Intraoperative ultrasound (US) imaging. Comparison of pathomorphological findings in US and CT

Development of a Standardized Semantic Feature-Based Reporting Proforma for Intraoperative Ultrasound Findings in Brain Tumors and Application in High-Grade Gliomas - A Preliminary Study

Purpose A semantic feature-based reporting proforma for intraoperative ultrasound findings in brain tumors was devised to standardize reporting. It was applied as a pilot study on a cohort of histologically confirmed high-grade supratentorial gliomas (Grade 3 and 4) for internal validation.

Materials and Methods This intraoperative semantic ultrasound proforma was used to evaluate 3D ultrasound volumes using Radiant DICOM software by 3 surgeons. The ultrasound semantic features were correlated with histological features like tumor grade, IDH status, and MIB index.

Results 68 patients were analyzed using the semantic proforma. Irregular crenated was the most common margin (63.2%) and lesions were heterogeneously hyperechoic (95.6%). Necrosis was commonly seen and noted as single (67.6%) or multiple (13.2%) in over 80% cases. A separate perilesional zone, which was predominantly hyperechoic in 41.8% and both hypo and hyperechoic in 12.7%, could be identified in 54.5% of cases. Grade 4 tumors were more likely to have an irregular crenated margin (71.2%) with a single large area of necrosis, while Grade 3 tumors were likely to have smooth (31.3%) or non-characterizable margins (31.2%) with no or multiple areas of necrosis. IDH-negative tumors were more likely to have a single large focus of necrosis. Among the GBMs (52 cases), MIB labelling index of>15% was associated with poorly delineated, uncharacterizable margins, when compared with MIB labelling index<15% (23.5 vs. 0%), (p=0.046).

Conclusion A detailed semantic proforma was developed for brain tumors and was internally validated. A few ultrasound sematic features were identified correlating with histological features in high-grade gliomas. It will require further external validation for refinement and acceptability.

Ultrasound Imaging versus Radiographs in Differentiating Periapical Lesions: A Systematic Review

BACKGROUND

Ultrasonography is a non-invasive method of diagnosing periapical lesions while radiologic methods are more common. Periapical lesions due to endodontic infection are one of the most common causes of periapical radiolucency that need to be distinguished to help determine the course of treatment. This review aimed to examine the accuracy of ultrasound and compare it to radiographs in distinguishing these lesions in vivo.

METHODS

This review process followed the PRISMA guidelines. A literature search of databases (PubMed, Scopus, Embase, and Web of Science) was conducted without any restrictions on time. Articles available in English were included. The selection was done according to the inclusion and exclusion criteria. The QUADAS-2 tool was used to assess the quality of the studies.

RESULTS

The search provided a total of 87 articles, out of which, five were selected for the final review. In all the studies, ultrasound had higher accuracy in distinguishing periapical lesions. All the studies indicated a risk of bias, especially in patient selection.

CONCLUSION

Within limitations, the study indicates that ultrasound is a better diagnostic tool to distinguish periapical lesions compared to radiographs but further studies with well-designed, rigorous protocols and low risk of bias are needed to provide stronger evidence.

Endodontic Periapical Lesion: An Overview on the Etiology, Diagnosis and Current Treatment Modalities

Nonsurgical and surgical endodontic treatments have a high success rate in the treatment and prevention of apical periodontitis when carried out according to standard and accepted clinical principles. Nevertheless, endodontic periapical lesions remain in some cases, and further treatment should be considered when apical periodontitis persists. Although several treatment modalities have been proposed for endodontically treated teeth with persistent apical periodontitis, there is a need for less invasive methods with more predictable outcomes. The advantages and shortcomings of existing approaches for the diagnosis and treatment of endodontic periradicular lesions are discussed in this review.

