Epilepsy Surgery

When I started as a consultant in Bristol there was no epilepsy surgery service. My predecessor Michael Torrens had worked with Dr Jonathan Bird, a consultant neuropsychiatrist to do a small number of cases and establish the need for a service in the south west. My training in Liverpool and Manchester had included the overall management of epilepsy including exposure to some conventional epilepsy surgery. The need for a local surgical service for epilepsy was clear and in the absence of anyone else in the department to take on this challenge I began to work with Dr Bird.

The problem with starting a new service in the modern health service is that there is no mechanism that encourages service development. The truth is that the system resists all attempts to do this. Initially all we could do was to treat patients on an individual case basis. Once we had established a clinical need, we were able to put together a business case for a formal service which we did in the mid 1990’s and in 1994 this was supported by the trust. We now have the infrastructure for a proper epilepsy surgery service. This includes input from neurology (Dr Kasia Sieradzan and Dr Sam Lhatoo) as well as neuropsychiatry (Dr Jonathan Bird), neuropsychology (Dr Margaret Newsom) and neuroradiology (Dr Marcus Likeman). We now have access to Mr Spectroscopy and functional MRI. We have two videotelemetry units but this remains the rate limiting step in the epilepsy surgery assessment ptocess.

The service has a regional and national referral base. We treat adults with both lesional and non lesional intractable epilepsy. My paediatric colleague, Michael Carter provides the surgical input to a paediatric epilepsy surgery team. Patients are assessed by the epilepsy physicians and then investigated according to protocol. This includes specialized imaging, Video telemetry and neuropsychology assessment including a WADA test. Cases are discussed at a monthly epilepsy surgery meeting. Where concordance between the clinical findings, the semiology and the radiology can be identified patients are waitlisted for resective surgery. Waiting times for surgery are approximately one year at the present time. The trust provides dedicated theatre time for epilepsy surgery with a fortnightly list on Wednesday afternoons. Unfortunately this is not supported by dedicated in patient beds so admissions are cancelled on a regular basis due to lack of beds. It is now standard of care for patients undergoing craniotomy for epilepsy to be nursed on in a high dependency unit for a night postoperatively. We have no dedicated HDU beds so this is another reason why patient’s operations have to be cancelled at short notice.

My input to the service is to provide the sole surgical input to the epilepsy team. The service does not generate enough surgery to allow the involvement of more than one surgeon at the moment. The establishment of the service coincided with the arrival of image guidance in the department. All our epilepsy surgery has therefore made use of this technology allowing for a minimally invasive approach to temporal lobe and lesional surgery and the facilitation of functionally guided surgery for extratemporal epilepsy. In the early days of the service we carried out a very minimally invasive procedure removing only part of the hippocampus, the inner part of the temporal lobe. I now use the same trans-sulcal approach but perform a more standard amygdalohippocampectomy.

Vagus Nerve Stimulation

Where a focus for seizures cannot be identified we have offered patients non curative surgery in the form of Vagus nerve stimulation. This is a contentious technique not supported by many epilepsy surgery units in the UK. A further criticism has been made that we have used the technique too freely in place of more detailed investigation of extratemporal epilepsy. In response to the first criticism that VNS does not work I want to go on record as stating that no one was more skeptical of the technique when it was introduced than I was. I was effectively forced to offer the surgery to our worst affected patients by public opinion and the patient support groups. My cynicism relating to the hard sell techniques of the American company supplying the stimulators was overcome by the fact that my end stage patients improved! The improvement was not dramatic – there were no long term cures, but at least 50% of patients were more than 50% improved, which is the criterium required to introduce a new drug. A recent patient satisfaction survey asking patients to scale the effectiveness of their VNS on a scale of 0 - 10 produced the following results. 30% scored the treatment as 1 -2 (no good), 30% scored the treatment as 5 -6 (some use) while the rest scored the treatment as 8 - 9 (useful but nor curative). On this basis it is hard to deny patients with intractable epilepsy the chance to improve their epilepsy control. The use of VNS does not preclude someone from undergoing further evaluation in the future.

The commonest cranial operation for epilepsy is temporal lobe resection. Traditionally a full temporal lobectomy has always been done on the non dominant (usually the right) hemisphere with more selective techniques being reserved for the dominant hemisphere that controls speech and memory. The photo of the cadaveric brain demonstrates the difference. The blue highlighted area represents the extent of a conventional temporal resection. The red area is the extent of a selective operation. The small white arrow outlines the image guided approach to the medial temporal lobe. I have always used image guidance for epilepsy surgery and as a result I seldom carry out a full temporal lobectomy in non tumour cases. The technique I use I first described in 1992 when it was the subject of a ‘Tomorrow’s world’ program. The procedure is done under general anaesthetic. Once the patient is asleep, the image guidance is set up. (temporallobe1) We now use the Medtronic SNT StealthStation. This allows us to plan a minimally invasive approach across the temporal lobe.(temporallobe2) The medial structures of the temporal lobe, the Pes Hippocampus, the source of seizures of temporal lobe origin are identified (temporalobe3). The operation then consists of carrying out an en bloc resection of the mid hippocampus for histology followed by a resection of the anteromedial temporal lobe, the amygdala and the posterior hippocampal tail. The lateral temporal structures are preserved in this procedure, thereby preserving speech and memory function.

