As a result of reading this article, physicians should be able to:
1. Recognize the epidemiológica I data and clinical manifestations of chordorna.
2. Discuss the imaging and histological features.
3. Formulate a reasonable differential diagnosis.
4. Determine recommended treatment of patients with chordoma, including surgery and adjuvant modalities.
Chordoma is an uncommon malignant bone tumor that occurs in the midline of the axial skeleton. Excluding plasmalocyioma, chordoma is the most frequent primary malignant tumor of the spine, occurring mainly in elderly men.M Chordoma may develop at any point of the original notochordal tract but it is usually noted at the rostral and caudal ends (the basiocciput and the sacrococcyx).
In 1857, Virchow was the first to recognize chordoma as a pathological entity and described the "bubble-bearing" physaUferous cells as being typical of the tumor.5 He later confirmed the lesion's embryonic origin from remnants of the notochord and explained its characteristic location at the vertebral column and skull base.5 During skeletal development the notochord degenerates and remains as the nucleus pulposus component of the vertebral disk. It has been proposed that the incomplete degeneration of the residual notochord can become neoplastic. Interestingly, the tumor seems to arise from within the vertebral body and not directly from the nucleus pulposus, with more than one vertebral body affected in half of the cases.6-7
Chordomas account for only 1% to 4% of primary bone tumors.1·4 However, more than half of the primary bone tumors of the sacrum are chordomas. Chordomas are usually located in the sacrum (50%), followed by the clivus (35%). More specifically, one-sixth of chordomas arise in cervical, thoracic, and lumbar spine, with the latter involved in 33% of cases.2·8·9 If the cervical spine is affected, this preferentially concerns its upper part.6,8
The majority of sacrococcygeal located lesions present in patients aged between 50 and 70 years and are rare in patients aged <30 years. The lesions arising at the spheno-occipital region present a decade earlier than sacrococcygeal lesions, possibly because they have less space to grow before causing symptoms.7 Both genders are equally affected by cranial chordomas, whereas in sacrococcygeal tumors, the male-to-female ratio is approximately 2:10-12
Figure 1 : Sacral chordoma in a 50-year-old man. AP (A) and lateral (B) radiographs show osteolysis of the S2-S4 segments. CT scan shows destructive lésion (C). Sagittal (D) and transverse (E) T1 -weighted MRI of the sacrum show Involvement of the right part of the sacrum with posterior tumor soft-tissue extension.
Signs and symptoms depend on the location of the tumor. In most series, the mean time lapse between the beginning of the symptoms and diagnosis was 15 months (range: 2 weeks to 8 years). This is due to rare location, slow growth, occult clinical presentation, and nonspecific low-back or cervical pain and imaging appearance. By that time, the tumor can be quite large.
In the sacrococcygeal region, the tumor has space to grow and it is large enough at the time of the diagnosis. The primary presenting symptoms are extremity weakness (55%), painful and palpable sacral mass (35%), sacral pain/altered sensation (25%), bowel (constipation) and urinary (frequency and incontinence) dysfunction (20%). l2 According to a series reported by Boriani et al,1-1 the constant complaint was a slow and gradual onset of pani in 82% of patients. With further neoplastic progression, pain may be referred to the hip or knee and late in the course, it may become severe and intractable. Pain may be caused by anterior displacement of the soft tissues and tension on the presacra] fascia. The tumor usually displaces but does not invade the rectum or the bladder, and on recta] examination, a presacral mass is usually palpable.7·14 In a series of patients with sacrococcygeal chordomas, none of the lesions was found to have breached the rectal wall, reinforcing the argument that the presacrai fascia is very resistant to tumor invasion.12-15
Neurological symptoms and signs are more common in chordomas of the mobile spine than in the sacrococcygeal region.2,9,16,17 Neurological deficits vary from compressive myelopathy or nerve root compression as result of tumor invasion into the foramina, or pressure on nerve roots or the spinal cord. Patients may have numbness in an extremity followed by pain and many develop motor weakness. Paralysis is a late complication.
