Practical application of intraoperative ultrasound imaging

Clinical Application of Shear Wave Elastography for Assisting Brain Tumor Resection

Background

The clinical outcomes for brain tumor resection have been shown to be significantly improved with increased extent of resection. To achieve this, neurosurgeons employ different intra-operative tools to improve the extent of resection of brain tumors, including ultrasound, CT, and MRI. Young’s modulus (YM) of brain tumors have been shown to be different from normal brain but the accuracy of SWE in assisting brain tumor resection has not been reported.

Aims

To determine the accuracy of SWE in detecting brain tumor residual using post-operative MRI scan as “gold standard”.

Methods

Thirty-four patients (aged 1–62 years, M:F = 15:20) with brain tumors were recruited into the study. The intraoperative SWE scans were performed using Aixplorer^® (SuperSonic Imagine, France) using a sector transducer (SE12-3) and a linear transducer (SL15-4) with a bandwidth of 3 to 12 MHz and 4 to 15 MHz, respectively, using the SWE mode. The scans were performed prior, during and after brain tumor resection. The presence of residual tumor was determined by the surgeon, ultrasound (US) B-mode and SWE. This was compared with the presence of residual tumor on post-operative MRI scan.

Results

The YM of the brain tumors correlated significantly with surgeons’ findings (ρ = 0.845, p < 0.001). The sensitivities of residual tumor detection by the surgeon, US B-mode and SWE were 36%, 73%, and 94%, respectively, while their specificities were 100%, 63%, and 77%, respectively. There was no significant difference between detection of residual tumor by SWE, US B-mode, and MRI. SWE and MRI were significantly better than the surgeon’s detection of residual tumor (p = 0.001 and p < 0.001, respectively).

Conclusions

SWE had a higher sensitivity in detecting residual tumor than the surgeons (94% vs. 36%). However, the surgeons had a higher specificity than SWE (100% vs. 77%). Therefore, using SWE in combination with surgeon’s opinion may optimize the detection of residual tumor, and hence improve the extent of brain tumor resection.

Shear wave elastography for intracranial epidermoid tumors

BACKGROUND

Ultrasound elastography (USE) is a novel technique that assesses the mechanical properties of body tissues in real time. Based on elasticity measurements, USE enables the differentiation of tumor tissue from surrounding normal tissue.

OBJECTIVES

We aimed to evaluate an intraoperative SWE technique for differentiating tumor tissue (epidermoid cyst) from the surrounding normal brain tissue based on elastic properties.

METHODS

We prospectively report the intraoperative elasticity assessments of four patients diagnosed with epidermoid cysts. Along with standard ultrasonography, intraoperative shear wave elastography (SWE) was used to identify tumor tissue and assess the elasticity of each tumor and the surrounding normal brain.

RESULTS

USE enabled the differentiation between epidermoid cysts and the surrounding normal brain tissue in real time intraoperatively; visual data (SWE elasticity map) and quantitative data (elasticity measurements in kilopascals) were utilized to identify the epidermoid cyst based on its elastic properties. The area representing the epidermoid cyst had an increased elasticity on SWE view and high mean elasticity values (193.7 ± 70.9 kPa in case 1, 168 ± 24.5 kPa in case 2, 205.1 ± 6.7 kPa in case 3, and 101.3 ± 12.6 kPa in case 4). The area representing the adjacent normal brain tissue on SWE view had lower mean elasticity values (14.9 ± 1.9 kPa in case 1, 22.6 ± 8.3 kPa in case 2, and 23.8 ± 1.4 kPa in case 4).

CONCLUSION

This study demonstrates the feasibility and promising value of SWE as an intraoperative tool during epidermoid cyst resection. Epidermoid tissue remnants that are hidden from the microscopic view can be detected using SWE.

Difference-Frequency Ultrasound Imaging With Non-Linear Contrast

Conventional ultrasound imaging is based on the scattering of sound from inhomogeneities in the density and the speed of sound and is often used in medicine to resolve pathologic compared to normal tissue. Here we demonstrate a difference-frequency ultrasound (dfUS) imaging method that is based on the interaction of two sound pulses that propagate non-collinearly and intersect in space and time. The dfUS signal arises primarily from the second-order non-linear coefficient, a contrast mechanism that differs from linear and harmonic US imaging. The distinct contrast mechanism allows dfUS to image anatomic features that are not identifiable in conventional US images of salmon and pig kidney tissue. Further, dfUS produces enhanced contrast of glioblastoma tumor implanted in the mouse brain, revealing its potential for improving medical diagnosis. Progress towards a real-time system is discussed.

