Psammomatous 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. Psammomatous meningioma is a Grade I tumour according to the WHO classification. It is laden with concentric laminated eosinophilic or slightly basophilic bodies that tend to calcify or even ossify. Psammomatous meningiomas need to have over half of the tumour mass composed of psammoma bodies. They probably start out as transitional meningioma that over time undergoes calcification obscuring the underlying meningothelial cells. This variant occurs most frequently in the spinal canal of older women.