Grading based on 4 features:

Nuclear atypia

Mitoses

Microvascular proliferation

Necrosis

WHO Grades

Grade 1 tumours: infiltrating astrocytomas (not diffuse).

Grade 2 Diffuse Astrocytoma: looks like ill-defined intra-axial masses that are grey to gelatinous. On micro tumour cells aggregate near neurons and vessels. No mitosis, microvascular proliferation or necrosis.

Grade 3 Anaplastic Astrocytoma: looks like grade 2 AND has mitoses. No microvascular proliferation or necrosis.

Meningiomas

Most common of all the brain tumours. More common in women or previous radiation.

Arises from the meninges of dura mater and choroid plexus, so will find them on the brain surface or in ventricles.

Rarely seen as multiple masses.

Mostly benign.

Macro

Looks like a little brain - round, well circumscribed, peels off the brain easily, has dura attached.

Micro

Architecture: looks like a whorl.

Cells: rounded nuclei with eosinophilic cytoplasm. 

Pseudoinclusions may be in the nucleus. 

Some psammoma bodies.

Cyto

...

Stains

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WHO grades

Grade 1 benign: ...

Grade 2 increased likelihood of recurrence: ...