Transitional meningioma, light micrograph. Meningioma is the most common primary intracranial tumour in adults. Most meningiomas are WHO Grade I and behave in a benign fashion. The remaining 20% are WHO Grade II or III with atypical to anaplastic (malignant) features and an aggressive clinical course. As its names implies, this variant demonstrates features of both meningothelial and fibrous types. The meningothelial cells arranged in fascicles of variable length and also exhibit some lobularity. It is a WHO Grade I tumour.