Pilocytic Astrocytoma
The Common Vein Copyright 2010
Definition
A pilocytic astrocytoma is a type of non infiltrating glioma characterized as a well circumscribed mass often with cytic components. Microscopically it is made up of bipolar cells with thin processes which create a fibrillary meshwork with other areas of microcyst. These tumors are most commonly seen in children or young adults and are located in the posterior fossa. They can also be located in the third ventricle, the optic nerve, or in the cerebrum.
There is a link between neurofibromatosis type I and these tumors, particularly tumors of the optic tract. They occur in 15% of NF-1 patients and appear to have a particular genetic alteration distinct from those in other patients.
This mass can obstruct the flow of CSF and cause hydrocephalus in which case they present with signs of increased intracranial pressure such as headache, nausea and vomiting. Posterior fossa lesions can also cause ataxia or cranial nerve palsies. Optic lesion often present with vision loss.
On imaging, pilocytic astrocytomas are classically described as a cyst with enhancing mural nodule in the cerebellum. The cystic component is T2 hyperintense and the solid component is T1 isointense or hypointense to gray matter and demonstrates enhancement. When affecting the optic nerve, it may appear as enlargement of the affected components with variable enhancement.
Treatment for posterior fossa pilocytic astrocytomas is primary resection. Incomplete resection of the solid enhancing nodule can result in cyst reaccumulation. Lesions of the optic pathway are generally treated with radiation and chemotherapy once they become symptomatic.