Clinicians at Barrow have thoroughly researched all aspects of managing patients with hypothalamic hamartomas (HHs). The following is our assessment of what we have learned about the management of HH using Gamma Knife radiosurgery.
The surgical removal of an HH lesion leads to complete control of epilepsy in 50% of these patients and more than 90% reduction in seizures in another 30%. Therefore, about 80% of patients obtain substantial control of their seizures after surgery.
Several small series of patients treated with Gamma Knife have shown that carefully selected patients can achieve excellent seizure control 6 months after Gamma Knife treatment.
The dose of the Gamma Knife treatment is controversial. The data strongly suggest that treatment of the edge of the HH is essential to control epilepsy. Doses to the edge of the hamartoma that are less than 12 Gy are ineffective in managing the epilepsy. Doses of 17 Gy or greater at this margin effectively manage epilepsy.
The optic chiasm lies just underneath the HH. Doses higher than 10-12 Gy to this structure are very likely to lead to visual loss. The other tissues that surround the HH are much less sensitive to the toxicity of radiation and tolerate doses of 17 to 20 Gy with little or no difficulty.
The work done by Dr. Rosenfeld in his large series in Australia and our experience show that it is unnecessary to remove the entire hamartoma. However, it is necessary to remove the top of the lesion and to disconnect the side areas of the mass. The implication is that if the center of the HH is the target, the low dose that must be used will be inadequate while a dose high enough to be effective risks damage to the optic chiasm and visual loss.
Patients who unsuccessfully undergo Gamma Knife treatment can have further treatment by a second Gamma Knife treatment or by surgical resection. Undergoing radiosurgery does not increase a patient's risk; an excellent outcome is still possible.
The Barrow Approach to Treatment
Each patient is thoroughly reviewed by the entire team, and treatment options are individualized to the needs and desires of the patient and family. If Gamma Knife treatment is selected, the treatment plan delineates the HH as the target and the optic chiasm as the region of concern. The dose delivered to the HH is at least 17 Gy to the roof and sides of the HH and no more than 8 Gy to the optic chiasm.
The patient has the stereotactic frame placed on the skull under general anesthesia or under conscious intravenous sedation (the patient is asleep for only 10 to 15 minutes) The choice depends on the needs of the patient. A specialized MRI is obtained, reviewed, and transmitted to the Gamma Knife Planning Computer.
When the plan for treatment is complete and double-checked, the patient is brought to the Gamma Knife unit and treated. During treatment 201 very thin beams of radiation intersect only on the target (the hypothalamic hamartoma). The treatment is painless. After treatment, the frame is removed immediately and the patient is sent to recovery where he or she remains until the effects of the anesthesia or medications used during the procedure are no longer a concern.
Follow up is primarily by clinical examination. Improvement in problems such as seizures is one of the endpoints. MRI spectroscopy is recommended before and 6 months after treatment. This test best shows the effect of Gamma Knife treatment on the HH.