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Although epilepsy surgery is safe and effective, it is not free of complications. This type of surgery shows some peculiarities that are not common in other neurosurgical procedures. A unique feature is that removal or disconnection of functionally normal brain areas are often an essential part of surgical strategy, which may lead to functional deficits. Furthermore, patients prior to undergoing surgery frequently require invasive diagnostic procedures in order to lateralize and/or localize the epileptic focus, adding to the risk of complications. Potential complications from both invasive diagnostic and surgical treatment should be well recognized and the surgeon must inform the patient, family members, or caregivers. Although a low morbidity is reported for epilepsy surgery, a complication such as intracranial hemorrhage or direct injury to a highly functional area can be catastrophic and overshadow an otherwise successful surgery.
Definition of a complication
There is no universal definition of a complication after epilepsy surgery but based on a few previously published reports we have defined a complication as an unwanted, unexpected, and uncommon event after either a diagnostic or therapeutic procedure. In this chapter, the severity of surgical and neurological complications following surgery is graded as minor if transient and of no significant functional impact or major if causing significant disability that can be permanent. However, it should be noted that the definition of a complication is open for discussion because some postoperative disturbances may be considered acceptable side effects and not complications if they resolve completely within a few days. For example, brain edema may cause simple transient side effects such as dysphasia or mild hemiparesis that generally resolves after anti-edema medication and passage of time. Furthermore, a permanent or temporary visual (upper quadrantanopia) field defect should not be classified as a complication, because it may be unavoidable in temporal lobe surgery. In the same context, homonymous hemianopsia after occipital lobe resection is not a complication since the deficit would have been discussed in detail with the patient prior to surgery and would be expected after surgery. An expected paresis after a functional tissue removal in the sensorimotor area should not be considered a complication.
Techniques in Epilepsy Surgery presents the operative procedures used in the treatment of intractable epilepsy in a practical, clinically relevant manner. Founded by pioneering neurosurgeon Wilder Penfield, the Montreal Neurological Institute (MNI) is a leading global centre of epilepsy surgery and this volume reflects the Institute's approach, combining traditional techniques with modern neuronavigation-based approaches. There is an emphasis on mastering the important trilogy of topographic, vascular and functional anatomy of the brain. The basic anatomical and physiological mechanisms underlying epilepsy are presented in a practical manner, along with the clinical seizure evaluation that leads to a surgical hypothesis. The consultation skills and investigations necessary for appropriate patient selection are discussed, as well as pitfalls and the avoidance of complications. This is an invaluable resource not only for neurosurgeons, neurosurgical residents and fellows in epilepsy surgery, but also for neurologists, and others who provide medical care for patients with intractable epilepsy.
Epilepsy surgery is an effective treatment for reducing or eliminating seizures in patients with medically intractable epilepsy. Seizure control can be expected in 60–80% of patients with temporal and 50–80% with extra-temporal lobe epilepsy. However, the evaluation of seizure outcome alone is not sufficient in the assessment of surgical effectiveness. The final goals of epilepsy surgery are to reduce the frequency and intensity of seizures without catastrophic complications as well as improvement in quality of life (QOL). Seizure cessation is correlated with improved QOL and seizure-free patients have the potential to realize a normal life. Epilepsy leads to more psychosocial problems compared to those without epilepsy, most notably anxiety, depression, and low self-esteem. Stigma of epilepsy has a major negative impact on QOL. Additionally, people with epilepsy are more likely to be unemployed or under-employed, have lower rates of marriage, and greater social isolation.
In this chapter, we will summarize the impact of epilepsy surgery on QOL including psychosocial life in temporal and extra-temporal lobe epilepsy. The long-term results in patients with temporal and extra-temporal lobe epilepsies will be discussed with respect to seizure outcome, antiepileptic medication (AED) use, employment, and QOL pre- and postoperatively.
This chapter will discuss techniques that depart from the classical epilepsy surgery of seizure focus resection. The treatments vagus nerve stimulation and multiple subpial transection discussed below are currently being used and are generally accepted as standard surgical options, but brain stimulation and radiosurgery are continuing to be studied to define their roles in the treatment of intractable epilepsy. For the newer therapies, we cannot know at this time whether they will be embraced as a useful and efficacious treatment option for our patients. With that caveat in mind, the goal of this chapter is to serve as an introduction to the current state of knowledge for investigational approaches, as well as to describe the indications and surgical technique for alternative procedures that have become accepted for use in surgery for epilepsy.
Multiple subpial transections
Often the most difficult and complex treatment decisions are in patients with a seizure focus that involves important functioning areas. In some patients, a minor neurological deficit may be acceptable for a reasonable chance at seizure freedom. However, if the complete resection of a seizure focus poses an unacceptable risk to neurological function, an alternative technique such as multiple subpial transection (MST) can be considered. The technique of MST was refined in animals by Morrell and colleagues. It was first utilized in humans by John Handbery in three patients and later translated to a large series of patients by Whisler at the Rush Epilepsy Center in Chicago.
