Pilocytic astrocytomas are the most common primary brain tumors in children. They are classified as WHO grade I tumors because of their benign and slow-growing nature . They represent 85% of cerebellar and 10% of cerebral astrocytomas . Approximately, 15% of patients with Neurofibromatosis type 1 (NF1) develop PA .
Peak incidence is between 5 and 15 years of age. Approximately, 80% of PA occurs in patients less than 20 years . There is no sex predilection.
Most of the lesions occur in or near the midline. Common locations include the cerebellum, the optic nerve and chiasm, and the hypothalamus. Less common locations include basal ganglia, brainstem, cerebral hemispheres, and spinal cord . They are rare in extra-axial locations. After an extensive Medline search, we could find only three cases of primary extra-axial pilocytic astrocytoma of the CPA reported till now. Two of them were seen in adults and one in a 12 year old boy. All of them presented with progressive hearing loss and mimicked cystic schwannoma. In all three cases, the tumor was adhered to the cochlear and vestibular nerves. In two of them, the nerves had to be sacrificed for gross total resection, while in one case the mass could be resected without nerve sacrifice. In our case, gross total resection was accomplished without any nerve sacrifice.
Microscopically, PA displays low cellularity with a typical biphasic pattern: compacted bipolar cells with Rosenthal fibers and loose-textured multipolar cells with granular bodies and microcysts.
On Computed Tomography (CT), PAs are typically discrete localized cystic and solid masses located in the posterior fossa. The solid components of these tumors are iso-to slightly hypodense compared with the adjacent brain on non-contrast CT and nearly always enhance following contrast administration. 20–30% of PAs may be entirely solid . Calcification is present in up to 20% . Hemorrhage is rare.
On MR, the solid components of these tumors appear iso-to slightly hypointense relative to grey matter, while the cyst contents are iso-to slightly hyperintense to CSF on T1 weighted images. On T2 weighted images, the solid portions are hyperintense to grey matter. Cyst contents are slightly hyperintense relative to CSF on both T2 weighted images and FLAIR . Peritumoral edema is not usually present. Virtually, all these tumors enhance and enhancement is usually intense but heterogeneous. Cyst wall enhancement may also be seen.
The definitive therapy for PAs is the complete resection of the tumors. The recurrence-free survival rates after gross total resection are higher than 90% [11, 12]. Radiotherapy (RT) can be used as adjuvant treatment in residual tumors or surgically inaccessible tumors such as brainstem/thalamic/optic nerve Pas . However, in young children chemotherapy has been used to delay the need for RT because of well-documented side effects like neurocognitive and neuroendocrine deficits [14, 15].
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.