Intraoperative localization of functional regions in the sensorimotor cortex by neuronavigation and cortical mapping

Surgery of lesions within the central region requires exact intraoperative anatomical orientation and knowledge of the position of functional cortical regions to minimize the surgical trauma and to avoid postoperative neurological deficits. We combined somatosensory evoked potential (SSEP) phase reversal and/or cortical electrical stimulation with neuronavigation in 26 patients for localization and visualization of functional cortical areas and their anatomical site in relation to the lesion. After location of the central sulcus by means of SSEP phase reversal, the precentral gyrus was electrically stimulated to detect functional motor regions. Electrode position was documented, and the functional regions were related to the site of the lesion using a specially developed neuronavigation system. In 11 of 15 patients the central fissure was located with SSEP phase reversal. Electrical stimulation yielded motor evoked potentials in 23 of the total 26 patients. The anatomical site of these functional regions and their relation to the lesion were evaluated with the neuronavigation system. The precentral gyrus, central sulcus, and postcentral gyrus could be identified in all 23 cases. The combination of intraoperative electrophysiological mapping and neuronavigation provides safe and reliable localization of the sensorimotor cortex. This technique is a promising tool to minimize the risk of surgically caused sensory and motor deficits.     

An increase in extracellular glutamate is a sensitive method of detecting ischaemic neuronal damage during cranial base and cerebrovascular surgery. An in vivo microdialysis study

All patients undergoing neurological surgery are at risk for serious complications. Ischaemic damage presenting with hemiparesis or speech difficulties occurs in up to 6% of patients undergoing cerebral bypass procedures and other complicated neurosurgical procedures. Currently available methods for detection of such damage include the use of somatosensory evoked potentials (SSEPs) and electro-encephalography (EEG). Unfortunately, these techniques have false positives and may remain normal in the presence of severe focal neurological deficits. Early detection of potential deficits may prevent or minimize damage through a change in operative or anaesthetic strategy. With the availability of several potential neuroprotective compounds, it is also possible to treat patients at risk of developing ischaemic complications if the individuals are identified early. The excitatory neurotransmitter glutamate is not only a metabolic product, but is also thought to promote ischaemia induced cell injury if released into the extracellular space. It may be a significant parameter for ischaemic brain metabolism. In this report we describe 10 patients who underwent extracranial-intracranial (EC-IC) high flow bypass procedures with routine intra-operative monitoring (IOM) as well as intra-operative in-vivo microdialysis measurement of glutamate. Our aim was to compare intra-operative microdialytic findings and IOM findings with respect to patients' early postoperative clinical courses. Three patients had significant intra-operative glutamate increases indicating ischaemia. Two of these patients awoke with a new neurological deficit (hemiparesis). Routine IOM findings were either normal or showed only transient changes during the time the glutamate levels were high. Our study shows that an increase in extracellular glutamate, as monitored by in-vivo microdialysis, is an excellent early market of neuronal damage. While our glutamate measurements were done off-line, it may be possible to get in future continuous on-line measurements to serve as an early warning system for potential ischaemic damage.     

Role of the premotor cortex in recovery from middle cerebral artery infarction

OBJECTIVE: To study the mechanisms underlying recovery from middle cerebral artery infarction in 7 patients with an average age of 53 years who showed marked recovery of hand function after acute severe hemiparesis caused by their first-ever stroke. INTERVENTIONS: Assessment of motor functions, transcranial magnetic stimulation, somatosensory evoked potentials, magnetic resonance imaging, and positron emission tomographic measurements of regional cerebral blood flow during finger movement activity. RESULTS: The infarctions involved the cerebral convexity along the central sulcus from the Sylvian fissure up to the hand area but spared the caudate nucleus, thalamus, middle and posterior portions of the internal capsule, and the dorsal part of the precentral gyrus in each patient. After recovery (and increase in motor function score of 57%, P<.001), the motor evoked potentials in the hand and leg muscles contralateral to the infarctions were normal, whereas the somatosensory evoked potentials from the contralateral median nerve were reduced. During fractionated finger movements of the recovered hand, regional cerebral blood flow increases occurred bilaterally in the dorsolateral and medial premotor areas but not in the sensorimotor cortex of either hemisphere. CONCLUSIONS: Motor recovery after cortical infarction in the middle cerebral artery territory appears to rely on activation of premotor cortical areas of both cerebral hemispheres. Thereby, short-term output from motor cortex is likely to be initiated.     