Epilepsy arising from the temporal lobe can be divided into two main types, lateral neocortical and mesial temporal lobe epilepsy (MTLE), based on the location of the seizure focus. In lateral epilepsy, the seizure focus is localized to the six-layered cortex of the temporal lobe found lateral to the collateral fissure. Several studies have attempted to identify features of the seizure pattern or history that can distinguish between these two types of epilepsy, but they share too many features to make a clear distinction in a single patient. In general, MTLE more commonly displays the typical temporal lobe seizure elements of an epigastric or cephalic aura, loss of awareness, automatisms, posturing, and postictal amnesia. Lateral temporal epilepsy often manifests signs related to perisylvian structures such as an auditory hallucination or postictal aphasia, in the dominant hemisphere. It should be suspected when a temporal seizure pattern is present without mesial temporal sclerosis. MTLE is more related to childhood febrile convulsions and its structural sequela, mesial temporal sclerosis. In a series of 878 patients operated on for temporal lobe epilepsy at the MNI (1928–1973), discrete focal lesions were identified in the lateral cortex of 202. More recent surgical series have identified even more lateral cortical lesions in temporal lobe epilepsy representing an increased recognition of dysplasia and benign tumors on preoperative imaging.
The two main modalities of temporal lobe surgery are the cortico-amygdalohippocampectomy (CAH) and the selective amygdalohippocampectomy (SelAH). These will be discussed separately. In this chapter we will address the surgical anatomy of the temporal lobe as well as describe the technique of CAH. In Chapter 10 the SelAH will be described in detail.
The purpose of this chapter is not to present an exhaustive review of the history of surgery of epilepsy from the beginning until today but rather to present a gallery of portraits of individual neurosurgeons who have contributed significantly in developing the field. The period covered extends from the late nineteenth century to the advent of magnetic resonance imaging (MRI) around 1984. This single event was to cause a revolution in the field and led to the creation of numerous comprehensive epilepsy centers as well as the advent of important international conferences such as the historical Palm Desert symposium organized by P. Engel in 1986. From that time onward, numerous workers from all branches of neurosciences have contributed to the development of this subspecialty that has had no equivalent in other fields of neurosurgery over the last 30 years. The reader will also note and forgive the strong emphasis on the role played by the Montreal Neurological Institute (MNI) in the development of epilepsy surgery and the creation of a diaspora that has had a widespread and continuous effect over the years.
Surgery for occipital lobe epilepsy has its own specific difficulties mainly related to the uncertainty of diagnosis and the visual loss associated with most resective surgery in the absence of an already existing visual deficit. In no other brain region is the patient and the surgical team confronted to such a degree with the possibility of a postoperative situation characterized by a poor result on the seizure tendency in addition to a new and permanent visual deficit. Consequently, all efforts must be made, often including SEEG intracranial recording, to prove the seizures are arising within a specific part of the occipital lobe and not for example within the temporal or parietal area.
The literature is sparse on the surgical treatment of occipital epilepsy and even more so on the modern surgical and technical aspects. In this chapter, a summary of the surgical anatomy of the occipital lobe and the clinical manifestations of occipital epilepsy, which are so crucial in establishing the hypothesis of the site of seizure onset, will be presented from a practical surgical perspective. Next, the technical aspects and various resection modalities will be addressed. The core of the presentation consists of an analysis of several representative cases with stress on the operative approaches, findings, and results.
There has been a considerable resurgence of interest in the procedure of callosotomy for the surgical treatment of some intractable epilepsies, but this interest seems to have again waned over the last decade. Better-defined indications, the promise of newer generation antiepileptics, and newer palliative treatments such as vagal nerve stimulation are factors that have led to a reduction in the number of callosotomies being performed in most centers. Furthermore, although the efficacy of this procedure to reduce certain debilitating seizures has been questioned, it has been proven to be effective if well-defined indications are observed.
Callosotomy was first used in the human by Van Wagenen and Herren in 1940 with encouraging results, although it did not become an accepted mode of surgical treatment until much later. Bogen reintroduced callosal section in the early 1960s but again in spite of its demonstrated effectiveness, the procedure did not gain wide popularity. The explanation for this course of events was likely due to the fact that the early modalities of callosotomy were not restricted to the section of the corpus callosum proper but rather included most if not all of the forebrain commissures i.e. the corpus callosum in its entirety, the anterior commissure and at times the massa intermedia of the thalamus. These divisions resulted in high morbidity procedures at a time when technical facilities were not available. We owe to Wilson the introduction of microsurgical techniques to perform callosotomy in selected cases of intractable epilepsies. Wilson's efforts were in large part responsible for the resurgence of interest in callosotomy as a surgical modality in the late 1970s.
