Pilomyxoid astrocytoma: An immunohistologic study and review

We report a rare case and review of literature of an unusual pilomyxoid astrocytoma (PMA). A 9-year-old girl was admitted because of headache and vomiting. Computed tomography revealed a calcified tumor in the right temporal lobe. Magnetic resonance imaging showed a well-enhancing tumor and an intratumoral hemorrhage. A subtotal resection of the tumor was performed. The histologic findings revealed that tumors are composed of a monotonous population of the cells with delicate piloidlike processes, loosely arranged within a prominent myxoid background. The tumor cells radiated from the vessels that produced an angiocentric pattern, vaguely resembling perivascular pseudorosettes. Neither mitosis, necrosis, nor endothelial proliferation was found and the MIB-1 index was 1.3%. Two years later, local recurrence was observed and a tumor resection was again performed. The histologic pattern was quite similar to the original tumor. Inummohistochemical staining showed positivity for S100, vimentin, and microtubule-associated protein 2. No glial fibrillary acidic protein, synaptophysin, or neurofilament protein positivity was seen. Because the MIB-1 index rose to 3.3%, radiotherapy (50 Gy) was performed. Radiotherapy was effective and there has been no sign of tumor regrowth for 7 years. The histologic findings were similar to pilomyxoid astrocytoma, however, the immunohistologic and clinical features were not identical, thus indicating a new subtype of tumor.