Review of the potential of optical technologies for cancer diagnosis in neurosurgery: a step toward intraoperative neurophotonics

Advances in image-guided therapy enable physicians to obtain real-time information on neurological disorders such as brain tumors to improve resection accuracy. Image guidance data include the location, size, shape, type, and extent of tumors. Recent technological advances in neurophotonic engineering have enabled the development of techniques for minimally invasive neurosurgery. Incorporation of these methods in intraoperative imaging decreases surgical procedure time and allows neurosurgeons to find remaining or hidden tumor or epileptic lesions. This facilitates more complete resection and improved topology information for postsurgical therapy (i.e., radiation). We review the clinical application of recent advances in neurophotonic technologies including Raman spectroscopy, thermal imaging, optical coherence tomography, and fluorescence spectroscopy, highlighting the importance of these technologies in live intraoperative tissue mapping during neurosurgery. While these technologies need further validation in larger clinical trials, they show remarkable promise in their ability to help surgeons to better visualize the areas of abnormality and enable safe and successful removal of malignancies.

A hybrid method for non-rigid registration of intra-operative ultrasound images with pre-operative MR images

In recent years intra-operative ultrasound images have been used for many procedures in neurosurgery. The registration of intra-operative ultrasound images with preoperative magnetic resonance images is still a challenging problem. In this study a new hybrid method based on residual complexity is proposed for this problem. A new two stages method based on the matching echogenic structures such as sulci is achieved by optimizing the residual complexity (RC) value with quantized coefficients between the ultrasound image and the probabilistic map of MR image. The proposed method is a compromise between feature-based and intensity-based approaches. The evaluation is performed on both a brain phantom and patient data set. The results of the phantom data set confirmed that the proposed method outperforms the accuracy of conventional RC by 39%. Also the mean of fiducial registration errors reached to 1.45, 1.94 mm when the method was applied on phantom and clinical data set, respectively. This hybrid method based on RC enables non-rigid multimodal image registration in a computational time compatible with clinical use as well as being accurate.

Intraoperative low-field MR-guided frameless stereotactic biopsy for intracerebral lesions

BACKGROUND

To present our intraoperative low-field magnetic resonance imaging (ioMRI) technique for stereotactic brain biopsy in various intracerebral lesions.

METHOD

Seventy-eight consecutive patients underwent stereotactic biopsies with the PoleStar N-20/N-30 ioMRI system and data were evaluated retrospectively. Biopsy technique included ioMRI before surgery, followed by insertion of the biopsy cannula in the lesion, and ioMRI before and after biopsy. Statistical analysis was performed to compare subgroups using Excel and SPSS statistic software.

RESULTS

In all patients, stereotactic biopsy was possible, with a mean intraoperative surgery time of 86.2 ± 28.6 min and a mean hospital stay of 11.6 ± 4.6 days. In 97.4 % (n = 76), histology was conclusive, representing 58 brain tumors and 18 other pathologies. Five patients were biopsied previously without conclusive diagnosis, and all biopsies were conclusive this time. Mean cross-sectional lesion size in MRI T1 with contrast (n = 64) was 6.9 ± 5.7 cm(2), and in lesions without T1 contrast enhancement (n = 14), T2 mean cross-sectional lesion size was 5.5 ± 3.9 cm(2). Mean distance from the cortex surface to the lesion was 3.4 ± 1.2 cm. One patient suffered from a postoperative wound dehiscence; neither clinically or radiologically significant hemorrhage after surgery, nor intraoperative complications occurred.

CONCLUSIONS

Low-field ioMR-guided frameless stereotactic biopsy accurately diagnosed different intracerebral lesions without major complications for the patients, and within an acceptable surgery time and hospital stay. In repeated non-conclusive biopsies in particular, low-field ioMRI offers a technique for arriving at a diagnosis.

