[Pilomyxoid astrocytoma: a clinicopathologic study of three cases].

OBJECTIVE

To study the clinicopathologic features of pilomyxoid astrocytoma (PmA).

METHODS

The clinical and pathologic features in 3 cases of PmA were analyzed. Immunohistochemical study for glial fibrillary acidic protein (GFAP), CD34 and Ki-67 was performed on paraffin-embedded sections by standard EnVision method.

RESULTS

All the 3 cases occurred in female patients at the age of 10 months, 10 years and 19 years respectively. Two cases were located in the third ventricle, while the remaining case was located at the optic pathway. Histologically, the tumor was composed of bipolar spindle cells setting in a strikingly mucinous background. There was a marked proliferation of vessels within the tumor. In some areas, the tumor cells exhibited an angiocentric growth pattern. The biphasic pattern noted in a classic pilocytic astrocytoma was not found in PmA. Rosenthal fibers and eosinophilic granular bodies were also not identified. Immunohistochemcal study showed that the tumor cells were diffusely positive for GFAP. The Ki-67 labeling index measured less than 1%. CD34 highlighted mainly the vascular networks.

CONCLUSIONS

PmA is a distinctive variant of pilocytic astrocytoma with subtle histologic differences. Compared with conventional pilocytic astrocytoma, PmA behaves more aggressively. Some cases tend to occur in older children and adolescents. Immunohistochemical study for GFAP is helpful in differential diagnosis.