Combined utility of functional MRI, cortical mapping, and frameless stereotaxy in the resection of lesions in eloquent areas of brain in children

We studied 16 children with lesions in the eloquent brain to determine if the amalgamation of information from functional magnetic resonance imaging (fMRI), frameless stereotaxy, and direct cortical mapping and recording could facilitate the excision of these lesions while minimizing potential neurological deficits. The mean age of the children was 10 years. Fourteen children presented with seizures. All lesions were located in or near eloquent cerebral cortex. fMRI was successful in all patients in delineating the relationship between the lesion and regions of task-activated cortex. The ISG wand was utilized in all cases for scalp and bone flap placement, and for intraoperative localization of the lesion. Direct cortical stimulation or recording of phase reversals with somatosensory evoked potentials helped delineate the central sulcus and language cortex in patients with lesions near the motor or language cortex. Intraoperative electrocorticography (ECoG) was utilized in all patients who presented with seizures to guide the extent of resection of the epileptiform cortex. Ten children had benign cerebral neoplasms, nine of which were totally resected. The other diagnoses included vascular malformations, Sturge-Weber, tuberous sclerosis, Rasmussen's encephalitis, and primitive neuroectodermal tumor. Only 1 patient with a left Rolandic AVM developed a new neurological deficit postoperatively. Thirteen of fourteen patients who presented with seizure disorders were rendered either seizure free or improved in terms of seizure control postoperatively. Follow-up has ranged from 12 to 18 months, with a mean follow-up of 15 months. We conclude that the techniques of fMRI, frameless stereotaxy, direct cortical stimulation and recording can be utilized in sequence to accurately localize intracerebral lesions in eloquent brain, and to reduce the morbidity of resecting these lesions in children.     

Consonant and vowel production of right hemisphere patients

Recent reports of subclinical phonetic deficits in posterior and most particularly in Wernicke's aphasics have challenged the traditional dichotomy which characterized speech deficits in aphasia as anterior/phonetic and posterior/phonological. It is unclear whether the basis of the phonetic deficit in posterior aphasics reflects the fact that the speech production system extends to more posterior regions of the left hemisphere than previously thought or alternatively is the result of generalized brain damage effects. The present study explores the latter possibility by investigating the patterns of speech production in right hemisphere brain-damaged, non-aphasic patients with anterior and posterior lesions. Acoustic analyses conducted on a range of consonant and vowel parameters showed differences between the speech patterns of both anterior and posterior right hemisphere patients and that of Wernicke's aphasics. These findings suggest that the subclinical deficit of Wernicke's aphasics can not simply be ascribed to a generalized brain-damage effect and raise the possibility that the right hemisphere also plays some role, if only a minor one, in the phonetic implementation of speech.     

Mismatch negativity in the neurophysiologic/behavioral evaluation of auditory processing deficits: a case study

The subject of this case report is an 18-year-old woman with grossly abnormal auditory brain stem response (ABR), normal peripheral hearing, and specific behavioral auditory processing deficits. Auditory middle latency responses (MLRs) and cortical potentials N1, P2, and P300 were intact. The mismatch negativity (MMN) was normal in response to certain synthesized speech stimuli and impaired to others--consistent with her behavioral discrimination of these stimuli. Behavioral tests of auditory processing were consistent with auditory brain stem dysfunction. A neuropsychological evaluation revealed normal intellectual and academic performance. The subject was in her first year of college at the time of the evaluation. This case study is important because: (1) Although there have been several reports of absent/abnormal ABR with preserved peripheral hearing and deficits in auditory processing, little is known about the specific nature of the auditory deficits experienced by these individuals. Such information may be valuable to the clinical management of patients with this constellation of findings. (2) Of interest is the information that the mismatch negativity (MMN) cortical event-related potential can bring to the evaluation of patients with auditory processing deficits. The MMN reflects central auditory processing of small acoustic differences and may provide an objective measure of auditory discrimination. (3) From a theorectical standpoint, a patient with neural deficits affecting specific components of the auditory pathway provides insight into the relationship between evoked potentials and physiological mechanisms of auditory processing. How do various components of the auditory pathway contribute to speech discrimination? How might evoked potentials reflect the processes underlying the neural coding of specific features of speech stimuli such as timing and spectral cues?     

