Surgical Options

Seizures and circumscribed mass lesions
Temporal lobe epilepsy
Extratemporal seizures
Corpus callosum section
Infantile hemiplegia syndromes and intractable epilepsy

Seizures and circumscribed mass lesions

When neuroimaging demonstrates circumscribed lesions involving the cerebral cortex in patients with epilepsy, the causal relationship of the lesions to the epilepsy is almost 100 percent. This concept is relatively new, and is the combined product of modern neuroimaging and the expansion of epilepsy surgery programs. Previous teaching was that cause and effect had to be proven, but surgical results have shown that resection of the lesion and limited surrounding brain produces excellent results in over 90 percent of patients, regardless of other findings. This, of course, presumes that the lesions are not located in critical brain regions. When a lesion is located in a critical brain region, subdural grid electrodes can be placed over the lesion to determine where the seizures originate with respect to the lesion and for purposes of functional mapping around the lesion.

Temporal lobe epilepsy

Approximately 70 percent of patients with complex partial seizures referred for surgery have their seizure origin in the medial temporal lobe. About half of these patients can be identified by virtue of certain risk factors, age of seizure onset, seizure evolution, clinical seizure characteristics, scalp EEG findings, and MRI results. Most of these patients can safely undergo surgery without intracranial monitoring. The other half will require intracranial monitoring, usually using a combination of depth and subdural electrodes. If very rigid selection criteria are used, surgical success in patients with temporal lobe epilepsy can approach 100 percent. However, the use of rigid criteria will deprive many patients who might benefit enormously from surgery. Using less than rigid criteria, most modern epilepsy surgery programs report that 70-80 percent of carefully selected patients become seizure-free following temporal lobectomy with an additional 15 percent to 20 percent of patients experiencing substantial seizure reduction. The exact selection criteria for less-than-ideal patients is difficult to define, but is largely the result of the investigator's experience.

Extratemporal seizures

About 30 percent of patients with partial seizures have seizure origin outside of the temporal lobe. Some will have findings that help identify their region of seizure origin, while others will have findings that closely mimic typical temporal lobe epilepsy. Whatever the clinical presentation, patients with extratemporal seizure origins, who do not have identifiable structural lesions, can have seizures that are very different to localize. Some will have multifocal or diffuse seizure onsets. When seizure are localized, surgical results can be excellent, but the success rate is lower than for patients with temporal lobe epilepsy. Currently, these patients represent the greatest challenge for epilepsy surgery programs.

Corpus callosum section

Corpus callosum section is a palliative procedure (although 5 percent to 10 percent of patients from different series do become seizure-free) that can be very beneficial in certain patients who are not candidates for resective surgery. Since palliation is the expected goal, the procedure is aimed at reducing the frequency and severity of seizures. The seizures that are best targeted by callosum section are secondary generalized seizures; atonic, tonic and tonic/clonic. These seizures produce falls and injuries. Although partial seizures are helped in about 50 percent of patients, the results are less predictable. New or more severe partial motor seizures occur infrequently.

Infantile hemiplegia syndromes and intractable epilepsy

In patients with infantile hemiplegia, severe seizures and, often, disruptive behavior can be very difficult to manage. In the late 1950s and early 1960s, remarkable results were reported in such patients following hemispherectomy. Both seizure control and behavior improved substantially. However, often fatal and delayed complications of cerebral hemosiderosis and hydrocephalus in more than a third of patients caused the procedure to be abandoned. Subsequently, very good results were reported following callosal section in patients with infantile hemiplegia, but seizures were seldom completely eliminated. Modified, or functional, hemispherectomy was then introduced as a surgical option for these patients. In this procedure, the frontal and occipital lobes are left in place with intact blood supplies but are disconnected from the remaining brain. Functional hemispherectomy is not associated with delayed complications and is now the procedure of choice in patients with infantile hemiplegia, if the hemiplegia is complete. Preserved useful finger movement would mitigate against hemispherectomy and favor callosal section.