These are tumors of notochordal origin and are characteristically centered on the sphenooccipital synchondrosis. Local destruction of the clivus with extradural compression of the neuraxis is a characteristic feature (Fig. 11.2). Extension to the nasopharynx or upper cervical spine is well recognized though intradural extension is unusual. CT scanning is useful to delineate the extent of bony involvement. On MRI the lesion is hypointense on T1, hyperintense on T2, and commonly shows only modest enhancement.

In a review of the literature, Borba et al. found that only 57 % of children with chordoma were alive at a mean follow-up of 39 months [16]. Poor prognostic factors include young age at presentation (less than 5 years), atypical pathology [17], and the presence of metastases. At the time of presentation, these tumors are large and locally infiltrative compromising the prospects for complete resection. Surgery does however play an important role in the multidisciplinary management of these tumors in establishing accurate histological diagnosis and combining maximal resection with decompression of the neuraxis. Whilst surgery alone is ineffective in providing long-term tumor control the combination of surgery and radiotherapy confers a significant benefit. Given the proximity of the brain stem, proton beam irradiation is now the preferred irradiation modality for this tumor resulting in better local control and survival [18]. Using combined proton and photon irradiation, almost 60–70 % 5-year local control has been reported [19, 20]. While many of the publications are predominantly adult series, there is increasing evidence that the benefit of proton therapy can be extended to chordoma and other aggressive tumors of the skull base in the pediatric population as well [21].

These are benign cystic lesions of the bone that may occur either in isolation or in the context of an underlying bone neoplasm such as giant cell tumor, osteoblastoma or osteosarcoma. They more commonly present with pain than neuraxial compression. Pathologically ABCs consist of large cystic spaces separated by connective tissue trabeculae. In the craniovertebral region they most commonly arise within the axis or atlas vertebrae; involvement of the skull base is rare. They are expansile lesions best demonstrated on CT. The observation of fluid levels, indicative of hemorrhage into the cysts, is a useful aid to diagnosis. These lesions can be exceedingly vascular, and preoperative embolization should be considered particularly in the larger lesions [22]. Embolization has been advocated as the definitive treatment modality [23]; however, at the craniovertebral junction the potential for extension of the embolic material compromising brain or spinal cord perfusion must be recognized [24]. The surgical goal is complete extirpation; subtotal removal is associated with high rate of local recurrence. If the tumor (or its removal) threatens the integrity of the anterior vertebral column, then concomitant spinal reconstruction or stabilization will be required as there is significant risk of postsurgical deformity and instability.

Chondrosarcoma, Ewings sarcoma, and epitheloid sarcoma are among the sarcomas that may occur in the posterior skull base in children. Surgery for skull base sarcoma is rarely the sole treatment modality; precise histological diagnosis is essential in guiding therapy. These can be highly vascular, infiltrative tumors, and this strategy may optimize the prospects of safe complete resection. It may be necessary to use more than one surgical approach to achieve decompression of the neuraxis and maximal tumor debulking prior to adjuvant therapy (Fig. 11.3). In some instances, for example, in Ewings sarcoma once the tissue diagnosis is established, neoadjuvent treatment with chemotherapy followed by surgical resection of the involved field of any residual tumor is the preferred strategy.

A variety of other rare lesions of the posterior skull base may be encountered in the pediatric population; these include Langerhans cell disorders, meningiomas, and nerve sheath tumors. These benign lesions can be treated successfully with surgery alone.

While the principles of the surgical technique are broadly the same as in adults, there are additional considerations that need to be taken into account when performing transoral surgery in children. The most obvious of these is the smaller size and thus potential for more limited access. In reality however we have used the standard transoral instrumentation in children without particular difficulty; in our recent experience there have been six children under the age of 5 years (the youngest 2 years). Many children are operated on because of congenital deformity at the craniovertebral junction; in these circumstances the usual anatomical landmarks may be absent or misleading. Image guidance can be of help in negotiating distorted anatomy and may help in achieving a more predictable resection in the case of tumors accessed through this route [25].

The distance along the craniocaudal axis that can be accessed by the transoral approach is illustrated in Fig. 11.4. In most circumstances the standard transoral approach will permit access from the upper border of C1 to the base of C2. More cranial access has traditionally required complex craniofacial approaches such as the open-door maxillotomy [7]. Using this technique the clivus can be accessed as far as its upper third. There is significant morbidity associated with these extended approaches. There are now increasing reports of the use of skull base endoscopic techniques to access the upper clivus, and these have already virtually replaced the need for these extended approaches [26].

MRI is the most sensitive modality by which to evaluate tumors in the region of the craniovertebral junction and posterior skull base. The effect on the brain stem and upper cervical spinal cord can be demonstrated, and the MR characteristics will aid in refining the differential diagnosis. Many of the tumors of this region will be of mesenchymal origin, arising in the bone or soft tissues and secondarily compromising the neuraxis. The extent of bone involvement by a tumor is better evaluated on CT scan; additionally CT will demonstrate the extent to which the craniovertebral joints are involved and provide a means of assessing the suitability of the upper cervical vertebrae for instrumented stabilization should this be required.

Tumors at the craniovertebral junction may be the cause of craniovertebral instability; more commonly however instability occurs as a consequence of violating the apical, alar, and transverse ligaments in the course of the transoral approach. Preoperative flexion/extension cervical spine X-rays will reveal significant instability and will provide a baseline evaluation for comparison postoperatively.

In those situations where instability can be demonstrated prior to surgery or where it is felt to be inevitable as a consequence of the intervention (e.g., large tumors replacing bone or involving the craniovertebral joints), prior immobilization in a halo body orthosis will provide temporary pre- and postoperative stability. This not only protects against inadvertent intra- and postoperative neurological damage due to hypermobility but also obviates the need to proceed to a posterior stabilization procedure in the same sitting. The immobilization also affords the opportunity to use intraoperative image guidance using the halo frame as a reference [25].

The vertebral and the vertebrobasilar vessels may be involved or distorted by tumor and so may be vulnerable during the transoral procedure. In some cases CT angiography, combining bone and vascular imaging may assist in the planning of a safe resection [27].

An endonasal intubation is preferred to oral intubation as the latter risks further compromising the surgical access by crowding the oral cavity. Aqueous chlorhexidine is used to prepare the oral cavity, and metronidazole or co-amoxiclav is added to the usual neurosurgical antibiotic prophylaxis.

An integrated transoral retractor system (Codman/Crockard) is used (Fig. 11.5). The smaller tongue blades are usually more suitable for pediatric use. Care is needed to ensure that the tongue is not trapped between the blades and the occlusal surface of the teeth. The retractor system incorporates smaller blades for retraction of the soft palate and uvula. Once the retractors are in place, it is useful to assess the extent of rostrocaudal exposure using image intensifier or image guidance. The posterior pharyngeal wall is infiltrated with local anesthetic and adrenaline solution.