10.1177/1051228403257619ARTICLEJournal of Neuroimaging Vol 13 No 4 October 2003Sun et al: MRI of Spinal Ependymomas

MRI Features of IntramedullarySpinal Cord Ependymomas

Bo Sun, MD

Chungcheng Wang, MD

James Wang, MD

Ali Liu, MD

A B S T R A C T

Background and Purpose. To assess the magnetic resonance(MR) imaging characteristics of spinal intramedullaryependymomas. Methods. MR images were obtained from 60patients with spinal intramedullary ependymomas. All patientswere treated surgically, and pathological diagnoses were con-firmed. MR images of ependymomas and associated cystswere correlatedwith surgical findings.Results. Among 60 casesof intramedullary ependymomas, 39 were cervical and 11 tho-racic, and 10 were located at the conus medullaris and filumterminale. The lesions measured 1 to 10 vertebral segments inlength along the neuraxis, with a mean length of 3.7 segments.All tumors had slightly hyperintense signals on T2-weighted MRimages. Clear tumormarginswere seen in 77%of patients; 75%had uniform contrast enhancement. Rostral and caudal cystswere seen in 90% of all patients; all cysts were hypointense onT1-weighted images and hyperintense on T2-weighted images.The rostral cysts were 1 to 5 segments in length and caudalcysts 2 to 10 segments in length. Conclusion. Ependymomasoccur most often at the upper cord rather than in the conusmedullaris and filum terminale. Of the cervical and thoracicependymomas, most were cellular or epithelial types. Papillaryependymomas occurred exclusively in the conusmedullaris andfilum terminale. Rostral and caudal cysts are frequently associ-ated with intramedullary ependymomas. Clear tumor margins,more uniform enhancement, and central locations can help dif-ferentiate ependymomas from other intramedullary spinal cordtumors.

Key words: MRI, intramedullary ependymomas, spinal cord.

Sun B, Wang C, Wang J, Liu A.MRI features of intramedullary

spinal cord ependymomas.J Neuroimaging 2003;13:346-351.DOI: 10.1177/1051228403257619

Magnetic resonance (MR) imaging (MRI) is the diagnos-tic procedure of choice for intramedullary spinal cordtumors. Ependymomas and astrocytomas account for >

90% of all intramedullary tumors; however, because ofthe lack of specific imaging patterns, reliable differentia-tion between these 2 common intramedullary tumors canbe very difficult, if not impossible.1–6 With recentadvances in neurosurgical techniques, ependymomas,because they can be surgically cured in most cases, carry amuch better prognosis than astrocytomas. MRI, espe-cially contrast-enhanced imaging, not only shows theexact locations and extensions of intramedullary tumorsbut also allows the differentiation of tumor cysts com-pared with tumor-related benign fluid collection.Through the analysis of 60 cases of surgically proved spi-nal cord ependymomas, we found a few unique MRI fea-tures that can help distinguish ependymomas from otherintramedullary spinal cord tumors.

Methods

Between 1988 and 2000, MR images were obtained from60 patients with spinal intramedullary ependymomas atthe Beijing Neurosurgical Institute. All patients weretreated surgically, and pathological confirmations wereobtained. There were 40 male and 20 female patients.The patients’ ages ranged from 8 to 65 years, with a meanage of 37.6 years. In this group of patients, clinical historiesvaried from 10 days to 9 years, with a mean duration of25.6 months. MRI scans were performed with a 1.5-T unit(Signa). Routine MRI includes sagittal and axial spin-echo T1-weighted MRI (TR = 400 milliseconds, TE = 16-20 milliseconds) and sagittal fast-spin-echo T2-weightedMRI (TR = 3500 milliseconds, TE = 102 milliseconds).

346 Copyright © 2003 by the American Society of Neuroimaging

Received August 22, 2002, and in revised form January13, 2003, and April 24, 2003. Accepted for publicationApril 26, 2003.

From the Beijing Neurosurgical Institute, Beijing, People’sRepublic of China.

Address correspondence to Bo Sun, MD, Department ofNeuroradiology, Beijing Tiantan Hospital, Tiantan Xili,Beijing, People’s Republic of China. E-mail: paulsun@btamail.net.cn.

