DOI: 10.1148/rg.26si065020
RadioGraphics 2006;26:S111-S116
© RSNA, 2006
Best Cases from the AFIP
Myxopapillary Ependymoma of the Sacrum
Stephanie M. Shors, MD,
Tera A. Jones, MD,
Miral D. Jhaveri, MD and
Michael S. Huckman, MD
1 From the Department of Diagnostic Radiology and Nuclear Medicine (S.M.S., M.D.J., M.S.H.) and the Department of Pathology (T.A.J.), Rush University Medical Center, 1653 W Congress Pkwy, Chicago, IL 60612. Received March 6, 2006; revision requested April 12 and received May 10; accepted May 23. All authors have no financial relationships to disclose.
Address correspondence to S.M.S. (e-mail: sshors{at}yahoo.com).
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History
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A previously healthy 28-year-old man presented to the emergency department with right lower extremity swelling, which had been progressively worsening over the past 2–3 weeks. The patient had no history of fever, trauma, back pain, or bowel or bladder dysfunction. He had previously undergone ultrasonography of the right lower extremity, with the results being negative for deep venous thrombosis. Physical examination demonstrated 3+ pitting edema in the right lower extremity to the level of the inguinal ligament. Laboratory results were normal. Computed tomography (CT) revealed a large soft-tissue mass in the sacrum and probable thrombus extending from the distal inferior vena cava (IVC) to the right common femoral vein. The patient was admitted to the hospital for further evaluation.
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Imaging Findings
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The initial contrast material–enhanced CT scan of the pelvis showed a large, heterogeneously enhancing soft-tissue mass in the sacrum, eroding the sacral canal and invading the adjacent soft tissues (Fig 1). In addition, there was poor enhancement of the distal IVC, right and left common iliac veins, right external iliac vein, and right common femoral vein, findings that suggested the presence of thrombus.
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Figure 1. Contrast-enhanced CT scan shows an expansile soft-tissue mass located in the sacral canal (solid arrow) and extending into the presacral space (open arrow). The right common iliac vein (arrowhead) is poorly enhanced, a finding that suggests the presence of thrombus.
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Magnetic resonance (MR) imaging demonstrated a large, well-circumscribed lobulated mass arising from the sacrum and extending anteriorly into the pre-sacral space, posteriorly into the subcutaneous tissues, and superiorly into the spinal canal to the L5-S1 level (Fig 2). The mass measured approximately 10 x 7 x 5 cm in its greatest craniocaudal, anteroposterior, and transverse dimensions, respectively. The mass was isointense relative to the spinal cord on the T1-weighted images and heterogeneous but predominantly hyperintense on the T2-weighted images. There was heterogeneous enhancement after the administration of gadolinium-based contrast material, with a central unenhanced area that suggested necrosis (Fig 3). The contrast-enhanced MR images also demonstrated enhancing soft-tissue-intensity material in the mildly dilated distal IVC, right common iliac vein, and distal left common iliac vein, findings that were compatible with thrombus (Fig 4). Subsequent CT of the chest, abdomen, and pelvis showed no lymph node enlargement and no evidence of distant metastatic disease.
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Figure 2a. Sagittal T1-weighted (a) and T2-weighted (b) MR images show a lobulated expansile mass that has destroyed the sacrum and extended anteriorly into the presacral space and superiorly into the spinal canal. The mass is isointense relative to the spinal cord on the T1-weighted image and heterogeneous but predominantly hyperintense on the T2-weighted image.
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Figure 2b. Sagittal T1-weighted (a) and T2-weighted (b) MR images show a lobulated expansile mass that has destroyed the sacrum and extended anteriorly into the presacral space and superiorly into the spinal canal. The mass is isointense relative to the spinal cord on the T1-weighted image and heterogeneous but predominantly hyperintense on the T2-weighted image.
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Figure 4a. Sagittal unenhanced (a) and contrast-enhanced (b) T1-weighted MR images of the pelvis show enhancing soft-tissue-intensity material in the distal IVC (solid arrow) and in both proximal common iliac veins (open arrows), findings that are compatible with thrombus.
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Figure 4b. Sagittal unenhanced (a) and contrast-enhanced (b) T1-weighted MR images of the pelvis show enhancing soft-tissue-intensity material in the distal IVC (solid arrow) and in both proximal common iliac veins (open arrows), findings that are compatible with thrombus.
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Pathologic Evaluation
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The patient underwent open biopsy of the sacral mass, which revealed a myxopapillary ependymoma, followed by en bloc resection of the sacrum. During sacral resection, the retroperitoneal cavity was found to contain extensive adhesions, which resulted in adherence of the sacral mass to the rectum. The iliac veins were surrounded by these adhesions and appeared thickened and thrombosed. The vessels immediately surrounding the sacral mass were resected, but the large veins were left in place.