Primary symptoms of skull base located chordomas are visual disturbances (75%), craniofacial pain (38%), headaches (25%), dysphagia (12%), and neurologic dysfunction such as transient ischemie attacks on the contralateral side (middle cranial fossa and clivai tumors).6,7,12 Diplopia and facial pain are prime clinical presentations in cranial lesions. Cervical pain with or without radicular brachialgia may be caused by bone destruction, nerve compression, or by increased mobility of the vertebral segments. Posterior tumor growth leads to radicular pain or compressive myelopathy with paraparesis. Anterior growth is reported in 12% of the cases, leading to local compression symptoms such as dysphagia, breathing difficulties, and anterior cervical palpable soft-tissue mass.6,18,24
Whether occurring in the sacrum or above it, the plain radiographie appearance of the tumors is similar. On standard radiographs it is difficult to detect lesions in their early phase of development6,24 and occasionally the lesion is not discovered and is detected only by computed tomography (CT) or magnetic resonance imaging (MRI) scan. 13 They appear mainly as large osteoiytic lesions, with focal areas of amorphous calcification due to reactive bone formation, and adjacent soft-tissue mass.2,6,7,12,13 The lesions are poorly marginated and may be difficult to discern in the sacrococcygeal region (Figure 1). In the vertebral body, the chordoma is rytic and centrally located. Vertebral collapse may occur, and adjacent vertebral bodies and disk spaces may be involved. The disks usually are spared. Extension of the sacrococcygeal lesions into the pelvic cavity and invasion of the glutea! muscles and sacroiliac joints are findings indicative of their aggressive nature.12
Figure 2: Ghordoma of C-2 vertebra in a 68-year-old woman. Lateral radiograph shows a destructive osteotytic lesion of C-2 vertebra (A). Bone scintigram shows increased radioisotope uptake (B). CT scan shows osteotysis of the C2 vertebral body (C). T1- (O) and T2- (C) weighted MRI shows anterior and posterior tumor soft-tissue extension.
Computed tomography is of particular importance to assess bony involvement and soft-tissue extension, and can identify calcified areas not evident on plain radiographs (Figure 2). After intravenous contrast administration, the lesions have been reported to become mottled.6,25,26 Computed tomograph- myelography is helpful in evaluating the epidural extension and the degree of compression on neural elements, to detect subarachnoidal métastases, and in the planning of surgical resection of a vertebral lesion.6,7,20,22,27-29
Magnetic resonance imaging is the best method to detect the tumor extension and cord compression, and to identify local recurrence and islands of tumor in the surgical scar tissue after surgical resection.6,7-30 In Tl-weighted images, the tumor is either isointense or slightly hypointense to surrounding muscles (Figure 3). In T2-weighted images, they show high signal, and intralesional septations, particularly obvious in the sacrococcygeal lesions, and a tendency to dense enhancement after administration of intravenous contrast (Figure 1 ).
The role of bone scan is questionable in assessment of chordomas and the accumulation of radioisotope in the bladder can obscure the sacral area.7
Angiography is occasionally indicated to identify the proximity of a cervical chordoma to adjacent arteries.7 In a series of 19 patients with chordoma, tumor encasement of the internal carotid artery was depicted in post contrast scans in virtually all patients in which the petrous apex, the middle cranial fossa, and the parasellar regions were invaded, although none of the vessels were constricted.12
The radiographie differential diagnosis includes metastatic disease, and other primary or secondary spine tumors, such as multiple myeloma, giant-cell tumor, chondrosarcomas, neurogenic tumors, and tumor-like conditions such as spinal Paget's disease. Extension of the tumor into the neural foramen leads to its erosion, giving images similar to neurofibromatosis.2 2.4,7.16.30
Figure 3: Chordoma of L5 vertebra In a 60-year-old man. Sagittal T2-wetghted MRI shows increased signal of L5 with epidural tumor extension (A). Transverse T1 -weighted MRI shows significant spinal canal compromise (BJ.