On mixed reality environments for minimally invasive therapy guidance: systems architecture, successes and challenges in their implementation from laboratory to clinic

Mixed reality environments for medical applications have been explored and developed over the past three decades in an effort to enhance the clinician's view of anatomy and facilitate the performance of minimally invasive procedures. These environments must faithfully represent the real surgical field and require seamless integration of pre- and intra-operative imaging, surgical instrument tracking, and display technology into a common framework centered around and registered to the patient. However, in spite of their reported benefits, few mixed reality environments have been successfully translated into clinical use. Several challenges that contribute to the difficulty in integrating such environments into clinical practice are presented here and discussed in terms of both technical and clinical limitations. This article should raise awareness among both developers and end-users toward facilitating a greater application of such environments in the surgical practice of the future.

Objective assessment of utility of intraoperative ultrasound in resection of central nervous system tumors: A cost-effective tool for intraoperative navigation in neurosurgery

Background:

Localization and delineation of extent of lesions is critical for safe maximal resection of brain and spinal cord tumors. Frame-based and frameless stereotaxy and intraoperative MRI are costly and not freely available especially in economically constrained nations. Intraoperative ultrasound has been around for a while but has been relegated to the background. Lack of objective evidence for its usefulness and the perceived “user unfriendliness” of US are probably responsible for this. We recount our experience with this “forgotten” tool and propose an objective assessment score of its utility in an attempt to revive this practice.

Materials and Methods:

Seventy seven intraoperative ultrasound (IOUS) studies were carried out in patients with brain and spinal cord tumors. Seven parameters were identified to measure the “utility” of the IOUS and a “utility score” was devised (minimum 0 and maximum 7). Individual parameter and overall scores were calculated for each case.

Results:

IOUS was found to be useful in many ways. The median overall score was 6 (mean score 5.65). There were no scores less than 4 with the majority demonstrating usefulness in 5 or more parameters (91%). The use of the IOUS significantly influenced the performance of the surgery in these cases without significantly prolonging surgery.

Conclusions:

The IOUS is a very useful tool in intraoperative localization and delineation of lesions and planning various stages of tumor resection. It is easy, convenient, reliable, widely available, and above all a cost-effective tool. It should be increasingly used by neurosurgeons in the developing world where costlier intraoperative localization and imaging is not available freely.

Reliability of intraoperative high-resolution 2D ultrasound as an alternative to high–field strength MR imaging for tumor resection control: a prospective comparative study

Object

Ultrasound may be a reliable but simpler alternative to intraoperative MR imaging (iMR imaging) for tumor resection control. However, its reliability in the detection of tumor remnants has not been definitely proven. The aim of the study was to compare high-field iMR imaging (1.5 T) and high-resolution 2D ultrasound in terms of tumor resection control.

Methods

A prospective comparative study of 26 consecutive patients was performed. The following parameters were compared: the existence of tumor remnants after presumed radical removal and the quality of the images. Tumor remnants were categorized as: detectable with both imaging modalities or visible only with 1 modality.

Results

Tumor remnants were detected in 21 cases (80.8%) with iMR imaging. All large remnants were demonstrated with both modalities, and their image quality was good. Two-dimensional ultrasound was not as effective in detecting remnants < 1 cm. Two remnants detected with iMR imaging were missed by ultrasound. In 2 cases suspicious signals visible only on ultrasound images were misinterpreted as remnants but turned out to be a blood clot and peritumoral parenchyma. The average time for acquisition of an ultrasound image was 2 minutes, whereas that for an iMR image was ~ 10 minutes. Neither modality resulted in any procedure-related complications or morbidity.

Conclusions

Intraoperative MR imaging is more precise in detecting small tumor remnants than 2D ultrasound. Nevertheless, the latter may be used as a less expensive and less time-consuming alternative that provides almost real-time feedback information. Its accuracy is highest in case of more confined, deeply located remnants. In cases of more superficially located remnants, its role is more limited.

Is the image guidance of ultrasonography beneficial for neurosurgical routine?

BACKGROUND

Intraoperative US has been widely used in neurosurgical procedures. However, images are often difficult to read. In the present study, we evaluate whether the image guidance of ultrasonography is helpful for the interpretation of US scans.

