Patient Selection

In general, surgical treatment of epilepsy should be considered when (1) the seizures have not been controlled by adequate attempts at treatment with maximally tolerable doses of correct anticonvulsant medications; (2) the seizures interfere with psychological and intellectual development, employment, or social performance; (3) all potentially epileptogenic areas have matured, the seizure tendency (pattern and frequency) is stable, and there is no tendency toward spontaneous regression; and (4) the patient must be strongly motivated to cope with an exhaustive diagnostic regimen and a lengthy operative procedure, possibly under local anesthesia.^12–14 Chronic psychosis is a contraindication to surgical treatment, but epilepsy-related acute psychosis is not. Mental retardation is not a contraindication.^15,16

The length of time that patients have seizures before being referred for surgery has become shorter as referring physicians recognize that superior surgical results may be obtained when the period of uncontrolled seizures is shortened, particularly in children.¹⁷ Currently, adequate, but unsuccessful antiepileptic drug therapy for 1 to 5 years may be a sufficiently long trial period to warrant referral for consideration of epilepsy surgery.¹⁶ In exceptional cases, urgent cortical resection may be considered for the relief of status epilepticus.^18,19

Table 65-2 is a representative list of neurological diagnoses that may be considered for surgery involving focal cortical resection.²⁰ Topectomy can be considered when the seizure arises from a focal and functionally silent area of the brain, which usually means that the focus is not in the speech or motor cortex. Additionally, neuropsychological testing is performed to identify any functional deficits that may be related to the epileptic cortical region.²¹ Multiple widespread or bilateral foci are generally contraindications to resective surgery. A series of diagnostic studies, including EEG, are necessary to confirm the site of seizure onset. In eloquent brain regions, MST may be considered.

TABLE 65-2 Representative Conditions Treatable by Topectomy

Presurgical Evaluation

The optimal surgery for epilepsy is resection of just enough neuronal tissue to eliminate the patient’s seizures without causing unacceptable neurological deficits. Presurgical evaluation enables the surgeon to determine the volume of cortex involved in seizure initiation and propagation and whether it can be safely resected. As stated by Rasmussen, epileptogenic lesions outside the temporal lobe are considerably more varied in extent and geographic configuration than the more common temporal lobe epileptogenic lesions.²² A variety of diagnostic tests are used for this purpose, but there is no consensus on how much information is actually needed before a particular surgical intervention can be recommended.²³

The initial preoperative evaluation process includes careful examination of clinical seizure characteristics, ictal and interictal scalp EEG, neuroimaging, and neuropsychological testing. The results of this testing should provide considerable lateralizing and localizing information. Video-EEG monitoring is the “gold standard” of the evaluation. When noninvasive tests do not show the source of seizures clearly, invasive testing is considered. Localization of the seizure focus is difficult in patients with extratemporal epilepsy, and invasive EEG is almost always required.⁵

Invasive Evaluation

The Wada Test

The Wada test (intracarotid amobarbital [Amytal] test) is performed to identify the dominant hemisphere for language functions and to determine the degree to which memory functions are subserved by each hemisphere.⁴⁰ In the series from the Montreal Neurological Institute, in right-handers, 96% had speech lateralized to the left cerebral hemisphere and 4% to the right hemisphere. In left-handed or ambidextrous individuals 70% had speech on the left, 15% had it on the right, and 15% had some representation of speech in each hemisphere. Therefore, the Wada test is necessary in all left-handed and ambidextrous patients and in right-handed patients with some ambiguous evidence of lateralization from psychological tests, x-ray films, EEG studies, or the seizure pattern.¹³ Unusual language lateralization can be seen in patients who sustain left hemisphere injury in early life or have early onset of intractable epilepsy.¹⁵ Recently, work has been done to supplant the invasive Wada test with functional MRI (fMRI).^41,42 Although fMRI has some cost and risk advantage,⁴³ the diagnostic accuracy of the technique is insufficient to completely supplant the WADA test at this time.

