Table 1.

Overview of 2016 World Health Organization (WHO) classification system for grading meningiomas. HPF, high-power fields; N/C, nuclear/cytoplasmic.

	Grade I	Grade II	Grade III
Histologic Subtypes	Meningothelial Fibrous Transitional Psammomatous Angiomatous Microcystic Secretory Lymphoplasmacyte-rich Metaplastic	Atypical Clear cell Choroid	Anaplastic Rhabdoid Papillary
Diagnostic Criteria	-Presence of <4 mitoses per 10 HPF	-Presence of 4–19 mitoses per 10 HPF or -Brain invasion or -At least 3/5 of the following: -Patternless sheeting architecture -Small cell formation with high N/C ratio -Prominent nucleoli -Hypercellularity -Spontaneous intratumoral micronecrosis	-Presence of ≥20 mitoses per 10 HPF or -Overtly malignant morphology (carcinomatous, sarcomatous, and melanomatous cytology)