METHODS

Twenty-nine patients with tumor were operated on with the aid of intraoperative US from January to June 2005. Image-guided sonography was used in 13 cases and nonnavigated US technology in the remaining cases. We compared the 2 technologies retrospectively.

RESULTS

Although image quality was good in most cases, orientation remained difficult in 8 of the 16 patients where conventional sonography was used. With the aid of image fusion for navigated sonography, the orientation was judged superior to nonnavigated US.

CONCLUSION

In our experience, integration of the US into the navigation system facilitates anatomical understanding. Thus, we feel that this technology is beneficial for neurosurgical routine.

Intra-operative 3D ultrasound in neurosurgery

In recent years there has been a considerable improvement in the quality of ultrasound (US) imaging. The integration of 3D US with neuronavigation technology has created an efficient and inexpensive tool for intra-operative imaging in neurosurgery. In this review we present the technological background and an overview of the wide range of different applications. The technology has so far mostly been applied to improve surgery of tumours in brain tissue, but it has also been found to be useful in other procedures such as operations for cavernous haemangiomas, skull base tumours, syringomyelia, medulla tumours, aneurysms, AVMs and endoscopy guidance.

Ultrasound guidance in intracranial tumor resection: correlation with postoperative magnetic resonance findings

PURPOSE

To determine the inter-method agreement between intraoperative ultrasonography and postoperative contrast-enhanced magnetic resonance imaging (MRI) in detecting tumor residue.

MATERIAL AND METHODS

After resection was completed, the cavity borders of 32 tumors were examined with a 7 MHz intraoperative probe. Any echogenic region >5 mm in thickness extending from the surgical cavity into the brain substance was taken as the sonographic criterion for residual tumor. A continuous echogenic rim< 5 mm was considered normal. Results were correlated with gadolinium-enhanced MRI obtained within 48 h after surgery.

RESULTS

The kappa value for inter-method agreement was 0.72. There were four cases in whom MRI showed residue despite a negative sonography: extensive edema or Surgicel along the cavity borders (three cases with glioblastoma multiforme) and the cystic component in the vicinity of cerebrospinal fluid (a case with pituitary macroadenoma) may be the reason for the residue going undetected. In a case with glioblastoma multiforme, residual enhancement was < 5 mm in thickness.

CONCLUSION

Intraoperative ultrasound is an effective tool for maximizing the extent of intracranial tumor resection. Surgical use has to be minimized if intraoperative ultrasound is to be used as an adjunct to surgery. Tumors with preoperatively detected cystic components in the proximity of CSF-containing spaces have to be carefully evaluated with intraoperative ultrasound if residual cystic components are to be detected. A low-thickness echogenic rim should not be considered a reliable sign of the absence of residue.

Intraoperative MRI to guide the resection of primary supratentorial glioblastoma multiforme--a quantitative radiological analysis

Patients with supratentorial high-grade glioma underwent surgery within a vertically open 0.5-T magnetic resonance (MR) system to evaluate the efficacy of intraoperative MR guidance in achieving gross-total resection. For 31 patients, preoperative clinical data and MR findings were consistent with the putative diagnosis of a high-grade glioma, in 23 cases in eloquent regions. Tumor resections were carried out within a 0.5-T MR SIGNA SP/i (GE Medical Systems, USA). The resection of the lesion was carried out using fully MR compatible neurosurgical equipment and was stopped at the point when the operation was considered complete by the surgeon viewing the operation field with the microscope. We repeated imaging to determine the residual tumor volume only visible with MRI. Areas of tissue that were abnormal on these images were localized in the bed of resection by using interactive MR guidance. The procedure of resection, imaging control and interactive image guidance was repeated where necessary. Almost all tissue with abnormal characteristics was resected, with the exception of tissue localized in eloquent brain areas. The diagnosis of glioblastoma was confirmed in all 31 cases. When comparing the tumor volume before resection and at the point where the neurosurgeon would otherwise have terminated surgery ("first control"), residual tumor tissue was detectable in 29/31 patients; the mean residual tumor volume was 30.7 +/- 24%. After repeated resections under interactive image guidance the mean residual tumor volume was 15.1%. At this step we found tumor remnants only in 20/31 patients. The perioperative morbidity (12.9%) was low. Twenty-seven patients underwent sufficient postoperative radiotherapy. We found a significant difference (log(rank)p = 0.0037) in the mean survival times of the two groups with complete resection (n = 10, median survival time 537 days) and incomplete resection (n = 17, median survival time 237 days). The resection of primary glioblastoma multiforme under intraoperative MR guidance as demonstrated is a possibility to achieve a more complete removal of the tumor than with conventional techniques. In our small but homogeneous patient group we found an increase in the median survival time in patients with MRI for complete tumor resection, and the overall surgical morbidity was low.

