Pilocytic astrocytoma with anaplastic transformation
A. Transorbital biopsy of the right optic nerve for grading and immunohistochemistry
The patient’s progression was more rapid than would be expected with a typical optic pathway glioma, as optic nerve gliomas do not tend to grow as rapidly. Given the rate of aggressive progression and risk of vision loss to the left eye, the best decision is to proceed with biopsy of the right optic nerve. Complete surgical excision was not possible because of the involvement of the tumor at the chiasm; the biopsy was to evaluate the grade and immunohistochemistry of the tumor prior to starting radiation. Performing the biopsy via a transorbital (choice A) rather than transcranial route would allow radiation to start more expeditiously. Transcranial biopsy (choice B) is not preferred because of longer recovery and potential delay of radiotherapy. Chemotherapy and/or radiation prior to knowing the grade of the tumor (choice C) would not be preferred. Observation of a tumor with chiasmal involvement places the patient at significant risk for visual loss on the left side (choice D). Tumor at the chiasm, described as “masslike expansion,” would potentially threaten the entering fibers from the left optic nerve.