Macroscópica!] y, chordoma is a lobulated, grayish, soft mass with a gelatinous consistency.1 It can be focally cystic or hemorrhagic and may be deceptively well circumscribed, although the tumor tissue often extends beyond visible boundaries. Translucent areas may give the appearance of a chondrosarcoma or mucous carcinoma. The periosteum of the affected bone may be elevated and a large soft-tissue mass is a common finding.2,7,16,17,31
Microscopically, the chordoma tissue resembles fetal notochord, with lobules separated by fibrous septa and different cell types (Figure 4). The basophilic extracellular matrix contains mucin and stains positive for glycogen. Occasionally, islands of bone or cartilage are visible. Immunohistochemicai stains show the different cell types to be positive for cytokeratin, which excludes the diagnosis of chondrosarcoma. Accurate diagnosis can be assessed with a small specimen obtained from trocar biopsy. They are also positive for epithelial membrane antigen, which supports its epithelial origin, and can be marked with S-100 protein.7,13,32 The most classic cell types, "physaliferous cells," have a round nucleus with multivacuolated cytoplasm giving it a bubbly appearance. Vacuoles may displace the nucleus at the periphery of the cell. The second classic cell type, "signet ring cells," has a single large vacuole giving it the characteristic appearance.2,7 In some chordomas, there is extensive nuclear pleomorphism and mitotic figures. However, no evidence has been found to correlate histológica! features of a conventional chordoma with clinical prognosis or the ability to metastasize.
Two histologie variants of chordoma have been described. The first is a chondroid chordoma, found almost exclusively in the spheno-occipital region and named for its similarity to cartilage neoplasms, lmmunohistochemically examination of any tissue having a cartilaginous appearance is necessary to avoid misdiagnosis of the lesion as a skull-base chondrosarcoma.33 In the initial description given in 1973, patients with this chordoma variant were thought to have a better outcome with prolonged survival. That finding has not been confirmed and recent studies show similar oncological outcome with patients having a conventional chordoma. It has also been proposed thai these variants, with features resembling cartilage but with epithelial phenotype, be termed "hyalmized chordomas."
The second variant is a dedifferentiated chordoma, predominantly consisting of mesenchyma! cells, found almost exclusively in the sacrococcygeal region. It possibly stems from a failure of differentiation of primitive cell types, so that the neoplastic cells are capable of differentiation to either epithelial or mesenchymal phenotypes. Usually, it is not found at the initial presentation, but rather after multiple recurrences of a sacrococcygeal chordoma and it has been reported to occur with and without prior radiation therapy of a conventional chordoma.
Histological differential diagnosis includes Iiposarcoma, metastatic carcinoma, and myxoid chondrosarcoma of the spine, and is based on the characteristic histological features of the tumor (physaJiferous bubble-like cells, signetring cells, immunohistochemical stains and markers).1·4,7,32-33
Figure 4: Histological features of chordoma. High power appearance of a chordoma shows the characteristic small round nuclei and abundant vacuolated cytoplasm (A). A lobule of chordoma with mucmous background and chords of cells (B). (Printed with permission from Unni KK. Ghordoma. In: Dahlin's Bone Tumors: General Aspects and Data on 1 1,087 Cases. 5th ed. Copyright © 1996, Lippincott Williams and Wilkins.)
In every case of a destructive lesion of the spine and sacrum, a biopsy should be performed after all imaging studies have been completed. Although it is reported in the literature, a transrecta] biopsy should not be performed, given the possibility of contamination of intervening tissue planes and tumor cell spreading.7,14,34 A posterior CT-guided needle or an incisional biopsy can be performed; and the definite treatment should not begin until a final pathologic diagnosis is made.
There is general agreement that complete surgical "en bloc" resection with wide, histologically proved, tumor-free margins is the treatment of choice in chordomas.2,6,7,12"14,35 Chordomas have a wellknown tendency to recur locally, and the recurrence rate seems to be related to incomplete resection.6·29 For recurrent tumors, surgery also is the treatment of choice.
