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Adam N. Mamelak, Nancy Lopez, Massoud Akhtari and W. William Sutherling

Object. Magnetoencephalography (MEG) and magnetic source (MS) imaging are techniques that have been increasingly used for preoperative localization of epileptic foci and areas of eloquent cortex. The use of MEG examinations must be carefully balanced against the high cost and technological investments required to perform these studies, particularly when less expensive alternative localization methods are available. To help elucidate the value of MEG, the authors have critically reviewed their experience with whole-head MEG in the case management of patients undergoing epilepsy surgery.

Methods. The authors identified 23 patients with suspected focal epilepsy who underwent whole-head MEG and MS imaging at Huntington Memorial Hospital and, subsequently, underwent invasive intracranial electrode monitoring and electrocorticography (ECoG) to localize the zone of seizure origin for surgical resection. The results of the MS imaging were retrospectively stratified into three groups by the number of interictal spikes recorded during a 4-hour recording session: Class I (no spikes), Class II (≤ five spikes), and Class III (≥ six spikes). Class III was further subdivided according to the clustering density of the interictal spikes: Class IIIA represents a mean distance between interictal spikes of 4 mm or greater (that is, diffusely clustered) and Class IIIB represents a mean distance between interictal spikes of less than 4 mm (that is, densely clustered). The authors analyzed these groups to determine to what extent the results of MS imaging correlated with the ECoG-determined zone of seizure origin. In addition, they assessed whether the MS imaging study provided critical localization data and correlated with surgical outcome following resection. A statistical analysis of these correlations was also performed.

Of the 40 patients studied, 23 underwent invasive monitoring, including 13 with neocortical epilepsy, four with mesial temporal lobe epilepsy, and six with suspected neocortical epilepsy that could not be clearly localized by ECoG. Depth electrodes were used in nine cases, subdural grids in nine cases, depth electrodes followed by subdural grids and strips in four cases, and intraoperative ECoG in one case. Electrocorticography was able to localize the zone of seizure origin in 16 (70%) of 23 cases. In 11 (69%) of the 16 cases in which ECoG was able to localize the zone of seizure origin, the interictal spikes on the MS images were classified as Class IIIB (densely clustered) and regionally correlated to the MS imaging—determined localization in all cases (that is, the same lobe). In contrast, no Class IIIB cases were identified when ECoG was unable to localize the zone of seizure origin. This difference showed a trend toward, but did not achieve, statistical significance (p < 0.23), presumably because of the relatively small number of cases available for analysis. In three cases (all Class IIIB), MS imaging was used to guide invasive electrodes to locations that otherwise would not have been targeted and provided unique localization data, not evident from other imaging modalities, that strongly influenced the surgical management of the patient. The classification of findings on MS images into subgroups and subsequent statistical analysis generated a model that predicted that Class IIIB MS imaging data are likely to provide reliable information to guide surgical placement of electrodes, but all other data groups do not provide localization information that is reliable enough to guide surgical decision making.

Conclusions. Magnetic source imaging can provide unique localization information that is not available when other noninvasive methods are used. Magnetic source imaging appears most useful for cases of neocortical epilepsy. In particular, when an MS imaging study revealed six or more interictal spikes that were densely clustered in a single anatomical location, the MS image was highly correlated with the zone of seizure origin identified by ECoG. In these cases the MS imaging data may be useful to guide placement of intracranial electrodes.

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Adam N. Mamelak, Gregory J. Withers and Xuedong Wang

✓ The authors report the case of a woman who presented during her 30th week of pregnancy with a large brain metastasis from a previously undetected metastatic choriocarcinoma. The metastasis caused significant neurological deficit due to mass effect, necessitating rapid intervention. Medical management included a regimen of high-dose corticosteroid medications for 36 hours, followed by cesarean delivery of the fetus and craniotomy to remove the metastatic tumor; chemotherapy and radiation therapy were begun within 1 week postsurgery. Both the baby and mother survived, and as of the 1-year follow-up examination, there was no evidence of disease in the mother. This is only the second report of a metastatic choriocarcinoma associated with a simultaneous viable intrauterine pregnancy, and the only case in which surgical removal of a brain metastasis was required. Coordinated multidisciplinary treatment of mother and fetus by members of the neurosurgery, medical oncology, neonatology, and obstetrics services facilitated a good outcome in this case.

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Adam N. Mamelak, Philip H. Cogen and A. James Barkovich

✓ This report describes the unique case of a child born with paraplegia and a neurogenic bladder who was found to have a dysplastic, nonossified T-12 vertebral body, midline fusion of the T-12 neural arches, obliteration of the spinal canal at T-12, and an extraspinal thecal sac in the T11—L1 region. Neural tissue was focally absent from T9–12, but neural structures above and below were preserved. Narrowing of the thecal sac on myelograms and sagittal magnetic resonance images signifies in utero focal infarction of the spinal cord after neurulation but before formation of the posterior half of the spinal canal. The infarction resulted in severe focal narrowing of the thecal sac from T10—L1, resembling a premature and duplicated filum terminale; to denote the radiographic appearance of these anomalies, the authors have coined the term “filum intermedium” sign.

