O. Suess

Intra-operative mapping of the motor cortex during surgery in and around the motor cortex.

Summary¶u2003The intra-operative use of neurophysiological techniques allows reliable identification of the sensorimotor region, and constitutes a prerequisite for its anatomical and functional preservation. The present prospective study combines monopolar cortical stimulation (MCS) with the recording of phase reversal of somatosensory evoked potentials (SEP-PR) in a protocol for the intra-operative mapping of the motor cortex. Functional mapping of the motor cortex by SEP-PR and MCS was performed in 70 patients during surgery in and around the motor cortex. The central sulcus was identified by SEP-PR. Cortical motor mapping was then performed by monopolar anodal (400 Hz) stimulation. Motor responses were recorded by needle electrodes placed in the muscles of the contralateral extremities. Surgery was performed under general anaesthesia without muscle relaxants.Intra-operative localization of the central sulcus by SEP-PR was possible in 68 patients (97.14%). Motor evoked potentials (MEP) were elicited following MCS in 67 cases (95.7%). In 3 cases no MEP was recorded, not even after maximal stimulation intensity, the central sulcus being localized by SEP-PR only. On the other hand, MCS allowed localizing the motor cortex in the 2 cases with no recordable SEP-PR. Thus, combining SEP-PR and MCS allowed intra-operative localization of the sensorimotor cortex in 100% of the cases.

Ruptured intracranial dermoid cysts.

BACKGROUNDnIntracranial dermoid cysts are rare congenital neoplasms that are believed to arise from ectopic cell rests incorporated in the closing neural tube. The rupture of an intracranial dermoid cyst is a relatively rare event that typically occurs spontaneously. In the past it was believed that rupture is always fatal, a hypothesis that is not supported by more recently reported cases. The symptoms associated with rupture vary from no symptoms to sudden death.nnnMETHODSnThe present paper analyzes published cases of ruptured intracranial dermoid cysts in terms of their age profile and their clinical presentation and describes an additional case.nnnRESULTSnAnalysis of published cases revealed headache (14 out of 44 patients; 31.8%) and seizures (13 out of 44 patients; 29.5%), to be the most common signs of rupture followed by, often temporary, sensory or motor hemisyndrome (7 out of 44 patients; 15.9%), and chemical meningitis (3 out of 44 patients; 6.9%).nnnCONCLUSIONnHeadache occurred primarily in younger patients (mean age 23.5 +/- 9.3 years), whereas seizures primarily occurred in older patients (mean age 42.8 +/- 11.3 years). The patients with sensory or motor hemisyndrome associated with rupture of an intracranial dermoid cyst showed a more homogeneous age distribution (mean age 38.4 +/- 23.5 years).

Comparison between monopolar and bipolar electrical stimulation of the motor cortex.

Summary¶u2003Intra-operative neurophysiological techniques allow reliable identification of the sensorimotor region and make their anatomical and functional preservation feasible. Monopolar cortical stimulation has recently been described as a new mapping technique. In the present study this method was compared to the “traditional” technique of bipolar stimulation.u2003Functional mapping of the motor cortex was performed in 35 patients during surgery in the central region. The central sulcus (CS) was identified by somatosensory evoked potential (SEP) phase reversal. Cortical motor mapping was first performed by monopolar anodal stimulation with a train of 500 Hz (7–10 pulses) followed by bipolar stimulation (pulses at 60 Hz with max. 4 sec train duration). Surgery was performed under general anaesthesia without muscle relaxants. Of 280 motor responses elicited by bipolar cortical stimulation, 54.28% [152] were located in the primary motor cortex (PMC), 37.85% [106] outside the motor strip in the secondary motor cortex (SMC), and 8% [22] posterior to the CS. Of 175 motor responses elicited by monopolar cortical stimulation, 68.57% [120] were located in the SMC, 23.42% [41] in the SMC and 8% [14] posterior to the CS.u2003Contrary to the general clinical view, there is considerable overlapping of primary motor units over a cortical area much broader than the “classical” narrow motor strip along the CS. Bipolar cortical stimulation is more sensitive than monopolar for mapping motor function in the premotor frontal cortex. Both methods are equally sensitive for mapping the primary motor cortex.

Intracranial haemorrhage following lumbar myelography: case report and review of the literature.

