Abstract
Tanycytic ependymoma is an unusual morphological variant of WHO grade II ependymoma, typically arising from the cervical or thoracic spinal cord. Although the literature deals extensively with pathological features of this tumour entity, imaging features have not been well characterised. The purpose of this study was to review magnetic resonance imaging (MRI) features of spinal tanycytic ependymomas reported in the literature to date, exemplified by a case of a patient with tanycytic ependymoma of the conus medullaris presenting to our hospital.
A Medline search of the English literature for all previously published cases of spinal tanycytic ependymoma was carried out and the reported MRI features reviewed. The tumours were found to be typically well-demarcated masses, predominantly showing isointensity on T1-weighted signal, and T2-weighted hyperintensity, with variable patterns of contrast enhancement. A cystic component was seen in half of the cases, and in a minority a mural nodule was present within the cyst wall. Associated syrinx formation was observed in one-third of the cases and haemorrhage was rare, which may be helpful pointers in differentiating the lesion from other ependymoma subtypes.
In conclusion, MRI characteristics of spinal tanycytic ependymoma are variable and non-specific, and radiological diagnosis thus remains challenging, although certain predominant features are identified in this report. Knowledge of these is important in the diagnostic differentiation from other intramedullary and extramedullary spinal tumours in order to guide appropriate surgical management.
Keywords: MRI, conus medullaris, spinal tumour, ependymoma
Introduction
Tanycytic ependymoma is a rare subtype of World Health Organization (WHO) grade II ependymoma, most commonly found in the cervical and thoracic spinal cord.1–3 The cells of this unusual tumour entity are thought to share morphological features with tanycytes, ependymal cells with distinct bipolar morphology. Histologically, tanycytic ependymomas demonstrate spindle cells arranged in a fascicular pattern, absence of ependymal rosettes, and inconspicuous perivascular pseudorosettes.4
Tissue analysis remains the gold standard for diagnosis of these tumours. Consequently, prior reports have predominantly focused on pathological features, and imaging characteristics have not been well defined. In this study we present a review of imaging features of spinal tanycytic ependymomas reported to date, together with a rare case of an extramedullary tanycytic ependymoma at the level of conus medullaris. Important radiological differential diagnoses are discussed.
Case history
A 66-year-old female presented to our hospital with low back pain and reduced mobility, progressively worsening over several months. The patient had a history of thoracic spinal meningioma, completely resected 10 years ago; at the time, magnetic resonance imaging (MRI) revealed a small, incidental intradural lesion at the conus medullaris. Follow-up imaging over the subsequent decade showed no evidence of recurrence of the thoracic tumour, but a gradual progressive increase in the size of the lumbar lesion was demonstrated. At current presentation, MRI revealed a well-circumscribed T1-isointense and T2-hyperintense solid lesion seen caudal to the conus medullaris with displacement of the caudal nerve roots and filling most of the spinal canal at L1. Patchy contrast enhancement was demonstrated (Figure 1). The provisional diagnosis at the time was that of a second meningioma or a nerve sheath tumour.
Figure 1.
Magnetic resonance imaging (MRI) on sagittal T2-weighted (a), pre- (b) and post-contrast (c) T1-weighted as well as axial T2-weighted (d) and post-contrast T1-weighted (e) acquisitions of the lower spinal cord/lumbosacral spine demonstrating a well-circumscribed T2-weighted hyperintense mass caudal to the conus medullaris with patchy enhancement. Incidental grade II spondylolisthesis of L4 on L5 with degenerative intervertebral disc disease is noted.
Given the worsening symptoms and the progressive increase in size, L2 laminectomy for tumour removal was subsequently carried out. Exposure revealed an intradural, extramedullary oval-shaped mass of beige colour, adherent to a nerve root. The tumour was completely excised, and the patient had an uncomplicated recovery with significant improvement in her symptoms. She remained well on follow-up, with no evidence of recurrent or residual disease on MRI seven months post-operatively.
Histological analysis of the lesion showed a non-encapsulated but well-demarcated, moderately cellular neoplasm composed of short, vaguely intertwining fascicles of elongated, cytologically bland cells within a fibrillary stroma (Figure 2). Areas of perivascular pseudorosette formation were seen, and only focal pleomorphism and inconspicuous mitotic activity were present. There was no microvascular endothelial proliferation or necrosis. Immunostaining for glial fibrillary acid protein (GFAP) showed diffuse labelling in the cytoplasm and tumour cell processes. Widespread perinuclear epithelial membrane antigen (EMA) immunoreactivity was seen, and S-100 showed positive labelling in scattered cells throughout the lesion. The Ki67 proliferation index was extremely low (<1%). The diagnosis of tanycytic ependymoma was established.1
Figure 2.