Invasive Electroencephalography

When an epileptogenic focus is not clearly lateralized, invasive EEG monitoring is necessary for cortical resection. In extratemporal epilepsy, subdural strip electrodes are used primarily to lateralize an epileptogenic focus (Fig. 65-1), and large subdural grids are used to define the limits of a focus that has already been lateralized but not sufficiently localized (Fig. 65-2). It is important to cover as much of the suspected area as possible for accurate lateralization and localization.^29,44 In our center, we routinely identify electrode locations in image space by coregistering postoperative MRI and CT images.⁴⁵ If the electrodes are properly indexed in the image, an electroradiographic record of the eloquent and epileptogenic regions can be obtained and used as a navigational tool during resection.

FIGURE 65-1 A, Fused postoperative MRI and CT demonstrate three subdural strip electrodes over the surface of the right frontal and temporal lobes. B, The same data set shows the left frontal and temporal electrodes. The data processing was performed with the Dextroscope virtual reality system (Volume Interactions, Ltd., Singapore).

FIGURE 65-2 Cingular depth electrodes from the same patient as in Figure 65-1. The patient had intractable frontal lobe epilepsy. The goal was to determine from which side the seizures arose.

Subdural strip electrodes are placed through a bur hole and passed blindly into the subdural space. Multiple electrodes may be inserted through one bur hole to cover wide regions of the brain. In patients with bifrontal discharges, strip electrodes are placed over the medial and lateral surfaces of the posterior frontal lobe from bur holes at the coronal suture, just off the midline (see Fig. 65-1).¹⁵

Subdural grid electrodes are placed with a craniotomy (see Fig. 65-2). They are used not only for determining the site of seizure onset over the convexity of one hemisphere but also for extraoperative functional mapping (motor, sensory, speech, and so on) by stimulation of each electrode. The maximal extent of an epileptogenic focus and areas of cortical function are determined with these evaluation methods.⁴ With invasive EEG methods, the electrode leads are brought out through the scalp and the patient is monitored for many days. The most common complications are infection and leakage of cerebrospinal fluid, especially with a large subdural grid.⁴²

Surgical Topectomy Procedure

Surgical Technique

Unlike temporal lobectomy, there are no anatomically standard operations for extratemporal cortical resection.

A craniotomy is performed to expose the epileptic focus that will be resected. The extent of neocortical resection is based on the gross pathology and the results of ECoG and functional mapping. In general, effort is made to resect all areas with interictal discharges. Essential motor and language areas should be preserved (preferably with a 2- or 1-cm margin), regardless of involvement in the epileptic focus.¹⁵ Special attention is also given to the vascular supply of the area to be resected.⁴⁷ The extent of the resection is individually tailored to each case.

A subpial dissection technique is used for cortical resection (Fig. 65-3).^{9,14,15,16,47,54} This procedure was used by Horsley (1909) and has remained the technical basis of surgery for epilepsy to this day. The pial surface is coagulated and incised in a relatively avascular area. Gyral resection is then carried out in a subpial fashion. An ultrasonic aspirator at a low suction/vibration setting is extremely useful for focal resections in a subpial plane. Meticulous, slow removal of epileptogenic gray matter is carried to the bottom of the sulcus without damaging vessels within the pia that might supply other nonresected tissue. Hemostasis is achieved principally with topical agents such as Gelfoam or Surgicel and minimal use of electrocautery. With the topectomy procedure, unnecessary resection of the underlying white matter is avoided to preserve the integrity of projection, association, and commissural fibers.

FIGURE 65-3 Simple cartoon illustrating basic microsurgical principles. 1. Open the pia with bipolar cautery and microscissors. 2. For cortical resection, it is not necessary to remove tissue deeper than the bottom of the sulcus. 3. The cortical veins and arteries are preserved when traversing a sulcus. 4. Use the arachnoid flap to retract veins and arteries. 5. Use an ultrasonic aspirator on low power to resect to the pia of the parallel sulcus.

Appropriate antiepileptic medication and dexamethasone are administered after cortical resection.

Surgical Outcome

Extratemporal nonlesional resection is associated with worse seizure control rates and a higher incidence of major postoperative morbidity than is lesional or temporal lobe resection surgery. Table 65-3 presents the seizure outcome reported by Engel and colleagues in 1993.⁵⁵ Extratemporal surgery results in seizure-free rates of 45% and improvement in 35%. More recent work is highlighted in Table 65-4.