Abstract We describe a subacute intracranial subdural haematoma following lumbar myelography. This rare but potentially life-threatening complication has been reported both after lumbar myelography and following lumbar puncture for spinal anaesthesia. We review 16 previously reported cases of intracranial haemorrhage following lumbar myelography, and discuss the pathogenesis. In all reported cases post-puncture headache was the leading symptom and should therefore be regarded as a warning sign.

Intracranial image-guided neurosurgery: experience with a new electromagnetic navigation system.

Summary.Summary.Background: The aim of image-guided neurosurgery is to accurately project computed tomography (CT) or magnetic resonance imaging (MRI) data into the operative field for defining anatomical landmarks, pathological structures and tumour margins. To achieve this end, different image-guided and computer-assisted, so-called “neuronavigation” systems have been developed in order to offer the neurosurgeon precise spatial information.Method: The present study reports on the experience gained with a prototype of the NEN-NeuroGuardTM neuronavigation system (Nicolet Biomedical, Madison, WI, USA). It utilises a pulsed DC electromagnetic field for determining the location in space of surgical instruments to which miniaturised sensors are attached. The system was evaluated in respect to its usefulness, ease of integration into standard neurosurgical procedures, reliability and accuracy.Findings: The NEN-system was used with success in 24 intracranial procedures for lesions including both gliomas and cerebral metastases. It allowed real-time display of surgical manoeuvres on pre-operative CT or MR images without a stereotactic frame or a robotic arm. The mean registration error associated with MRI was 1.3 mm (RMS error) and 1.5 mm (RMS error) with CT-data. The average intra-operative target-localising error was 3.2 mm (± 1.5 mm SD). Thus, the equipment was of great help in planning and performing skin incisions and craniotomies as well as in reaching deep-seated lesions with a minimum of trauma.Interpretation: The NEN-NeuroGuardTM system is a very user-friendly and reliable tool for image-guided neurosurgery. It does not have the limitations of a conventional stereotactic frame. Due to its electromagnetic technology it avoids the “line-of-sight” problem often met by optical navigation systems since its sensors remain active even when situated deep inside the skull or hidden, for example, by drapes or by the surgical microscope.

Neoplasm of Endolymphatic sac Origin: Clinical, Radiological and Pathological Features

Summaryu2003This paper reports on a 55-year-old female who had undergone middle ear surgery 12 years previously and was admitted with a 6-months history of unilateral hearing loss and facial weakness. MRI and CT demonstrated a space-occupying lesion arising from the temporal bone and extending into the posterior fossa. Treatment consisted in complete tumour removal. Temporal and mastoid bone destruction associated with typical histological features led to the diagnosis of neoplasm of endolymphatic sac origin. Clinical, histological, radiological and intra-operative features of these rare tumours are described and discussed. The pertinent literature is reviewed.

Intraventricular cavernoma: unusual occurrence in the region of the foramen of Monro

A 36-year-old female was admitted with symptoms of progressive hydrocephalus and short-term memory deficits. CT and MRI revealed a partly calcified lesion with slight contrast enhancement located in the region of the right foramen of Monro. Diagnosis of cavernoma was not made by these images. On surgery, a deep purple mass composed of tightly packed thinwalled vessels was found attached to the foramen of Monro lying completely within the ventricular system. Histological diagnosis was cavernous malformation. The lesion was completely removed. Postoperatively, nausea and vomiting resolved immediately, whereas short-term memory deficits improved slowly. FIG. 1. (A) Computed tomography and (B) MRI demonstrating a mixed, hypoand hyperintense lesion with calcifications and slight contrast enhancement located in the region of the right foramen of Monro

Neurosurgical procedures in Jehovah's Witnesses: an increased risk?