In the sacrococcygeal region, wide tumor resection is more feasible than in the spine above. However, these lesions usually are large and adherent to surrounding musculature and tend to adhere to the bowel; so a marginal resection is often the best that can be done. Low sacrococcygeal lesions are approached posteriorly and more cephalad lesions often require a combined anterior and posterior approach in the same operative setting. The sacral nerve roots should be sacrificed, if necessary, to obtain a wide margin, although preservation of the S2 roots is imperative for patients to retain rectal and bladder control. Transabdominal approach allows creating a plane between the rectum and the sacrum, removing the rectum away from it, prior to bone cuts, which are made via sacral approach, thus protecting the rectal wall from damage. In addition, transabdominal ligation of the hypogastric vessels helps decrease blood loss. For high sacral lesions, a complete lumbosacral resection including plans for a colostomy should be anticipated.7,14,36
In the mobile spine, wide tumor resection (vertebrectomy or total spondylectomy) should be followed by spinal instrumentation to maintain stability or to reconstruct the spine after tumor removal. Spinal reconstruction can be achieved with the use of allograft or autogenous bone graft (ribs and iliac crest) and anterior or posterior stabilization using instrumentation.13 Anterior methylmethacrylate reconstruction after vertebral tumor resection and posterior segmental instrumentation has already been proved useful in spinal neoplasms.2-17'4-1' Thoracic lesions should be approached via thoracotomy, although when both anterior and posterior vertebral components are involved, a staged total spondylectomy must be preferred, including an anterior approach for tumor resection and spine reconstruction, followed by a posterior approach for completion of the resection, arthrodesis and stabilization. The same can be attempted in the lumbar spine, although a retroperitoneal approach is usually adequate for middle to lower lumbar lesions.2,9,16,46
In the cervical spine, wide "en bloc" resection is rarely feasible, and more often the surgeon must perform intralesional procedures, removing the tumor piecemeal, carefully protecting the surrounding tissues from tumor dissemination.8 The dura is commonly invaded, and to achieve a "wide margin" it must be resected together with the tumor.4 Therefore, a primary tumor debulking is indicated, taking care not induce spinal stability, and secondary, the further therapeutic scheme is set between additional surgery or adjuvant radiotherapy and chemotherapy. Because of the nature and course of these neoplasms, total removal should be the goal.4 The tumor can be approached via a lateral interscalene approach, a bilateral anterolateral approach as proposed by Lesoin,6·47 or via a unilateral (left) anterior approach. Intercorporal fusion is achieved by bone grafting and spine instrumentation. Stabilization in a halo vest has also been proposed, as an alternative for spine osteosynthesis. Bony fusion over several segments has been described as well as fusion with PMMA.6,20,28'47,48 Chordomas at the base of the skull, although small, are usually difficult to remove because of their inaccessibility and proximity to vital structures.
Although chordomas are relatively radioresistant, adjuvant radiotherapy has been used for surgically inaccessible lesions, contaminated surgical margins, when incomplete surgical excision of the tumor occurs, and to improve the quality of life and relieve pain in patients with widespread recurrences. The value of radiation for controlling the disease is not conclusively proved.12-15,49 There are reports of increased disease-free intervals with radiation therapy, as well as reports mat suggest no benefit from its use. The real value of radiotherapy needs to be addressed in future prospective studies, which however are difficult given to the rarity of this tumor.
There is no consensus in the literature regarding the optimal irradiation scheme for chordomas. In most series, the range of irradiation dosage is 4000-7000 cGy, with a mean dose of 5500 cGy.l3J5JO The amount of irradiation is limited by the sensitivity of the spinal cord in cranial and cervical lesions, and by the sensitivity of the pelvic organs and the skin in more caudal regions. Wound healing problems contribute to high morbidity after radiotherapy and there are reports of post-irradiation malignant neoplasms development in patients with chordomas.
There is no consensus about the time of administration of adjuvant radiation therapy. The therapist is often faced with the choice of either administering radiation after the initial treatment of the primary tumor (initial radiation), or saving it for use at a later stage, if a local relapse should occur. The current results indicate that when the surgical margin is positive, the earlier use of radiotherapy is associated with a better prognosis and disease-free interval.14,35,49,51'53 Generally megavoltage radiotherapy is used, ideally proton beam radiation to facilitate the use of high local concentration without structural damage.