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BACKGROUND: The purpose of this study was to find out whether specific cortical potentials can be evoked and identified after word stimulation. The clinical relevance was to be investigated in patients with aphasic syndromes. MATERIALS AND METHODS: In 20 young adults with no signs of hearing impairment and in patients with manifest aphasic syndromes, word-evoked cortical potentials were compared with those after an equivalent noise stimulus. The test words were selected from the Freiburger Speech Comprehension Test. The duration of the words was between 450 and 640 ms. The stimulus was presented monaurally. The peak level was 70 dB HL. The noise stimulus was produced by modifying a low-band noise. Potentials were measured between the ipsilateral mastoid and the contralateral forehead. Data were analysed offline. RESULTS: In healthy persons, the potentials after word and noise stimulation did not differ until 100 ms after the stimulus onset. After noise stimulation a negative maximum could be seen 100 ms after the stimulus onset, and a positive maximum 200 ms after the stimulus onset. After word stimulation, a positive maximum of higher amplitude than after noise stimulation was measured 150 ms after the stimulus onset, and a negative maximum was measured 270 ms after the stimulus onset. In all test persons the difference curve of word-and noise-evoked potentials revealed a speech-specific component 170 ms (N 170) after the stimulus onset. The single-word analysis showed that the potentials depend on the phonemes of the test word. The potentials do not alter when the stimulus side is changed. In patients with aphasia the potentials depend on the grade of the disturbance of speech perception: global and Wernicke's aphasia show no significant difference of speech-and noise-evoked potentials, whereas in Broca's aphasia a speech specific maximum is apparent. CONCLUSION: The speech-specific component may be regarded as a paradigm of cortical speech detection processes. Electrophysiological speech audiometry by means of word-evoked cortical potentials seems possible and may be used for clinical purposes.     

Comparison of magnetoencephalography, functional MRI, and motor evoked potentials in the localization of the sensory-motor cortex

To clarify the topographical relationship between peri-Rolandic lesions and the central sulcus, we carried out presurgical functional mapping by using magnetoencephalography (MEG), functional magnetic resonance imaging (f-MRI), and motor evoked potentials (MEPs) on 5 patients. The sensory cortex was identified by somatosensory evoked magnetic fields using MEG (magnetic source imaging (MSI)). The motor area of the hand region was identified using f-MRI, during a hand squeezing task. In addition, transcranial magnetic stimulation localized the hand motor area on the scalp, which was mapped onto the MRI. In all cases, the sensory cortex was easily identified by MSI and the results of MSI correlated well with the findings obtained by the intraoperative recording of somatosensory evoked potentials. In contrast, the motor cortex could not be localized by f-MRI due to either the activated signal of the large cortical vein or the lack of any functional activation in the area of peri-lesional edema. MEPs were also unable to localize the entire motor strip. Therefore, at present, MSI is considered to be the most reliable method to localize peri-Rolandic lesions [corrected].     