The extremely unusual radiographic findings in this child illustrate the important interactions between neural tube, neural crest, and somite in the development of the spinal cord and spinal column. Correlation of the radiographic findings with the embryological differentiation and migration of these structures suggests that the spinal anomalies were caused by a focal insult, probably vascular in origin, occurring between the sixth and eighth weeks of gestation. The identification of a focally narrowed thecal sac and spinal cord (the “filum intermedium” sign) localizes the time of the insult to between the first and third month of gestation, and therefore is a useful marker in understanding developmental malformation of the spinal cord.

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Adam N. Mamelak, Michael D. Prados, William G. Obana, Philip H. Cogen and Michael S. B. Edwards

✓ Little is known about the risk of developing multicentric disease in patients with juvenile pilocytic astrocytoma (JPA), and even less about its prognosis. Only five cases have been reported. Between 1986 and 1992, the authors treated 90 patients with either primary or recurrent JPA, 11 of whom developed multicentric spread. Ten patients had primary tumors in the hypothalamic region, eight were under 4 years of age at initial diagnosis, all had initially undergone a subtotal resection or biopsy, and 10 received postoperative multiagent chemotherapy or irradiation for residual disease. Multicentric spread was discovered immediately to 108 months after initial diagnosis; nine patients were asymptomatic at the time. Most patients received chemotherapy for the multicentric disease, which was found throughout the craniospinal axis. During 21 to 148 months of follow-up monitoring, seven patients had stabilization or regression of multicentric disease and four died. Patients with hypothalamic region tumors were 23 times more likely to develop multicentric spread than were those with primary tumors located elsewhere (p < 0.001). Based on this review, it is concluded that multicentric spread of JPA occurs more frequently than was previously recognized. In patients with subtotally resected JPA and several years of follow-up review via magnetic resonance imaging, the incidence of recurrence in a site different from the original was 12%. Patients with subtotally resected JPA in the hypothalamic region should be considered to be at high risk for developing multicentric spread. Chemotherapy appears useful in stabilizing multicentric disease. Earlier detection and intervention may result in longer disease-free survival in patients with multicentric spread of JPA.

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Adam N. Mamelak, Nicholas M. Barbaro, John A. Walker and Kenneth D. Laxer

✓ Corpus callosotomy is valuable for controlling medically intractable generalized seizures in appropriate patients, but postoperative development of language disorders, neuropsychological impairment, and motor dysfunction have all been noted. The extent of callosum resection has been implicated as a possible determinant of outcome, but this hypothesis has not been formally tested. Analysis of the records of all patients who underwent corpus callosotomy at the University of California, San Francisco, from 1986 to 1991 showed that, of 15 patients who underwent anterior or complete callosotomy, seven were entirely or nearly seizure-free, four had at least a 50% reduction in seizure frequency, and four had no change.

To determine callosal size and extent of callosotomy, preoperative and postoperative magnetic resonance images were measured with computer-based planimetry. Seizure outcome was not significantly associated with preoperative callosal size or extent of callosotomy. Intelligence quotient scores did not change significantly after callosotomy. No severe neuropsychological deficits developed after anterior or complete callosotomy, even in patients with mixed cerebral dominance or bilateral language representation. These results indicate that division of the anterior one-half to two-thirds of the corpus callosum is nearly as effective as more extensive anterior sectioning or complete callosotomy in reducing drop-attack and generalized tonic-clonic seizures in appropriate patients, and that the extent of callosotomy is not an important factor on outcome when at least 50% to 65% of the callosum is divided. Mixed cerebral dominance and other unusual patterns of language and memory organization do not appear to increase the postoperative risk for neuropsychological deficits, regardless of the extent of anterior section.

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Adam N. Mamelak, William M. Kelly, Richard L. Davis and Mark L. Rosenblum

✓ Hypertrophic cranial pachymeningitis is a rare, idiopathic form of granulomatous pachymeningitis. This report describes three cases of hypertrophic cranial pachymeningitis and discusses the clinical, radiographic, and pathological findings in these and other reported cases. These lesions typically cause progressive cranial nerve palsies, headaches, and cerebellar dysfunction. They occur in patients of all age groups; the peak incidence is in the sixth decade. Hypertrophic cranial pachymeningitis is best identified by magnetic resonance imaging. The diagnosis is established by excluding all other granulomatous and infectious diseases. A dural biopsy is essential to confirm the diagnosis. Hypertrophic cranial pachymeningitis is initially responsive to steroid therapy, but in most cases it recurs or progresses despite treatment. Surgical excision of granulomas is occasionally necessary to alleviate a mass effect. The long-term outcome remains uncertain for most patients, but progressive disease is usually fatal owing to cranial neuropathies.

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