The German anatomist Reil named the insula the island, insula in Latin, because it is surrounded and completely hidden from view by the opercula of the frontal, parietal, and temporal lobes. The insula represents a large cortical area that the nineteenth century French anatomists identified as the fifth lobe of the brain. However, it has remained a somewhat obscure cortical structure mostly because it is covered from view by the opercula making it difficult to access and study. Perhaps due to the challenges inherent in studying the insula, it has generated considerable interest by anatomists and physiologists over the years. From an epilepsy perspective, the role of the insula in the epileptic network is poorly understood, and the decision to include the insula in a resection for epilepsy continues to be controversial.
Guillaume and Mazars reported their approach to insula resection when the electrocorticography revealed epileptic activity arising from or spreading to the insula as early as 1949. The technique described an opercular resection to expose the insula fully. At the Montreal Neurological Institute (MNI), Penfield and Jasper recognized epileptic activity arising from the insula and postulated its being an epileptic focus, as well as the possibility that an insula seizure focus may be a reason for failure in surgery for temporal lobe epilepsy. This notion led to an enthusiasm to investigate the insula with ECOG during temporal lobe surgery and many insular lobe resections were performed up to the 1960s. The experience of insula resection at the MNI was reported by Silfvenius et al. in 1964, which was the most comprehensive review of surgery in the insula for a presumed seizure focus. The analysis revealed no improvement in seizure freedom in those individuals with either a resection of the EEG abnormal region in the insula or complete resection of the insula itself. In addition, significantly more neurological morbidity was associated with surgery in the insula.
By the year 2005 the senior author had carried out over 2500 surgical procedures for the treatment of intractable epilepsies. The procedures were all carried out at the Montreal Neurological Institute and Hospital. Most of the surgical approaches and techniques of brain mapping and cortical resections were taught to me by Theodore Rasmussen. I was fortunate enough to practice neurosurgery during a period which saw dramatic improvement in neurosurgical techniques, namely microsurgery and image-guided surgery. Most of the microsurgical techniques had been applied to extracerebral vascular and tumoral lesions. We made a constant effort to apply these techniques to the intragyral endopial resection. In 1992, we started applying neuronavigation to virtually all procedures for epilepsy from preoperative brain mapping to intracranial recording and various types of cortical resections.
The book is mainly concerned with surgical techniques in epilepsy and reflects the authors’ bias concerning the importance of mastering the trilogy of topographic, vascular and functional anatomy of the brain. It is not only a book on surgical techniques but also a guide for neurosurgeons who specialize or will specialize in that field. I like to think of it as a manual for the Fellows in Epilepsy Surgery, to help them understand in a practical way the basic anatomical and physiological mechanisms of epilepsy and the clinical seizure patterns leading to the surgical hypothesis. The best surgical techniques will only be effective if applied to well-selected patients with sound indications. The neurosurgeon must be familiar with all the investigation techniques and especially those of intracranial recording and stimulation. He must develop consultant skills; skills in evaluating the patient, not only as a surgical candidate but as an individual overwhelmed by the occurrence of seizures who could have false expectations of surgery. He must develop skills in teaching basic anatomy to patients and their families for their own understanding. The neurosurgeon must develop also a technique for database collection for each patient where the essential of his history and investigation are gathered and fully analyzed before any decision to operate is reached. This will go a long way to avoid pitfalls which can result not only from lack of knowledge of surgical anatomy and poor surgical techniques but also from inadequate patient selection.
There are many obstacles encountered in the pursuit to obtain excellent surgical results in parietal lobe epilepsy. Some of the most formidable difficulties are interpreting the semiology, absence of a visible lesion on imaging, the presence of highly eloquent cortical areas, bypassing visual fibers in the vicinity of the resection zone, and the intricacies of the surgical anatomy including its vascular components. However, the discovery of more discrete lesions with high-resolution MRI as well as the ability to navigate with pre- and peroperative functional mapping of sensory, motor, and speech functions has been particularly helpful in overcoming some of the obstacles in parietal lobe surgery.
The approach taken in this chapter is to consider the parietal lobe proper as well as some aspects of the central area because of the close anatomical and functional relationships. It is indeed impossible to discuss surgery of the parietal lobe without consideration of the central area and in particular the postcentral gyrus. Few series have been published on the surgical treatment of parietal lobe epilepsy and even fewer on the modern surgical and technical aspects. After a brief historical overview, a summary of the surgical anatomy of the parietal lobes is presented. The clinical manifestations of parietal epilepsy that are so crucial in establishing the hypothesis of the site of seizure onset are then presented from a practical surgical perspective. The technical aspects and various modalities of resections pertaining to the parietal lobe are addressed. Finally, an analysis of several representative cases is presented with stress on the operative approaches, findings, and results.