Cryotherapy has been used in the treatment of a small number of patients with chordoma. Short-term results are good, however serious complications occur as a result of this treatment, including infection of the locally frozen bone and postoperative bladder dysfunction. Chemotherapy has no current role in the management of chordoma.
PROGNOSIS AND OUTCOME
In sacrospinal chordomas, complete excision with adjuvant radiotherapy achieves the best results. In most series, the disease-free survival is reported to be >5 years.14,35,54 In a study at the University of Minnesota Cancer Center,35 in 23 patients with chordoma, the 5-year overall survival (time interval from diagnosis to death) was 86±15%, decreased to 49±-27% at 10 years. In the same study, ss the 5-year continuous free-disease survival was 58±-24%, decreased to 22±-25% at 10 years, and the 5-year local recurrence-free survival rate was 60±-25%, decreased to 43± -27% at 10 years.
Chordoma has a characteristic tendency to recur locally, and the recurrence rate appears to be related to incomplete resection.6,29 Complete surgical excision is the goal of therapy, especially for tumors in the sacrococcygeal region.12 Only primary and complete tumor excision offers a major prognostic advantage.6 A positive or close-cut surgical margin invariably leads to local recurrence and patients who develop recurrences are rarely disease free.14,55
In a series, 23 cases of chordoma were studied using univariate and multivariate analysis to identify the prognostic factors that affect survival.35 These factors include the proximal extension and size of the tumor, patient age and gender, rectal invasion, duration of symptoms, tumor extension beyond cortical bone, and the histologie features of the tumor.35 In this study, patient age was found significant only for local recurrence-free survival. Patient gender, rectal invasion, duration of symptoms, and tumor's extension beyond cortical bone were not found statistically significant. The tumor's size was found close to prognostic significance (P=.54) for metastasis.
ChoMomas of the mobile spine metastasize more often than sacrococcygeal lesions, with an incidence from 3% to 60%, between 1 and 16 years after the initial diagnosis.6,22,56 Métastases occur in the regional lymph nodes, as well as the skin, lung, liver, and bones. The presence of métastases seems not to affect the vital prognosis.6*22'56 Almost all patients die as a result of complications from local treatment failure rather than métastases, which are commonly asymptomatic and can also be irradiated.7 The proximal extent of the tumor is a strong predictor of tumor relapse, especially related to the tumor's size.35 The histologie features of the tumor are also of prognostic value. Chondroid chordomas have the same prognosis with conventional chordomas, compared to the dedifferentiated type that is quickly fatal, with metastatic lesions often comprised of the sarcomatous pattern.7
The functional outcome depends on the location of the tumor, the level of the surgical resection, and the remaining sacral roots.57,58 Spine stability can be assessed with the various known techniques of spine instrumentation. Pelvic stability can be retained as long as half the first sacral body is left intact (as shown in a cadaver study).7 In functional deficiency after sacral nerve resection, there is some disagreement in the literature. If only the S I level is preserved, loss of motor function is minimal, but no sphincter control will remain. The patient must then depend on abdominal muscles and posterior manual pressure for voiding, and if both S3 nerve roots are resected, the patient requires routine intermittent bladder selfcatheterization and bowel medications. If bilateral S2 roots are preserved, up to 50% of the patients may retain partial bowel and bladder control, and if at least one S3 root is spared, sphincter control will most likely be retained.7,58 Even if both S2 roots are preserved, some urinary and bowel dysfunction will exist in all patients, which may be managed with medications or intermittent catheterization. Only with the preservation of both S3 nerve roots bladder and bowel function is found to remain normal.35,57,58
Chordoma is a slow-growing, locally invasive, rare malignant tumor of the adult spine that possibly arises from the primitive notochord, and generally is located in the midline of the axial skeleton. It is known for its local recurrence tendency and late métastases, especially in cases of sacrococcygeal lesions. "En bloc," complete, wide margin surgical excision of the tumor, even if marginal in some areas (eg, epidural space), combined with adjuvant megavoltage radiotherapy seems to be the most effective treatment of the neoplasm.
