(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York
Subject
Meningioma; Sheath; Radiation
Description
Dr. Lee lectures medical students on optic nerve sheath meningioma.
Transcript
"So I want to talk to you a little bit about optic nerve sheath meningioma. The major thing you need to know right off the bat is meningioma is usually a benign tumor and sheath meningiomas are typically WHO grade 1 benign meningiomas. If differentiating the secondary from the primary optic nerve sheath meningioma, the primary means it's just in the sheath, the secondary tumor came from intracranial and went into the sheath. Secondary meningiomas are going to neurosurgery and are going to have surgery. The ones we are going to talk about today are the primary optic nerve sheath meningiomas. What that means is it's just in the nerve sheath itself, not inside the head meninges, just the sheath of the meninges. When you have a sheath meningioma, it often makes this tram track sign, which is enhancement within the sheath and the coronal view will look like a target where the sheath is enhancing. Sometimes the tumor can grow and takes on this kind of configuration where it looks like a bubble around the lollipop stick of the nerve. Both of these are common sheath meningioma imaging characteristics. Because we don't want to take this out as the sheath contains the blood supply, we are going to use the primary treatment modality which is radiation there. Either we can observe this person, and that's typically what we do, looking for vison loss. Or, if the goal is to preserve the visual acuity or visual field or decrease the rate of progression then we are going to be doing radiation therapy. Typically, what we are going to be using is stereotactic radiotherapy. Because we want to conform the radiation onto this lesion, that is what we call conformal. We use a three-dimensional modality where we modulate the intensity of the radiation therapy so that we can conform the isodose curve onto the shape of the lesion in a three-dimensional conformal pattern. We are going to use fractionation to reduce the toxicity to the nerve and so the treatment of choice for a sheath meningioma that is primary (if you are trying to spare the vision or slow the progression) is stereotactic, conformal intensity-modulated stereotactic fractionated radiation therapy."