TABLE 65-3 Outcome of Seizures

ATL, anterior temporal lobectomy; ETR, extratemporal resection.

From Engel J, Ness PCV, Rasmussen TB, et al. Outcome with respect to epileptic seizures. In: Engel J, ed. Surgical Treatment of the Epilepsies, 2nd ed. New York: Raven Press; 1993:609-621.

With localized resective surgery, less than 5% of patients have some postoperative neurological deficit as a result of unintended vascular compromise or other accidental damage to essential neural tissue. Most of these deficits are transient and resolve within months, however. Postoperative bleeding and infection are uncommon. Seizures in the acute postoperative period may portend a poor prognosis, and most patients will continue to require pharmacologic treatment.

Conclusion

Extratemporal epilepsy encompasses a broad range of diagnoses and is associated with greater difficulty in identifying a discrete seizure focus. There is no “standard” operation to treat these disorders; the surgical procedure must be customized to each individual patient. This variability and the comparatively poor seizure control results after surgery support the contention that extra–temporal lobe epilepsy is a much more complex and variable disorder than temporal lobe epilepsy. Extratemporal epilepsy surgery requires a more extensive and invasive preoperative diagnostic evaluation, and the probability of an excellent outcome is lower with this type of epilepsy surgery than with temporal lobe epilepsy. Nevertheless, topectomy can decrease and sometimes eliminate disabling epilepsy at a reasonable neuropsychological cost. Topectomy should be considered for carefully selected patients who have the highest probability of benefiting from the procedure and unattractive management alternatives.

History

In the 1930s, two treatments emerged for patients with chronic epilepsy that brought hope for better seizure control. The anticonvulsant effects of phenytoin were discovered in 1938, and it was effective in controlling the seizures of patients with chronic epilepsy.⁶⁵ At the same time, Wilder Penfield at the Montreal Neurological Institute expanded the use of surgical resection of seizure foci, primarily in the temporal lobe, for “psychomotor seizures.”⁶⁶ News of Penfield’s success spread, and in 1951, Percival Bailey and Fred Gibbs at the University of Illinois Neuropsychological Institute reported their results of temporal lobectomy for psychomotor seizures guided by EEG findings.⁶⁷ One class of patients who would not benefit from standard surgical therapy consisted of those with a seizure focus in eloquent cortex because excision of this seizure focus would lead to unacceptable deficits.

Several discoveries in neuroscience in the 1950s and 1960s, along with his own work, led Frank Morrell to believe that nonresective surgical therapy might be safe and effective. The first discovery, by Mountcastle, was that gray matter in the neocortex was organized in vertical functional columns with afferent and efferent connecting fiber tracts oriented perpendicular to the surface of the cortex.^62,63 Although some horizontal interconnections between neurons exist, experiments by Sperry and colleagues demonstrated that if these horizontal connections are interrupted in the cat visual cortex, the function of that cortex is largely preserved.^68–70 In these experiments, they placed mica plates in gray matter perpendicular to the cortical surface, thus severing the horizontal fibers in the cortex but preserving the vertical fibers. Visual testing showed preservation of function. Experiments by Morrell demonstrated the role of these horizontal fibers in the synchronization and spread of an epileptic discharge.^71,72 He found that in the monkey, he could inhibit the seizure focus but preserve motor function when he transected through a penicillin-induced seizure focus in the motor cortex.⁶¹ These findings led to a long-term collaboration in the surgical treatment of seizure foci in eloquent cortex between the neurologist Morrell and the neurosurgeon Walter Whisler, who had worked at the Illinois Neuropsychological Institute with Gibbs. By 1999, Morrell and Whisler had used MST to treat more than 120 patients at Rush Epilepsy Center in Chicago, where they developed and perfected the technique. Since the report of their original series,⁶¹ many other epilepsy centers have duplicated that success and reported their findings.^73–99

Patient Selection

The great majority of surgical epilepsy cases can be treated by standard resective techniques such as temporal lobectomy with amygdalohippocampectomy and extratemporal resection in noneloquent cortex. Subpial transection is reserved for patients in whom the seizure activity originates in eloquent cortex. MST has been used to treat patients with epileptogenic lesions of the speech, motor, or primary sensory cortex. Although MST has been used for Rasmussen’s encephalitis, it is of questionable benefit for progressive disease states when the underlying disease cannot be controlled.^100,101