Chordomas are generally radioresistant tumors, but radiation therapy must be used as adjuvant, for contaminated surgical margins and surgical inaccessible lesions, for pain relief, and when complete tumor excision was not achieved. The functional outcome after surgery depends on the level of resection, the remaining sacral nerve roots, and the stability of the vertebral spine. Statistically significant prognostic factors that affect disease-free survival were found to be the histologie features of the tumor, the size and location of the tumor, the proximal extension of the lesion, the patient's age, and especially, the type of surgical excision with tumor-free surgical margins.
1. Unni KK. Chordoma. In: Unni KK, ed. Dahlin 's Bone Tumors: General Aspects and Data on I i,087 Cases. 5th ed. Philadelphia, Pa: Lippincoti-Raven; 1996:291-305.
2. Manzone P. Fiore N, Furiino D, Alcalá M, Cabrera CF. Chordoma of the lumbar L2 vertebra: case report and review of the literature. Ear Spine J. 1998; 7:252-256
3. Parke W, Development of the spine. In: Rothman R, Simeone F, eds. The Spine. VoI I. 3rd ed. Philadelphia, Pa: W.B. Saimders; 1992:3-33.
4. Papagelopoulos PJ, Mavrogenis AF, Currier BL, et al. Primary malignant tumor of the cervical spine. Orthopedics. 2004; 27: 10671075.
5. Watkins L, Khudados ES, Kaleoglu M, Revesz T. Sacares P, Crockard HA. Skull base chordomas: A review of 38 patients, 1958-1988. Br J Neurvsurg. 1993; 7:241248.
6. D'HaenBD, DeJaegereT, Coffin J. Dom R, Demaerel P, Plels C. Chordoma of the lower cervical spine: case report. Clin Neural Neuivsurg. 1995; 97:245-248
7. Weber K, Sim FH. Chordoma. In: Bulstrode C, Buckwalter J, Carr A, et al (eds). Oxford Textbook of Orthopaedics and Trauma. New York, NY: Oxford University Press Ine; 2002:294-299.
8. Bahlman HH, Sachs BL, Carter JR, Riley L, Robinson RA. Primary neoplasms of the cervical spine. Diagnosis and treatment of twenty-three patients. J Bone Joint Surg Am. 1986; 68:483-494.
9. Bjornsson J, World LE, Ebersold MJ, Laws ER. Chordoma of the mobile spine. A clinicopathological analysis of 40 patients. Cancer. 1993,71:735-740.
10. Ashwood N, Hosicin PJ, Saimders MI. Metastatic Chordoma: pattern of spread and response to chemotherapy. Clin Oncoi (R Coll Radio!). 1994; 6:341-342
11. Forsyth PA, Cascino TL, Shaw EG et al. lntracranial cbordomas: a clinicopathological and prognostic study of 51 cases. J Neurosurg. 1993; 78:741-747.
12. Soo MY. Chordoma: review of clinicoradiological Features and factors affecting survival. Australas Radial. 2001; 45:427-434.
13. Soriani S. Chevalley F, Weinstein JN, et al. Chordoma of the spine above the sacrum. Treatment and outcome in 21 cases. Spine. 1996; 21:1569-1577.
14. Chandawarkar RY. Sacrococcygeal chordoma: review of 50 consecutive patients. World J Sarg. 1996:20:717-719.
15. Yonemoto T. Tatezaki S, Takenouchi T, Ishii T, Satoh T, Moriya H. The surgical management of sacrococcygeal chordoma. Cancer. 1999; 85:878-883.
16. Sundaresan N. Schmidek HH Schiller AL Rosenthal D. Tumors of the Spine: Diagnosis and Clinical Management. Philadelphia, Pa: W.B. Saunders: 1990.