Gadolinium–diethylenetriamine pentaacetic acid (Gd-DPTA) (Magnevist, Schering, Berlin, Germany) was ad-ministered intravenously to all patients, and enhancedsagittal and axial spin-echo T1-weighted MR images werethen obtained. Tumors were categorized as cervical, tho-racic, or lumbar (including the conus medullaris andfilum terminale). The sizes of the lesions were classifiedaccording to the number of spinal segments involved.During the same period of time, 30 patients with astro-cytomas and 27 patients with hemangioblastomas wereoperated on at the Beijing Neurosurgery Institute; allcases were pathologically confirmed and provided thebasis for comparison with ependymomas. The tumor-enhancement patterns, tumor margins, and tumor cysts ortumor-associated syringes were analyzed and correlatedwith surgical findings.

Results

Among the 60 cases of intramedullary ependymomas, 39cases were cervical, 11 thoracic, and 10 lumbar. Allependymomas were centrally located inside the cord ascylindrical elongated masses (Figs 1–4). On axial images,rims of cord tissue could be identified in all patients. Incontrast with cases of astrocytomas and hemangio-blastomas, a complete rim of cord tissue could be seen inonly 43% of astrocytomas (13/30 cases) and 22% ofhemangioblastomas (6/27 cases).

Tumor Length

The lesions varied from 1 to 10 vertebral segments inlength along the neuraxis, with a mean length of 3.7 seg-ments. The lengths of cervical tumors ranged from 1 to 8vertebral segments, with a mean length of 4.4 segments.Thoracic tumors ranged from 1 to 6 segments in length,with a mean length of 3.2 segments. Lumbar tumorsranged from 1 to 4 segments long, with a mean length of 2segments.

Tumor Signal Characteristics

On unenhanced T1-weighted MR images, 42 lesionswere isointense, 16 slightly hypointense, and 2 slightlyhyperintense. All tumors were slightly hyperintense onT2-weighted MR images. Ependymomas enhanced in allpatients (60 cases) after the injection of Gd-DTPA. Forty-seven tumors enhanced slightly, and 13 enhanced mark-edly. Forty-five tumors (75%) had uniform enhancement;among them, 30 were cervical, 9 thoracic, and 6 lumbar.Fifteen tumors had heterogeneous enhancement; 9 werecervical, 2 thoracic, and 4 lumbar. On enhanced T1-weighted MR images, 77% (46 of 60 cases) of tumors hadclearly defined margins. Among 30 cases of intra-

Sun et al: MRI of Spinal Ependymomas 347

Fig 1. Male, 31 years old, cervical intramedullaryependymoma. Typical appearance of an intramedullaryependymoma on a T2-weighted (MR) image (top left) and T1-weighted MR image (top middle). Whereas the tumor wasisointense, the associated cyst had low signal intensity on T1-weighted MR imaging (MRI) and high signal intensity on T2-weighted MRI. Note the abnormal signal in the cord above theobvious cyst behind C1 to C2; this represented the early stageof tumor-related cyst, so it did not enhance (top right).This pa-tient had only mild neck pain and upper extremity dysesthesiaat that time; surgery was offered but was declined by the pa-tient. T2-weighted MR image (bottom left) and T1-weightedMR image (bottom middle) of the same patient 3 years later.Although the size of the tumor did not increase much, thetumor-related cyst enlarged tremendously, with the rostralcyst extending to the medulla, elevating the floor of the fourthventricle. By this time, the patient had developed quadri-paresis and dyspnea. Note that the early tumor-related cyst(hypeiintense on T2-weighted MRI, isointense on T1-weightedMRI, top left and middle) matured into a terminal-stage cyst(hyperintense on T2-weighted MRI, hypointense on T1-weighted MRI, bottom left and middle). The cyst signal wasdifferent from that of cerebrospinal fluid. Following gadolin-ium–diethylenetriamine pentaacetic acid injection, the tumorenhanced with a clear margin on T1-weighted MRI (bottomright).

medullary astrocytomas, only 5 cases had uniform en-hancement, and 7 cases had clear tumor margins (Fig 5).

Tumor-Associated Cyst

Tumor-associated cysts were seen in 54 patients (90%).Cysts were located centrally in the expanded spinal cord.All cysts were hypointense on T1-weighted images and

hyperintense on T2-weighted images. Sixty-five percentof cysts had slightly different signals than that ofcerebrospinal fluid (CSF) (Fig 1); the rest (35%) had a sig-nal identical to that of CSF (Fig 4). The rostral cystsranged from 1 to 5 segments in length, with a mean lengthof 2 segments. The caudal cysts ranged in length from 2 to10 segments, with a mean length of 4.8 segments. In 26 pa-tients, cervical cysts extended above the level of the py-

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Fig 3. Female, 12 years old, cervical-thoracic intramedul-lary ependymoma. T2-weighted magnetic resonance (MR)image (left) and T1-weighted MR image (middle). Isointensetumor extended from C4 to T3, with associated rostral andcaudal syringes. Note that there is a diaphragm within therostral syrinx. T1-weighted MR image (right) after contrastshows that the tumor enhanced homogeneously, with a clearmargin. Note that the diaphragm within the syrinx did not en-hance.Biopsy of the diaphragm showed fibrous tissue withouttumor cells.

