Infiltration in Pilocytic Astrocytoma: A Diagnostic Pitfall

Area of Science:

• Neuro-oncology
• Central Nervous System (CNS) Tumor Classification
• Histopathology

Background:

• Gliomas are classified by infiltrative capacity, distinguishing circumscribed from diffuse types.
• Pilocytic astrocytoma is classified as circumscribed in the 2021 World Health Organization (WHO) CNS tumor classification.
• Differentiating pilocytic astrocytoma from diffuse glioma is crucial for grading (CNS WHO grade 1 vs. grade 4).

Purpose of the Study:

• To investigate the infiltrative nature of pilocytic astrocytoma across different brain locations.
• To determine if histological infiltration impacts the diagnosis of pilocytic astrocytoma.

Main Methods:

• Retrospective review of pilocytic astrocytoma cases diagnosed between 2008 and 2021.
• Analysis of clinical data, pathological reports, and histological slides.
• Assessment for infiltrative versus circumscribed tumor characteristics and immunostaining.

Main Results:

• Of 39 cases, 38 were confirmed as pilocytic astrocytoma; one was reclassified.
• 18 out of 38 pilocytic astrocytoma cases showed histological infiltration into adjacent brain tissue.
• Infiltration was observed in cerebellar, supratentorial, brainstem, and spinal cord tumors.

Conclusions:

• Pilocytic astrocytoma can exhibit histological infiltration, irrespective of tumor location.
• The presence of infiltration does not negate a diagnosis of pilocytic astrocytoma.
• This finding has implications for understanding glioma behavior and classification.