Intraoperative ultrasound imaging: practical applicability as a real-time navigation system

Experience with the use of Intaoperative Ultrasound (US) imaging as real time navigation system in neurosurgery is presented and discussed. Since 1987 we have performed US routinely in a wide variety of intracerebral and intramedullar pathologies. In this analysis we define useful intraoperative applications. Accurate definition of deep-seated lesions and their delineation from surrounding anatomical structures is possible with an US frequency of 5 MHz. Small subcortically located lesions can clearly be visualized with a high frequency probe. Differentiation between solid tumor, cyst and necrosis can be delineated. Identification of residual tumor is difficult. Dural sinuses and eventual invading tumor can be visualized by a 10 MHz probe. US guidance can be helpful for puncturing with a catheter, needle or endoscope. Postoperative percutaneous US imaging through a burr hole did not prove to be useful. The intraoperative use of US imaging is a reliable method for determining the size, shape and localization of lesions. It can be used as a practicable, cost effective and timesaving real time navigation system.

Intraoperative ultrasound imaging: comparison of pathomorphological findings in US versus CT, MRI and intraoperative findings

Since 1987, Ultrasound (US) is performed routinely as real time navigation system in our neurosurgical practice. In 374 cases with different pathologies the preoperative CT and MRI images were compared with the intraoperative US images and the operative findings. In all instances, the lesion could be localized and described in detail. US findings correlated with the findings an CT/MRI, concerning size and shape of lesions. US allowed the differentiation of more structural details within tissue compartments. The demarcation of gliomas was not as well defined in US as compared to CT/MRI, which correlated with the intraoperative situation. As for CT/MRI imaging, a correlation between US findings and histopathology of the lesion was not possible. In our opinion. intraoperative US imaging is an excellent tool for localization of cerebral and medullar lesions and for detailed description of their interior. This indicates a widespread applicability of this method in neurosurgery as an anatomical link between preoperative imaging and the reality of the operative field.

Intraoperative Nutzung eines offenen Mittelfeld-MRT während der chirurgischen Therapie zerebraler Gliome

The aim of the present study was to evaluate the effectiveness of intraoperative MRI guidance in achieving more gross-total resection in case of primary brain tumors. We studied 12 patients with low-grade glioma and 19 patients with high-grade glioma who underwent surgery within a vertically open 0.5 T MR system. After initial imaging, the resection was stopped at the point in which the neurosurgeon considered the resection complete by viewing the operation field. At this time, intraoperative MRI was repeated ("first control") to identify any residual tumor. Areas of tumor-suspected tissue were localized and resected, with the exception of tissue adjacent to eloquent areas. Final imaging was carried out before closing the craniotomy. Comparison of "first control" and final imaging revealed a decrease of residual tumor volume from 32% to 4.3% in low-grade gliomas, and from 29% to 10% in high-grade gliomas. Intraoperative MRI allows a clear optimization of microsurgical resection of both low-grade and high-grade gliomas.

Ultrasound-guided surgery of deep seated brain lesions

OBJECTIVE

Computer aided navigation systems have been introduced to optimize the neurosurgical strategies minimizing the damage to the healthy brain tissue. As the loss of cerebrospinal fluid and surgical manipulation alter the position of the lesion in the external reference system, there is a risk of being misguided to deep seated brain tumors. In this context we present our experiences with intraoperative ultrasound which represents a real-time navigation system.