MST can be used for the treatment of carefully selected cases of

Operative Procedure

In most cases, subdural grid recording and mapping have been done, and general anesthesia with methohexital is used. Methohexital has been shown to induce epileptic activity, with some evidence that it preferentially induces epileptiform activity within the primary seizure focus.^104–106 If intraoperative mapping is planned, lighter doses of methohexital are used, along with intravenous sedation and generous use of local anesthetic. Patients are positioned so that the planned operative exposure is superior in the field and the head is in three-point fixation. A standard frontotemporal craniotomy with an exposure large enough to allow ECoG is carried out. ECoG is performed with a grid, and additional strip electrodes are placed as needed. In many patients in whom MST is being considered, the seizure focus lies in both eloquent and noneloquent cortex. In these cases, surgical resection is performed in the noneloquent cortex to within 1.5 cm of eloquent cortex, as delineated by intraoperative or subdural grid stimulation mapping with standard techniques.^107,108 If repeat ECoG does not show significant resolution of the interictal activity and the primary residual focus lies within eloquent cortex, MST is performed on the crown of the involved gyri at 5-mm intervals through the gray matter. Transections are made in parallel rows in the direction perpendicular to the long axis of the gyrus (Fig. 65-4). If significant resolution of the seizure focus is noted on ECoG, no further transection is done. If no significant resolution is noted and a clearly focal area is active despite transection of the crown of the gyrus in that area, transection is sometimes carried out vertically into the gray matter within the depth of the sulcus. This is illustrated in a cadaver in Figure 65-5. This transection is performed along the same plane as transection of the crown. If the primary seizure focus is truly in the MST area, these maneuvers usually stop or significantly reduce the intraictal epileptic discharges. If they do not, it is possible that the preoperative evaluation and ECoG have not shown the primary seizure focus, which may be projecting abnormal electrical activity from a distance.

FIGURE 65-4 A, The transection hook enters through the hole. B, The hook is advanced stepwise across the gyrus, with the tip of the hook visible beneath the pia. The transector is then withdrawn along the same path.

FIGURE 65-5 On a cadaver specimen in the coronal plane, the transector is seen advancing into the depth of a sulcus. The tip is reversed and pointed away from the sulcus to lessen the possibility of vessel injury.

In the less common scenario, the seizure focus is located entirely in eloquent cortex. In such cases, MST is the only surgical option. The procedure is done as described earlier, the only exception being that no cortical resection is performed. All intraoperative decision making relies on ECoG, grid mapping, and the preoperative evaluation. Evidence of a true focal-onset seizure focus with spread through the surrounding cortex must be differentiated from mere cortical “spiking,” which is not appropriate for treatment with MST. This requires an experienced epileptologist familiar with the interpretation of ECoG.

Transections

Transections are performed with a specially designed fine, malleable wire that is bent into a 4-mm blunt hook at the tip (Fig. 65-6). The hook of the subpial transector (Whisler-Morrell Subpial Transector, Redman Neurotechnologists, Lake Zurich, IL) measures 4 mm in length to match the average depth of gray matter in the neocortex.⁶³ This hook is bent at an obtuse angle of 105 degrees relative to the main shaft of the wire. The wire is connected to a rectangular handle with the tip of the hook aligned with the flat sides of the handle. This is important because it prevents the hook from going into the cortex at any angle other than perpendicular. If the hook is advanced through the cortex at an angle off the perpendicular, extensive undercutting of the cortex will result, with corresponding deficits. The transection hook shank can be bent to any shape necessary for use in technically difficult locations. This is useful in the intrahemispheric motor and visual cortices and in the posterior temporal lobe when the sylvian fissure is opened to allow access to the depths of the fissure.

FIGURE 65-6 The transector has three parts. The rectangular handle is connected to a malleable wire with a 4-mm tip. The tip is angled 105 degrees to prevent snagging of vessels.

