page_title: Pilocytic astrocytoma
section_title: Diagnosis
hierarchical_section_title: Pilocytic astrocytoma / Diagnosis
caption_attribution_description: English: Sagittal T1-weighted MRI pre contrast enhancement showing a well circumscribed hypointense mass in the tectum of the brainstem with compression of the aqeduct
context_page_description: A pilocytic astrocytoma is a brain tumor that occurs more often in children and young adults. They usually arise in the cerebellum, near the brainstem, in the hypothalamic region, or the optic chiasm, but they may occur in any area where astrocytes are present, including the cerebral hemispheres and the spinal cord. These tumors are usually slow growing and benign. The neoplasms are associated with the formation of one or more cysts, and can become very large.
  Pilocytic astrocytomas are often cystic, and, if solid, tend to be well-circumscribed. They are characteristically easily seen on computed tomography and magnetic resonance imaging.
  Juvenile pilocytic astrocytoma is associated with neurofibromatosis type 1, and optic gliomas are among the most frequently encountered tumors in patients with this disorder. The majority of pilocytic astrocytomas have a unique KIAA1549L-BRAF fusion gene.
context_section_description: Usually – depending on the interview of the patient and after a clinical exam which includes a neurological exam and an ophthalmological exam – a CT scan and/or an MRI scan will be performed.  A special dye may be injected into a vein before these scans to provide contrast and make tumors easier to identify.  The neoplasm will be clearly visible.
  If a tumor is found, it will be necessary for a neurosurgeon to perform a biopsy of it. This simply involves the removal of a small amount of tumorous tissue, which is then sent to a (neuro)pathologist for examination and staging. The biopsy may take place before surgical removal of the tumor, or the sample may be taken during surgery.
caption: Sagittal T1-weighted MRI showing a well circumscribed hypointense mass in the tectum presumably a tectal plate glioma.  These lesions are a distinct subset of pilocytic astrocytomas which present with hydrocephalus in 6 to 10 year olds and are rarely progressive lesions, when imaging is characteristic, biopsy is usually not performed because of the risks to adjacent structures, often shunting is the only treatment required.
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