Pilocytic Astrocytoma (PCA)

Diagnosis Definition

• Astrocytomas are the largest group of primary central nervous system (CNS) neoplasms and range from grade I (benign) to IV (highly malignant)
• Pilocytic astrocytomas (PCAs) are relatively localized and slow growing and considered grade I
• PCAs are common childhood neoplasms frequently seen in the cerebellum (60%); in adults, approximately 55% of patients present with supratentorial lesions; other common locations are the optic pathway, hypothalamus, and brainstem 
• Optic gliomas seen in the setting of neurofibromatosis type 1 (NF1) have a tendency to affect the optic nerves and chiasm and histologically the majority are pilocytic astrocytomas  

Imaging Findings

• The most common appearance of a PCA is a cystic tumor with a solid enhancing mural nodule (67%, despite being a grade I tumor); the cyst wall also commonly enhances (~50%)
• Less common appearances include a solid mass or a heterogeneous collection of mixed solid and cystic masses; central necrosis, calcification and hemorrhage are very uncommon 
• On MRI, the cystic portion may or may not follow cerebrospinal fluid (CSF) signal as it may contain proteinaceous material but is typically low signal on T1-weighted images and high signal on T2; the solid portion is also typically hypointense on T1 and hyperintense on T2 

KEY IMAGES

Pearls

• If complete surgical resection is possible, PCAs have a very good prognosis (5-year survival greater than 90%); as a rule, diffuse optic chiasm or brainstem astrocytomas are not treated surgically 

References

1. Koeller KK, Rushing EJ.  From the archives of the AFIP: pilocytic astrocytoma: radiologic-pathologic correlation.  RadioGraphics 2004; 24(6):1693-1708
2. Chourmouzi D, Papadopoulou E, Konstantinidis M, et al.  Manifestations of pilocytic astrocytoma: a pictorial review.  Insights Imaging 2014; 5(3):387-402