Chordomas, Esthesioneuroblastomas, and Orbital Metastases
Tumors affecting the skull base, that is, arising from the extra-dural tissues at the base of the skull, are rare in infants and children. They account for 2 to 10% of brain tumors in children, depending on the type and location of the practice. There is a wide range of possible pathology ( Table 39.1 ), and a firm diagnosis and accurate categorization of the tumor are important if the best therapeutic plan is to be selected. Advances in imaging techniques, better surgical approaches, improved molecular diagnosis, and advances in radiation and chemotherapy have all played a role in the improved outcome of children harboring these lesions.1 Despite such advances, the long-term survival or cure rates remain poor. These are difficult diseases to study because of the rarity of the entities and the inability to collect large series of patients.
This chapter discusses chordomas, esthesioneuroblastomas, and metastatic disease to the orbits and skull base. The majority of skull base tumors require a combined therapeutic strategy with surgery, radiation, and/or chemotherapy. Preplanning based on the expected tumor type is very important for minimizing complications and maximizing outcome. In all of these tumors a careful plan for complete multimodal therapy should be developed prior to any intervention, even if it requires a biopsy first. If a plan is not developed, the wrong approach could be used and the child could have a lower chance of cure and could be exposed to a greater risk of complications.
Chordomas are the skull base lesions most frequently encountered by pediatric neurosurgeons, probably because these tumors are now amenable to diagnosis with computed tomography (CT) and magnetic resonance imaging (MRI) scans. Surgery with at least subtotal resection is the primary therapy, as chordomas remain resistant to chemotherapy. Chordomas are usually mid-line tumors affecting the skull base (35%),2 spinal column, or sacrum. Tumors that arise in the sellar region can be confined to one petrous apex or one side of the cavenous sinus. When involving the cavernous sinus the tumor is usually intercavernous rather than intracavernous. They are still believed to arise from notochordal elements, although with the development of chordoma cell lines and now an animal implant model,3 more accurate information on these rare tumors is being developed. Not only will this information clarify the tissue of origin, but it is hoped it also will produce new strategies for therapy. The presence of brachyury in familial chordomas and now in sporadic chordomas supports the origin from the notochord.4 Recently a role for epidermal growth factor in the development and growth of chordomas has been proposed.5 Pathologically these tumors are rather benign looking with psaliferous cells showing low rates of division, although necrosis may be present. Two main types have been described, the standard chordoma (58%) and a chondroid subtype (23%). In addition, malignant chordomas do occur (19%) and must be recognized. These aggressive tumors demonstrate less well differentiated cells with high mitosis rates. Since the founding of the Chordoma Foundation 3 years ago, there has been considerable progress with respect to the interest in and information on this rare tumor. My personal experience has been that chordomas represent 14% of skull base tumors (12 of 85) in children and 90% or more arise from the clivus or foramen magnum. Chordomas account for 0.1% of all brain and central nervous system (CNS) tumors.
Presentation varies with the location of the tumor. Headaches are common but are often very nonspecific. The rare lesions in the anterior fossa or parasellar area can produce visual disturbances by affecting cranial nerves II, III, IV, or VI. Lesions in the middle or lower clivus may produce nerve IV palsy or swallowing difficulties. Those at the lower clivus/cervical spine junction can present with long tract signs. Frequently chordomas are identified by the finding of a submucosal mass on physical examination, with few if any accompanying symptoms ( Fig. 39.1 ). Chordomas have been reported at all ages of infancy and childhood. Diagnosis is usually by CT scan and MRI ( Table 39.2 ). Both studies are usually necessary, because although MRI is not a good study for defining the bony involvement ( Fig. 39.2 ), an MRI is necessary to delineate the soft tissue spread of the tumor and the degree of intrathecal involvement. The MRI usually shows a high intensity mass on T2 imaging, low density on T1, and variable enhancement ( Fig. 39.3 ). Malignant chordomas are often isodense or slightly hyperdense to brain on T1 and do not show the usual hyperintensity on T2 ( Fig. 39.4 ).
