Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Chordomas of the Skull Base Chordomas are relatively rare neoplasm arising from embryonic notochordal remnants and comprise less than 1% of intracranial neoplasms. They typically occur along the neuraxis, especially at the developmentally more active cranial and caudal ends, notably in the spheno-occipital, sacrococcygeal, and vertebral locations. Twenty-five percent to 40% of chordomas occur in the speno-occipital or skull base region. These tumors occur predominately in the 30 to 50 year old age range and show a slight predominance in men. These tumors can occur extra-axially, in unusual locations, and are then termed primary. They probably arise from ectopic notochordal elements. Chordomas have been described in the nasopharynx, mandible, maxillary sinus, frontal sinus, and, as in our case report, in the petrous apex of the temporal bone. In 1856 Luschke, working in Virchow's lab, described jelly-like tumors in the region of the clivus of Blumenbach. In 1857 Virchow also examined these tumors and named them "ecchondrosis physaliphora." He believed they arose from the spheno-occipital synchondrosis and were of cartilaginous origin. Muller, in 1858, examined embryonic tissues and, after noting their histologic similarities, postulated these tumors derived from embryonic notochord. In 1895 Ribbert demonstrated the origin of these tumors when he pierced the nucleus pulposus of the vertebral column and found that similar tumors developed. He applied the term "chordoma" to these tumors. The embryonic development of the notochord is important in understanding the anatomic distribution of these tumors. The primitive streak forms in the third week of fetal development and forms the notochord. During the fifth week of life, it extends from the coccyx cephalad to the skull base, where it courses through the odontoid process, the posterior sphenooccipital plate and ends at Rathke's pouch. The notochord becomes surrounded by mesodermal tissue which then forms the vertebral column. Ultimately the notochord disappears, but remnants persist in the nucleus pulposus of the intervertebral discs. Binkhorst et al described seven points of origin of craniocervical chordomas: the dorsum sellae, the Blumenbach's clivus, retropharyngeal region, squama occipalis, nuclei pulposi of cervical vertebrae, and the ligament of the dens. SYMPTOMS The clinical presentation depends on the origin and extension of each particular tumor. Delay in diagnosis is common, secondary to the occult nature of the disease and poorly localizing signs and symptoms. A headache arising in the vertex, ipsi-parietal, orbital, or frontal regions is a typical early symptom. This is due to stretching of middle fossa dura and is often severe. Patients may also present with paresthesias or anesthesia of the jaw region, serous otitis media, hearing loss, nasal obstruction/anosmia, syncope and, rarely, vertigo. Recurrent meningitis has also been noted in these patients. The late symptoms generally depend on the direction of tumor extension. Anterior extension leads to diplopia and ophthalmoplegia, or both. Posterior extension presents as facial or other lower cranial nerve neuropathies. RADIOGRAPHIC FEATURES CT findings of an expansile, destructive, lytic lesion with associated soft tissue mass are characteristic of chordomas. However, they are also seen with chondrosarcomas and other similar lesions. Foci of calcification may also be seen. The CT scan is useful in defining the anatomy of bone destruction. MRI is better than CT for defining the limits of a lesion and any vascular relationships, especially on the T2-weighted images. MRI of chordomas show hyperintensity in T2 and hypointensity in the T1-weighted images. The T1 images are especially useful in defining any tumor-SCF interfaces. On arteriogram, an avascular may be seen displacing the basilar artery. Radiographic studies cannot reliably distinguish chordomas from chondrosarcomas and other similar lesions, but can help eliminate other possible diagnoses. DIFFERENTIAL DIAGNOSIS Benign lesions most frequently occurring at the skull base include: meningiomas, neuromas/schwannomas, glomus tumors, vascular anomalies (e.g., internal carotid aneurysms), congenital cholesteatoma, mucocele, osteomyelitis, eosinophilic granuloma, and cholesterol cysts. Malignant lesions of this location include