The area to be transected is carefully inspected. The gyral and microgyral patterns are noted. The course of the vascular supply and bypassing vessels is traced. After ECoG, transections are usually begun in the most dependent area because subarachnoid bleeding may occur. If a large amount of subarachnoid blood accumulates, a small opening can be made in the pia to let the blood escape. Each transection is begun by opening a hole in an avascular area of the pia. This is done at the edge of a sulcus with a 20-gauge needle. As the transector hook enters the gray matter through this opening, it is important to keep the hook vertically oriented to avoid undercutting and advancing the tip too deep and thus injuring white matter. The hook is advanced in stepwise fashion in a straight line across the crown of the gyrus in a direction perpendicular to the long axis of the gyrus. The hook is then withdrawn along the same path, with the tip of the hook visible just below the pia.^109–111 As the hook is withdrawn from the pial puncture site, a small amount of blood sometimes escapes. This is easily controlled with a small piece of Gelfoam and gentle pressure. The next transection line is made parallel to and 5 mm from the first. Because the hook is 4 mm long, it can be used to estimate the distance to the next transection line. The transections are thus done along the gyrus in the area of the seizure focus. Great care must be taken to note the course of the major blood vessels, particularly around the sylvian and intrahemispheric fissures. When transection must be performed in the depths of a sulcus or fissure, the hook is inserted upside down, with the tip pointed away from the pial surface. This lessens the likelihood of damaging a vessel in the sulcus or fissure. The obtuse angle of the hook also helps lessen the likelihood of injury to vessels. In cases of perisylvian-onset epilepsy, it is often useful to open the sylvian fissure to record from the depths of the fissure and transect under direct vision. In some cases, transection at 5-mm intervals is not possible because of microgyral patterns or a large confluence of vessels that may cover the area to be transected (Fig. 65-7).

FIGURE 65-7 After transections are completed, fine lines can be seen beneath the pia at 5-mm intervals. Petechial bleeding is easily controlled with Gelfoam and gentle pressure.

An alternative approach to transection was proposed by Wyler and colleagues in which the transection device is inserted with the point projected downward into the cortex.⁷⁴ Other authors have described alterations of the technique.^86,87

A recent publication by Shimizu and coauthors reported hippocampal transection in patients with temporal lobe epilepsy.⁹⁷ Shimizu and associates stated that the primary indication for this procedure was normal hippocampal cases in which there is a high risk for memory loss with hippocampal resection. In their technique, the ventricle is accessed from above via a corticotomy in the superior temporal gyrus. Hippocampal ECoG is followed by transections in the hippocampus in a coronal plane to varying depths by a specially designed transection device. The amygdala is resected if ECoG shows epileptic discharges. They reported that active epileptic discharges usually disappear after transection. If further discharges are noted, they may resect the basal temporal region. In their series, they reported the results of this procedure in 21 patients with normal preoperative MRI findings. In the 17 patients who had at least 1 year of follow-up, 14 were free of seizures. Postoperative neuropsychological testing (Rey auditory verbal learning test, Benton Visual Retention Test, and Wechsler Adult Intelligence Scale–Revised) was reported to be unchanged from preoperative testing in all patients by 6 months after surgery. The confounding variables of having performed a corticotomy on the superior temporal gyrus, transgression of the temporal stem, resection of the amygdala, and in some cases, resection of basal cortex make it difficult to determine that the efficacy of the procedure is entirely due to transection of the hippocampus. Regardless, the reported stability of memory testing makes this procedure intriguing. Long-term follow-up in these patients will be required to determine the potential usefulness of this procedure.

Pathology

When tissue that has been treated with the MST method has been removed and analyzed, the acute pathologic changes are consistent with microscopic focal injury along the transection line (Fig. 65-8). On the transection line, microscopic hemorrhage, edema, and mild cell injury are seen. When the transection lines are done properly and perpendicular to the gyral surface, the columns of cell bodies and their vertical afferent and efferent fibers are preserved. In the study by Pierre-Louis and colleagues,¹¹² the majority of transections were entirely in gray matter and were perpendicular to the gyral surface. Limiting transections to surface gray matter may explain the kainic acid–induced animal models of epilepsy, which show evidence that MST suppresses epileptic activity in the transected cortex but does not stop subcortical spread of epilepsy. Kaufmann and associates described more variable results with transections deviating from the perpendicular and at varying depths.¹¹³

FIGURE 65-8 The pathology of multiple subpial transection is illustrated with hematoxylin-eosin staining. The transection shown reaches down to the white matter but remains within gray matter. Edema and mild inflammatory changes are noted on higher power. Intervening vertical cell columns are preserved.

