{'fraction_non_alphanumeric': 0.024541720925573475, 'fraction_numerical': 0.014825202844836221, 'mean_word_length': 5.032628398791541, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Extra and Intramedullary Anaplastic Ependymoma in Thoracic Spinal Cord

Spinal ependymoma occupies 40-60% of primary spinal cord tumors and has a feature of intramedullary tumor. The tumor most commonly arises from the central canal of the spinal cord, the conus medullaris or the filum terminale and its pathological features are usually benign. Unlike above characteristics, intra and extramedullary ependymomas are reported very rarely and have wide variety of histological features. We present a rare case of spinal anaplastic ependymoma with an accompanied exophytic lesions extramedullary as well. The tumor was poorly delineated between a spinal cord and the extramedullary components in operative view. After we had confirmed the frozen biopsy as anaplastic ependymoma, the remnant mass embedded in the spinal cord was remained because of its unclear resection margin and the risk of neurological deterioration. She underwent radiotherapy with 50.4 Gy, and there were newly developed mass lesions at the lumbosacral region on the MRI, 14 months postoperatively.


INTRODUCTION
Spinal cord ependymoma, that is one of spinal cord glioma, is a slow growing tumor emerging from cells lining of central canal within the spinal cord 1,7,9) . They account for 60% of all intramedullary tumors 2,12) and their histopathological classification includes myxopapillary ependymoma (WHO grade I), subependymoma (WHO grade I), ependymoma (WHO grade II) and anaplastic ependymoma (WHO grade III) 14,24) . Ependymoma is usually presented as intramedullary tumor of spinal cord, however coexisting of intradural extramedullary (IDEM) components of spinal ependymoma is very rare. Most tumors located in the intradural extramedullary portion are schwannoma or meningioma, so ependymoma is not even considered in the differential diagnosis of IDEM spinal tumors 21) . According to the previous reports, there were 21 cases of primary IDEM ependymomas and 5 cases of exophytic ependymomas 11) . In this article, we report a rare case of thoracic anaplastic ependymoma with an exophytic component.

CASE REPORT
A 48-year-old woman had experienced a radiating pain on both legs for 6 months. For 1 month before visiting our department, a radiating pain was getting worse and she recognized newly developed lower extremity motor weakness and urinary incontinence. She underwent magnetic resonance imaging (MRI) that showed suspicious IDEM spinal mass which was well-enhanced on T1-weighted image with contrast and isosignal intensity on T2-weighted image at T7-T9. There were also intramedullary component and cord edema at T9-T10. The mass lesion was well-enhanced under gadolinium administration displacing the cord to opposite side severely (Fig. 1,  2). There was no evidence of mass lesion in the other site of central nervous system.
We planned the total resection of the intra and extramedullary mass lesions under the laminectomy. When the dura mater was opened, a dark-pink colored and encapsulated extramedullary component of the tumor was observed. The compressed spinal cord was displaced to right side and there were severe adhesion and ill-defined interface between the extramedullar mass and spinal cord. Under microscope, we removed extramedullary component totally, dissected the arachnoid layer around the cord connecting to extramedullary component and attempted to remove the intramedullary component in the spinal cord. However, we stopped resection   and left the residual portion of mass lesion on the cord with concern for the risk of neurological deterioration and intraoperative frozen biopsy of the extramedullary component.
Histological examination revealed a sort of high grade glial tumor. The cells were characterized by high cellularity and nuclear pleomorphism (Hematoxylin-Eosin stain, ×200) and there were perivascular pseudorosettes and microvascular proliferations. The cells presented immunoreactivity for glial fibrillary acidic protein (GFAP) and the S100, but negative for epithelial membrane antigen (EMA) and CD34 (Fig. 3). Ki-67 index was approximately 40%. The final diagnosis was anaplastic ependymoma, WHO grade III.
Postoperatively, the patient's neurological condition was improved in a lower extremity motor weakness except urinary incontinence. Six weeks after operation, she was planned to perform radiotherapy with 1.8 Gy in 28 fractions and total came to 50.4 Gy. There was recurrence of the tumor at the ventral epidural space with remnant component at the spinal cord of T8 level on the follow-up MRI just before the initiation of radiotherapy. The mass lesions of T8 level were disappeared and spinal cord atrophy was found on the follow-up MRI after radiotherapy. However, the patient's neurologic condition of the lower extremities was deteriorated again and there were newly developed mass lesions at the lumbosacral region on the MRI, 14 months postoperatively. It might be CSF dissemination. We recommend further treatment, but she refused.

