Biomedical subjects

Alireza Gharabaghi

Publications and source records attributed to Alireza Gharabaghi.

14 recordsLinked to original sources

PubMed2006

The role of the right superior temporal gyrus in visual search-insights from intraoperative electrical stimulation.

Intraoperative electrical stimulation in awake patients is a seminal technique during brain surgery allowing one to infer the function of brain areas by temporary inactivation. Using this technique, we found that inactivation of the middle portion of the superior temporal gyrus (STG) leads to disturbed serial exploratory visual search. The data supplement recent findings by Ellison et al. [Ellison, A., Schindler, I., Pattison, L. L., & Milner, A. D. (2004). An exploration of the role of the superior temporal gyrus in visual search and spatial perception using TMS. Brain, 127, 2307-2315] using repetitive transcranial magnetic stimulation over the STG in healthy subjects. Our data demonstrate that the STG is integral to human exploration behaviour and challenge the traditional view that only the right posterior parietal cortex is involved in the mediation of visual search processes.

Aged↗

PubMed2006

Virtual reality augmentation in skull base surgery.

OBJECTIVE: Skull base anatomy is complex and subject to individual variation. Understanding the complexity of surgical anatomy is faster and easier with virtual models created from primary imaging data of the patient. This study was designed to investigate the usefulness of virtual reality in image guidance for skull base procedures. DESIGN: Primary volumetric image data from 110 patients was acquired using magnetic resonance, computed tomography (CT), and CT angiography. Pathologies included lesions in the anterior, middle, and posterior skull base. The data were transferred to an infrared-based image-guidance system for creation of a virtual operating field (VOF) with translucent surface modulation and optional "fly-through" video mode. During surgery, the target registration error for anatomical landmarks was assessed and the VOF was compared with the patient's anatomy in the operative field. RESULTS: Complex structures like the course of the sigmoid sinus, the carotid artery, and the outline of the paranasal sinuses were well visualized in the VOF and were recognized by the surgeon instantly. Perception was greatly facilitated as compared with routine mental reconstruction of triaxial images. Accurate assessment of the depth of field and very small objects was not possible in VOF images. CONCLUSION: Supported by sound anatomical knowledge, creation of a virtual operating field for a surgical approach in an individual patient offers a déjà vu experience that can enhance the capabilities of a surgical team in skull base approaches. In addition, application of this technique in image-guided procedures assists in targeting or avoiding hidden anatomical structures.

Journal Article↗

PubMed2006

The impact of petrosal vein preservation on postoperative auditory function in surgery of petrous apex meningiomas.

OBJECTIVE: The importance of preserving the superior petrosal vein has received increasing attention in the surgical treatment of pathologies involving the petrous apex. Recent reports have associated postoperative auditory nerve dysfunction with petrosal vein sacrifice. However, there is no systematic clinical study available thus far focusing on the postoperative auditory function after petrosal vein obliteration. METHODS: In 55 patients with meningiomas involving the petrous apex, pre- and intraoperative findings including petrosal vein sectioning were analyzed retrospectively concerning their impact on postoperative auditory function. RESULTS: The petrosal vein was preserved in 26 (47%) cases. In 27 (49%) cases, this vein was not preserved. Hearing loss occurred in 11% of all cases. In the preserved-vein group, postoperative hearing loss occurred in 3 of 26 (11%) cases and in the sacrificed-vein group in 3 of 27 (11%) cases. CONCLUSION: Sacrifice of the petrosal vein during surgery of petrous apex meningiomas seems not to have an impact on postoperative auditory function.

Adult↗

PubMed2006

Applicability of an electrosurgical device based on electromagnetics in neurosurgery.

Because of electrical and thermal spread to healthy nervous tissue, the application of electrosurgical tools in neurosurgery has specific limitations. This is true for both bipolar and monopolar devices. These limitations are not inherent to an instrument in which action is based on electromagnetic interaction with human tissue. We evaluated the indications and the clinical applicability of a new radiofrequency electrosurgical unit that works on this biophysical principle. The system was found to be a useful addition for the resection of morphologically tougher tissue with keyhole approaches in which the ultrasound aspirator cannot easily be applied.

Brain Injuries↗

PubMed2006

The impact of hypotension due to the trigeminocardiac reflex on auditory function in vestibular schwannoma surgery.