17. Mindell E. Chordoma. J Bone Joint Surg Am. 1981; 63:501-505.
18. Bianchì PM, Marsella P, Masi R, et al. Cervical chordoma in childhood: clinical statistical contribution. Ini J Pediaír Otorhinolaryngoi. 1989; 18:39-45.
19. Chevalier X, Voisin MC. Brugieres P, et a!. Chordoma of the mobile spine. Report of 9 cases. Review of the literature [in French]. Revue da Rhumatisme et des Maladies OsíeO'Articulaires. 1990; 57:767-778.
20. Healey JH, Lane JM. Chordoma: a criticai view of diagnosis and treatment. Onhop Clin North Am. 1989; 20:417-426.
21 . Kamrin RP. Pótanos JN, Pool JL. An evaluation of lhe diagnosis and treatment of chordoma. J Neurol Neurosurg Psychiatry. 1964; 27:157-165.
22. Sundaresan N, Galicich JH, Chu FC, Huvos AG. Spinal chordomas. J Neurosurg. 1979; 50:312-319.
23. Sundaresan N. Chordomas. Clin Onhop. 1 986; 204: 1 35- 1 42.
24. Yuh WT, Lozano RL, Ftinckinger FW, Sato Y, Kao SS, Menezes AH. Lumbar epidural chordoma: MR findings. J Compai Assist Tomogr, 1989; 13:508-510.
25. Firooznia H, Golimbu C, Rafii M, Reede DL, Kricheff 11, Bjorkengren A. Computed tomography of spinal chordomas. J Comput Assist Tomogr. 1986; 10:45-50.
26. Meyer JE, Lepke RA, Lmdfors KK, et al. Chordomas: their CT appearance in the cervical, thoracic and lumbar spine. Radiology. 1984; 153:693-696.
27. Firooznia H, Pinto RS, Lin JP, Baruch HH, Zausner J. Chordoma: radiologie evaluation of 20 cases. AJR Am J Raentgenol. 1976; 127:797-805.
28. Godard J, Jacquet G, Pageaut G, Farhat O, Steimle R. Cervical chordoma. Apropos of a case Iin French]. Nettrosurg. 1990; 36:388393.
29. Krol G. Sze G, Arbit E. Marcove R, Sundaresan N. Intradural métastases of chordoma. AJNK Am J Neuroradioì. 1989: 10:193-195.
30. Lane J, MerJcow R, Finerman G, HeaJey J. Paget's disease. In: Lane J, Heaiey J, eds. Diagnosis and Managemem of Pathologic Fractures. New York, NY: Lippincott Williams & Wilkins; 1993:65-81.
31. Rich TA, Schiller A. Suit HD. Mankín HJ. Clinical and pathological review of 48 cases of chordoma. Cancer, 1985; 56:182-187.
32. Walaas L, Kindblom LG. Fine needle aspiration biopsy in the preoperative diagnosis of chordoma: a study of 17 cases with application of electron microscopic, histochemical and imrminocytochemical examination. Hum Pathol 1991:22:22-28.
33. Mitchell A, Scheithauer BW, Unni KK, Forsyth PJ, Wold LE, McGivney DJ. Chordoma and chondroid neoplasms of the spheno-occiput. An immunohistochemicaf study of 4 i cases with prognostic and nosologie implications. Cancer. 1993: 72:29432949.
34. Bethke KP, Neifeld JP, Lawrence W Jr. Diagnosis and management of sacrococcygeal chordoma. J Surg OncoL 1991; 48:232-238.
35. Cheng EY, Ozerdemogfu RA, Transfeldt EE, Thompson RC Jr. Lumbosacral chordoma. Prognostic factors and treatment. Spine. 1999: 24:1639-1645.
36. Sung HW. Shu WP. Wang HM. Yuai SY, Tsai YB. Surgical treatment of primary tumors of the sacrum. CWn Orlkop. 1987; 215:91-98.
