Pilocytic Astrocytoma – Molecular testing to aid histologic diagnosis.

Pilocytic Astrocytoma (PA) characteristically exhibits biphasic morphology featuring densely fibrillar, compact regions alternating with loosely-cohesive microcystic or myxoid areas; the latter is pictured here.  Diagnosis can be difficult, especially on small biopsies, but molecular testing can help.  BRAF-KIAA1549 fusion occurs in about 70% of PAs, whereas BRAF V600E mutation occurs in about 5-10% of PAs. 

Pilocytic Astrocytoma Cytology

Pilocytic astrocytoma is a circumscribed glioma (WHO Grade I) commonly found in children and young adults. Characteristic features include piloid cells with long, thin, hair-like cytoplasmic processes and a myxoid background, which are both seen here in this medium power image of a cytologic smear preparation performed during intraoperative consultation.  

Pilocytic Astrocytoma

Stemming from the Latin word "Pilos", meaning "resembling or composed of hair", pilocytic astrocytomas are named as such because of their long hair-like gliofibrillary processes (clear arrows) that stem off of slender bipolar nuclei (black arrows), which are best seen on smear preparation of fresh tissue (depicted here).

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