Epilepsy and Multiple Subpial Transection (MST)
What Is Multiple Subpial Transection?
Sometimes, brain seizures begin in a vital area of the brain -- for example, in areas that control movement, feeling, language, or memory. When this is the case, a relatively new epilepsy treatment called multiple subpial transection (MST) may be an option. MST stops the seizure impulses by cutting nerve fibers in the outer layers of the brain (gray matter), sparing the vital functions concentrated in the deeper layers of brain tissue (white matter).
Who Is a Candidate for Multiple Subpial Transection?
Most people with epilepsy can control their seizures with medication. However, about 20% of people with epilepsy do not improve with drugs. In some cases, surgery to remove the part of the brain causing the seizures may be recommended.
MST may be an option for people who do not respond to medication and whose seizures begin in areas of the brain that cannot be safely removed. In addition, there must be a reasonable chance that the person will benefit from surgery. MST may be done alone or with the removal of a section of brain tissue (resection). MST also may be used as a treatment for children with Landau-Kleffner syndrome (LKS), a rare childhood brain disorder which causes seizures and affects the parts of the brain that control speech and comprehension.
What Happens Before Multiple Subpial Transection?
Candidates for MST undergo an extensive pre-surgery evaluation -- including seizure monitoring, electroencephalography (EEG), magnetic resonance imaging (MRI), and positron emission tomography (PET). These tests help to pinpoint the area in the brain where the seizures occur and determine if surgery is feasible.
Another test to assess electrical activity in the brain is EEG-video monitoring, in which video cameras are used to record seizures as they occur, while the EEG monitors the brain's activity. In some cases, invasive monitoring -- in which electrodes are placed inside the skull over a specific area of the brain -- is also used to further identify the tissue responsible for seizures.
What Happens During Multiple Subpial Transection?
MST requires exposing an area of the brain using a procedure called a craniotomy. ("Crani" refers to the skull and "otomy" means "to cut into.") After the patient is put to sleep with anesthesia, the surgeon makes an incision (cut) in the scalp, removes a piece of bone and pulls back a section of the dura, the tough membrane that covers the brain. This creates a "window" in which the surgeon inserts his or her surgical instruments. The surgeon utilizes information gathered during pre-surgical brain imaging to help identify the area of abnormal brain tissue and avoid areas of the brain responsible for vital functions.
Using a surgical microscope to produce a magnified view of the brain, the surgeon makes a series of parallel, shallow cuts (transections) in gray matter, just below the pia mater (subpial), the delicate membrane that surrounds the brain (it lies beneath the dura). The cuts are made over the entire area identified as the source of the seizures. After the transactions are made, the dura and bone are fixed back into place, and the scalp is closed using stitches or staples.