Magnetic resonance imaging features of pilocytic astrocytoma of the brain mimicking high-grade gliomas.

Objective: The typical magnetic resonance/computed tomographic imaging appearance of pilocytic astrocytoma (PA) is that of a cyst with an intensely enhancing mural nodule. The purpose of this study was to illustrate the aggressive imaging features of PA.

Methods: One hundred patients referred to the cancer center with brain tumors histologically proven to be PA were retrospectively reviewed (95 by magnetic resonance imaging and 5 by computed tomographic imaging) and analyzed.

Results: The patient population includes 76 pediatric patients younger than 18 years and 24 adults ranging from 19 to 45 years old. Tumor locations consisted of the following: optic chiasm (22), lateral ventricle (3), thalamus (12), basal ganglia (1), cerebral hemisphere (10), corpus callosum (2), brain stem (26), fourth ventricle (1), and cerebellum (23). The imaging appearance of PA consisted of typical features in 71 cases and aggressive features in 29 cases.

Conclusions: It is important to recognize the aggressive imaging appearance of PA (grade 1 astrocytoma) because it can be mistaken for high-grade gliomas and may thus lead to inappropriate therapy. Despite the aggressive imaging appearance of PA, there is no histopathologic evidence of anaplasia.