37. Bridwell KH, Jenny AB, Saul T, Rich KM, Gruhb RL. Posterior segmentai instrumentation (PSSI) with posterolateral decompression and debulking for metastatic thoracic and lumbar spine disease. Limitations of the technique. Spine. 1988; 13:1383-1394.
38. Emery SE. Hughes SS, Junglas WA, Herrington SJ, Pathria MN. The fate of anterior vertebral bone grafts in patients irradiated for neoplasms. CUn Orthop. 1994; 300:207-212.
39. Galasko CS. Spinal instability secondary to metastatic cancer. / Bone Joint Surg Br. 1991:73:104-108.
40. Harrington KD. The use of methylmethacrylate for vertebral-body replacement and anterior stabilization of pathological fracture-dislocations of the spine due to metastatic malignant disease. / Bone Joint Surg Am. 1981:63:36-46.
41. Kostuik J. Anterior spinal cord decompression for lesions of the thoracic and lumbar spine, techniques, new methods of internal fixation and results. Spine. 1983; 8:512-531.
42. O'Neil J. Gardner V, Armstrong G. Treatment of tumors of the thoracic and lumbar spinal column. Clin Orthop. 1988; 227:103-112.
43. Onimus M. Papin P, GangloffS, Laurain JM. Results of the surgical treatment of thoracic and lumbar vertebral metastasis. Rachis, 1995; 7:275-82.
44. Onimus M, Schraub S. Bertin D, Bosset JF, Guidet M. Surgical treatment of vertebral metastasis. Spin«- '986; 11:883-891.
45. Winter R. Anterior spinal cord decompression and spine stabilization for metastatic disease. A case report. Spine. 1982: 7:70-72.
46. Bas T, Bas P, Prieto M, Ramos V, Bas JL, Espinosa C. A lumbar chordoma treated with a wide resection. Ear Spine J. 1994; 3:1 15117.
47. Lesoin. Table Ronde de la Société de Neurochirurgie de langue Française (Dec 1988). Tumeurs primitives du rachis. Neurasurg. 1 989; 35:309-356
48. Murali R. Rovit RL, Benjamin MV. Chordoma of the cervical spine. Neurosurgery. 1981:9:253-256.
49. Catton C, O'Sullivan B, Bell R, et al. Chordoma: long term follow up after radical photon irradiation. Radiother Oncol. 1996; 41:67-72.
50. Lybeert ML, Meenvalddt JH. Chordoma: report on treatment results in eighteen cases. Acta Radiai Oncol. 1986; 25:41-43.
51. Azzarelii A, Quagliuolo V, Cerasoli S, et al Chordoma: natural history and treatment results in 33 cases. J Surg Oncol. 1988; 37:185-191.
52. Breteau N, Demasiare M, Favre At Leloup R, Lescraínier J, Sabattier R. Fast neutron therapy for inoperable or recurrent sacrococcygeal ehordomas, BH// Cancer. 1996; 83:142S-145S.
53. Samson IR. Springfield DS, Suit HD, Mankin HJ. Operative treatment of sacrococcygeal chordoma. A review of 21 cases. J Bone Joint Surg Am. 1993; 75:1476-1484.
54. Gray SW, Singhbandhu B, Smith RA, Skandalakis JE. Sacrococcygeal chordoma: Report of a case and review of the literature. Surgery. 1975:78:573-582.
55. Sundaresan N. Huvos AG, Krol G, Lane JM. Brennan M. Surgical treatment of spinal ehordomas. Arch Surg. 1987: 122:14791482.
56. Benoît J, Videcoq P. Hardy P. Durigon M. Spinal chordoma, A case report on chordoma of the L3 vertebra [in French]. Revue da Rhumatisme et des Maladies OsteoArticulaires. 1990; 57:557-561.
57. Gunterberg B, Norlen L, Stener B, Sundin T. Neurologic evaluation after resection of the sacrum. Invest Uroi(Berl). 1975:13:183-188.
58. Todd LT Jr, Yaszemski MJ, Currier BL, Fuchs B, Kim CW, Sim FH. Bowel and bladder function after major sacral resection. Clin Orthop. 2002; 397:36-39.