OBJECT: Surgical manipulation of the fifth cranial nerve during its intra- or extracranial course may lead to bradycardia or even asystole as well as arterial hypotension, a phenomenon described as the trigeminocardiac reflex (TCR). The authors studied the impact of this reflex on postoperative auditory function in patients undergoing vestibular schwannoma (VS) surgery. METHODS: One hundred patients scheduled for VS surgery were studied prospectively for parameters influencing the postoperative auditory function. The evaluation included sex, age, pre- and postoperative auditory function, preoperative mean arterial blood pressure, preoperative medical diseases or medication (for example, antiarrhythmia drugs), tumor size and localization, and the intraoperative occurrence of the TCR. The TCR, which occurred in 11% of the patients, influenced the postoperative hearing function in the patients with Hannover Class T3 and T4 VSs. With an overall hearing preservation of 47%, 11.1% of the patients in the TCR group and 51.4% of those in the non-TCR group experienced preserved hearing function postoperatively. In cases involving larger tumors (Hannover Class T3 and T4), an intraoperative TCR was associated with a significantly worse postoperative hearing function during VS surgery (p = 0.005). CONCLUSIONS: The hypotension following TCR is a negative prognostic factor for hearing preservation in patients undergoing VS surgery. Patients' knowledge of this can be increased pre- and postoperatively. Further study of this phenomenon will advance the understanding of the underlying mechanisms and may help to improve hearing preservation by controlling the occurrence of the TCR.

Adolescent↗

PubMed2005

Evolution of vestibular schwannoma surgery: the long journey to current success.

The extraordinary improvement of patient outcome after surgical treatment for vestibular schwannomas is relatively recent and has occurred mainly over the last 30 years. The introduction of microsurgical techniques has resulted in increasing degrees of precise anatomical and functional preservation of the facial and cochlear nerves. An expanded microsurgical technique accompanied by continuous electrophysiological monitoring has resulted in marked changes in the primary goals for this surgery. Whereas in the past the primary goal of vestibular schwannoma management was to preserve the patient's life, the objective in vestibular schwannoma treatment today is to preserve neurological function. Long-term follow-up examinations show negligible recurrence rates, indicating that the aim of preservation of nerve function does not limit the completeness of tumor removal with modern neurosurgical techniques. Despite these advances in preserving the anatomical integrity of, for example, the cochlear nerve, losses of function and even deafness may occur postoperatively in some cases. Current biological and technical research in experimental and clinical settings addresses these problems. In this article, the authors report in detail the developments achieved in vestibular schwannoma surgery and the great clinicians to whom these results can be credited.

Deafness↗

PubMed2005

A universal algorithm for an improved finite element mesh generation Mesh quality assessment in comparison to former automated mesh-generators and an analytic model.

The FE-modeling of complex anatomical structures is not solved satisfyingly so far. Voxel-based as opposed to contour-based algorithms allow an automated mesh generation based on the image data. Nonetheless their geometric precision is limited. We developed an automated mesh-generator that combines the advantages of voxel-based generation with improved representation of the geometry by displacement of nodes on the object-surface. Models of an artificial 3D-pipe-section and a skullbase were generated with different mesh-densities using the newly developed geometric, unsmoothed and smoothed voxel generators. Compared to the analytic calculation of the 3D-pipe-section model the normalized RMS error of the surface stress was 0.173-0.647 for the unsmoothed voxel models, 0.111-0.616 for the smoothed voxel models with small volume error and 0.126-0.273 for the geometric models. The highest element-energy error as a criterion for the mesh quality was 2.61x10(-2) N mm, 2.46x10(-2) N mm and 1.81x10(-2) N mm for unsmoothed, smoothed and geometric voxel models, respectively. The geometric model of the 3D-skullbase resulted in the lowest element-energy error and volume error. This algorithm also allowed the best representation of anatomical details. The presented geometric mesh-generator is universally applicable and allows an automated and accurate modeling by combining the advantages of the voxel-technique and of improved surface-modeling.

Algorithms↗

PubMed2005

Epidermoid cysts of the cavernous sinus.

BACKGROUND: Epidermoid cysts involving the cavernous sinus are rare lesions. They can be divided into 3 different categories: extracavernous, interdural, and true intracavernous. METHODS: This classification of cavernous epidermoid cysts is correlated with the extent of tumor resection and the clinical outcome in reported cases here and elsewhere. RESULTS: Patients with cysts invading or compressing the cavernous sinus present with an excellent functional recovery after surgery independent of the extent of tumor resection. In cases of interdural cysts, there is often an adherence of the tumor capsule to the third and fourth cranial nerves. Therefore, in this group, subtotal resection is a safe strategy to prevent surgical morbidity. However, this policy may lead to a higher incidence of tumor recurrence in these cases. In true intracavernous lesions, a higher rate of total removal is possible despite the increased occurrence of internal carotid artery encasement and cranial nerve displacement. CONCLUSION: Postoperative outcome with preservation of neural and vascular structures in cavernous epidermoid cysts is more likely related to surgical strategy than to tumor localization. Independent of the different tumor origins in these cases, a subtotal resection is usually sufficient to achieve postoperative improvement of the symptoms without additional morbidity.