Radiology and Functional Imaging

The acute changes as a result of MST seen on CT and MRI include small subcortical hemorrhages and edema, along with loss of definition of the gray-white junction. On MRI, the transections themselves can often be seen acutely. At 6 months, MRI shows clear, fine transections in gray matter. If subcortical hemorrhage occurs, microcystic changes and focal gyral atrophy may be seen.

Hashizume and Tanaka demonstrated the effects of MST on an experimental seizure focus.¹¹⁴ In a kainic acid rat seizure model, they found that MST suppressed the spread of seizure activity to the ipsilateral hemisphere and reduced the frequency of seizures but did not eliminate them. They tested glucose metabolism in the transected cortex and found that it was not altered, thus suggesting that function of the cortex was preserved.

Leonhardt and coworkers reported PET findings after MST.¹¹⁵ In one patient who had undergone MST in the central sensorimotor cortex, they found that PET activation during a hand motor task was maintained in the transected cortex. They also found that there was more widespread activation in motor association cortex bilaterally, thus suggesting active recruitment of cortex after MST.

Complications

In our series of more than 100 patients and in published series by others, no deaths have been reported (Table 65-5). In the early postoperative period, most patients who undergo MST in eloquent cortex have subtle, transient deficits corresponding to the area transected. These deficits are most pronounced in the first week after surgery. As the edema and microhemorrhage resolve, most patients return to their baseline function within 2 to 4 weeks. In many patients undergoing careful, detailed examination, deficits in fine motor control or speech can be detected. Moo and coworkers reported a prospective evaluation of motor recovery after MST.¹¹⁶ fMRI was performed before and after transection and then repeated 6 weeks postoperatively. Findings included an initial loss of dexterity corresponding to an initial loss of focal fMRI activation. The focal fMRI activation and the dexterity had returned by 6 weeks.

In the series reported by Morrell, there was a 5% incidence of permanent, disabling complications corresponding to the area transected. In two patients, motor deficits arose after retraction and transection of the intrahemispheric leg motor cortex. Two cases of permanent postoperative dysphasia occurred after transection of speech areas. One case of hemiparesis occurred after a basal ganglia hemorrhage distant from the site of transection. Eight patients had deficits corresponding to the area transected that lasted longer than the expected 2 to 4 weeks, but they eventually resolved over a period of several months. One was related to speech, and seven were related to sensory or motor function. Seven other complications occurred that were clearly related to the resection or craniotomy. Permanent visual field loss and permanent sensory loss were clearly related to the surgical resection. A transient sixth nerve palsy was attributed to temporal lobe resection. A single case of meningitis, orchitis, and phlebitis was associated with the craniotomy procedure but resolved with appropriate treatment. The final permanent complication rate was 7% as reported by Morrell. A later publication by Smith and Byrne on 84 patients with MST, with or without additional resection, reported a complication rate of 17%.¹⁰⁰

Complication rates similar to ours have been reported in other series (Table 65-6). A period of transient dysfunction has also been commonly noted. Higher complication rates can be expected if the interval of transection is narrowed to 4 mm or less.⁷⁶ Although perpendicular transection through cortex causes little damage to the surrounding neurons, as the pathologic studies indicate, it does cause some damage.^112,113 As the interval is narrowed, one would expect a higher percentage of neurons in the cortex to be injured. This would also be expected if the depths of the sulci in the cortical area were transected. This maneuver is not routinely done at our center but is performed routinely by some surgeons.

In a multicenter meta-analysis reported by Spencer and coworkers, the complication rate for MST without resection was 19% and that for MST with resection was 23% in a series of 211 patients.¹¹⁷ These results are similar to those reported by Smith and Byrne and reflect the nature of operating in eloquent cortex in patients with severe medically intractable epilepsy.¹⁰⁰ Results from other series are listed in Table 65-6.

