Case 1: At low power, there is simply more cellularity compared to a diffuse (grade II) astrocytoma. Note the perivascular cuffing by lymphocytes.

The astrocytes are plump and atypical.

The nuclear pleomorphism is evident at higher power.

Anaplastic astrocytoma is considered a WHO grade III neoplasm. Compared to diffuse astrocytoma (grade II), there is increased cellularity, nuclear pleomorphism and mitotic activity.