Efficacy of intraoperative ultrasonography in neurosurgical tumor resection

OBJECTIVE Intraoperative ultrasonography (IOUS) is a widely accessible imaging modality that provides real-time surgical guidance with minimal identified risk or additional operative time. A recent study by the authors found a strong correlation between IOUS and postoperative MRI findings when evaluating the extent of tumor resection, suggesting that IOUS might have significant clinical implications. The objective of this study was to expand on results from the previous study in order to provide more evidence on the usage of IOUS in the determination of gross-total resection (GTR) in both adult and pediatric patients with brain tumors. METHODS This study consisted of a retrospective review of adult and pediatric neurosurgical patients who were treated at Albany Medical Center between August 2009 and March 2016 for a tumor of the brain. All patients were treated with IOUS and then underwent postoperative MRI (with and without contrast) within 1 week of surgery. RESULTS A total of 260 patients (55% of whom were males) met inclusion criteria for the study (age range 3 months to 84 years). IOUS results showed a strong association with postoperative MRI results (φ = 0.693, p < 0.001) and an 81% intended GTR rate. In cases in which GTR was pursued, 19% had false-negative results. IOUS was able to accurately identify residual tumor in 100% of subtotal resection cases where resection was stopped due to invasion of tumor into eloquent locations. Cases involving gliomas had a 75% intended GTR rate and a 25% false-negative rate. Cases involving metastatic tumors had an 87% intended GTR rate and a 13% false-negative rate. The sensitivity, specificity, negative predictive value, and positive predictive value are reported for IOUS in all included tumor pathologies, glioma cases, and metastatic tumor cases, respectively. CONCLUSIONS The use of IOUS may allow for a reliable imaging modality to achieve a more successful GTR of brain tumors in both adult and pediatric neurosurgical patients. When attempting GTR, the authors demonstrated an 81% GTR rate. The authors also report false-negative IOUS results in 19% of attempted GTR cases. The authors support the use of IOUS in both adult and pediatric CNS tumor surgery to improve surgical outcomes. However, further studies are warranted to address existing limitations with its use to further improve its efficacy and better define its role as an intraoperative imaging tool.

Correlation between intraoperative ultrasound and postoperative MRI in pediatric tumor surgery

OBJECTIVE Malignant disease of the CNS is the primary etiology for deaths resulting from cancer in the pediatric population. It has been well documented that outcomes of pediatric neurosurgery rely on the extent of tumor resection. Therefore, techniques that improve surgical results have significant clinical implications. Intraoperative ultrasound (IOUS) offers real-time surgical guidance and a more accurate means for detecting residual tumor that is inconspicuous to the naked eye. The objective of this study was to evaluate the correlation of extent of resection between IOUS and postoperative MRI. The authors measured the correlation of extent of resection, negative predictive value, and sensitivity of IOUS and compared them with those of MRI. METHODS This study consisted of a retrospective review of the medical charts of all pediatric patients who underwent neurosurgical treatment of a tumor between August 2009 and July 2015 at Albany Medical Center. Included were patients who were aged ≤ 21 years, who underwent brain or spinal tumor resection, for whom IOUS was used during the tumor resection, and for whom postoperative MRI (with and without contrast) was performed within 1 week of surgery. RESULTS Sixty-two patients met inclusion criteria for the study (33 males, mean age 10.0 years). The IOUS results very significantly correlated with postoperative MRI results (φ = 0.726; p = 0.000000011; negative predictive value 86.3% [95% CI 73.7%-94.3%]). These results exemplify a 71% overall gross-total resection rate and 80% intended gross-total resection rate with the use of IOUS (i.e., excluding cases performed only for debulking purposes). CONCLUSIONS The use of IOUS may play an important role in achieving a greater extent of resection by providing real-time information on tumor volume and location in the setting of brain shift throughout the course of an operation. The authors support the use of IOUS in pediatric CNS tumor surgery to improve clinical outcomes at low cost with minimal additional operating-room time and no identified additional risk.

Neurosurgical tools to extend tumor resection in hemispheric low-grade gliomas: conventional and contrast enhanced ultrasonography

PURPOSE

Pediatric low-grade gliomas (LGGs) are the most frequent solid tumor in childhood. Based on an increasing number of literature reports, maximal safe resection is recommended as the first line of treatment whenever possible. However, distinguishing tumor tissue from the surrounding normal brain is often challenging with infiltrating neoplasms, even with the assistance of intraoperative, microscopic and conventional neuronavigation systems. Therefore, any technique that enhances the detection and visualization of LGGs intraoperatively is certainly desirable.

METHODS

In this paper, we reviewed the role of intraoperative conventional ultrasound and contrast-enhanced ultrasound (CEUS) as a tool for extending tumor resection in LGGs. Moreover, our experience with this technology is reported and discussed.

RESULTS

Both B-mode and CEUS are helpful in highlighting LGGs, detecting tumor margins and providing additional information such as vascularization, thus improving the safety of a more radical resection.

CONCLUSIONS

Although the full potentialities of the method are yet to be explored, intraoperative ultrasound is a promising tool in oncologic surgery and LGG surgery.

The value of intraoperative ultrasonography during the resection of relapsed irradiated malignant gliomas in the brain

Purpose

The aim of this study was to investigate whether intraoperative ultrasonography (IOUS) helped the surgeon navigate towards the tumor as seen in preoperative magnetic resonance imaging and whether IOUS was able to distinguish between tumor margins and the surrounding tissue.