DISCUSSION
Spinal ependymoma is almost presented as intramedullary tumor, and primary IDEM and exophytic ependymoma are rare.

Extra and Intramedullary Anaplastic Ependymoma
Korean J Spine 10(3) September 2013 179 It is thought that the spinal primary IDEM ependymoma may arise from heterotopic ependymal cells which were left in the intradural extramedullary space when the neural tube closes 6,7,19,21) . This hypothesis is supported by the following Cooper's descriptions 6,7,19,21) : (1) lack of an apparent attachment to the central nervous system, (2) absence of a primary neoplastic process within the brain or spinal cord, (3) the encapsulated appearance, location along the neuraxis and frequent association with congenital anomalies. The review of 21 cases of IDEM ependymoma 11) shows the ages ranging from 24 to 69 years old with female predominance 3,4,17,19) . The hormonal theory was proposed by Duffau et al. 7) , but it was not confirmed by any cytogenic or molecular study. Thoracic spine is the most common location for spinal IDEM ependymoma in contrast to intramedullary ependymoma that mainly affect the cervical spinal cord, the conus medullaris and filum terminale regions 3,7,22) . Intramedullary ependymoma with an exophytic component to IDEM space is very rare. There were only 5 reports about it 20) . Subependymoma, however, has a marked tendency to grow eccentrically within the cord or to show an exophytic component. The histogenesis of subependymoma has been a matter of debate over years, but it is currently thought that they may represent a variant of ependymoma 15, 16,23) . The tumor has a tendency to originate from the ependymal cells of the central canal, rather than from the IDEM space. It is highly improbable that the tumor grew into the spinal cord from outside of it. As tumors of brain stem and spinal cord grow along the path of least resistance, exophytic ependymoma of the spinal cord may grow longitudinally along the sensory and motor tracts or transversely along the root entry zone 8,23) . The intraoperative findings of primary IDEM ependymoma had shown well-circumscribed and encapsulated tumors that can be easily removed from the surface of the spinal cord. In the case of exophytic ependymoma, mid portion of the tumor arise from an intramedullary component and has not a clear dissection plane from the spinal cord 20) . However, exceptional cases were also reported that a thin stalk between tumor and spinal cord could be easily amputated by Kinsman et al. 18) and its pathological feature was WHO grade III. Moreover, primary IDEM ependymomas infiltrating arachnoid membrane were noted by Graca et al. 10) and Iunes et al. 17) . Abundant vascular infiltration into the pia mater was also reported by Robels et al. 22) and Guppy et al. 11) Their pathological findings were WHO grade III. Although the possibilities that tumor invades into the spinal cord from outside of it in high grade pathology, there were no reports to offer definite evidences on neither operation field nor MRI until now. In our case, an enhanced mass with an oval shape at T7-9 and a cord signal change at T9-11 were presented on MRI ( Fig.   1-A, B). The interface between mass lesion and spinal cord was ill-defined, and a small suspicious intramedullary mass connected with IDEM component was noted on T1-weighted axial MRI with contrast ( Fig. 1-C, D). The cord was displaced to the opposite side by IDEM component, T1-weighted axial image with contrast and T2-weighted image differentiate edematous changes from mass lesion on the spinal cord (Fig. 2). The disturbed venous outflow such as venous stasis caused by mass volume effect produces edematous change presented by a high signal intensity on T2-weighted image 13) . This finding was a peritumoral edema, which is usually found on the typical intramedullary tumor 5) , this could be a clue implying the exophytic ependymoma. The extramedullary component was large and its histopathological finding was anaplastic ependymoma, WHO grade III.
We thought the possibility that primary IDEM spinal ependymoma with high WHO grade may spread into the intramedullary space at first. However, the shape of intramedullary component was round and smooth not enough to explain invasion from outside, and there were only amount of leptomeningeal invasion like that of high grade tumor in the previous reports. So we concluded our case as the exophytic ependymoma developed intramedullary and spread out extramedullary.

CONCLUSION
Spinal ependymoma is usually located intramedullary and benign pathology. We report a rare case of anaplastic ependymoma with an exophytic component of the thoracic spine. The existence of the enhanced intramedullary component with edematous change could be an important clue to diagnose a high grade of spinal ependymoma. Radiotherapy and careful follow-up are essential after operation, because of the residual component of tumor and a high risk of dissemination or recurrence.