytoreductive surgery during the first attempt itself. While safe, maximal cytoreductive surgery is the goal, the aggressiveness of the resection should be determined by the patient's age, physiological status, as well as the desire to reduce the neurological morbidity due to resection, especially cranial nerve palsies, which can be sometimes debilitating.
The appropriate surgical approach depends upon the extent of the tumor. Al Mefty and Borba  have provided a useful classification for management of these tumors: Type I lesions are restricted to one compartment of the skull base, defined as a solitary anatomical area (e.g., sphenoid sinus, occipital condyle, cavernous sinus, and lower clivus), Type II lesions involve two or more contiguous areas of the skull base and whose radical removal can be achieved by using a single skull base approach, and Type III lesions involve multiple compartments and whose surgical removal requires more than one surgical approach, often in stages, to achieve radical resection. Most chordomas encountered in clinical practice fall into the second and third types. The classification provided by Al Mefty and Borba  along with the knowledge of the indications and limitations of different skull base surgical techniques assist the surgeon in planning the most effective surgical approach. The case reported by Hagihara and colleagues  in this issue falls into the third category. The various surgical options available for skull base chordomas include: endoscopic endonasal, extended subfrontal, transmaxillary, transmandibular, transcervical, orbitozygomatic, preauricular infratemporal, combined supra- and infratentorial transtentorial, and transcondylar approaches.  In the index case, Hagihara and colleagues  have used the transoral approach to remove the portion of the tumor ventral to the upper cervical spine, and then they used staged C2 ganglion sectioning approach on either side to remove the remaining tumor. In this context, it should be noted that in contemporary practice, most surgeons would have preferred an endoscopic approach to remove the portion of the tumor in the retropharyngeal space as it would significantly decrease the morbidity associated with the classical transoral approach in a child. The authors have very correctly refrained from resecting the odontoid (even though a significant portion of the tumor is retro-odontoid) in this very young patient as this would have necessitated an avoidable posterior fusion. Hagihara and colleagues performed a posterior midline approach without resecting the occipital condyle which is also appropriate as resecting the condyle on both sides, even partially, would have once again entailed an avoidable posterior fusion. However, it is important for the readership to remember that such an approach is not always feasible in all cases of skull base chordomas. There are certain radiological features of this case that made such an approach possible. As shown in the axial images, there is an asymmetric distortion of the brainstem-upper cervical cord and the tumor itself had created a space between the cord-brainstem and presented itself posteriorly beneath the C2 ganglion. This space can be used by the surgeon to remove the tumor without unnecessarily sacrificing the occipital condyle. As shown by previous studies,  the shape of the foramen magnum should be taken into consideration while deciding on the need to drill the occipital condyle. An oval foramen magnum with a foramen magnum index of >1.2, where the longitudinal diameter is more than the transverse diameter along with a lesion that has not displaced the brainstem-cord would necessitate drilling of the occipital condyle, whereas a round foramen magnum where the transverse diameter is almost equal to the longitudinal diameter, especially when associated with brainstem displacement by the tumor (with space being created by the tumor itself) would not require occipital condyle resection. This is exactly what was done in the index case reported by Hagihara and colleagues.  The space provided by sectioning the C2 ganglion provided an added surgical corridor that enabled the radical removal of the tumor. This reviewer has sectioned the C2 ganglion/root to access anteriorly placed lesions at the cervicomedullary junction. However, such sectioning is usually done on one side only as the tumor usually distorts/displaces the neural structures to one side. Despite this, one of this reviewer's patient developed trophic ulcers in the occipital region during follow-up. However, this might be considered by many surgeons as small price to pay for achieving a radical resection.
The case report by Hagihara and colleagues  also emphasizes the role of multimodality approach in the management of skull base chordomas as their patient was also subjected to cyberknife radiosurgery to treat the tumor residue and the patient was followed for 7 years without obvious recurrence. The role of stereotactic radiosurgery as an adjunct to the surgical management of chordomas is well-known.  Recently, gene duplication of brachyury has been identified in patients with chordomas.  In vitro studies have shown that silencing of brachyury leads to growth arrest of chordoma cells in vitro.  Hence, the ultimate answer to the management of skull base chordomas in future might be a multimodal therapy that includes: Cytoreductive skull base surgery, stereotactic radiosurgery, and molecular targeted therapies (such as those aimed at brachyury gene duplications), the latter two taking care of the tumor residues. If this prediction was to come true, longer progression-free survivals for these vexing tumors might be in sight in the foreseeable future.
In summary, awareness of the advantages and limitations of different surgical techniques, vast experience, "custom made" approaches to suit specific tumour locations and peculiarities imposed by individual patient's anatomy should guide the surgeon in choosing the appropriate surgical corridor for each lesion.
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