A cystic meningioma misdiagnosed as malignant glioma by radiologic and intraoperative histological examinations.

Cystic meningiomas are radiologically difficult to differentiate from malignant brain tumors, particularly when the tumors are intraparenchymally located. In such cases, a surgical strategy relies on intraoperative histological diagnosis. A 60-year-old man had a tumor with multiple cysts in the left parietal lobe that was diagnosed radiologically as malignant glioma. In operative findings, there was no dural attachment of the tumor, and the border between the tumor and normal brain tissue was unclear. Intraoperative histological examination supported the diagnosis of malignant glioma based on a high cellularity and an existence of a multinuclear giant cell in the tumor tissue. We finished the surgery with partial tumor resection; however, postoperative histological diagnosis of the tumor was a typical meningothelial meningioma showing characteristic whorl formations, and in conclusion, a definite diagnosis of the tumor was an intraparenchymal cystic meningioma. In further histological investigations, the tumor tissue around cysts exhibited significantly different features from meningothelial meningioma, demonstrating small lymphocytes and histiocytes with a large nucleus, which resembled intraoperative histological findings. We deliberated that the removal of the tumor tissue from the degenerated portion for intraoperative histological examination might lead to the misdiagnosis of malignant glioma. Operative strategy is strongly influenced by intraoperative histological diagnosis. Therefore, surgeons are obliged to facilitate more precise intraoperative histological examinations by obtaining sufficient tissue from different parts of the tumor.