Adult↗

PubMed2005

Volumetric image guidance for motor cortex stimulation: integration of three-dimensional cortical anatomy and functional imaging.

OBJECTIVE: Epidural electrical stimulation of the motor cortex is a promising treatment option in patients with intractable pain. Varying rates of success in long-term pain relief have been attributed to inaccurate positioning of the electrode array, partly because the sulcal landmarks are not directly visualized. We describe an integrated protocol for precise electrode placement, combining functional image guidance and intraoperative electrical stimulation in the awake patient. METHODS: Volumetric rendering of a three-dimensional (3-D) magnetic resonance data set was used to visualize the cortical surface and to superimpose functional magnetic resonance imaging data in six patients with refractory chronic pain. The intraoperative positioning of the quadripolar electrode array was monitored by functional 3-D image guidance. Continuous electrophysiological monitoring and clinical assessment of the motor effects complemented the procedure. RESULTS: Volumetrically rendered 3-D images were advantageous for the location of the burr hole over the perirolandic area by revealing individual cortical morphological features (e.g., the hand knob) and function at the same time. The exact position of the electrodes was verified reliably by cortical stimulation. No complications were observed throughout the procedures. CONCLUSION: The combination of 3-D functional neuronavigation, intraoperative electrical stimulation, and continuous motor output monitoring in awake patients provides optimal information for the identification of the appropriate somatotopic area of motor cortex. This combined imaging and stimulation approach for electrode positioning offers a safe and minimal invasive strategy for the treatment of intractable chronic pain in selected patients.

Adult↗

PubMed2005

Nausea and dizziness after vestibular schwannoma surgery: a multivariate analysis of preoperative symptoms.

OBJECTIVE: Nausea and dizziness are very discomforting for patients after vestibular schwannoma surgery and they impair recovery. METHODS: To identify preoperative symptoms and conditions that increase the risk of development of nausea after vestibular schwannoma surgery, a multivariate analysis was performed. One hundred fifteen patients with vestibular schwannoma had a microsurgical tumor removal in a standardized procedure in 2001 and 2002. Eighteen patients were excluded from the study because of previous surgery (recurrent tumors, 7 patients) or bilateral tumor occurrence (neurofibromatosis, 11 patients). Analysis was performed regarding postoperative amount of antiemetic medication, vomiting, and subjective feeling of the patient. Tumor grading, body mass index, sex, previous complaints, examination at admission, and side of the tumor were taken in consideration. RESULTS: Women had significant longer postoperative complaints (mean, 3.0 d; standard error, 0.47) and needed longer antiemetic therapy (mean, 3.3 d; standard error, 0.49) than men (mean, 1.72 d; standard error, 0.21). Patients developing no significant postoperative complaints were all in the higher tumor grading group, Grades 3a, 4a, and 4b. There was a significant difference in the duration of antiemetic therapy between tumors graded 1 and tumors graded 3 or 4. Patients with a positive stepping test preoperatively had a tendency to demand less antiemetic medication. Women with small tumors are most likely to develop significant complaints after vestibular schwannoma surgery. CONCLUSION: It is possible to identify patients with a higher risk of postoperative nausea and dizziness after vestibular schwannoma surgery. This allows one to inform these patients preoperatively and to initiate an early postoperative drug therapy to ease their symptoms.

Adult↗

PubMed2005

Evaluation of a new concept for the management of skull base chordomas and chondrosarcomas.

OBJECT: Chordomas and chondrosarcomas of the skull base are rare locally invasive tumors associated with high recurrence rates. The aim of this study was to evaluate the concept of microsurgical tumor volume reduction followed by early gamma knife surgery (GKS). METHODS: Thirteen patients with 15 tumors were treated between October 2000 and June 2003. There were three patients (23.1%) with chordomas and 10 (76.9%) with chondrosarcomas. There were nine men and four women who ranged in age between 19 and 69 years. All patients first underwent maximal tumor resection. Within 2 to 10 months after surgery they were treated with GKS. The mean postoperative tumor volume treated with GKS was 9.7 cm3 (range 1.4-20.3 cm3). Follow-up computerized tomography and magnetic resonance imaging examinations with volumetric tumor analysis were performed every 6 months after GKS. The mean treatment dose was 17 Gy and the mean isodose was 52%. The mean follow-up duration was 17 months during which there was only one tumor recurrence at the margin of the radiation field. The mean volume reduction was 35.4%. CONCLUSIONS: Results of this treatment strategy are encouraging but the efficacy of this multimodal treatment combining surgery and early GKS requires a longer follow up.

