Contributed by Anca Florea, MD and Geoffrey Murdoch, MD, PhDFINAL DIAGNOSIS MIXOPAPILLARY EPENDYMOMA, WHO GRADE 1.
DISCUSSION
Myxopapillary ependymoma is a slow-growing tumour, arising predominantly in the region of the filum terminale . In most of the published series, the lumbosacral ependymomas have been classified as a distinct sub-group and regarded as a tumor of low-grade malignancy (WHO grade 1).
Myxopapillary ependymomas have also been described in extra-spinal locations including extradural/subcutaneous tissue, cervical thoracic spine, lateral ventricle, and the brain.
The age at presentation ranges from 6 to 82 years, with a mean age in the mid fourth decade of life. There is a slight male predominace.
Etiology
Cauda equina myxopapillary ependymomas are assumed to arise from the ependymal cell nests normally present in the filum terminale.The reason for the myxopapillary appearance is not well understood; ultrastructural evidence shows that the myxoid material represents excess basement membrane material deposition around the tumor cells induced by the abnormal juxtaposition of collagen that abuts directly onto ependymal cells in the normal filum terminale.
Symptomatology
Myxopapillary ependymomas of the filum terminale most commonly present with pain in the lower back or coccygeal region, sometimes accompanied by sciatic radiation. Lower limb sensory disturbance and urinary sphincter disturbance can also occur.
Radiology
MRI scanning is nowadays the best technique for imaging cauda equina myxopapillary ependymomas. A significant proportion of cases are hyperintense in T1weighted-images.
Macroscopic features
Myxopapillary ependymomas are well defined, elongate, sausage shaped tumors with a smooth surface. Some are encapsulated and usually displace or compress the adjacent cauda eguina nerve roots. The cut sections often reveal areas of old or recent hemorrhage. Calcification is rarely encountered.
Microscopic features
Myxopapillary ependymoma has a distinctive cytological appearance on smear preparations; at low power, smears show organized papillary structures with palisades of tumor cells arranged around branching vessels. The perivascular gliofibrillary stroma of regular ependymomas is replaced by abundant mucinous matrix, strongly metachromatic on toluidine blue staining.
Permanent histologic sections reveal numerous small papillary structures surrounded by single layer of cuboidal or columnar cells. The cells have round nuclei and delicate chromatin and lack obvious cytoplasmic processes. The cores of the papillae are either completely filled up with the mucinous/myxoid matrix or have a central blood vessel surrounded by the matrix. Where central blood vessels are present there is extensive thickening and hyalinization of the vessel wall. Other areas can show a looser structure with microcystic spaces formation or more compact gliofibrillar areas resembling tipical ependymomas with perivascular pseudorosettes or even true ependymal rosettes.
These tumors may be highly fibrous with elongated neoplastic cells with a glial quality, resembling schwannoma.
Mitotic figures are not usually seen.
Immunohistochemistry
Myxopapillary ependymomas are usually diffusely expressing GFAP and Vimentin; they are also positive for mucin (PAS or Alcian blue, including vessel walls). Focal positive staining for S100 is demonstrated. Cytokeratin staining is negative.
Electron microscopy
Ultrastructural studies demonstrate cilia, complex interdigitations and abundant basement membrane substance. A distinctive feature of is the aggregation of microtubules within rough endoplasmic reticulum complexes. Occasionally polar inversion with microvillus-bearing apical surface of one cell abutting directly against the flattened basal surface of an adjacent cell may be demonstrated.
Molecular/Cytogenetic signature
Very few isolated cases with specific molecular and cytogenetic abnormalities have been documented. A rearranged chromosome 1p has been noted in a single case. Dicentric chromosomes and deletions of chromosome 11q in a subcutaneous sacroccoygeal myxopapillary ependymoma has been reported.
Differential diagnosis
Cauda equina paraganglioma
Choroid plexus tumors
Metastatic adenocarcinoma
Chordoma
Chondroma/Chondrosarcoma
Schwannoma
Prognosis
The recognition of this tumor as a distinct entity is of considerable clinical importance, since they are most amenable to radical surgical resection than most other forms of ependymoma and the gross total resection at the primary surgery is the most predictive factor for the outcome. Patients who undergo gross total resection of intradural myxopapillary ependymomas have a good prognosis, with a mean survival time of 19 years.
The risk of local recurrence is higher in cases of sub-total (resection of greater than 90% of the tumor) or partial (resection of less than 90% of the tumor) as opposed to complete resection. These recurrences, however, are usually confined to the same site as the primary.
Direct extension to adjacent tissues after surgery has been reported in some instances. Myxopapillary ependymoma may invade the dura mater and form large masses of tissue infiltrating the sacrum, vertebrae and soft tissue. Even under these conditions, the tumor does not show cytological anaplasia.
Dissemination and metastasis is extremely rare.
In our case the tumor has essentially all of the histologic features of a myxopapillary ependymoma, although the actual amount of myxoid material in the sample sections is minimal. The central focus of hemorrhagic necrosis may have caused an acute increase in tumor volume and be responsible for the recent onset of symptoms.
REFERENCES
Contributed by Anca Florea, MD and Geoffrey Murdoch, MD, PhD
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