Joseph F. Hahn

Intractable epilepsy and structural lesions of the brain: mapping, resection strategies, and seizure outcome.

Summary: Forty‐seven patients with structural brain lesions on neuroimaging studies and partial epilepsy intractable to medical therapy were studied. Prolonged noninvasive interictal and ictal EEG recording was performed, followed by more focused mapping using chronically implanted subdural electrode plates. Surgical procedures included lesion biopsy, maximal lesion excision, and/or resection of zones of epileptogenesis depending on accessibility and involvement of speech or other functional areas. The epileptogenic zone involved exclusively the region adjacent to the structural lesion in 11 patients. It extended beyond the lesion in 18 patients. Eighteen other patients had remote noncontiguous zones of epileptogenesis. Postoperative control of epilepsy was accomplished in 17 of 18 patients (94%) with complete lesion excision regardless of extent of seizure focus excision. Postoperative control of epilepsy was accomplished in 5 of 6 patients (83%) with incomplete lesion excision but complete seizure focus excision and in 12 of 23 patients (52%) with incomplete lesion excision and incomplete focus excision. The extent of lesion resection was strongly associated with surgical outcome either in itself (p < 0.003), or in combination with focus excision. Focus resection was marginally associated with surgical outcome as a dichot‐omous variable (p = 0.048) and showed a trend toward significance (p = 0.07) only as a three‐level outcome variable. We conclude that structural lesions are associated with zones of epileptogenesis in neighboring and remote areas of the brain. Maximum resection of the lesion offers the best chance at controlling intractable epilepsy; however, seizure control is achieved in many patients by carefully planned subtotal resection of lesions or foci. Strategies for mapping and for resection of lesions and foci are discussed, including cases in which invasive recordings may or may not be necessary.

Chiari Malformation Presenting in Adults: A Surgical Experience in 127 Cases

We reviewed 127 patients who were operated upon for adult presentation Chiari malformation and made six conclusions: (a) The clinical examination remains crucial in the diagnosis. (b) The surgical anatomy is highly varied. (c) Syrinxes can be missed on preoperative contrast studies. (d) By a conservative grading system, we determined that 46% of the patients improved during long term follow-up. One-quarter deteriorated over the long run in spite of any treatment. (e) The overall results did not differ whether the treatment was plugging of the central canal plus decompression or decompression alone. (f) In patients with progression, plugging of the central canal obtained superior results. A review of the literature shows that the natural history of this complex disease process has not been established. This history is needed to identify the course of what may be several important factors that lead to the pathological condition in this disease.

Complications of invasive video-EEG monitoring with subdural grid electrodes

Objective: To evaluate the risk factors, type, and frequency of complications during video-EEG monitoring with subdural grid electrodes. Methods: The authors retrospectively reviewed the records of all patients who underwent invasive monitoring with subdural grid electrodes (n = 198 monitoring sessions on 187 patients; median age: 24 years; range: 1 to 50 years) at the Cleveland Clinic Foundation from 1980 to 1997. Results: From 1980 to 1997, the complication rate decreased (p = 0.003). In the last 5 years, 19/99 patients (19%) had complications, including two patients (2%) with permanent sequelae. In the last 3 years, the complication rate was 13.5% (n = 5/37) without permanent deficits. Overall, complications occurred during 52 monitoring sessions (26.3%): infection (n = 24; 12.1%), transient neurologic deficit (n = 22; 11.1%), epidural hematoma (n = 5; 2.5%), increased intracranial pressure (n = 5; 2.5%), and infarction (n = 3; 1.5%). One patient (0.5%) died during grid insertion. Complication occurrence was associated with greater number of grids/electrodes (p = 0.021/p = 0.052; especially >60 electrodes), longer duration of monitoring (p = 0.004; especially >10 days), older age of the patient (p = 0.005), left-sided grid insertion (p = 0.01), and burr holes in addition to the craniotomy (p = 0.022). No association with complications was found for number of seizures, IQ, anticonvulsants, or grid localization. Conclusions: Invasive monitoring with grid electrodes was associated with significant complications. Most of them were transient. Increased complication rates were related to left-sided grid insertion and longer monitoring with a greater number of electrodes (especially more than 60 electrodes). Improvements in grid technology, surgical technique, and postoperative care resulted in significant reductions in the complication rate.

Cortical somatosensory evoked potentials in response to hand stimulation

Somatosensory evoked potentials were recorded from chronically implanted subdural electrodes in six patients with intractable seizures. The following conclusions were reached: 1) The initial cortical negativity-positivity (N1 with a latency of about 20 msec and P2 with a latency of about 24 msec) recorded in the postcentral area was an expression of the classical primary surface positivity, but N1 was generated by the posterior pole of an early horizontal dipole in area 3b, and P2 was generated by the positive pole of a slightly delayed vertical dipole in area 1 and 2.2) P2 permitted the most accurate localization of the primary somatosensory area. 3) No potentials were elicited in the primary somatosensory area by stimulation of the ipsilateral hand. 4) No cortical potentials were seen at stimulation intensities below the sensory threshold. The cortical distribution of evoked potentials evoked by weak and strong intensities had significantly different distribution. 5) The recovery function of cortical evoked potentials showed a U-curve with an early period of facilitation (10 to 30 msec) followed by a prolonged period of subnormality which peaked at about 50 msec. The recovery curve at different cortical loci differed.