Fig 4. Male, 25 years old, cervical intramedullaryependymoma. T2-weighted magnetic resonance (MR) image(left) and T1-weighted MR image (second from left).Isointense expansion of the cord from C2 to T1, with large sy-ringes at both the rostral and caudal ends of the tumor. T1-weighted MR image (second from right) after contrast showshomogeneous tumor enhancement with sharp demarcation.Postoperative T1-weighted MR image demonstrates com-plete tumor resection and resolution of large rostral cyst.

Fig 5. Female, 29 years old, cervical intramedullaryastrocytoma. T2-weighted magnetic resonance (MR) image(left) and T1-weighted MR image (middle). Cord was ex-panded from C3 to C7 by a uniform mass lesion. The tumorwas hyperintense on T2-weighted MR image and slightlyhypointense on T1-weighted MR image. Note that the tumorwas not accompanied by any syrinx. T1-weighted MR image(right) after contrast shows that the tumor enhanced heteroge-neously without clear tumor margins.

Fig 2. Female, 49 years old, cervical intramedullaryependymoma. T2-weighted magnetic resonance (MR) image(left) and T1-weighted MR image (second from left).Isointense expansion of the cord from the foramen magnum toT2, with small syringes at both the rostral and caudal ends ofthe tumor. T1-weighted MR image (second from right) aftercontrast shows homogeneous tumor enhancement with sharpdemarcation. Note that the portion of the cervical cord be-tween the top syrinx and main tumor started to form a syrinx aswell. Postoperative T1-weighted MR image demonstratescomplete tumor resection and resolution of tumor-relatedsyrinx.

ramidal decussation, elevating the lower half of the fourthventricle floor (Figs 1, 4). Most rostral cysts (75%) werelarger than caudal cysts. Cysts inside the tumors from ne-crosis were seen in 6 patients (Fig 6). Cystic tumors can bedifferentiated from tumor-related benign cysts by theircapsule enhancement (Fig 6).

Surgical and Pathological Findings

A midline surgical approach was used for all our patients.After laminectomies and opening the dura, tumors wereresected under microscopes. Ependymomas, thoughlacking true tumor capsules, had well-defined marginsthat separated them from the surrounding cord tissue.Fifty-eight patients underwent total tumor resections. Themajority of rostral and caudal cysts contained clear andyellowish fluid. In 5 patients, cyst fluids were quite thickand viscous, even coagulating after being aspirated. In 2patients, rostral cysts contained no fluid at all but werefilled with fibrous tissue.

Ependymomas were soft and vascular tumors, mostrepresented as grossly tan to dark purple in color. Theywere lobulated and well circumscribed. Microscopically,tumor cells were either cuboidal or columnar aroundblood vessels. True rosettes, though not as common asperivascular pseudorosettes, could be seen. Seventy per-cent of spinal cord ependymomas were either cellular or

epithelial; myxopapillary variant was seen only at thefilum terminale.

Discussion

Ependymomas, as the most common spinal cord tumors,account for about 60% of intramedullary cord tumors.1,7

Correct preoperative diagnosis is crucial for neurosur-geons, because most ependymomas are well demarcatedfrom cord tissue and can be totally removed, whereasastrocytomas always infiltrate the surrounding cord tis-sue, making total resection impossible.

Ependymomas originate from ependymal cells liningthe spinal central canal, and they grow along the long cordaxis in both directions. Pathologically, ependymomas areclassified into 4 types: cellular, epithelial, papillary, andmyxopapillary. Mixed types can also be seen. In ourseries, most spinal cord ependymomas were either cellu-lar or epithelial. Some previous reports showed that inadult populations, ependymomas most commonlyoccurred in the lower cord, the conus medullaris, and thefilum terminale,1 but our series demonstrated that cervicaland thoracic ependymomas well outnumber lumberependymomas (50 to 10), similar to the findings of Fineet al.8 Whereas ependymomas from the upper cord aremore likely to be epithelial or cellular, lower cord ependy-momas are commonly either papillary or myxopapillary.It is generally believed that compared with that of intra-medullary astrocytomas, the incidence of ependymoma ishigher with increasing age1, however, in our series, themean age of patients was 37.6 years, with 80% (48 cases) ofpatients younger than 30 years old. The majority ofependymomas (52 cases) were symmetrically located inthe center of the cord, with cord tissue all around thetumors, a useful diagnostic feature.