Functional reinnervation in patients with a diagnosis of lower motor neuron neurogenic bladder: prognostic and therapeutic considerations

OBJECTIVE: To evaluate bladder and urethral sphincter reinnervation mechanisms during long-term follow-up in patients with lower motor neuron neurogenic bladder following neurological surgical injury. METHODS: A urodynamic study was conducted in 30 patients (21 male and 9 female; mean age 53.4 years) with lower motor neuron neurogenic bladder dysfunction arising from neurological injury sustained during surgery. The protocol included cystometry and periurethral electromyography (EMG) at 3, 6, 9, 12 months and once a year for 7 years, and videocystography at 3, 12 months and once a year for 7 years. Functional parasympathetic (detrusor) reinnervation criteria were cystometric. Functional sympathetic (bladder neck) reinnervation criteria were cystographic. Functional pudendal (periurethral sphincter) reinnervation criteria were electromyographic (increase of polyphasic and long amplitude and/or long time potentials). RESULTS: Detrusor reinnervation was demonstrated in 6 male patients (20%) with an average period of 44.6 months. Pudendal reinnervation was demonstrated in 17 patients (77.2%) with an average period of 17.6 months. EMG potentials were polyphasic in 17 cases and long amplitude/long time potentials in 3 cases. Sympathetic reinnervation was demonstrated in one patient (16.6%) at 60 months. CONCLUSIONS: Functional pudendal reinnervation of the periurethral sphincter was more frequent and was demonstrated earlier than reinnervation in vegetative elements (parasympathetic and sympathetic). Parasympathetic reinnervation had long-term therapeutic implications. Ongoing urodynamic assessment in patients with lower motor neuron neurogenic bladder following abdominoperineal resection or intervertebral disc prolapse surgery is warranted. Sympathetic reinnervation was scanty and was demonstrated later in relation to distal postganglionic fibers.     

Spontaneous disappearance of arteriovenous malformation during staged treatment of multiple cerebral arteriovenous malformations--case report

A 36-year-old male presented with aphasia and right hemiparesis due to the rupture of the larger of two arteriovenous malformations (AVMs) coexisting in the left hemisphere. The two AVMs had completely separate locations and different feeding arteries and draining systems. Two months after resection of the larger AVM and evacuation of the hematoma, carotid angiography showed the residual AVM had spontaneously disappeared. He was discharged without deficits. Change of cerebral hemodynamics after removal of the larger AVM presumably caused the spontaneous regression of the smaller one. Cerebral angiograms should be carefully examined because cerebral hemodynamics may be altered after removal of an AVM.     

Correlations between clinical deficits, motor and sensory evoked potentials and radiologic aspects of MRI in malformative syringomyelia. 27 Cases

Twenty-seven patients (15 males, 12 females, age range: 16-66 years) were admitted for malformative syringomyelia diagnosed on MRI with measures of syrinx extending and transverse diameter. Posterior tibial somatosensory evoked potentials (PT SEP), median (M SEP), trigeminal (V3 SEP), brain stem auditory evoked potentials (BEAP), cortical and cervical motor evoked potentials (MEP) were correlated with clinical and radiological findings. SEP abnormalities were not correlated with the duration of symptoms. PT SEP proved to be more sensitive than M SEP. MEP abnormalities were very frequent (87% of the cases), even without clinical motor deficits. Trigeminal SEP were more sensitive than BEAP which were not related to the presence of associated cranio-vertebral abnormalities. We found no significative relationship between clinical and radiological results. Moreover, there was a positive relationship between electrophysiological and radiological results: abnormal trigeminal SEP were detected in 85% of the patients with high cervical syringomyelia. In all cases, trigeminal SEP and MEP should be done in association with M and PT SEP as both of them detect subclinical evidence of spinal cord dysfunction in syringomyelia.     

Effects of reversible inactivation of the supplementary motor area (SMA) on unimanual grasp and bimanual pull and grasp performance in monkeys

