Corpus Callosotomy

David W. Roberts

Introduction

A number of newer procedures—most notably, multiple subpial transection, vagal nerve stimulation, and deep brain stimulation—have become available in the treatment of seizure disorders, and these have legitimate roles either as alternatives to resective procedures or as strategies when a resective procedure is not an option.¹⁵^,³⁵^,⁴⁹^,⁸⁹^,¹³⁹ The role of the corpus callosotomy in this setting warrants reevaluation.

Surgical division of the corpus callosum for the treatment of certain medically intractable seizure disorders, at one time about the only alternative to resective surgery, was first undertaken >60 years ago on the basis of two lines of evidence. The first was the observation of Van Wagenen that epileptic patients who subsequently suffered strokes or tumors involving the corpus callosum often had concurrent improvement in their seizure disorders.¹²⁸ The second was a growing experimental literature demonstrating, most notably in the work of Erickson in monkeys,²⁵ that the corpus callosum was the major route of seizure propagation from epileptogenic focus to generalization.²⁵^,⁵²^,⁵³^,⁷⁰^,⁷¹ Van Wagenen went on to perform callosal section in a small number of patients with some success,¹²⁸ and similar clinical experiences were reported by Bogen and coworkers¹¹^,¹²^,¹³ and Luessenhop.⁶⁴^,⁶⁵ It was not until the series of Wilson and coworkers¹³⁶ that a sustained clinical experience developed, and over the last three decades, there has been widespread adoption of the surgical procedure.

Removing an epileptogenic region with the goal of surgical cure has always been preferred, but in those patients with generalized seizures in whom a discrete epileptogenic region could not be identified or resected, surgical disruption of secondary generalization was logical. Consequently, the earliest patients for this surgery were those who were not candidates for resective surgery but who demonstrated secondary generalization.

It was quickly appreciated that of the types of seizures most likely to be helped—drop attacks (variously classified as atonic and akinetic seizures)—are among the most responsive, often being eliminated altogether; tonic and tonic–clonic generalized seizures also have been shown in multiple series to be similarly affected.³^,⁴^,⁷^,¹⁰^,¹⁴^,¹⁷^,¹⁸^,²⁰^,²⁶^,²⁹^,³¹^,³³^,³⁴^,³⁵^,⁴¹^,⁴³^,⁴⁵^,⁴⁶^,⁴⁷^,⁴⁸^,⁵⁰^,⁵¹^,⁵⁵^,⁵⁶^,⁵⁷^,⁵⁹^,⁶⁶^,⁶⁷^,⁶⁸^,⁶⁹^,⁷²^,⁷³^,⁷⁶^,⁷⁷^,⁷⁸^,⁷⁹^,⁸⁰^,⁸¹^,⁸²^,⁸³^,⁸⁷^,⁸⁸^,⁹⁰^,⁹³^,⁹⁴^,⁹⁵^,⁹⁶^,⁹⁷^,⁹⁸^,⁹⁹^,¹⁰²^,¹⁰³^,¹⁰⁴^,¹⁰⁶^,¹⁰⁸^,¹¹¹^,¹¹²^,¹¹⁴^,¹¹⁵^,¹¹⁶^,¹¹⁷^,¹¹⁸^,¹¹⁹^,¹²²^,¹²³^,¹²⁴^,¹²⁵^,¹³⁰^,¹³¹^,¹³²^,¹³³^,¹³⁴^,¹³⁵^,¹³⁶^,¹³⁷ Whereas corpus callosotomy had been performed in fewer patients than had most other epilepsy operations, and in many respects the procedure was not as well understood as other surgeries, it was reasonable that many patients underwent callosal section largely on the basis of their seizure semiology.

From a historical perspective, the role of pathology, as well as that of electrophysiologic studies, has been secondary. A spectrum of disease has been encompassed in clinical series. Williamson¹³¹) looked at surgical outcomes in terms of clinical diagnoses and classified patients into groups of infantile hemiplegia, forme-fruste infantile hemiplegia, Rasmussen syndrome, Lennox-Gastaut syndrome, frontal lobe epilepsy, and other secondarily generalized epileptics. Slightly better outcomes were found in the first two groups, but there was sufficient improvement in all categories to justify surgical intervention.

The electrophysiologic role has been an indirect one, by demonstrating the absence of a resectable epileptic region. In addition, however, electroencephalogram (EEG) findings in patients selected for callosotomy have been analyzed by a number of investigators.⁴⁴^,⁵⁴^,⁵⁸^,⁶²^,⁷⁴^,⁸⁴^,⁹² Correlating EEG with surgical results, Geoffroy et al.,⁴¹ Spencer et al.,¹²⁴ and Matsuzaka et al.⁷⁵ all reported better results in patients with lateralized EEG abnormalities. The majority of patients have evidence of bilaterally synchronous epileptiform activity, and this does not necessarily represent a bad prognostic sign. The significance of bilateral, independent foci is undetermined.

The impact of neuroimaging on the callosotomy experience has been limited. Lateralized structural lesions have been believed to be associated with a better surgical outcome,¹²⁴^,¹³⁶ but in the selection process their presence or absence has always been secondary to clinical and electrophysiologic information. As imaging technologies continue to evolve with increasing sensitivity and specificity, they are directing such aspects of the seizure evaluation as intracranial recording electrode placement. This increased sophistication of seizure investigation affects both patient selection and perhaps the surgery itself.

From the isolated clinical experiences of Van Wagenen,¹²⁸ Bogen and coworkers,¹¹^,¹²^,¹³ Luessenhop,⁶⁴^,⁶⁵ and Wilson and coworkers,¹³²^,¹³³^,¹³⁴^,¹³⁵^,¹³⁶ callosum section has seen a cautious but marked increase in application over the last several decades. Less than a dozen centers were performing callosal section in 1982 when the first Dartmouth workshop on the corpus callosum was held; nearly every surgical epilepsy center performs this surgery today. A survey of epilepsy centers in 1986 found 197 patients who had undergone corpus callosum section²³; a follow-up survey 5 years later reported 563 patients so treated.²⁴

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