Macroscopic and microscopic features of the tumour. Gross examination (a) reveals a well-circumscribed, firm tumour attached to a nerve root. The cut surface appears homogeneous and solid. Haematoxylin-eosin-stained paraffin section (b) shows a moderately cellular neoplasm comprising fascicles and occasional perivascular pseudorosettes of cytologically bland elongated cells. Immunostaining for glial fibrillary acid protein (GFAP) (c) reveals diffuse labelling confirming glial origin of the tumour cells. Immunostaining for epithelial membrane antigen (EMA) (d) shows frequent perinuclear dot-like and ring-like labelling in keeping with ependymal differentiation.
Scale bar corresponds to 1 cm in (a); 100 µm in (b) and (c); and 50 µm in (d).
Review of MRI features
A literature review was performed to look for previous cases of spinal tanycytic ependymoma. A Medline search of the English literature using terms ‘tanycytic ependymoma’ and ‘spine’ returned 17 reports of 24 patients with histologically proven diagnosis of tanycytic ependymoma. A summary of the cases, together with the present case, is given in Table 1. The patient age range was 10–69 years, with a mean of 42 years and female-to-male ratio of 1:1. Eleven (44%) cases occurred in the cervical region, eight (32%) were thoracic, and six (24%) were located at the level of the cauda equina. The majority of these were intramedullary, with only five (21%) showing extramedullary location. MRI findings were documented in 18 of these. In the majority of cases a well-demarcated lesion confined to the spinal canal was seen, although on one occasion a dumbbell-shaped lesion with extra-canal extensions was observed. In 13 cases, data on T1/T2-weighted signal intensities were included; the tumours were T1-isointense in six (60%) cases, T1-hypointense in three (30%), and T1-hyperintense in one (10%) case. T2-hyperintensity was seen in nine (69%) of the tumours and T2-isointensity in four (31%) cases. One study reported presence of restricted diffusion within the tumour. Contrast enhancement was observed in 17 out of 18 (94%) patients, showing a heterogeneous pattern in eight (50%) and a homogeneous pattern in five (31%) cases. Rim-enhancing lesions were present in three (19%) cases. Cystic component was documented in nine (53%) cases, and cysts with distinct mural nodules were seen in two (12%) patients. In addition, associated syrinx formation was observed in six (33%) patients, and on one occasion a peritumoural haematoma was documented. The majority of the tumours were treated with a gross total resection. Post-operative tumour recurrence was observed in two cases, both of which had been treated by partial resection only.
Table 1.
Summary of spinal tanycytic ependymoma cases published to date.
| First author | Age/Sex | Level | Location | T1 | T2 | Gd (pattern) | Cystic | Syrinx | Treatment | Follow-up | Comments |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Friede,2 1978 | 38/F | C | I | – | – | – | – | – | STR | – | |
| 46/F | T | I | – | – | – | – | – | – | – | ||
| 45/M | C | I | – | – | – | – | – | – | – | ||
| 17/M | C | I | – | – | – | – | – | – | – | ||
| 36/F | C | I | – | – | – | – | – | PR | Recurrence | ||
| 35/F | T | – | – | – | – | – | – | – | – | ||
| Spaar,5 1986 | 52/M | T | I | – | – | – | – | – | GTR | Death (post-operative complication) | |
| Langford,6 1997 | 32/M | C | I | – | ↔ | 1 (Hom) | 0 | 1 | GTR | No recurrence (24 m) | |
