Surgery Types: Risks & Benefits
All epilepsy surgery involves the brain. The operations generally involve removal of epileptogenic tissue from the area where seizures arise or interruption of nerve pathways along which seizure impulses spread.
Lobectomy and Cortical Resection
The most common form of epilepsy surgery is a lobectomy or cortical resection. With recent refinements in diagnostic methods, the procedure is now available to more people. It is estimated that approximately 30 percent of persons with partial epilepsy have seizures that are not well controlled with medications and could benefit from this surgery. All or part of a left or right lobe may be removed surgically. These areas of the brain are common sites of simple and complex partial seizures, some of which may secondarily generalize. Seizures in the temporal, parietal, frontal or occipital lobes may be treated surgically if the seizure-producing area can be safely removed without damaging vital functions.
The operations described above usually remove a relatively small area of the brain. However, when a child has Rasmussen’s encephalitis, a rare, progressive disease affecting one whole hemisphere of the brain, a hemispherectomy to remove all or almost all of one side of the brain may be performed. While it seems impossible that someone could function with only half a brain (the other side fills up with fluid), children manage to do so because the half that remains takes over many of the functions of the half that was removed. Weakness on the side opposite the operation will continue, however. Hemisperectomies may also be performed when children are born with conditions that cause excessive damage to one side of the brain, such as bleeding in the brain prior to birth.
Sectioning, or separating, the corpus callosum (a nerve bridge which connects the two halves of the brain and integrates its functions) was first reported in the medical literature in 1940. By separating the cerebral hemispheres, the spread of an epileptic discharge can be confined to one cortex, reducing generalized seizures.
A corpus callosotomy may be performed when partial seizures secondarily generalize and it is not possible to identify a single epileptic focus or when resection of a localized focus would cause a pronounced neurological deficit. Uncontrolled generalized seizures, especially atonic seizures (drop attacks), may also be treated with this type of surgery.
Some type of seizure activity on one or both sides will continue after the operation, but the effects are generally less severe than the repeated drop attacks or convulsions. The operation may be done in two steps. The first operation partially separates the two halves of the brain, but leaves some connections in place. If the generalized seizures stop, no further surgery is done. If they continue, a second operation to complete the separation may be performed.
Multiple Sub-pial Transection
This operation also seeks to control seizures by cutting nerve pathways. It is used when the seizure focus is located in a vital area of the brain that cannot be removed, such as the speech area. Instead of taking out the affected tissue, the surgeon severs the parallel connections between cells in the affected area.