[Operative case of isomorphic astrocytoma]

Diffuse astrocytomas are classified as WHO Grade II tumors. Recently, a subtype presenting with better prognosis has been proposed, and it is known as "isomorphic astrocytoma." A clinical case that we encountered was believed to be categorized as this subtype; it has been presented in this report. The patient was a 20-year-old male with a chief complaint of intractable epileptic seizures. He experienced his first attack at 16 years of age in July 2001, and it was a generalized seizure. Anticonvulsants prescribed by a previous doctor had no effect on controlling the seizures. MRI performed in March 2004 showed a lesion approximately 2.0 cm in diameter in the left temporal lobe. The patient was referred to our institution for further investigation of the lesion and therapy. Electroencephalography and magnetoencephalography were used to assess the lesion at seizure focus. The tumor was resected under awake surgery. The pathological diagnosis was diffuse astrocytoma, but this tumor was considered to be the isomorphic subtype. Some parts of the tumor showed a relatively high MIB-1 labeling index (LI) of 9.2%, and additional 50-Gy radiotherapy was performed. The postoperative course was uneventful and despite decreasing the anticonvulsant dosage, he has remained seizure free. Isomorphic astrocytoma is characterized by prolonged epileptic seizures, a low MIB-1 LI, and better prognosis. In our case, since the MIB-1 LI was higher in some parts of the tumor, the appropriate therapy for WHO Grade II tumors was performed. However, this case was considered representative of isomorphic astrocytoma. No reports of this tumor subtype have been previously described in Japan. Therefore, this report is the first case of isomorphic astrocytoma reported to Japanese literature.