The supplementary motor area (SMA) was reversibly inactivated by muscimol microinfusion in two monkeys while they were performing two motor tasks: (1) a delayed conditional bimanual drawer pulling and grasping sequence which was initiated on a self-paced basis; (2) a unimanual reach and grasp task (modified Kluver board task). Unilateral or bilateral inactivation of the SMA induced a prominent deficit in trial initiation of bimanual sequential movements, affecting the hand contralateral to the inactivated side or both hands, respectively. The deficit was a long lasting (10-15 min or more) inability of the monkey to place its hand (s) in the ready position on start touch-sensitive pads, a condition required to initiate the drawer task. However, if after such a deficit period, the experimenter put his hand on the start touch-sensitive pad to initiate the trial, then the monkey executed the drawer task without obvious motor deficit. SMA inactivation did not affect unimanual reaching and grasping movements in the board task. In contrast to the SMA, inactivation of other motor areas (primary, premotor dorsal, anterior intraparietal area) did not affect the initiation of movement sequences in the drawer task. These data thus indicate that the SMA plays a crucial and specific role in initiation of self-paced movement sequences. However, SMA inactivation did not prevent the monkeys to perform coordinated movements of the two forelimbs and hands, indicating that SMA is not necessary for bimanual coordination.     

Magnetic source imaging combined with image-guided frameless stereotaxy: a new method in surgery around the motor strip

OBJECTIVE: In this study, information about the localization of the central sulcus obtained by magnetic source imaging (MSI) was intraoperatively translated to the brain, using frameless image-guided stereotaxy. In the past, the MSI results could be translated to the surgical space only by indirect methods (e.g., the comparison of the MSI results, displayed in surface renderings, with bony landmarks or blood vessels on the exposed brain surface). METHODS: Somatosensory evoked fields were recorded with a MAGNES II biomagnetometer (Biomagnetic Technologies Inc., San Diego, CA). Using the single equivalent current dipole model, the localization of the somatosensory cortex was superimposed on magnetic resonance imaging with a self-developed contour fit program. The magnetic resonance image set containing the magnetoencephalographic dipole was then transferred to a frameless image-guided stereotactic system. Intraoperatively, the gyrus containing the dipole was identified as the postcentral gyrus, using neuronavigation, and the next anterior sulcus was regarded as the central sulcus. With intraoperative cortical recording of somatosensory evoked potentials, this assumption was verified in each case. RESULTS: In all cases, the preoperatively assumed localization of the central sulcus and motor cortex with MSI agreed with the intraoperative identification of the central sulcus using the phase reversal technique. CONCLUSION: The combined use of MSI and a frameless stereotactic system allows a fast orientation of eloquent brain areas during surgery. This may contribute to a safer and more radical surgery in lesions adjacent to the motor cortex.     

Bilateral hemispheric activation in the early recovery of motor function after stroke

BACKGROUND AND PURPOSE: Functional recovery after cerebral infarction is a complex phenomenon that depends on various factors. The aim of this study was to investigate changes in cerebral perfusion during motor activity in stroke patients with very early recovery of motor function. METHODS: We included 9 consecutive patients hospitalized for acute-onset hemiparesis who showed complete functional recovery within 24 hours. CT of the brain showed an ischemic or hemorrhagic cerebral lesion in areas compatible with the symptomatology. Within 36 hours (range, 28 to 36) all patients were examined for the effects of a thumb-to-finger opposition task on cerebral blood flow in the middle cerebral arteries, evaluated by means of bilateral transcranial Doppler ultrasonography. Data were compared with those of 9 healthy subjects matched for age and sex. In patients, the evaluation was repeated 2 to 4 months later. RESULTS: A comparable increase in flow velocity (% mean+/-SD) was observed with respect to baseline in the contralateral middle cerebral artery during motor activity with patients' normal (8.8+/-2.0%) and recovered hand (9.7+/-4.1%) and with both hands of control subjects (10.6+/-1.4%). In the middle cerebral artery ipsilateral to the hand performing the motor task, the increase in flow velocity was significantly higher (P<0.0001) during movement of the recovered hand in patients (8.6+/-2.7%) than during movement of the normal hand in both patients (2.6+/-1.6%) and control subjects (1.4+/-0.7%). In patients, pattern of changes in flow velocity during motor performance remained the same in the second evaluation. CONCLUSIONS: These observations suggest that areas of the healthy hemisphere can be activated soon after a focal injury and contribute to the positive evolution of a functional deficit in some patients. This phenomenon of ipsilateral activation cannot be considered transient because it is evident months after stroke onset.     

