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Myxopapillary ependymomas are a variant type of ependymoma that occurs predominantly in the filum terminale and/or conus medullaris. They represent 13% of all spinal ependymomas and are the most common tumors of the cauda equina region.
They tend to have an earlier clinical presentation than other spinal ependymomas, with a mean age of presentation of 35 years. There is a slight male predominance.
The most common presenting symptoms are low back, leg or sacral pain. Up to 25% of patients may present with leg weakness or sphincter dysfunction.
They may occasionally present as a subarachnoid hemorrhage 8.
They are thought to arise from the ependymal glia of the filum terminale.
The vast majority are intradural and extramedullary spinal tumors, occurring in the lumbosacral spine involving the filum terminale and/or conus medullaris. Less commonly, they extend from the lumbar to the thoracic spine 10. Rarely, they can arise in the cervicothoracic spine or fourth ventricle 11.
Historically, myxopapillary ependymomas were considered grade I tumors, however, in the 5th edition (2021) of the WHO classification of CNS tumors they have been upgraded to grade 2 tumors in recognition of the fact that local recurrence is similar to that of other spinal cord ependymomas 12,13.
They are typically lobulated, encapsulated, and oval or sausage-shaped. They often have associated hemorrhage and may calcify or undergo cystic degeneration 9.
Histologically, they contain papillary elements arranged radially around a hyalinized fibrovascular core, forming perivascular pseudorosettes, with myxoid material between the blood vessel and tumor cells 9. "Balloons" (rounded eosinophilic PAS positive structures) are sometimes encountered 9.
Plain radiograph / CT
If they become large, myxopapillary ependymomas may expand the spinal canal, cause scalloping of the vertebral bodies and extend out of the neural exit foramina.
They are well-defined intradural tumors. Classically, they present when larger and sausage-shaped, spanning more than one vertebral level, but small oval tumors are also seen. Smaller tumors tend to displace the nerve roots of the cauda equina; larger tumors often compress or encase them 8.
prominent mucinous component occasionally results in T1 hyperintensity
hemorrhage and calcification can also lead to regions of hyper- or hypointensity
overall high intensity
low intensity may be seen at the tumor margins because of hemorrhage, called the cap sign (myxopapillary ependymomas are the subtype of ependymomas that are most prone to hemorrhage 8)
calcification may also lead to regions of low T2 signal
T1 C+ (Gd)
enhancement is virtually always seen
the enhancement pattern is typically homogeneous, however, they can have a variable enhancement pattern that, in part, depends on the amount of hemorrhage present
Treatment and prognosis
Myxopapillary ependymomas are generally slow-growing but are considered WHO grade 2 tumors 13. Occasionally, CSF dissemination occurs and multiple lesions are seen in ~30% (range 14-43%) of cases 4. Some sacral lesions are locally aggressive and metastasize to lymph nodes, lungs, and bone. Aggressive behavior is more commonly seen in children 9.
They can often be excised completely. In these cases, the prognosis is excellent, with 5-year-survival over 98% 9.
If the tumor has extended to the conus medullaris, resection is often incomplete, with a greater risk of local recurrence, and there is a greater risk of neurologic deficit 11.
Differential diagnosis of a small conus and filum terminale myxopapillary ependymoma includes:
Differential diagnosis of a large myxopapillary ependymoma that causes sacral destruction: