Josef Zentner

Noninvasive motor evoked potential monitoring during neurosurgical operations on the spinal cord.

We present the results of monitoring descending pathways with motor evoked potentials (MEP) in 50 patients during neurosurgical operations on the spinal cord. The electromyographic responses of the anterior tibial muscles were recorded. In addition, in 24 patients responses of the thenar muscles after transcranial electrical stimulation of the motor cortex were recorded. Usually, the averages of 5 to 15 signals were evaluated. Although potentials were obtained preoperatively in all 50 patients, during neuroleptanesthesia intraoperative recording from the anterior tibial muscles was possible in 43 patients (86%) and from the thenar muscles in 21 patients (87.5%). Amplitudes were superior to latencies as evaluation criteria for intraoperative changes in potentials. On the basis of acceptable changes in amplitudes of up to 50% at the end of the operation, 16 recordings from the thenar muscles (76.2%) and 35 from the anterior tibial muscles (81.4%) correlated correctly with the postoperative neurological status; there were false positive results in 5 (23.8%) and 8 (18.6%) patients, respectively. We did not observe false negative findings. Postoperative neurological complications coincided in every case with permanent reduction in amplitudes of more than 50% of the base lines or with intraoperative loss of potentials as observed in 3 and 1 patient, respectively. MEP monitoring during neurosurgical operations on the spinal cord is a sensitive method for early detection of impending neurological complications. Major problems are the influence of anesthesia and the definition of acceptable limits for changes in amplitudes.

Pterional Approach for Surgical Treatment of Olfactory Groove Meningiomas

We present our experience with the surgical treatment of olfactory groove meningiomas using a pterional approach. This approach provides the advantages of previous techniques, such as preserving the frontal brain and superior sagittal sinus, early devascularization of the tumor, and late dissection of tumor borders. Moreover, it also compensates for the shortcomings of other techniques, e.g., compression of frontal bridging veins, late dissection of dorsal tumor aspects involving vessels and optic nerves as well as facultative infection and cerebrospinal fluid fistula-related complications caused by opening of frontal sinuses. To date, 11 patients were treated in this way. As we encountered no surgical complications in our series we are encouraged to present our procedure.

Intramedullary cavernous angiomas

Two cases of histologically verified intramedullary cavernous angiomas at C3 and D5-6 are presented. Both patients suffered progressive myelopathy with intermittent improvement. In both cases preoperative diagnosis was possible by means of magnetic resonance imaging using spin echo techniques, fast imaging, and phase display, while spinal angiography was not helpful. Laminectomy and total removal of the tumors were performed with temporary increased neurological deficits. It is thought that magnetic resonance imaging provides a useful diagnostic tool in these tumors and is also essential for planning surgical strategy.

Radical osteoclastic craniectomy in sagittal synostosis.

We report our experience in the surgical treatment of sagittal synostosis using radical osteoclastic craniectomy in 60 consecutive patients. After surgery in children aged 6 months or younger (Group I), reossification usually started 2 weeks postoperatively and was complete within 6 months, resulting in an optimal skull contour. In children aged 7 to 12 months (Group II), reossification was prolonged and lasted for 12 months or longer. The skull contour normalized in its biparietal width and improved in sagittal diameter, remaining, however, slightly abnormal. In children older than 12 months (Group III), the skull contour partly improved in the biparietal diameter but did not change in the sagittal direction. Reossification was incomplete with persistent pseudosutures. Enlarged frontal subarachnoid spaces were reversible or improved in all patients independent of age at the time of surgery. We encountered no complications in our series. In our opinion, radical osteoclastic craniectomy is the simplest, most efficient, and most physiologically sound method for the treatment of sagittal synostosis in patients up to 6 months of age. This procedure allows the rapidly growing brain to form its skull vault, thus providing optimal cosmetic results. In older children, osteoplastic morcellation procedures should be the treatment of choice.

Motor evoked potential monitoring during neurosurgical operations on the spinal cord

In order to monitor descending pathways during neurosurgical operations on the spinal cord, motor evoked potentials (MEP) were recorded from the epidural space of the spinal cord and the cauda equina following transcranial electrical cortex stimulation in a total of 40 patients. It was the aim of our study to test this invasive recording technique with regard to recordability of potentials as well as correlation to post-operative neurological conditions. In 15 of 23 patients (65.2%) intraoperative potentials were obtained from the spinal cord and in 33 of 40 patients (82.5%) they were obtained from the cauda equina. On the basis of acceptable changes in amplitudes of up to 50% at the end of the operation, 13 of 15 (86.7%) recordings from the spinal cord and 28 of 33 (84.8%) from the cauda equina correlated correctly with the post-operative motor status. At the same time, there were false positive results in 2 (13.3%) and 5 (15.2%) recordings, respectively. False negative results were not observed. Post-operative deterioration of the motor status as observed in 3 patients coincided in 2 patients with a permanent reduction in amplitudes of more than 50% of the baselines and in 1 patient with an intra-operative loss of potentials. Thus both spinal cord and cauda equina recording of MEP clicited by transcranial electrical stimulation were proven to be sensitive methods for detection of impending neucological complications. Cauda equina recording, however, seems to allow recording in more cases.

Cavernous angioma of the optic nerve: Case Report

The case of a 24-year-old woman with a cavernoma of the right optic nerve is presented. She suffered recurrent headaches and showed a deficit of the right nasal visual field. A computed tomography scan, a computed tomography cisternography, and magnetic resonance imaging revealed a lesion in projection on the right suprasellar cistern, yet angiography was inconspicuous. On operation, an angiomatous tumor of the right optic nerve with a surrounding hemorrhage was found. Histological examination of the specimen confirmed the intraoperative diagnosis of a cavernoma. Postoperatively, the right nasal visual field deficit increased slightly.

Periventricular neurocytoma: A pathological entity

Three cases of periventricular neurocytomas are presented. All patients had a large but well-circumscribed, hyperdense tumor with insignificant contrast enhancement in the lateral and third ventricle, causing hydrocephalus. Calcification was present in one patient. Angiography revealed a blush tumor enhancement in two cases. Surgical removal was complete in two patients and incomplete in one. Light microscopy showed a cell pattern that resembled either ependymoma or oligodendroglioma. However, in all cases the tumor was confirmed to be a neurocytoma by immunocytochemical analysis that showed reactivity for synaptophysin and/or neuron-specific enolase in a high percentage of neoplastic cells. With respect to the literature it is concluded that neurocytomas represent an individual pathological entity of supratentorial midline tumors. Complete surgical removal without irradiation is the recommended treatment.

The prognostic value of somatosensory and motor evoked potentials in comatose patients.

Somatosensory and motor evoked potentials (SEP and MEP) were examined in a total of 213 patients in traumatic (n = 140) and nontraumatic (n = 73) coma. It was the aim of this study to compare the prognostic value of MEP elicited by both electrical and magnetoelectric transcranial stimulation with the use of SEP alone. According to the presence or absence of responses and the duration of central conduction time, SEP and MEP obtained during Days 1 through 3 after the onset of coma were divided into four categories and correlated with the outcome of the patients, as assessed by the Glasgow Outcome Scale. Our results clearly show that in terms of prognostic value, SEP are superior to MEP, with normal findings indicating a favorable outcome and absent responses an unfavorable outcome. On the other hand, patients with normal electromyographic responses after both electrical and magnetoelectric stimulation had favorable and unfavorable outcomes about equally. Thus, unlike SEP, normal MEP do not allow any prognostic conclusions. Only the bilateral absence of MEP in response to electrical stimulation was a definitely unfavorable prognostic sign because all of these patients died. In contrast, with magnetoelectric stimulation, neither normal nor absent responses allowed any prognostic conclusions. Therefore, the prognostic value of electrically evoked motor responses is limited, and magnetoelectric stimulation cannot be recommended in this context.

Diagnostic significance of motor evoked potentials in space-occupying lesions of the brain stem and spinal cord

SummaryMotor evoked potentials (MEP) were examined in 50 patients with space-occupying lesions of the brain stem and spinal cord. MEP findings were correlated with the motor status as established by clinical examination. The results clearly show the high sensitivity of MEP for detection of motor deficits: 17 recordings (77%) from the thenar muscle and 42 (84%) from the anterior tibial muscle correlated correctly with the clinical motor status. False-positive results were found in 5 (23%) thenar recordings and 8 (16%) and anterior tibial recordings. False-negative correlation was not observed. The high rate of false-positive results appears to indicate that MEP detect subclinical motor deficits. This electrophysiological test is therefore recommended, especially when involvement of the descending pathways is suspected and clinical examination reveals no abnormality.

Prevention of an air embolism by moderate hypoventilation during surgery in the sitting position.

The effect of ventilation (normo-, hypo-, and hyperventilation) on transverse sinus pressure (TSP), central venous pressure (CVP), mean arterial blood pressure (mABP), and heart rate was studied in 15 patients undergoing neurosurgical treatment in the sitting position for tumors of the posterior fossa, and the findings were compared with the influence of positive end expiratory pressure (PEEP) on these parameters. TSP was not influenced significantly by PEEP ranging from 0 to 15 mbar, whereas CVP increased. At the same time, mABP decreased slightly. In contrast, TSP showed characteristic changes with varying ventilation: during normoventilation [end expiratory CO2 pressure (PECO2), 38 mm Hg], TSP was 3 mm Hg and increased to 7 mm Hg on average with hypoventilation (PECO2, 44 mm Hg), whereas hyperventilation (PECO2, 32 mm Hg) caused a reduction in TSP to the atmospheric range. At the same time, CVP remained unchanged, whereas mABP increased with hypoventilation. Presuming that the risk of venous air embolism is closely related to the level of TSP, our results allow the following conclusions. 1) PEEP does not seem to be effective in preventing venous air embolism. 2) Hyperventilation is dangerous in the sitting position, as TSP is reduced to the atmospheric and even subatmospheric range. 3) To prevent air embolism, moderate hypoventilation is recommended during the most critical period of exposing the posterior fossa followed by normoventilation when surgery of the actual lesion has begun.