Pilocytic Astrocytoma (PCA)

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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

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

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

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