Pilocytic astrocytomas are slow-growing primary brain tumors and are classified as WHO Grade I tumors. In children aged 5–14 years, pilocytic astrocytoma is the most common primary brain tumor1 and has a 10-year survival rate of more than 90%2.
Epidemiology
Pilocytic astrocytomas are the most common gliomas in the pediatric population, with an incidence of 0.82/1000003. The incidence decreases significantly after the age of 15. 75% of all pilocytic astrocytomas occur in patients younger than 20 years4.
Pathology
According to the current 2021 WHO classification, pilocytic astrocytomas are classified as WHO Grade I. Pathognomonic for pilocytic astrocytomas are Rosenthal fibers, which appear as cytoplasmic eosinophilic inclusion bodies. In addition, long, thin bipolar cell processes are typically present; these give the tumor its name because they resemble hair to some extent.
Molecular pathology
The most common molecular genetic abnormality is found in the BRAF gene, which is responsible for activation of the MAPK signaling pathway. This abnormality can occur in all pilocytic astrocytomas, but is particularly common in cerebellar pilocytic astrocytomas5.
In 15-20% of patients with neurofibromatosis type 1, a pilocytic astrocytoma develops over the course of the disease6.
Imaging
Pilocytic astrocytomas are best visualized with MRI.
| Characteristics | Frequency7 |
|---|---|
| Non-enhancing cyst with an enhancing mural nodule | 21 % |
| Enhancing cyst and mural nodule | 46 % |
| Mass without an enhancing central area | 16 % |
| Solid mass with a minimal or absent cystic component | 17 % |
Calcifications may be observed on CT in some cases8
Localization
Pilocytic astrocytomas can occur along the entire neuraxis and are distributed by frequency as follows9:
| Location | Frequency |
|---|---|
| Cerebellum | 42 % |
| Cerebral hemisphere | 36 % |
| Optic nerve & Hypothalamus | 9 % |
| Brainstem | 9 % |
| Spinal cord | 2 % |
References
Ostrom, Quinn T., et al. "CBTRUS statistical report: primary brain and central nervous system tumors diagnosed in the United States in 2008-2012." Neuro-oncology 17.suppl_4 (2015): iv1-iv62. ↩ ↩
Collins, V. Peter, David TW Jones, and Caterina Giannini. "Pilocytic astrocytoma: pathology, molecular mechanisms and markers." Acta neuropathologica 129.6 (2015): 775-788. ↩ ↩
Handbook of Neurosurgery. Greenberg M, ed. 9th Edition. Thieme; 2019. ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩
Wallner KE, Gonzales MF, Edwards MSB, et al. Treatment of juvenile pilocytic astrocytoma. J Neurosurg. 1988;69:171-176. ↩ ↩
Listernick R, Charrow J, Greenwald M, et al. Natural history of optic pathway tumors in children with neurofibromatosis type 1: a longitudinal study. J Pediatr. 1994;125:63-66. ↩ ↩