Extraoperative cortical functional localization in patients with epilepsy

Functional localization prior to cortical resections for intractable seizures has usually been performed in the operating room in awake patients. Chronically placed subdural electrodes offer the possibility of performing such testing outside of the operating room and without the unavoidable stresses and time limitations of the surgical setting. The use of the technique is reviewed.

Symptomatic Chiari malformation in adults: a new classification based on magnetic resonance imaging with clinical and prognostic significance.

Thirty-five consecutive adults with Chiari malformation and progressive symptoms underwent surgical treatment at a single institution over a 3-year period. All patients underwent magnetic resonance imaging scan before and after surgery. Images of the craniovertebral junction confirmed tonsillar herniation in all cases and allowed the definition of two anatomically distinct categories of the Chiari malformation in this age group. Twenty of the 35 patients had concomitant syringomyelia and were classified as Type A. The remaining 15 patients had evidence of frank herniation of the brain stem below the foramen magnum without evidence of syringomyelia and were labeled Type B. Type A patients had a predominant central cord symptomatology; Type B patients exhibited signs and symptoms of brain stem or cerebellar compression. The principal surgical procedure consisted of decompression of the foramen magnum, opening of the fourth ventricular outlet, and plugging of the obex. Significant improvement in preoperative symptoms and signs was observed in 9 of the 20 patients (45%) with syringomyelia (Type A), as compared to 13 of the 15 patients (87%) without syringomyelia (Type B). Postoperative reduction in syrinx volume was observed in 11 of the 20 patients with syringomyelia, including all 9 patients with excellent results. Magnetic resonance imaging has allowed a classification of the adult Chiari malformation in adults based on objective anatomic criteria, with clinical and prognostic relevance. The presence of syringomyelia implies a less favorable response to surgical intervention.

Clinical outcome after complete or partial cortical resection for intractable epilepsy

This is the first epilepsy surgery series to analyze the definition of “completeness” of resection, based solely on results of chronic scalp and subdural EEG recording. When patients had complete removal of all cortical areas with ictal and interictal epileptiform discharges, the clinical outcome was usually good. When areas with epileptiform discharges were left behind, good outcome was significantly less frequent. This correlation between complete resection and good outcome was independent of the presence or absence of CT-detected structural lesions or sharp waves on post-resection electrocorticography. These results support completeness of resection, defined by prolonged extraoperative EEG, as an important factor in seizure surgery.

Extent of Resection in Temporal Lobectomy for Epilepsy. I. Interobserver Analysis and Correlation with Seizure Outcome

Summary: The extent of resection was assessed in 45 temporal lobectomies for medically intractable epilepsy with mapped temporal lobe foci. Postoperative magnetic resonance imaging (MRI) in the coronal plane was used to quantify the extent of resection of superior lateral, inferior lateral, basal, and medial structures, including the amygdalohippocampal complex. A new 20‐compartment model of the temporal lobe was used for this assessment. Blinded interobserver variability was minimal. Intraoperative measurements and maps routinely overestimated the actual extent of resection, especially of medial structures. One year after surgery, 70% of patients remained seizure‐free (except for auras). Seizure‐free outcome was accomplished despite varying degrees of resection, but was more likely achieved with more extensive resections in all compartments. Among patients with mesiobasal foci, seizure‐free outcome correlated significantly with extent of resection of amygdalohippocampal complex. We conclude that assessment of extent of resection by postoperative MRI provides an objective basis of evaluating outcome after temporal lobectomy. It allows a rational approach to understanding of operative failures and is potentially useful in comparing efficacy of various surgical approaches.

Spinal Neurofibromas: A Report of 66 Cases and a Comparison with Meningiomas

A series of 66 spinal cord neurofibromas was analyzed for history, signs, surgical approach, and outcome. The tumors presented primarily with sensory symptoms. Plain films were abnormal in 1/2 of cases and 1/2 had a complete block. They were primarily intradural, and primarily thoracic. A conservative exam system was used for follow-up and 85% with pain had complete relief; 50% with motor loss had normal motor function, and 88% had normal sensation who had prior sensory loss. In comparison to meningiomas, the principal differences were that neurofibromas had an even sex distribution, a lower incidence of cord signs and symptoms, more frequent findings on plain x-rays, and higher cerebrospinal fluid protein. Surgical outcome was similar. Sacrifice of the involved root during removal usually did not produce a deficit. The series is compared with a similar series of meningiomas from the same institution over the same time period.

Transient neuropsychological abnormalities (including Gerstmann' s syndrome) during cortical stimulation

A patient with intractable partial seizures was intensively studied before surgical removal of the epileptogenic focus. A subdural electrode array was surgically placed over the left temporoparietal cortex to better localizethe epileptogenic focus and localize cortical function. In addition to speech and sensory findings, acalculia, agraphia, right-left confusion, and finger agnosia were transiently produced by electrical stimulation in the perisylvian area. These findings and their relationship to the controversy surrounding Gerstmanns syndrome are discussed.