Gross pathologic analysis of the resected sacrum demonstrated a large necrotic mass occupying the sacral neural canal, extending posteriorly through the neural foramina and anteriorly into the sacral hollow, and destroying much of the sacrum (Fig 5). The total mass measured 10 x 9 x 8 cm. The exophytic portion of the mass in the sacral hollow was softer and more hemorrhagic than the rest of the mass and measured 6 x 5 x 3 cm. The tumor was covered by dura mater superiorly but extended through the dura mater anteriorly and posteriorly. Close pathologic inspection showed thrombi in the small and medium-sized vessels in the sacral hollow, and subsequent microscopic analysis revealed foci of tumor cells within and attached to the endothelium of these vessels (Fig 6).
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Figure 5. Photograph of the sagittally sectioned gross specimen from en bloc resection of the sacrum shows a large, lobulated mass occupying the sacral canal (solid arrow) and extending anteriorly into the sacral hollow (open arrow). Areas of hemorrhage and necrosis are present within the mass. S1 = sacral vertebra.
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Figure 6. Photomicrograph (original magnification, x 100; hematoxylineosin [H-E] stain) demonstrates a blood vessel (black arrows) containing tumor cells that distend the lumen and are focally attached to the endothelium. Fibrovascular cores can be appreciated within the tumor plug (white arrow). Arrowhead indicates a normal blood vessel.
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Microscopic pathologic analysis of the sacral tumor showed the typical histologic appearance of a myxopapillary ependymoma. The cells ranged from cuboidal to elongate. Despite the extensive permeation and destruction of the sacrum, there was only minimal nuclear variation and mitotic activity. In terms of architecture, the tumor had microcystic areas with cuboidal cells arranged around pools of basophilic mucinous material (Fig 7). The tumor cells were also arranged radially around fibrovascular cores with intervening mucinous material between the tumor cells and blood vessels (Fig 8). In some areas, the eosinophilic cytoplasmic processes could be seen oriented toward the fibrovascular cores (Fig 8, inset). The tumor cells were diffusely reactive for glial fibrillary acidic protein (GFAP) and S100 protein and negative for cytokeratins (Fig 9). Most of the tumor within the neural canal was necrotic and showed a reactive rim of neutrophils.
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Figure 7. Photomicrograph (original magnification, x200; H-E stain) shows cuboidal cells (arrows) arranged in a microcystic pattern with abundant basophilic mucinous material within the cystic spaces. There is minimal variation among the cells and no mitotic activity.
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Figure 8. Photomicrograph (original magnification, x 200; H-E stain) shows the cells, which range from cuboidal to more elongate, arranged around fibrovascular cores containing blood vessels (black arrows). Mucoid matrix material (arrowhead) is present between the cells and the fibrovascular cores. The photomicrograph in the inset, which was obtained at a higher magnification (x 400) with H-E stain, shows the eosinophilic cytoplasmic processes of the tumor cells oriented toward the blood vessel (white arrow).
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Figure 9. Photomicrographs (original magnification, x200) show the tumor cells to be diffusely reactive with GFAP (left), an immunohistochemical stain, and completely nonreactive with cytokeratins 8/18 (right), findings that support the diagnosis of myxopapillary ependymoma.
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Approximately 2 weeks after the initial surgery, the patient underwent bilateral common femoral cutdowns with thrombectomies of the IVC and bilateral common iliac, external iliac, common femoral, and superficial femoral veins. Pathologic analysis of the thrombectomy specimens from the iliac veins demonstrated recent thrombus without evidence of tumor infiltration.
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Discussion
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Ependymomas are the most common intramedullary spinal cord tumors in adults. Even so, they are quite rare, with only about 227 intradural spinal ependymomas diagnosed in the United States each year (1). The two most common ependymoma subtypes are cellular and myxopapillary ependymomas. Cellular ependymomas can arise anywhere but usually occur in the cervical cord, whereas myxopapillary ependymomas occur almost exclusively in the conus medullaris and filum terminale. Myxopapillary ependymomas demonstrate a slight male predilection and manifest earlier than do other spinal ependymomas, with a mean patient age at presentation of 36.4 years (2). Patients with these tumors typically present with low back pain with or without sciatica. Other symptoms, such as sensorimotor disturbances and bowel and bladder dysfunction, are much less common (2). Because most ependymomas of the cauda equina region are slow growing, the diagnosis is often delayed, with an average elapsed time of 2.3 years between symptom onset and diagnosis (3).