Motor recovery following spinal cord injury associated with cervical spondylosis: a collaborative study

A prospective multicenter study was conducted within the National Model Spinal Cord Injury System program to examine neurological deficits and recovery patterns following spinal cord injury (SCI) in individuals with cervical spondylosis and without a spinal fracture. Nineteen patients were evaluated. Sixty-eight percent presented initially with motor incomplete lesions. Of those who presented with motor incomplete injuries at their initial examination, 69 percent had less deficit in the lower than in the upper extremities, indicative of a central cord syndrome. At follow-up, 12 subjects were unable to ambulate, four required assistance and three were able to ambulate independently. On the average, subjects doubled their initial Asia Motor Score (AMS) scores by one year following injury. Residual upper extremity weakness, however, limited the ability to ambulate. Recovery of motor strength in this group is comparable to that of individuals with incomplete tetraplegia in general but the proportion who regain ambulatory function is less.     

Long-term cognitive deficits following posterior fossa tumor resection: A neuropsychological and functional neuroimaging follow-up study.

The posterior fossa syndrome (PFS) consists of transient cerebellar mutism, cognitive symptoms, and neurobehavioral abnormalities that typically develop in children following posterior fossa (PF) tumor resection. The pathophysiological substrate of the syndrome remains unclear. We investigated eight children of whom five presented with a variety of clinically relevant non-motor language symptoms associated with cognitive and behavioral disturbances after PF tumor resection. Four children developed transient cerebellar mutism followed by dysarthric speech. Non-motor language symptoms consisted of agrammatism, anomia, impaired verbal fluency, comprehension deficits, and aspontaneous speech. Neurocognitive deficits included executive dysfunctions, concentration deficits, and visuo-spatial disorders. In addition, all children presented with behavioral and affective disturbances. Functional neuroimaging studies during the phase of mutism by means of SPECT showed perfusional deficits in the anatomo-clinically suspected supratentorial areas subserving language dynamics, syntax, naming, executive functioning, affective regulation, and behavior. A significant improvement of frontal perfusional deficits paralleled the clinical remission of mutism. These results add to the view that the PFS might represent a cerebello-cerebral diaschisis phenomenon, reflecting the metabolic impact of the cerebellar lesion on supratentorial cognitive and affective functions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vascularized bone flaps versus nonvascularized bone grafts for mandibular reconstruction: an outcome analysis of primary bony union and endosseous implant success

We present a patient with a lesion of the mesial frontal cortex, including the supplementary motor areas bilaterally, who on clinical examination revealed no spontaneous movements, although neurophysiological examination indicated integrity of the corticospinal tract to thenar and tibialis anterior muscles bilaterally. The patient was alert, speech was hesitant, and he was able to move his hands only on command. The role of the supplementary motor areas in planning, setting, and execution of skillful voluntary movements has been previously established by direct cortical electrical stimulation and studies of regional cerebral blood flow. The findings in our patient support the role of the supplementary motor areas in initiating movements. The presence of motor evoked potentials after acute insults to the brain is considered to be associated with a good functional outcome. This is in contrast to our patient who did not show improvement in motor performance, despite preserved motor evoked potentials. Hence, in the case of bilateral lesions to the supplementary motor areas sparing the corticospinal tract, the presence of motor evoked potentials may not predict functional recovery.     

Magnetoencephalographic mapping: basic of a new functional risk profile in the selection of patients with cortical brain lesions