This operation has the great advantage from the patient’s point of view that it does not involve any surgical intervention on the brain itself. The risks of permanent neurological deficit after surgery are therefore less. The operation is not curative but in our practice it produces significant improvement in some patients. The operation is carried out under general anaesthetic. A small 2 cm incision is made on the left side of the neck and the vagus nerve dissected out of the carotid sheath. The Cyberonics bipolar electrode is applied to the nerve which is the secured and tunneled to a subcutaneous pocket on the anterior chest wall where it is connected to the stimulator battery itself. The operation takes about an hour and the patient goes home the day after surgery. Two weeks later they are reviewed at Frenchay Hospital where the stimulator is turned on. It is programmed to produce a cyclical stimulation for 30 seconds every five minutes which the patient feels as a tightness in their throat. Over the first few weeks the strength of stimulation is slowly increased to therapeutic levels. The efficacy of the stimulation is then assessed over the next few months.

An independent audit of the epilepsy surgery activity from 1990 to 2000 was carried out by Dr Sieradzan, Consultant neurologist when she joined the epilepsy surgery team. These results have been presented to the South west regional neurology audit meeting but have not been more widely disseminated. I reproduce some of them here. In addition I have added my own audit of epilepsy surgery from April 2000 to February 2003. The latter represents a further audit cycle with three major changes from the first ten years of the service. First we now have input from Consultant neurologists to the service which has changed the referral base of surgical patients, giving us a broader cross section of patients that are suitable for surgery. Secondly my surgical technique has changed in that I now perform a standard medial temporal lobe resection as opposed to the more minimally invasive operation that we performed originally. Thirdly we now have access to more sophisticated MRI scanning allowing a more accurate analysis of medial temporal anatomy. We still do not use quantitative volumetric analysis yet but this is the preference of our neuroradiologists, rather because of a lack of availability of this technique.

Activity

Deaths

* These deaths occurred in patients who were all seizures free after their surgery. They were classified as SUDEP’s – Sudden Unexplained Deaths in Epilepsy. All patients had undergone minimally invasive selective temporal lobe resections. One had been fit free for a year, another for 3 years and another for 4 years before the SUDEP occurred. While this is likely to reflect the severity of the epilepsy suffered by our patients in the early days of the program it was hard for me to escape the conclusion that by restricting the extent of hippocampal resection as much as I did, I had succeeded in preventing regular seizures but not rare severe seizures. This was one reason why I reverted to a standard volume amygdalohippocampectomy.

Complications

* The incidence of upper quadrantic defect is higher than this and is the subject of an ongoing audit. The difference is that this may not effect driving whereas a hemianopia definitely precludes a patient from driving irrespective of their seizure control.

Outcome after Temporal lobe surgery

The percentage of patients rendered seizure free by surgery has increased from 57% to 69% in the second audit cycle. The latter figures compare favorably with the data published in the last UCLA Palm Desert conference – 1992 (68% seizure free, 22% improved, 9% no change).

Operations – Primary insertion – 60

Revision of VNS – 9

Removal of VNS – 3

Total - 72

*Overall outcome – 60 cases

No seizures - 1

Worthwhile improvement in seizure frequency - 23

No Change in seizure frequency but general improvement 9

Improved mood – 3

Less severe seizures - 6

No Change at all 20

Worse 3

No data 4

Complications 4

(2 infections, 1 battery migration, 1 lead failure)

*This outcome data is generated by my recording the information available in copy outpatient letters sent to me after a patient’s surgery. It is therefore limited in detail. I await independent confirmation and detailed analysis by the epilepsy surgery team audit process.

Comment

I have been privileged to be involved in the development of the epilepsy surgery service since its inception in 1991. The service has been forced to evolve slowly but progressively throughout the 1990’s because of lack of proper funding. Despite this we have now reached the stage where we have an active multidisciplinary team in place with most, but not all of the resources to provide a full epilepsy surgery service. We still need dedicated neurophysiology consultant time, ring fenced in patient beds and functional imaging on site before we can say that we are as well resourced as other units. Our results are now comparable with the international standard. However we still need to continue to develop, in particular in the field of extratemporal epilepsy surgery. My aim is now to maintain and develop the epilepsy surgery service at Frenchay. Epilepsy surgery is one of the most rewarding things I do and it is a service I want to continue to provide in the South West. In the present political climate this may be easier said than done!