Methods

Twenty-five patients suffering from high-grade gliomas who were previously treated by surgery and radiotherapy were included. Intraoperatively, two histopathologic samples were obtained a sample of unequivocal tumor tissue (according to anatomical landmarks and the surgeon’s visual and tactile impressions) and a small tissue sample obtained using a navigated needle when the surgeon decided to stop the resection. This specimen was considered to be a boundary specimen, where no tumor tissue was apparent. The decision to take the second sample was not influenced by IOUS. The effect of IOUS was analyzed semi-quantitatively.

Results

All 25 samples of unequivocal tumor tissue were histopathologically classified as tumor tissue and were hyperechoic on IOUS. Of the boundary specimens, eight were hypoechoic. Only one harbored tumor tissue (P=0.150). Seventeen boundaries were moderately hyperechoic, and these samples contained all possible histological results (i.e., tumor, infiltration, or no tumor).

Conclusion

During surgery performed on relapsed, irradiated, high-grade gliomas, IOUS provided a reliable method of navigating towards the core of the tumor. At borders, it did not reliably distinguish between remnants or tumor-free tissue, but hypoechoic areas seldom contained tumor tissue.

The value of intraoperative ultrasonography in neurosurgery

Intraoperative ultrasonography is widely used in neurosurgery today. Here we attempt to clarify and demonstrate its usefulness in the operating room. Of 113 lesions, 112 were detected during surgery. The undetected lesion was a spinal arachnoid hematoma that had been absorbed during an intraoperative maneuver. No infection or complication occurred after surgery. Ultrasound guidance ensures safe tumor removal by minimizing injury to cerebral tissue and shortening operation time. Intraoperative ultrasonography improves the safety and efficiency of neurosurgery.

Intraoperative neuronavigation integrated high resolution 3D ultrasound for brainshift and tumor resection control

INTRODUCTION: The link between the neurosurgeon’s knowledge and the scientific improvements made a dramatic change in the field expressed both in impressive drop in the mortality and morbidity rates that were operated in the beginning of the XXth century and in operating with high rates of success cases that were considered inoperable in the past. Neuronavigation systems have been used for many years on surgical orientation purposes especially for small, deep seated lesions where the use of neuronavigation is correlated with smaller corticotomies and with the extended use of transulcal approaches. The major problem of neuronavigation, the brainshift once the dura is opened can be solved either by integrated ultrasound or intraoperative MRI which is out of reach for many neurosurgical departments. METHOD: The procedure of neuronavigation and ultrasonic localization of the tumor is described starting with positioning the patient in the visual field of the neuronavigation integrated 3D ultrasonography system to the control of tumor resection by repeating the ultrasonographic scan in the end of the procedure. DISCUSSION: As demonstrated by many clinical trials on gliomas, the more tumor removed, the better long term control of tumor regrowth and the longer survival with a good quality of life. Of course, no matter how aggressive the surgery, no new deficits are acceptable in the modern era neurosurgery. There are many adjuvant methods for the neurosurgeon to achieve this maximal and safe tumor removal, including the 3T MRI combined with tractography and functional MRI, the intraoperative neuronavigation and neurophysiologic monitoring in both anesthetized and awake patients. The ultrasonography integrated in neuronavigaton comes as a welcomed addition to this adjuvants to help the surgeon achieve the set purpose. CONCLUSION: With the use of this real time imaging device, the common problem of brainshift encountered with the neuronavigation systems is covered and any eventual tumor residue can be spotted by ultrasonography and resected

Intra-operative brain tumor detection using elastic light single-scattering spectroscopy: a feasibility study

We have investigated the potential application of elastic light single-scattering spectroscopy (ELSSS) as an adjunctive tool for intraoperative rapid detection of brain tumors and demarcation of the tumor from the surrounding normal tissue. Measurements were performed on 29 excised tumor specimens from 29 patients. There were 21 instances of low-grade tumors and eight instances of high-grade tumors. Normal gray matter and white matter brain tissue specimens of four epilepsy patients were used as a control group. One low-grade and one high-grade tumor were misclassified as normal brain tissue. Of the low- and high-grade tumors, 20 out of 21 and 7 out of 8 were correctly classified by the ELSSS system, respectively. One normal white matter tissue margin was detected in a high-grade tumor, and three normal tissue margins were detected in three low-grade tumors using spectroscopic data analysis and confirmed by histopathology. The spectral slopes were shown to be positive for normal white matter brain tissue and negative for normal gray matter and tumor tissues. Our results indicate that signs of spectral slopes may enable the discrimination of brain tumors from surrounding normal white matter brain tissue with a sensitivity of 93% and specificity of 100%.

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.