Seizure Outcome

To evaluate the effects of MST on seizure outcome, it is useful to examine MST procedures in the following categories:

Seizure outcome after MST is analyzed in this fashion because the cortical resection done in the majority of cases introduces a confounding variable: one cannot be certain whether MST or the resection had the effect on seizure outcome or on morbidity. In these cases, one can be certain only that MST had an effect on intraoperative ECoG. The group that underwent MST as the only surgical intervention gives the clearest indication of the effect of MST on seizure outcome because there are fewer confounding variables and the pathology is more uniform in this group. In 16 patients who underwent MST alone for focal-onset seizures in eloquent cortex with at least 2 years of follow-up, 6 were made seizure free (see Table 65-5). An additional 6 patients had only rare seizures or had a 90% or greater reduction in seizures. Four patients had no worthwhile benefit. Overall, 75% of patients in this category had a worthwhile Engel’s class I to III seizure outcome. Because all of these patients would have been rejected for standard resective surgery, their outcomes should be compared with best medical therapy. Other groups have reported similar results (see Table 65-6). In Wyler and coworkers’ series of 6 patients with uniform pathology in the sensorimotor cortex, all 6 had a significant reduction in their seizures.⁷⁴ There was only one permanent mild motor deficit. Schramm and colleagues reported on a series of 20 patients who underwent MST without resection.⁸⁷ Forty-five percent of the patients at the 1-year follow-up had a worthwhile outcome (Engel’s class I to III). They reported that lesional epilepsy and large areas of epileptic discharge predicted a worse outcome. Mulligan and coauthors reported a 42% rate of significant improvement in seizure frequency in a series of 12 patients.⁸⁶ Spencer and associates reported an international meta-analysis on 212 patients who underwent MST at six epilepsy centers.¹¹⁷ In cases of MST alone without resection, they reported rates of excellent outcome with regard to seizure control of 71% for generalized epilepsy, 62% for complex partial epilepsy, and 63% for simple partial seizures.

The next category of patients underwent a combination of MST and resection. This was the most common type of case in the series of Morrell and Whisler.⁶¹ It is rare for a seizure focus to lie entirely in eloquent cortex. A total of 82% of patients in this category were seizure free or had a significant reduction in their seizures (Engel’s class I to III; see Table 65-5). Although the majority of patients exhibited worthwhile improvement, the initial report by Morrell of 52% being free of seizures was not sustained later in the series.⁶¹ The meta-analysis reported by Spencer and coauthors showed similar results for patients who underwent resection plus MST, with excellent outcomes (>95% reduction) reported in 87% of patients with generalized seizures, 68% of patients with complex partial seizures, and 68% of patients with simple partial epilepsy.¹¹⁷ These collective data support the efficacy of MST, both as a stand-alone procedure for highly localized cases in eloquent cortex and for cases in which the epileptogenic zone overlaps eloquent cortex. The expected outcome of MST, however, is more likely to be improvement than cure. Results from other series are listed in Table 65-6.

The question of long-term efficacy has been raised. Orbach and coworkers reported an 18.5% seizure recurrence rate in a series of patients who underwent MST and had at least 5 years of follow-up.¹¹⁸ In a series of 20 patients who underwent pure MST, Schramm and coauthors reported that outcomes changed over time.⁸⁷ Five patients improved during the long-term follow-up period, whereas 7 worsened. This phenomenon has also been described in patients who have undergone resective epilepsy surgery.

Conclusion

The initial experience with MST was reported in 1989.⁶¹ In that group of patients with intractable seizures, 11 of 20 were free of seizures after a follow-up of at least 5 years. Subsequent cases in which MST was performed without resection proved the independent efficacy of the procedure. Since then, MST has proved helpful in patients with intractable epilepsy and foci in unresectable cortex. Similar results at other centers have confirmed its efficacy and safety if done properly on well-selected patients. The exact mechanism of action of MST is being delineated with functional testing. Other centers attempting MST have added different techniques and new protocols.^73,74,76 As we learn more about MST and about the nature of epileptogenic cortex, the technique will be further refined and will probably result in improved outcomes in patients with unresectable seizure foci.