Myxopapillary ependymomas are believed to arise from the ependymal glia of the filum terminale and, thus, are typically intradural. Extradural myxopapillary ependymomas are rare, probably arising from extradural remnants of the filum terminale or the coccygeal medullary vestige (4). At gross examination, myxopapillary ependymomas are soft, vascular, lobular or sausage-shaped masses. They are often encapsulated and may demonstrate hemorrhagic or mucinous degeneration. These tumors are usually located within the filum terminale but may also extend into and incorporate the conus medullaris. Small tumors tend to displace the lumbosacral nerve roots, whereas large tumors may encase them. Myxopapillary ependymomas may grow quite large, filling and expanding the spinal canal. Tumors located near the sacrum can cause large areas of bone destruction, although such cases are rare (5,6). At histologic analysis, myxopapillary ependymomas are characterized by cellular areas mixed with papillary regions containing vascular cores and extensive mucoid matrix (2,4). They are typically reactive for GFAP and S100 protein (2).
Radiographs of myxopapillary ependymomas are usually normal but may show a widened spinal canal or bone destruction. Myelograms may demonstrate a well-defined intradural mass at the conus medullaris (7). On unenhanced CT scans, myxopapillary ependymomas are typically isoattenuating relative to the spinal cord (7). Small tumors may cause nothing more than nonspecific canal widening, whereas larger tumors may produce scalloped vertebral bodies, neural foraminal enlargement, and bone destruction. On contrast-enhanced CT scans, myxopapillary ependymomas typically demonstrate intense homogeneous enhancement (7,8).
The MR imaging features of myxopapillary ependymomas are nonspecific. Tumors are typically isointense relative to the spinal cord on T1-weighted images and hyperintense on T2-weighted images (9,10). Occasionally, they may be hyperintense relative to the spinal cord on un-enhanced T1-weighted images due to the proteinaceous mucoid matrix (10), a feature that may be useful in distinguishing myxopapillary ependymomas from other ependymoma subtypes, which are virtually always hypo- or isointense on T1-weighted images. Like the other ependymoma subtypes, myxopapillary lesions enhance intensely after the intravenous administration of contrast material. Enhancement is usually homogeneous but may be heterogeneous when hemorrhage or necrosis is present. MR imaging may also demonstrate expansion of the spinal canal and neural foramina, bone destruction, and invasion of the surrounding soft tissues.
The differential diagnosis for small myxopapillary ependymomas in the conus medullaris and filum terminale includes schwannoma and subependymoma, both of which can demonstrate imaging characteristics that are almost identical to those of small myxopapillary ependymomas (8,9). The differential diagnosis also includes astrocytoma, hemangioblastoma, ganglioma, paraganglioma, and other ependymoma subtypes. For large myxopapillary ependymomas that cause sacral destruction, the differential diagnosis should include sacral tumors such as aneurysmal bone cyst, chordoma, plasmacytoma, metastasis, and giant cell tumor (5,8).
Intradural lumbosacral ependymomas can spread throughout the central nervous system but rarely metastasize beyond it (1), whereas extradural ependymomas seldom disseminate within the central nervous system but pose a significant risk for systemic metastases (1,11–14). In one review of 45 extraspinal ependymomas, the prevalence of extraneural metastases was found to be 7% for presacral ependymomas and 17% for postsacral ependymomas (11). Other studies have reported prevalences ranging from 18% to 27% (12,14). The lungs are the most common site of spread, but metastases may also be seen in the liver, skeletal system, and regional and distant lymph nodes (11–13). Although vascular invasion and tumor thrombus formation are rarely described, the high prevalence of pulmonary metastases suggests that hematogenous dissemination occurs more frequently than lymphatic spread (12).
The treatment of choice for both intradural and extradural lumbosacral ependymomas is gross total resection (1). This treatment makes possible a cure without the need for adjuvant therapy. If possible, en bloc resection rather than piecemeal resection should be performed, since the latter has been associated with higher recurrence rates (2). The role of radiation therapy has not been adequately studied. Radiation therapy is probably warranted in cases of subtotal resection or recurrence of intradural tumors but is controversial in cases of total resection and extradural ependymomas (1,6). Chemotherapy has not proved to be beneficial and is usually reserved for recurrent disease that is refractory to resection and irradiation.
Patients who undergo gross total resection of intradural myxopapillary ependymomas have a good prognosis, with a mean survival time of 19 years (2). Unfortunately, patients with extradural ependymomas do not have the same prognosis. For postsacral tumors, the local recurrence rate is approximately 25% at 15 years (15); for presacral tumors, local recurrence rates as high as 60% have been reported (16). If local recurrence occurs, the mortality rate is 50% after 15 years with postsacral tumors and 75% after 4 years with pre-sacral tumors (11). If metastases develop, survival beyond 5 years is unlikely in patients with presacral ependymomas (11).