PATIENTS AND METHODS

45 patients with subcortical intracerebral lesions were operated on with the support of ultrasound imaging. Tumor depth from the surface measured 5 (superficial) to 68 mm. The minimum size of a cavernoma was 8 mm. Histopathological diagnoses included 17 cavernomas, 12 metastases and 16 gliomas. Ultrasound localization was achieved by two perpendicular projections and the surgical trajectory of the lesion secured by catheter placement.

RESULTS

Intraoperative ultrasound allowed an easy identification of all brain lesions. Additionally, a reliable localization of the tumor margins, including gliomas and metastases, was reached in 23 of 28 (82%) cases. The remaining 17 cavernomas were located all by intraoperative ultrasound, even the deep seated brain lesions of less than 10 mm in diameter could be easily detected. The real-time mode enabled a control of the surgical procedure. Technical problems arose from irregular and vaulted cortex surface, head positioning and surgical manipulation causing air artefacts with distal reduction of the signal intensity.

CONCLUSION

Intraoperative ultrasound is a reliable intraoperative guidance tool in the localization of deep seated brain tumors because it operates in real-time, thus increasing the safety of the surgical procedure and of the tumor resection.

Intraoperative ultrasound for guidance and tissue shift correction in image-guided neurosurgery

We present a surgical guidance system that incorporates pre-operative image information (e.g., MRI) with intraoperative ultrasound (US) imaging to detect and correct for brain tissue deformation during image-guided neurosurgery (IGNS). Many interactive IGNS implementations employ pre-operative images as a guide to the surgeons throughout the procedure. However, when a craniotomy is involved, tissue movement during a procedure can be a significant source of error in these systems. By incorporating intraoperative US imaging, the target volume can be scanned at any time, and two-dimensional US images may be compared directly to the corresponding slice from the pre-operative image. Homologous points may be mapped from the intraoperative to the pre-operative image space with an accuracy of better than 2 mm, enabling the surgeon to use this information to assess the accuracy of the guidance system along with the progress of the procedure (e.g., extent of lesion removal) at any time during the operation. Anatomical features may be identified on both the pre-operative and intraoperative images and used to generate a deformation map, which can be used to warp the pre-operative image to match the intraoperative US image. System validation is achieved using a deformable multi-modality imaging phantom, and preliminary clinical results are presented.

Surgical treatment of insular gliomas

Surgical treatment of glial tumours arising in the insula is specially challenging due to the proximity of the internal capsule. Although small insular gliomas have been removed safely by a transylvian approach, in large dominant insular tumours only biopsy has been recommended to avoid postoperative deficits. Unfortunately that is a suboptimal form of treatment as low grade supratentorial gliomas should be removed radically to prevent tumour progression, malignization and to increase the recurrence-free-interval. Addition of radiotherapy to partial removal is associated with a much higher incidence of recurrences and early malignizations compared to radical removal and no radiotherapy. Between 1st October 1989 and 1st September 1996 we treated twenty-three patients harbouring insular gliomas. To increase the radicality of the resection the surgical procedure was performed under local anaesthesia whenever possible, as general anaesthesia usually leads to more conservative resections. In 20/23 (86.9%) patients complete resection was accomplished, and subtotal in three (13.1%). The removed tumours were: two oligodendrogliomas, five grade I astrocytomas, nine grade II, four grade III and three grade IV. Postoperative neurological deficits occurred in five patients. Four suffered a hemiparesis (that recovered in an average of 6 months) and one a motor dysphasia which took a week to recover. Two of the seventeen patients operated on for low grade insular gliomas underwent malignant change. We conclude that complete surgical removal of insular gliomas should be considered and at least attempted in all cases.

Use of intraoperative ultrasound for localizing tumors and determining the extent of resection: a comparative study with magnetic resonance imaging