primary carcinoma (squamous-, adeno-, acinic, adenoid cystic), metastatic carcinoma (breast, prostatic, renal cell, bronchogenic), rhabdomyosarcoma, nasopharyngeal cancer, lymphoma and chordoma, and other mesenchymal tumors (chondroma, chondrosarcoma, and osteoclastoma). HISTOPATHOLOGY Four criteria have been used in the histologic diagnosis of chordoma: 1) a lobular arrangement of cells; 2) a tendency of the cells to grow in cords, irregular bands, or pseudoacinar forms; 3) production of abundant intercellular mucinous matrix; and 4) the presence of large physaliphorous cells. A microscopically mixed population of cell types exist: stellate or primordial cells, intermediate cells and the physaliphorous cells. The stellate cell is the only actively proliferating cell. Chordoma cells then proceed through a stage of vacuolization until they reach the characteristic physaliphorous appearance. The cells then progress to destruction and rupture, completing their life cycle. Immunohistochemical tests have been developed in an effort to aid in the differentiation of these lesions. Chordomas are frequently positive for epithelial antigens - cytokeratin (CK) and epithelial membrane antigen (EMA), and negative for vimentin. A subtype of chordoma, chondroid chordoma, deserves special mention. Histologically these tumors are a mixture of chordoma, chondroma, and chondrosarcoma. PROGNOSIS AND TREATMENT The reported average survival for chordomas of the skull base is 4.1 years. There appears to be a better prognosis for chordomas of the nasopharynx and paranasal sinuses. Notably, chondroid chordomas have a reported 15.8 years average survival. The best treatment for these lesions is total surgical excision. Recurrence is the rule and metastases are extremely uncommon; patients usually succumb to local disease. Radiation therapy has been used in the postoperative care of these patients because of the tumor's usual relentless course to local recurrence and death with current conventional treatments. Fractionated proton radiation therapy is currently advocated for the treatment of chordomas. Because of its higher biological effectiveness, patients can be treated with a higher total equivalent radiation dose. Case Presentation A 57-year-old white female presented with a six- to nine-month history of intermittent left temporal headaches. They occurred monthly and usually lasted three days. She had no complaints of visual difficulties, hearing loss, vertigo, hoarseness, or dysphagia. Her past medical, surgical, and family histories were unremarkable. On physical exam she was found to be healthy. All cranial nerves were functionally intact. An MRI of the brain was done and revealed a signal abnormality of the left petrous apex and adjacent basiocciput with associated enhancement. A CT scan of the head and cervical spine showed a destructive, lytic lesion of the left basiocciput just anterior to the jugular foramen and anterolateral to the foramen magnum with probable erosion of the carotid canal. A full metastatic workup ensued including routine laboratory work, chest x-ray, mammogram, CT of the abdomen and pelvis, thyroid ultrasound, and serum protein electrophoresis. No significant abnormalities were found. A radionucleotide bone scan showed no additional bony lesions. Four vessel cerebral angiogram was negative for vascular abnormality. Three months later a follow-up CT scan of the head with thin cuts of the temporal bone showed a 1.5 X 2 X 1 cm lytic lesion corresponding with the previously identified lesion, but slightly increased in size. The bony margins of the lesions were irregular and suggestive of an aggressive process. She was then referred for surgical evaluation. She underwent a joint neurotologic and neurosurgical procedure comprised of a combination left type B infratemporal fossa and temporal fossa approach with biopsy and removal of the tumor. Frozen section revealed the tumor to be a chordoma. The patient tolerated the procedure well and had an uneventful postoperative course. The patient has been referred to Boston for fractionated proton radiation therapy. Bibliography Austin-Seymour M, Munzenrider J, Boitein M, Verhey L, Urie M, Gentry R, et al. Fractionated proton radiation therapy of chordoma and low-grade chondrosarcoma of the base of the skull. J Neurosurg 1989;70:13-17. Batsakis JG. 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