Our patient underwent en bloc resection of the sacrum with resection of the cauda equina. Although this surgical procedure resulted in the loss of sensorimotor function below the knees as well as the loss of bowel, bladder, and sexual function, it was believed to provide the best chance for long-term survival. The patient had a long, complicated hospital course but was ultimately able to return home to his family. Follow-up imaging performed 11 months after surgery demonstrated no evidence of tumor recurrence or metastatic disease.
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Footnotes
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Abbreviations: GFAP = glial fibrillary acidic protein, H-E = hematoxylin-eosin, IVC = inferior vena cava
Editor’s Note.—Everyone who has taken the course in radiologic pathology at the Armed Forces Institute of Pathology (AFIP) remembers bringing beautifully illustrated cases for accession to the Institute. In recent years, the staff of the Department of Radiologic Pathology has judged the "best cases" by organ system, and recognition is given to the winners on the last day of the class. With each issue of RadioGraphics, one or more of these cases are published, written by the winning resident. Radiologic-pathologic correlation is emphasized, and the causes of the imaging signs of various diseases are illustrated.
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References
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- Fassett DR, Schmidt MH. Lumbosacral ependymomas: a review of the management of intradural and extradural tumors. Neurosurg Focus 2003; 15(5):E13.[Medline]
- Sonneland PR, Scheithauer BW, Onofrio BM. Myxopapillary ependymoma: a clinicopathologic and immunocytochemical study of 77 cases. Cancer 1985;56:883–893.[CrossRef][Medline]
- Schweitzer JS, Batzdorf U. Ependymoma of the cauda equina region: diagnosis, treatment, and outcome in 15 patients. Neurosurgery 1992;30: 202–207.[Medline]
- Koeller KK, Rosenblum RS, Morrison AL. Neoplasms of the spinal cord and filum terminale: radiologic-pathologic correlation. RadioGraphics 2000;20:1721–1749.[Abstract/Free Full Text]
- Moelleken SM, Seeger LL, Eckardt JJ, Batzdorf U. Myxopapillary ependymoma with extensive sacral destruction: CT and MR findings. J Comput Assist Tomogr 1992;16(1):164–166.[Medline]
- Biagini R, Demitri S, Orsini U, Bibiloni J, Briccoli A, Bertoni F. Osteolytic extra-axial sacral myxopapillary ependymoma. Skeletal Radiol 1999;28: 584–589.[CrossRef][Medline]
- Chen MZ. Ependymoma, myxopapillary, spinal cord. In: Ross JS, Brant-Zawadzki M, Moore KR, Crim J, Chen MZ, Katzman GL, eds. Diagnostic imaging: spine. Salt Lake City, Utah: Amirsys, 2004; IV-1:110–113.
- Osborn AG. Tumors, cysts, and tumorlike lesions of the spine and spinal cord. In: Osborn AG, ed. Diagnostic neuroradiology. St Louis, Mo: Mosby-Year Book, 1994; 906–909.
- Wippold FJ, Smirniotopoulos JG, Moran CJ, Suojanen JN, Vollmer DG. MR imaging of myxopapillary ependymoma: findings and value to determine extent of tumor and its relation to intraspinal structures. AJR Am J Roentgenol 1995;165:1263–1267.[Abstract/Free Full Text]
- Kahan H, Sklar EM, Post MJ, Bruce JH. MR characteristics of histopathologic subtypes of spinal ependymoma. AJNR Am J Neuroradiol 1996; 17:143–150.[Abstract]
- Timmerman W, Bubrick MP. Presacral and post-sacral extraspinal ependymoma: report of a case and review of the literature. Dis Colon Rectum 1984;27:114–119.[Medline]
- Vagaiwala MR, Robinson JS, Galicich JH, Gralla RJ, Helson L, Beattie EJ. Metastasizing extradural ependymoma of the sacrococcygeal region: case report and review of literature. Cancer 1979;44: 326–333.[CrossRef][Medline]
- Thornton AS, Yudelman P. Anterior extrathecal ependymoma with systemic metastases: a case report and review of the literature. Clin Radiol 1988; 39:562–564.[CrossRef][Medline]
- Helwig EB, Stern JB. Subcutaneous sacrococcygeal myxopapillary ependymoma: a clinicopathologic study of 32 cases. Am J Clin Pathol 1984;81: 156–161.[Medline]
- Prins BA, Landsman JN. Sacrococcygeal myxopapillary ependymoma. Neth J Surg 1989;41:47–48.[Medline]
- Morantz RA. Ectopic ependymoma of the sacrococcygeal region. In: Doty JR, Rengachary SS, eds. Surgical disorders of the sacrum. New York, NY: Thieme Medical, 1992; 177–179.
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History
Imaging Findings
