Chordomas are uncommon tumors of bone, presumed to arise as neoplastic derivatives of embryonal notochord remnants (43-46). Accordingly, they can arise at any site along the axial skeleton, with 35% of all cases involving the clivus. Men are usually affected twice as often as women and curiously, despite their presumed embryonal origins, chordomas rarely affect individuals younger than 20 yr old. Although chordomas appear histologically benign, this aspect of their biology has been overemphasized because their locally destructive nature, unrelentingly progressive course, and variable metastatic potential collectively legitimize their inclusion as truly malignant tumors.
Fig. 2. Sagittal (A) and coronal (B) T1-weighted MRI of a sellar meningioma.
Usually, cranial chordomas are midline lesions and virtually all are, in some way, related to the clivus. Their precise site of origin determines their clinical presentation. Some arise in the mid and lower clival regions, producing multiple cranial nerve palsies and brain stem compression, whereas others originate from the ventral aspect of the clivus, producing symptoms of a nasopharyngeal mass. This discussion, however, concerns those chordomas whose origin in the most rostral extreme of the clivus and dorsum sellae warrants their inclusion as a sellar region mass (basis-sphenoidale chordomas) (47). Such lesions may extend into the sella, producing hypopituitarism or, with suprasellar extension, a chiasmal syndrome. Lateral penetration into the cavernous sinus may compromise cranial nerves transiting therein. Headache, usually the result of bony destruction, is a common accompaniment. All chordomas are locally invasive extra-axial lesions that begin with expansile bony destruction at their site of origin, followed later by infiltration and transgression of the dura, with eventual and widespread intra-cranial extension and encasement of cranial nerves, brain stem, and vascular structures. Metastatic dissemination is usually a late occurrence—one encountered clinically in 10%-20% of cases and at autopsy in up to 40% of cases.
The radiographic appearance of chordoma, as determined by CT and MRI, is fairly characteristic, consisting of a destructive and expansile process of the skull base in association with a coarsely calcified soft tissue mass (Fig. 3).
The combination of surgery and radiation therapy constitutes standard therapy for chordomas. Both have significant limitations, however, because the majority of patients treated eventually succumb to recurrent local disease. Surgical access to chordomas can be provided by a variety of standard intradural and extradural approaches. Selection of the most suitable approach for any given lesion depends primarily on whether the tumor is midline or lateral, and whether it is intradural or extradural. For intradural rostrally placed lesions of the parasellar region, particularly those having significant lateral, suprasellar, or cavernous sinus extension, a pterional or subfrontal craniotomy provides good access to the intracranial component of the tumor. When such tumors have a significant extradural component or for basis-sphenoidal chordomas, which are wholly extradural and midline, an anterior extradural approach is generally required. Accordingly, extradural involvement of the sphenoid sinus, sella, or upper clivus can best be approached by the transsphenoidal route. When the area or disease is below the anterior fossa floor, the transbasal/subcranial approach provides ideal exposure. Given the anatomic limits of all standard approaches, certain chordomas, depending on their particular geometry, require combined or multiple procedures. Although gross "total" removal is the surgical objective in most cases, it is difficult to achieve, even with the benefit of elaborate skull-base operation strategies currently employed.
Radiation therapy offers some measure of temporary tumor control, but because tumoricidal doses generally exceed levels of central nervous system (CNS) tolerance, tumor recurrence has proven to be inevitable. Stereotactic radiosurgical approaches continue to be evaluated.
As determined by various series, the mean survival of patients with chordoma ranged from 4.2 to 5.2 yr (43). The average time to first recurrence is approx 3 yr.
A variant of chordoma, containing conspicuous foci of cartilaginous material intertwined between tumor cells, is the chondroid chordoma. The variant accounts for approx one third of all cranial chordomas. Although its clinical presentation is indistinguishable from the standard chordoma, its prognosis is more favorable. The mean survival of patients with chondroid chordoma is almost 16 yr.
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