OBJECTIVE: Surgical management of cortical lesions adjacent to or within the eloquent cerebral cortex requires a critical risk: benefit analysis of the procedure before intervention. This study introduced a measure of surgical risk, based on preoperative magnetoencephalographic (MEG) sensory and motor mapping, and tested its value in predicting surgical morbidity. METHODS: Forty patients (21 men and 19 women; mean age, 36.5 yr) with cortical lesions (12 arteriovenous malformations and 28 tumors) in the vicinity of the sensorimotor cortex were classified into high-, medium-, or low-risk categories by using the MEG-defined functional risk profile (FRP). This was based on the minimal distance between the lesion margin and the sensory and motor MEG sources, superimposed on a magnetic resonance imaging scan. Case management decisions were based on the MEG mapping-derived FRP in combination with biopsy pathological findings, radiographic findings, and anatomic characteristics of the lesion. A recently developed protocol was used to transform MEG source locations into the stereotactic coordinate system. This procedure provided intraoperative access to MEG data in combination with stereotactic anatomic data displays routinely available on-line during surgery. RESULTS: It was determined that 11 patients diagnosed as having gliomas had high FRPs. The margin of the lesion was less than 4 mm from the nearest MEG dipole or involved the central sulcus directly. A nonoperative approach was used for six patients of this group, based on the MEG mapping-derived FRP. In the group with arteriovenous malformations, 6 of 12 patients with high or medium FRPs underwent nonoperative therapy. The remaining 28 patients, whose lesions showed satisfactory FRPs, underwent uneventful lesion resection, without postoperative neurological deficits. CONCLUSION: Our results suggest that MEG mapping-derived FRPs can serve as powerful tools for use in presurgical planning and during surgery.     

The predictive value of intraoperative somatosensory evoked potential monitoring: review of 244 procedures

INTRODUCTION: There is some controversy regarding the value of intraoperative neurophysiological monitoring in predicting postoperative neurological deficits. We discuss our experience with the use of intraoperative somatosensory evoked potentials (SSEPs) during surgery of cranial base tumors. METHODS: We retrospectively reviewed all of the procedures that had been performed for the resection of cranial base tumors from July 29, 1993, through March 16, 1995. One hundred ninety-three consecutive patients had undergone a total of 244 procedures. SSEP waveforms were classified as follows: Type I, no change; Type II, change that reverts to baseline; Type III, change that does not revert to baseline; and Type IV, complete flattening of the SSEP waveform without improvement. Two patients had no waveforms from the beginning of the case (Type V) and were excluded from further analysis. New immediate postoperative neurological deficits were recorded. RESULTS: There were 64 male and 129 female patients, with a mean age of 46.6 years. One hundred seventy-seven patients had Type I SSEP waveforms, 13 of whom had postoperative deficits (7%). Fifty-six patients had Type II SSEPs, and nine (16%) of them had postoperative neurological deficits. Six patients had Type III SSEPs, and three had Type IV SSEPs, all of whom (100%) had postoperative deficits. There was a correlation between SSEP type and the results of the postoperative neurological examinations. The positive predictive value is 100%, and the negative predictive value is 90%. Although a change in the waveform that did not revert to baseline (Types III and IV) always predicted a postoperative deficit, a normal waveform did not always rule out postoperative deficits. Pathological abnormality, vessel encasement, vessel narrowing, degree of cavernous sinus involvement, brain stem edema, middle fossa location, final amount of resection, age, and tumor size correlated with a high predictive value of SSEP monitoring on univariate analysis (P < 0.05). None of these variables correlated significantly on multivariate analysis (P > 0.05), although brain stem edema was close (P = 0.0571). CONCLUSION: Intraoperative SSEPs have a high positive predictive value during surgery for cranial base tumors, but they do not detect all postoperative deficits.     

Repetitive speech disorder resulting from infarcts in the paramedian thalami and midbrain

A repetitive speech disorder resulting from infarcts in the paramedian thalami and the midbrain is reported. Although the speech disorder seemed like stuttering, the compulsive repetitions, constant rate and monotonous tone were not associated with ordinary stuttering. Since repetition was restricted to the first syllable, the speech disorder in our patient could be distinguished from palilalia. The extrapyramidal system is considered responsible for repetitive speech disorders resulting from infarcts in the paramedian thalami and the midbrain but without good reason. Repetitive speech disorder in patients with infarcts in the supplementary motor area (SMA) have similar clinical features to our patient. It is suggested that interruption in the projective system to the SMA is a possible cause of "stuttering like repetition".