Final Diagnosis -- Anaplastic Ependymoma


FINAL DIAGNOSIS: ANAPLASTIC EPENDYMOMA


DISCUSSION

Ependymomas are the third most common brain tumor in the pediatric population. Over 90% of these cases are intracranial, while in adults, most ependymomas occur in the spinal cord. In children, most intracranial ependymomas are infratentorial, where their relationship to the floor of the fourth ventricle often makes complete resection difficult. Supratentorial ependymomas may occur in relation to the lateral ventricles or in the midline, as in this case. It has been noted that supratentorial midline ependymomas are more likely to exhibit clear-cell morphology (20) , which may so dominate the histologic picture as to warrant a diagnosis of clear-cell variant of ependymoma. In the case presented here, only focal areas showed clear-cell histology, while most areas showed the more "classic" architecture of a cellular ependymoma. This case also had numerous areas of necrosis, significant endothelial proliferation and an extrememly high mitotic rate: sometimes as many as 5 mitotic figures could be found in one high power field.

The histologic features required for the diagnosis of anaplastic ependymoma remain, to some degree, controversial (1). This is primarily because numerous retrospective clinical studies have yielded conflicting results regarding the prognostic significance of the diagnosis of "anaplastic ependymoma". In some studies, anaplasia had prognostic significance (3, 4, 8, 10, 18, 19) , while other studies have not shown significant differences in outcome for patients with ependymoma or anaplastic ependymoma (2, 5, 6, 9, 11, 12, 14, 15).

Most of these latter studies, however, did note a trend for worse outcome in anaplastic ependymomas. Several studies have analyzed specific anaplastic features as possible prognostic indicators, but these too, have failed to clarify the issue (5, 6, 10-12, 16, 17) . In a recent study of 37 cases, necrosis was associated with a poor outcome by univariant analysis, but was not significant by multivariant analysis (5) . A larger study of 298 cases, found that high mitoses (>20 per ten high power field) were prognostically significant only in supratentorial ependymomas (16, 17) . Nazar et. al., stratified infratentorial ependymomas into three groups based on mitoses, necrosis and dense cellularity and showed mitotic index to be the most important factor (10) , however, other studies using this method have not replicated these findings (6, 7) . To highlight the variable outcome in anaplastic ependymomas, Ross and Rubenstein (13) studied 15 cases of anaplastic ependymomas and found a 58% 5 year survival. They concluded that histologic criteria do not predict malignant behavior. What is apparent from these studies is that specific anaplastic features such as mitoses, necrosis and endothelial proliferation do not have the same well-defined relationship to prognosis as do the same features in fibrillary astrocytomas (5, 6, 10, 11, 16, 17) . Most studies have concluded that extent of resection is the critical prognostic factor (6, 7, 10, 11, 14, 19) . Following resection, most intracranial ependymomas are treated with local radiation; the use of whole brain or cranio-spinal radiation in the absence of documented CSF spread remains controvesial, especially in infants. Chemotherapy, at this time, has not been show to alter outcome.

REFERENCES

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Contributed by Ronald L. Hamilton, MD.

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