On precontrast-MR images, ependymomas were iso-intense on T1-weighted MR images and slightly hyper-intense on T2-weighted MR image; partial signal hetero-geneity may have been related to tumor necrosis orhemorrhage. After Gd-DTPA injection, most tumorswere slightly enhanced, as opposed to intracranialependymomas, which are usually markedly enhanced.This enhancement pattern may have been related to thedense surrounding cord tissue and the lower disruption ofthe blood-cord barrier. Most ependymomas enhancedhomogeneously (75%), as opposed to astrocytomas,which enhanced either heterogeneously or not at all. Inour series, 77% of ependymomas (46 cases) had clear mar-gins on enhanced MRI, a characteristic feature ofependymomas that is useful in differentiating them fromastrocytomas. This is also compatible with surgical find-ings that ependymomas, although lacking capsules, are

Sun et al: MRI of Spinal Ependymomas 349

Fig 6. Female, 46 years old, cervical intramedullaryependymoma. T2-weighted magnetic resonance (MR) image(left) and T1-weighted MR image (middle) shows extensivecord enlargement, with a focal nodule at the C6 to T1 level.Syrinx extended above and below the tumor nodule. T1-weighted MR image (right) after contrast: tumor nodule wasremarkably enhanced, with tumor margins sharpened. Notethat the signal within the tumor cyst was lower than that of thesyrinx. The capsule of the cystic tumor clearly enhanced. Bi-opsy of the capsule demonstrated tumor cells; therefore, thecapsule of the cystic tumor was completely removed surgi-cally.

well demarcated from cord tissue. Gross tumor hemor-rhages, as manifested by short T1 signals, were seen inonly 2 patients, similar to the findings of Li and Holtas9

and Dillon et al.10

Several MRI features of tumor-related syringes werehelpful in distinguishing ependymomas from other cordtumors. First, tumor-related syringes were seen far morecommonly in spinal cord ependymomas (54 of 60 cases)than in astrocytomas (5 of 30 cases). Second, the length ofdistal syringes was longer than that of proximal syringes(4.8 and 2 segments, respectively), but the diameter ofproximal syringes was larger than that of distal syringes.Third, syringes in the upper cervical cord could extend upto the medulla oblongata, or even above the normal loca-tion of pyramidal decussation, resulting in a characteristicsign (ie, the elevation of the lower half of the fourth ven-tricular floor).

Tumor-related cysts can be classified into 3 types. Thefirst type includes cystic tumors, most likely resultingfrom tumor necrosis or hemorrhage. The second typeoriginates from disturbances of CSF circulation, resultingin syrinx formation; in our series, these cysts had a signalidentical to that of CSF. The third type of tumor-associatedcyst, which is the most commonly seen, includes thoselocated at either the proximal or the distal end of thetumor. In our series, these cysts had slightly different sig-nals than that of CSF and tended to be smaller thantumor-related syringes. When proximal cysts extend to

the dorsal medulla or the floor of the fourth ventricle, theyare also called medullary cysts or bulbar cysts. The forma-tion mechanism of these tumor cysts remains elusive.9–12

Possible mechanisms include myelomalacia from poorcord blood supply, fluid accumulation resulting frompoor spinal cord drainage, and degrading products fromtumor necrosis or hemorrhage. According to our observa-tions, most rostral and caudal cysts are reactive productsof cord tumors. The accumulation of liquefied productsfrom tumor necrosis or hemorrhage may also contributeto cyst formation. The thick, yellowish cyst fluid foundduring the ependymoma surgery was clearly differentfrom the CSF-like fluid within a simple syrinx, indicatingthat the mechanism of cyst formation is quite different inthese 2 diseases. Our observations demonstrate thatependymoma-related cyst formation has 2 stages. In thefirst stage, small, isointense cysts appear within the centralgray matter at both ends of the tumor. Then the cystsextend along the cord axis, the initial isointense cystsmaturing to hypointense cysts in the second stage (Fig 1).The development of CSF circulation disturbance mayalso contribute to the enlargement of tumor-related cysts,as the inflow outpaces the outflow of CSF. This situationcan be aggravated by the tumor’s obstruction of spinalsubarachnoid space. This mechanism probably affectsdistal cysts more than proximal cysts. During surgicalresection, the cysts became communicated with sub-arachnoid space, and normal CSF circulation was rees-tablished, leading to the quick resolution of tumor-relatedcysts postoperatively (Fig 4). The fact that the distal cystsusually disappeared first also supports the above-men-tioned hypothesis.

