Diagnosis

Right frontal cortex and white matter: Diffusely infiltrating astrocytoma with a pattern consistent with gliomatosis cerebri (WHO Grade III).

Histology

The sections show a moderately cellular astrocytoma.  The astrocytes are unevenly distributed and they show enlarged hyperchromatic nuclei with mild pleomorphism.  The tumor cells extend into the cerebral cortex with perineuronal satellitosis.  One mitosis is seen.  There is no evidence of endothelial cell hyperplasia or necrosis.  The neuropil is focally edematous and vacuolated. Many cells are p53 positive. The Ki-67 index is about 1%.

The features are those of diffusely infiltrating astrocytoma with a pattern consistent with gliomatosis cerebri. Most of these lesions are regarded as grade III.

Importantly, whereas gliomatosis was previously considered a distinct entity, since the 2016 update to the WHO classification of CNS tumors it is now merely thought of as a growth pattern.