Callosal Section

This procedure was based upon observations in experimental models of epilepsy and a fortuitous observation that seizures improved in a patient whose glioma had invaded the anterior corpus callosum. Data from the Second Palm Desert meeting and the International League against Epilepsy (ILAE) survey show that no more than 3% of patients are seizure free but seizure control was improved, especially that of certain seizure types [17] [20]. Partial seizures and myoclonic jerks may not respond and may even be made worse by the procedure. In many patients subjected to callosotomy, there is no demonstrable structural lesion and, in these patients, the only absolute indication for callosal section seems to be bilateral synchronous EEG discharges. It is valuable to assess the degree of section post-operatively, using the MRI. Generally, complete callosotomy has been abandoned and an anterior two-thirds section substituted.

Callosotomy is performed under general anesthesia with the patient in the supine position, the head in the neutral position, neck slightly flexed and held in the 3-pin fixator. A right parasagittal craniotomy centered over the coronal suture is fashioned. A medially based dural flap is cut and held with stay sutures. The inter-hemispheric fissure needs to be opened up and fixed brain retractors are useful. The operating microscope is used to divide the adhesions and carefully preserve the pericallosal vessels. The corpus callosum is easily recognized by its glistening, pearly white appearance. Either a small sucker or the CUSA may be used to gently divide the anterior corpus callosum down to, but not through, the ependyma. The dissection is carried through the rest of the genu, rostrum and anterior body. On completion of the procedure, the anterior cerebral vessels are often visible around the divided genu. A fuller description of the operative techniques can be found in standard texts, e.g. Roberts (1995) [21]. In theory, carefully directed radiosurgery could be used but, at present, the location of the major midline vessels would make this potentially dangerous.

Complications from callosal section depend upon the extent of the section and the nature of the underlying disease process. In unilateral hemisphere disease, it is clearly sensible to approach the midline from the damaged side or otherwise from the known, or assumed, nondominant side. Planning the approach will depend upon whether a total or partial section is intended and should avoid interruption of major tributaries to the superior sagittal sinus. The complications are acute and chronic and related to the extent of the resection, being minimal with a truncal section and greatest with a total section. Venous ischemia, or even thrombosis, when unilateral, may manifest itself as a hemiparesis, with the possible addition of focal seizures. There may be transient paresis due to retraction on the medial surface of the hemisphere. More serious, however, is akinetic mutism, probably the result of bilateral anterior cerebral artery spasm. However, even in recent series, there is a significant incidence of both general and neurological complications, although they tend to be transient. Overall, the risk of death at callosotomy seems to be between 0 and 6%, of permanent neurological deficit less than 5% and transient deficit up to 20%.

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