In 6 patients, septa were observed inside the proximalcysts on saggital T1-weighted MR images (Fig 3). Biopsiesof these septa failed to show tumor cells. We concludedthat unenhanced septa or capsules, combined with a cystsignal identical to that of CSF, do not need to be removedsurgically.

Hemangioblastoma, on unenhanced T1-weighted andT2-weighted MR image, are usually isointense. They canalso be hyperintense on T2-weighted MR images, withprominent foci of high-velocity signal loss. Serpentineflow void signals, representing the dilated tortuous feed-ing arteries or draining pial veins, are commonly seen.Like ependymomas, cysts can be seen on either end of thetumor nodule, but they tend to be located near the pia sur-face rather than the center of cord. On T1-weighted MRimages, the signal intensity of the cysts is lower than that ofependymomas. On contrast-enhanced MRI, the tumornodules of hemangioblastomas often have strongerenhancement than that of ependymomas (Fig 7). Whenspinal hemangioblastomas are associated with Von

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Fig 7. Male, 49 years old, cervicomedullary hemangio-blastoma. T2-weighted magnetic resonance (MR) image (left)and T1-weighted MR image (middle). Homogeneously cystictumor, hyperintense on T2-weighted MR image, hypointenseon T1-weighted MR image, extending from dorsal medulla toC3.T1-weighted MR image (right) after contrast demonstratesa small, brightly enhanced tumor nodule; the cyst wall did notenhance.

Hippel-Lindou’s disease, multiple-enhancing nodulescan be seen, making it easier to differentiate fromependymomas.

Conclusion

Ependymomas occurred more commonly in the upperthan the lower spinal cord. The majority of patients (80%)presented before the age of 30. Ependymomas from theupper cord were more likely to be either epithelial or cel-lular; myxopapillary ependymomas were found almostexclusively at the conus medullaris or filum terminale.Rostral and caudal cysts could be identified in 90% of pa-tients. Compared with cases of astrocytomas, ependy-momas tended to be located more centrally and to haveclear margins and more enhancement on postcontrastMRI. The cervical cysts extended above the level of py-ramidal decussation, elevating the floor of the lowerfourth ventricle, a pathognomonic sign that is useful indistinguishing ependymomas from other cord tumors.

References

1. Osborn AG. Handbook of Neuroradiology. St. Louis, MO:Mosby; 1991:381-382.

2. Chamberlain MC, Sondy AD, Press GA. Spinal cordtumors, gadolinium-DTPA-enhanced MR imaging. Neuro-radiology 1991;33:469-474.

3. Parizel PM, Baleriaux D, Rodesch G, et al. Gd-DTPA-enhanced MR imaging of spinal tumors. Am J Roentgenol1989;152:1087-1096.

4. Scotti G, Scialfa G, Colombo N, Landoni L. MR diagnosis ofintramedullary tumors of the spinal cord. Neuroradiology1987;29:130-137.

5. Miyazawa N, Hida K, Iwasaki Y, Koyanagi I, Abe H. MRIat 1.5 T of intramedullary ependymoma and classification ofpattern of contrast enhancement. Neuroradiology 2000;42:828-832.

6. Koeller KK, Rosenblum RS, Morrison AL. Neoplasms ofthe spinal cord and filum terminale: Radiologic-pathologiccorrelation. Radiographics 2000;20:1721-1749.

7. Wiestler OD, Schiffer D, Coons SW, Prayson RA, Rosen-blum MK. Ependymoma. In: Kleihues P, Cavenee WK,eds. Pathology & Genetics of Tumours of the Nervous System.Lyon, France: IARC Press; 2000:72-77.

8. Fine MJ, Kricheff II, Freed D, Epstein FJ. Spinal cordependymomas: MR imaging features. Radiology 1995;197:655-658.

9. Li MH, Holtas S. MR imaging of spinal intramedullarytumors. Acta Radiol 1991;32:505-513.

10. Dillon WP, Norman D, Newton TH, Bola K, Mark A.Intradural spinal cord lesions: Gd-DTPA-enhanced MRimaging. Radiology 1989;170:229-237.

11. Kawakami N, Mimatsu K, Kato F. Intraoperative sonog-raphy of intramedullary spinal cord tumors. Neuroradiology1992;34:436-439.

12. Moriuchi S, Nakagawa H, Yamada M, Kadota T. Intra-medullary spinal cord meningioma: case report. Neurol MedChir (Tokyo) 1996;36:888-892.

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