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Spinal ependymoma

Spinal ependymomas are the most common spinal cord tumour overall, seen both in adult and paediatric population. 

This article specifically relates to spinal cord ependymomas. For a discussion of intracranial ependymomas and for a general discussion of the pathology refer to the main article: ependymoma. Additionally, due to different imaging features and demographics, myxopapillary ependymomas are also discussed separately. 

Epidemiology

Spinal ependymomas are the most common intramedullary neoplasm in adults, comprising 60% of all glial spinal cord tumours 7. They are the second most common intramedullary neoplasm in the pediatric population, representing 30% of pediatric intramedullary spinal neoplasms 6.

Peak incidence is in the fourth decade, with 39 years being the mean age at presentation. Males are more commonly affected than females.

There is an increased incidence with neurofibromatosis type 2.

Clinical presentation

Clinical presentation is similar to that of other intramedullary spinal tumours, with pain, weakness and sensory changes common.

The frequent presentation of sensory symptoms may be explained by the proximity of these centrally located tumours to the spinothalamic tracts. Dominant motor symptoms are commonly associated wtih very large ependymomas 5.

Pathology

Ependymomas arise from ependymal cells lining the central canal or cell rests along the filum.

6 histological subtypes are recognised:

  1. cellular (the most common intramedullary type)
  2. papillary
  3. clear cell
  4. tanycytic
  5. myxopapillary
    • virtually always located along the filum terminale with occasional extension into the conus medullaris
    • discussed separately: see myxopapillary ependymomas
  6. melanotic (the least common type)

On histologic evaluation, uniform moderately hyperchromatic nuceli are typically observed. Perivascular pseudorosettes are the classical finding.

Using the WHO classification, almost all intramedullary ependymomas may be classified as grade II or sometimes III (anaplastic). Malignant types are rare.

This is in contrast to myxopapillary ependymomas which are grade I lesions. 

Radiographic features

Ependymomas can occur anywhere along the spinal cord, however the cervical cord is the most common site (44%). An additional 23% occur within the cervical cord and extend into the upper thoracic cord. Twenty six percent occur in the thoracic cord alone 3.

Plain film

Plain film features that may be seen with a spinal ependymoma include:

CT

CT may demonstrate:

  • non-specific canal widening
  • isodense or slightly hyperdense compared with normal spinal cord
  • intense enhancement with iodinated contrast
  • large lesions may cause scalloping of the posterior vertebral bodies and neural exit foraminal enlargement
MRI

MRI is the modality of choice for evaluating suspected spinal cord tumours. Features include:

  • widened spinal cord (as ependymomas arise from ependymal cells lining the central canal, they tend to occupy the central portion of the spinal cord and cause symmetric cord expansion)
  • although unencapsulated, they are well-circumscribed
  • tumoral cysts are present in 22%. Non-tumoral cysts are present in 62% 5
  • syringohydromyelia occurs in 9-50% of cases
  • in contrast to intracranial ependymomas, calcification is uncommon
  • average length of four vertebral body segments 10

Typical signal characteristics:

  • T1: most are isointense to hypointense; mixed signal lesions are seen if cyst formation, tumour necrosis or haemorrhage has occurred
  • T2: hyperintense
    • peritumoural oedema is seen in 60% of cases
    • associated haemorrhage leads to the “cap sign” (a hypointense haemosiderin rim on T2 weighed images) in 20-33% of cases 5. The cap sign is suggestive of but not pathognomonic for ependymoma as it may also be seen in hemangioblastomas & paragangliomas.
  • T1 C+ (Gd): virtually all enhance strongly, somewhat inhomogeneously

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Treatment and prognosis

Most ependymomas are slow-growing. They tend to compress adjacent spinal cord tissue rather than infiltrate it, almost always leaving a cleavage plane between tumour and spinal cord tissue.

A complete curative excision may be achieved in approximately 50% of cases. In those patients, the 5-year survival rate is approximately 85%. In patients who are not able to achieve complete resection, the 5-year survival rate is approximately 57%. Recurrence is rare following complete excision 6.

Although metastatic spread is rare, the most common sites for metastases include the retroperitoneum and lymph nodes.

Differential diagnosis

On MRI, the main differential diagnosis is an astrocytoma. Certain imaging features may help to differentiate between the two:

  • astrocytoma
    • most common spinal cord tumour in children
    • eccentric location in spinal canal
    • ill-defined
    • haemorrhage is uncommon
    • patchy irregular contrast enhancement
    • bone changes infrequent
    • involvement of the entire cord diameter and longer cord segments favours an astrocytoma (i.e an intramedullary neoplasm involves the total spinal cord, it is more likely to be an astrocytoma )
  • spinal cavernous malformation
    • no enhancement
    • complete hemosiderin ring

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