| Dvoracek,7 2000 | 31/F | L | E | – | – | 1 (Heter) | – | 1 | STR | No recurrence (8 m) | Attached to nerve root |
| Ueki,8 2001 | 18/F | C | I | – | – | 1 (Heter) | 0 | 1 | GTR | – | Additional E nodules |
| Kawano,4 2001 | 45/M | T | I | – | – | 1 (?) | 0 | 0 | GTR | No recurrence (9 yr) | |
| 36/F | C | I | – | – | 1 (Rim) | 1 | 0 | GTR | No recurrence (9 yr) | ||
| 55/F | T | I | – | – | 1 (Hom) | 1 | 0 | GTR | No recurrence (24 m) | Mural nodule | |
| Kobata,9 2001 | 30/M | C | I | – | ↑ | 1 (Heter) | 1 | 0 | STR | No recurrence (24 m) | |
| Ito,10 2005 | 62/M | C | I | ↔ | ↔ | 1 (Heter) | 1 | 0 | PR | Recurrence (6 m) | Mural nodule |
| Sato,11 2005 | 58/M | C | I | ↑ | ↑ | 1 (Rim) | 0 | 1 | STR | No recurrence (24 m) | Associated haematoma |
| Mohindra,12 2008 | 10/F | L | I | ↓ | ↑ | 1 (Rim) | 1 | 0 | GTR | No recurrence (12 m) | Involvement of the cauda |
| Shintaku,13 2009 | 43/M | T | I | ↔ | ↔ | 0 | 0 | 1 | GTR | No recurrence (6 m) | |
| Shintaku,14 2009 | 55/F | L | E | ↔ | ↑ | 1 (Hom) | 1 | 0 | GTR | No recurrence (6 m) | Attached to filum term |
| Radnakrishnan,15 2010 | 44/M | L | I | ↔ | ↑ | 1 (Hom) | 1 | 1 | GTR | – | Involvement of the conus m. |
| Ishihama,16 2011 | 40/F | T | E | ↓ | ↑ | 1 (Heter) | 1 | 0 | GTR | No recurrence (16 m) | Dumbbell shaped |
| Tosun,17 2012 | 41/F | T | E | ↓ | ↑ | 1 (Heter) | 0 | 0 | STR | – | Restricted diffusion |
| Krisht,18 2013 | 50/M | C | I | – | ↑ | 1 (Hom) | 0 | 0 | GTR | No recurrence (16 m) | |
| Funayama,19 2013 | 53/M | L | I | ↔ | ↔ | 1 (Heter) | 1 | 0 | GTR | No recurrence (32 m) | Involvement of the conus m. |
| Present case | 69/F | L | E | ↔ | ↑ | 1 (Heter) | 0 | 0 | GTR | No recurrence (7 m) | Attached to nerve root |
C: cervical; T: thoracic; L: lumbar; I: intramedullary; E: extramedullary; ↓: hypointense; ↔: isointense; ↑: hyperintense; Gd: gadolinium; Hom: homogeneous; Heter: heterogeneous; GTR: gross total resection; STR: subtotal resection; PR: partial resection; Filum term: filum terminale; Conus m.: conus medullaris; M: male; F: female; m: months; yr: years.
Discussion
Ependymomas comprise a group of glial neoplasms that include the myxopapillary variant (WHO grade I), classic ependymoma (WHO grade II), and anaplastic ependymoma (WHO grade III).1 Tanycytic ependymoma is a rare subtype of WHO grade II ependymoma, with around 30 cases reported in the literature to date.6 Although long-term follow up data are scarce, aggressive behaviour has not been observed. The tumour can, however, recur in cases where incomplete resection is carried out.2,10
Tanycytic ependymoma most commonly arises in the spinal cord, followed by intraventricular and supratentorial extraventricular regions.6 The tumours arise most frequently in either the cervical or thoracic spine, and tanycytic ependymomas found in the lumbar or thoracolumbar region are rare, with only five cases described prior to this report.7,12,14,15,19 The great majority of spinal tanycytic ependymomas are intramedullary, with only four previously reported extramedullary tumours;7,14,16,17 all of the latter were found in the lower thoracic or lumbar spine.
The tumours are typically solid, although a cystic component is present in approximately half of the cases. Predominant T1-isointensity or hypointensity is characteristic, similar to other ependymoma subtypes, including the cellular and myxopapillary variant.20 However, while T2-weighted signal is variable in classic ependymoma, tanycytic ependymoma shows predominance of T2-hyperintensity.