A prospective study of 70 patients with intraparenchymal brain lesions (36 gliomas and 34 metastases) was performed to evaluate the efficacy of intraoperative ultrasound (IOUS) in localizing and defining the borders of tumors and in assessing the extent of their resection. Eighteen of the 36 glioma patients had no previous therapy. All of these 18 tumors were well localized by IOUS; margins were well defined in 15 and moderately defined in three. The extent of resection was well defined on IOUS in all 18 patients, as confirmed by measurements taken on postoperative magnetic resonance (MR) images (p = 0.90). The remaining 18 patients with gliomas had undergone previous surgery and/or radiation therapy; five had recurrent tumors and 13 had radiation-induced changes. The extent of resection of the recurrent tumors was well defined in all but one patient, as confirmed by postoperative MR imaging. The extent of resection was poorly defined in all 13 patients whose pathology showed radiation effects. All 34 metastatic lesions were well localized and had well-defined margins. In addition, IOUS accurately determined the extent of resection in all cases, the results were confirmed with postoperative MR imaging. In conclusion, IOUS is not only helpful in localizing and defining the margins of gliomas and metastatic brain lesions, it also accurately determines the extent of resection, as confirmed by postoperative MR imaging. This assessment does not apply, however when the lesion is due primarily to radiation effect.

Circumscribed low grade astrocytomas in the dominant opercular and insular region: a pilot study

Intraoperative mapping techniques allow a reliable identification or exclusion of eloquent brain areas and are well tolerated by the patients. In dominant opercular tumours radical surgery can only be achieved without lasting deficits with intraoperative histological examination of the resection line and mapping. If an early postoperative MRI shows residual opercular tumour in non-eloquent areas re-operation is recommended. In large dominant insular or opercular-insular tumours only biopsy is recommended, because only an incomplete removal can be accomplished, because the trial of radical removal carries a high risk of postoperative deficits due to possible vascular damage of the lenticulo-striate arteries or internal capsule. Because subtotal removal of low grade gliomas does not increase the progression free interval, we would not recommend surgery in these cases, as they carry a significant risk of a further deficit.

Ultrasound-guided craniotomy for minimally invasive exposure of cerebral convexity lesions

The authors describe a method of real-time ultrasound-guided craniotomy for an approach to cerebral convexity lesions. During surgery, a specially designed high frequency (7.5 MHz) sector probe with a thin (11 mm), extended tip is used to image the cerebral lesion through a single burr-hole. The distance between burr-hole and lesion and the direction of the target are then determined from the ultrasound images, and craniotomy is completed with the aid of these parameters. Errors in the preoperative planning of the approach, which might result in incorrect placement of the craniotomy, can easily be recognized and corrected at an early stage of the operation, before the craniotomy has been completed. This technique greatly improves the accuracy in placing craniotomy flaps. Since the risk of misplacing the craniotomy is virtually eliminated in lesions which are identifiable on ultrasound images, the technique allows the surgeon to keep the skull opening as limited as possible.

Ultrasound-guided brain biopsy: a personal experience with emphasis on its indication

Between January 1989 and June 1991, 40 ultrasound-guided biopsies of supratentorial brain lesions exceeding 15 mm in diameter were performed. The apparatus used was Berger's neurobiopsy set, intraoperative 5 = MHz transducer, and a B-mode scanner. In 38 cases (95%) the procedure provided a histological diagnosis at the first attempt; in two patients, early in the present series, biopsy was repeated by computed tomography-guided technique due to insufficient samples. Operative mortality was zero and there were no septic complications. Clinical symptoms were stationary after the procedure in 34 cases; two cases temporarily worsened due to postbiopsy edema and subcortical hemorrhage, respectively; and four other cases showed an improvement as a result of evacuation of neoplastic cysts. Histologically, there were 24 primary malignant tumors, eight low-grade glial tumors, five metastatic tumors, two abscesses, and one lymphoma. The ultrasound method for brain lesion biopsy was found to be a simple, quick, and low-cost method that gave reliable results. It is indicated for supratentorial lesions over 15 mm in diameter that do not demand absolute anatomical accuracy.

Ultrasound stereotaxic endoscopy in neurosurgery

Stereotaxic endoscopy assisted by laser- and video technique can be used in a circumscribed number of intracerebral lesions. In the present series of patients, ultrasound imaging has been used as a stereotaxic method to guide the tip of the endoscope to a target area in the depth of the brain via a burr hole in the cranial vault. Initial experience has been obtained in the evacuation of various intracerebral and ventricular as well as cerebellar haematomas; moreover, ventricular tumours can be laser-coagulated and resected. In cases of cystic hemispheric tumours biopsies can be taken under visual control and the inner surface coagulated with laser. The method is less traumatic compared to conventional neurosurgery.