Adult↗

PubMed2005

Volume reduction in meningiomas after gamma knife surgery.

OBJECT: The purpose of this study was to evaluate the volume-reducing effects of gamma knife surgery (GKS) of meningiomas with and without previous surgical treatment. METHODS: A group of 127 patients with a mean age of 57.1 years (range 9-81 years) with 142 meningiomas (128 World Health Organization Grade I and 14 Grade II) were included in this study. The management strategy reduces tumor volume with surgery when necessary (81 patients). Stereotactic GKS with a Gamma Knife model C was performed in all tumors of suitable size. Magnetic resonance imaging follow-up examinations with volumetric tumor analysis was performed 6 months after treatment and annually thereafter. The mean tumor volume was 5.9 cm3 (range < 5 to > 40 cm3). The mean follow-up time after GKS was 29.3 months (range 11-61 months). The mean prescription dose was 13.8 Gy (range 10-18 Gy). A reduction in volume occurred in 117 (82.4%) of all tumors, and in 20 tumors (14.1%) growth ceased. The overall tumor control rate of 96.4%. The mean volume reduction achieved with GKS was more than 46.1%. Only five tumors (3.5%) stowed a volume increase. CONCLUSIONS: Gamma knife surgery was effective in reducing meningioma volume at short-term follow up. Further studies are needed to examine the development of these findings over a longer period.

Adolescent↗

PubMed2003

C-Fos immunoreactivity mapping of the auditory system after electrical stimulation of the cochlear nerve in rats.

The aim of this study was to establish the use of c-Fos immunoreactivity as a marker for functional mapping in the auditory system in response to direct electrical stimulation of the cochlear nerve in the cerebellopontine angle. In rats the cochlear nerve was electrically stimulated with a biphasic current (120-250 microA, 5 Hz) for 30 min using a bipolar concentric Tungsten electrode. Bilateral cochlectomy was performed in a control group in order to investigate basal expression of c-Fos in the auditory brainstem nuclei. The response of auditory brainstem nuclei to electrical stimulation and the completeness of cochlear ablations were electrophysiologically verified. After the experiments, the animals were prepared for cryotomy and c-Fos immunohistochemistry. The results were morphologically analyzed and statistically compared among groups. In anesthetized animals with unilateral electrical stimulation of the cochlear nerve increased expression of c-Fos was detected in the ipsilateral ventral (VCN) and bilateral dorsal cochlear nucleus (DCN), whereas the VCN of the contralateral side revealed only few immunoreactive cells. In animals with bilateral cochlear ablation the number of c-Fos reactive cell nuclei representing basal expression was generally low in the VCN and DCN of both sides. Our data show that electrical stimulation of the cochlear nerve leads to increased expression of c-Fos in the cochlear nucleus. It also confirms bilateral connections between the cochlear nuclei. These experimental results suggest that c-Fos immunoreactivity mapping provides a powerful tool for functional investigations on the cellular level after direct electrical stimulation of the cochlear nerve. Future functional studies analyzing the effect of electrical stimulation of the central auditory system as performed by auditory brainstem implants could be investigated in detail by mapping c-Fos expression on cellular level.

Animals↗

PubMed2002

Skin markers for surgical planning for intradural lesions of the thoracic spine. Technical note.

BACKGROUND: Preparation for surgery for thoracic intraspinal lesions commonly involves rather difficult X-ray procedures in the operating room. The object of this report is to inform neurosurgeons about a modified technique for preoperative surface localization of intraspinal thoracic pathology. METHODS: Adhesive, disposable radiographic skin markers placed at the presumed level of an intraspinal lesion are visualized along with the lesion on sagittal magnetic resonance scans of the thoracic spine. RESULTS: The lesion and the skin markers were clearly identified within the same field of view. The lesion itself rather than the vertebral body becomes the reference point for localization. CONCLUSION: Preoperative imaging with adhesive skin markers facilitates positioning and draping for surgery for thoracic intraspinal lesions. It may even replace intra-operative X-ray procedures in selected cases.

Adhesives↗