A number of features appear to differentiate tanycytic ependymomas from the other ependymoma subtypes. First, while tanycytic ependymomas are most common in the cervical and thoracic spine,20 myxopapillary ependymoma is located almost exclusively at the conus medullaris; cellular spinal ependymoma has nevertheless also been reported to show a predilection for the cervical spine.21 Second, other ependymoma entities almost invariably present as central cord tumours on imaging due to their origin in the central canal,22 while some tanycytic ependymomas were observed to arise more eccentrically. This may be related to the unusual, radial morphology of tanycytes, which extend from the central canal into the subjacent neuropil. Third, haemorrhage is common in classic ependymoma, and focal areas of haemorrhage may give rise to the so-called haemosiderin cap, a peripheral crescent-shaped rim of T2-signal hypointensity.20 This finding has, however, not been reported in tanycytic ependymoma, although in one case a distinct area of tumoural haemorrhage was seen on T1-weighted sequence.11 Lastly, presence of syringomyelic cavity is considerably more common in tanycytic ependymoma, occurring in over one-third of cases.
Differential diagnosis on imaging must include other common intramedullary tumours, including spinal astrocytoma and haemangioblastoma. Similar to tanycytic ependymoma, spinal astrocytoma frequently exhibits T2-signal hyperintensity on MRI and about one-third are associated with cyst formation.20 However, as compared to ependymoma they are usually less well defined and commonly associated with surrounding oedema, although contrast enhancement is also almost always present. The differential diagnosis of haemangioblastoma is suggested by the observation of cysts with mural nodules, as seen in at least two previous cases of tanycytic ependymoma. These tumours exhibit diffuse cord expansion, and are most commonly isointense on T1-weighted images, and hyperintense on T2-weighted signal with intermixed flow voids. Intense homogeneous enhancement is characteristic.22
Given that tanycytic ependymoma can also present as an extramedullary lesion in the lower spine, the differential diagnosis in this location must also include neoplasms such as nerve sheath tumours and meningioma. Neurofibroma is typically shown to have intra-spinal extension with a classic dumbbell-shaped configuration, and intermediate signal on MRI. Meningioma and schwannoma often show similar signal characteristics, although schwannomas may demonstrate slightly more heterogeneous T2 signal hyperintensity. Presence of rim-enhancement, widening of neural foramina or vertebral scalloping is predictive of schwannoma, while lesions with calcification or dural tail are more likely to represent meningioma.23 Meningioma was in fact initially considered as a possible diagnosis in our case, given the incidental detection of the lesion in the context of a co-existent thoracic spinal meningioma, almost 10 years before causing any clinical manifestations. Notably, follow-up imaging over the following years demonstrated an extremely slow tumour growth, in keeping with the reported indolent nature of tanycytic ependymoma.4,7,17
Importantly, it should be noted that while some of the imaging features of tanycytic ependymoma reported in this series may offer helpful diagnostic pointers, radiological identification of the tumour remains challenging. In particular, the predominant features including contrast-enhancement (94%), heterogeneous enhancing pattern (50%), T1 isointensity (60%), T2 hyperintensity (69%), and presence of cystic component (53%), as well as existence of other rare patterns such as cystic-type tumours with mural nodule and dumbbell-type tanycytic ependymoma, are all non-specific and as such may contribute to difficulties in the differential diagnosis of the lesion. Moreover, the lack of a haemosiderin cap, detected relatively frequently in other ependymoma subtypes, further compounds the challenge of reliably distinguishing tanycytic ependymoma from other, more common spinal tumours.
Nevertheless, efforts to better characterise imaging features of tanycytic ependymoma are important as correct radiological diagnosis has crucial implications for decisions regarding appropriate surgical approach. For example, in contrast to spinal astrocytoma, which typically exhibits infiltrative growth, intramedullary ependymoma is a well-demarcated tumour, making surgical resection easier; complete curative excision should thus be the goal of surgery. Similarly, in tumours of cauda equina, a curative excision is more readily achievable for ependymoma as compared to schwannoma due to its connection to the filum terminale instead of a nerve root, as is typically the case in the latter.
Conclusion
In conclusion, we present a review of MRI findings of all cases of spinal tanycytic ependymomas reported to date, together with a case of this unusual tumour arising in the region of filum terminale. Imaging findings are variable, most commonly demonstrating a solid lesion with T1 hypo- or isointense signal and T2 hyperintensity, with or without a cystic component. Associated syringomyelic cavity is frequently present. Avid contrast enhancement is characteristic, although of inconsistent pattern. Given the non-specific nature of the reported MRI characteristics, radiological diagnosis of tanycytic ependymoma remains challenging. The small number of cases reported to date represents a significant limitation of this study, and larger series will be required to allow for a more definite characterisation of imaging features of this tumour.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Conflict of interest
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
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