These tumors arise outside the dura, although in older patients they frequently grow through the dura and present intradurally as well; this is much less common in children. The likely reason is that the dura is growing as the brain grows in children, and therefore can expand to accommodate tumor rather than have the tumor penetrate the dura. The most common site for intradural extension in children with lesions is the cervicomedullary junction ( Fig. 39.3 ).
Nasal carcinoma (lymphoepithelioma), granulocytic sarcoma
Giant cell tumor of bone, aneurysmal bone cyst, ossifying fibroma, fibrous dysplasia
Myxoma and other low-grade sarcomas
Angiofibroma, neurofibroma, meningioma
Metastatic tumors: neuroblastoma, melanoma, leukemia, rhabdomyosarcoma
Surgery is usually the first step in therapy. Prior to surgical intervention, the radiation therapist is consulted to help define the portion of the tumor that has to be removed to facilitate radiation therapy. High doses of radiation are required to get the maximum benefit, 70 to 80 Gy, and thus it is the portion of the tumor that is in contact with or closest to the neural tissue that has to be removed to permit maximum proton beam therapy. There is no point to removing the extracranial tumor mass without also decompressing the brain.
CT provides best bone definition
Generally extradural but can be intradural
Increased T2 signal on MRI
Decreased T1 signal on MRI
Isodense on T1
Lack hyperdensity on T2
Depending on the location of the tumor, the surgical route used is the extended subfrontal, the transfacial, the transpalatal, or the transoral. Now with the increasing use of endoscopic resection, tumors in the region of the upper clivus may be approached using a purely endoscopic technique. For those tumors that involve the craniocervical junction, endoscopic techniques are simply inadequate because of the complexity of the ligamentous structures that permit multiple small pockets of tumor to form. These can be very difficult to identify and remove even with open surgery. Because these tumors almost always begin outside the dura, it is better to use an extradural approach to avoid contaminating the intradural space. Even with small areas of penetration of the dura around the foramen magnum, the tumor can usually be removed from an epidural approach. Dural closure can be accomplished using small clips if the opening is large or simply with Gelfoam and tissue glue for small perforations. It is better not to use spinal drainage because it collapses the dural envelope and facilitates leakage.
Far lateral approaches have been utilized in adults, and often bilateral, far lateral approaches are necessary to remove the entire tumor and decompress the brain. A transoral approach in children is preferable because it allows both sides of the tumor to be removed in one procedure ( Fig. 39.5 ). In addition this is a relatively pain-free approach from which children recover quickly. If there is invasion of tumor behind the dens requiring resection of the dens to get to the inferior tumor, an occipitocervical fusion is often necessary if the apical ligaments have been destroyed by the tumor ( Fig. 39.6 ). The fusion can be done at the time of the initial surgery or postponed for a few days to allow some recovery. In the interim period the child is nursed in a cervical collar or halo depending on the degree of presumed instability. It is not uncommon to find residual tumor around the foramen magnum, C1, C2 area on postoperative imaging. If the residual tumor is impinging on the neural tissue, medulla, or spinal cord, a further resection is required to get a few millimeters of cerebrospinal fluid (CSF) between any residual tumor and neural tissue ( Fig. 39.7 ). This permits the radiation therapist, if proton radiation is being used, to boost the proton beam dose to the 70 to 80 Gy necessary for the best chance of cure. If the residual tumor is not impinging on the neural structures, then repeat surgery may not be necessary.
Surgical complications should be few because of the extra-dural approach. In personal experience with 12 children (age 2 to 16) undergoing surgery, there have been no deaths, no CSF leaks, and no postoperative infections. One patient with an intercavernous chordoma had transient worsening of a preoperative palsy in cranial nerve IV. One patient in whom a LeFort I approach was used had a palatal dehiscence requiring secondary repair.