OBJECTIVEBecause of the growing numbers of members worldwide in the sect of Jehovah’s Witnesses, the refusal of blood and blood products due to religious reasons is increasingly encountered in clinical practice. As an alternative to blood transfusion, Jehovah’s Witnesses accept blood-free volume substitution, and they sometimes accept the intraoperative reinfusion of autologous blood via a so-called cell saver. The aim of this study was to examine whether the refusal of blood transfusion affects the surgical indications for neurosurgery and whether morbidity and mortality rates are higher after neurosurgical interventions in Jehovah’s Witnesses. METHODSThe pre-, intra-, and postoperative hemoglobin and hematocrit values as well as coagulation parameters of a group of Jehovah’s Witnesses (n = 103) were compared with those of a valid control group. RESULTSThe total intraoperative blood loss during spinal and intracranial surgery in Jehovah’s Witnesses was often less than in controls, which suggests a less traumatic surgical procedure. Hemodynamically relevant blood loss occurred in two spinal and four intracranial interventions. The patients were managed without receiving blood transfusions or blood products, although increased time in the intensive care unit and increased convalescence days were necessary. Mean surgical times were 17.5 minutes longer for spinal interventions and 36.7 minutes longer for intracranial interventions than for patients in the control group. This may be attributed to a more careful and thus slower surgical technique and to longer and more extensive hemostasis. The length of hospitalization was 15% longer for Jehovah’s Witnesses than for controls. CONCLUSIONThe morbidity and mortality rates for Jehovah’s Witnesses undergoing neurosurgery were not higher than those of the control group. Thus, it can be concluded that Jehovah’s Witnesses did not have a higher risk when microsurgical techniques and extensive anesthetic monitoring were applied during neurosurgery. Because the surgical success rate for Jehovah’s Witnesses corresponded to that of the control group, the increase in costs because of longer treatment times is compensated in the long run by avoiding a lengthier illness, sometimes with more expensive conservative therapy.

A New Cortical Electrode for Neuronavigation-Guided Intraoperative Neurophysiological Monitoring: Technical Note

Summary¶u2003Intraoperative neurophysiological mapping and monitoring of eloquent brain areas can be combined with image-guided localisation to enhance the safety and efficacy of surgical procedures in the motor cortex. We designed a new type of cortical electrode which can be repeatedly placed on the cortical surface and allows accurate and reproducible stimulation by means of a navigation pointer.The newly designed device consists of a monopolar electrode contact for direct cortical stimulation, housed in a holder which allows placement, easy removal, and precise repeated placement of a surgical navigation pointer. It can be used for navigation-guided, high-frequency anodal monopolar cortical stimulation (MCS) for the mapping of eloquent cortex, and for monitoring of motor pathways. While the cortex is stimulated, compound muscle action potentials (CMAP) are recorded from muscles of the contralateral extremities and are assessed both qualitatively and quantitatively. When the device is used in combination with intraoperative navigation, the stimulation sites may optionally be registered or displayed on the system monitor. This allows repeated pinpointing and obviates the need for strip or grid electrodes in the operative field; although such electrodes may be useful for continuous monitoring, they often are in the surgeons way. In addition, the primary and supplementary motor cortex can be mapped by determining the location of the sites of stimulation on surface-projected images of the cerebral cortex.

Impact of brain shift on intraoperative neurophysiological monitoring with cortical strip electrodes.

Summary.u2003Background: Intraoperative neurophysiological monitoring has become the standard procedure for locating eloquent regions of the brain. Such continuous electrical stimulation of motor pathways is usually applied by means of flat silicon-embedded electrodes placed directly on the motor cortex. However, shifting of the silicon strip on the cortical surface as well as electrode displacement due to brain shift underneath the electrode can lead to inaccurate recordings not directly caused by intraoperative impairment of the motor cortex or the motor pathways.u2003Method: This prospective study was conducted to quantify cortical brain shift during open cranial surgery and to assess its impact on electrode positioning in 31 procedures near the precentral gyrus. Three groups of different lesion volumes were distinguished. Movement of the cortex between opening of the dura and completion of tumor removal as well as cortical electrode shifting were digitally measured and analyzed.u2003Findings: Cortical surface structures evidenced a significantly larger shift (up to 23.4 mm) in comparison to the electrode strips (up to 4.2 mm) in lesions with a volume of over 20 ml. Cortex shifting highly correlated with lesion volume, whereas strip electrode movement was almost unidirectional and did not differ significantly among the three groups. However, the way they were placed (completely on the cortex vs. partly underlying or overlapping the craniotomy borders) affected the magnitude of their intraoperative displacement. As a consequence, 3 of the 31 cases (9.3%) showed a significant change in the recorded motor responses due to intraoperative dislocation of the stimulating electrode.u2003Interpretation: Changes in the location of cerebral structures due to intraoperative brain shift may exert a marked influence on intraoperative neurophysiological monitoring if cortical strip electrodes are used. Therefore, long-term monitoring of the central region requires continuous checking of the position of stimulating electrodes and, if necessary, correction of their location.