A comparative analysis of coregistered ultrasound and magnetic resonance imaging in neurosurgery

OBJECTIVE

This work presents qualitative and quantitative side-by-side comparisons of oblique coregistered magnetic resonance imaging (MRI) scans and ultrasound images obtained during 35 neurosurgical procedures.

METHODS

Spatially registered series of ultrasound images were recorded for subsequent off-line evaluation and comparison with corresponding preoperative MRI studies. The degree of misalignment was reduced by reregistering the target volume directly with segmented features.

RESULTS

The initial apparent spatial misalignment of the target volume after craniotomy ranged from 0.11 to 8.73 mm (mean, 4.01 mm). After reregistration, the mutual information in overlapping segmented features was increased, presumably evidence of a better alignment locally. Additionally, the degree of feature congruence, which was assessed quantitatively through a convex hull approximation, demonstrated that the ultrasound volume was consistently smaller than its MRI counterpart.

CONCLUSION

Although intraoperative ultrasound tends to be difficult to interpret by itself, when accurately coregistered with preoperative MRI scans, its potential utility as a navigational guide is enhanced.

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.

Image-guided ultrasonography for recurrent cystic gliomas

BACKGROUND

Long-term survival of patients with recurrent gliomas depends on the extent of resection. Thus, the desirability of an intra-operative imaging modality that can augment the resection extension without affecting vital surrounding structures is more than obvious. It was the aim of the present study to evaluate a possible benefit of image-guided intra-operative ultrasonography for the surgery of recurrent gliomas.

METHOD

The authors performed ultrasonography-assisted image-guided resection of recurrent gliomas in 16 patients. An ultrasound device (IGSonic) was integrated into the VectorVision2 navigation system (BrainLAB, Heimstetten, Germany). The IGSonic Probe 10V5 was connected to the VectorVision Navigation station via an IGSonic Device Box. Following patient registration, MRI based neuronavigation was used to determine the skin incision and the bone flap. Before opening the dura, the underlying structures were explored by ultrasound combined with the corresponding MR images. The navigated ultrasound displayed the sonographic image of the intracranial anatomy on the navigation screen in a composed overlay fashion.

FINDINGS

The integration of intra-operative ultrasound into neuronavigation system offered quick and helpful intra-operative images in all 16 procedures. Due to the specific ultrasonic characteristics of the solid and the cystic parts, our technique created highly useful images in 10 patients with cystic recurrences. In these, user friendly images were obtained that were easy to understand even for neurosurgeons without major experience in intra-operative ultrasound.

CONCLUSIONS

Neurosonography is a time- and cost-effective technology offering intra-operative imaging. The improved orientation and visualization of tumour remnants, adjacent ventricles, and the enhanced intra- and peri-tumoural vasculature is one of the main advantages of ultrasonography-assisted image-guided surgery, which is most obvious during surgery for cystic gliomas.

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.

Ability of navigated 3D ultrasound to delineate gliomas and metastases--comparison of image interpretations with histopathology

BACKGROUND

The objective of the study was to test the ability of a 3D ultrasound (US) based intraoperative imaging and navigation system to delineate gliomas and metastases in a clinical setting. The 3D US data is displayed as reformatted 2D image slices. The quality of the displayed 3D data is affected both by the resolution of the acquired data and the reformatting process. In order to investigate whether or not 3D US could be used for reliable guidance in tumour surgery, a study was initiated to compare interpretations of imaged biopsy sites with histopathology. The system also enabled concomitant comparison of navigated preoperative MR with histopathology.

METHOD

Eighty-five biopsies were sampled between 2-7 mm from the tumour border visible in the ultrasound images. Biopsies were collected from 28 operations (7 low-grade astrocytomas, 8 anaplastic astrocytomas, 7 glioblastomas and 6 metastases). Corresponding cross-sections of preoperative MR T1, MR T2 and intraoperative US were concomitantly displayed, steered by the biopsy forceps equipped with a positioning sensor. The surgeons' interpretation of the images at the electronically indicated biopsy sites were compared with the histopathology of the samples.

FINDINGS

The ultrasound findings were in agreement with histopathology in 74% (n = 31) for low-grade astrocytomas, 83% (n = 18) for anaplastic astrocytomas, 77% (n = 26) for glioblastomas and 100% (n = 10) for metastases. Excluding irradiated patients, the results for glioblastomas improved to 80% concurrence (n = 20). As expected tumour cells were found in biopsies outside the US visible tumour border, especially in low-grade gliomas. Navigated 3D US have a significantly better agreement with histopathology than navigated MR T1 for low-grade astrocytomas.

CONCLUSION

Reformatted images from 3D US volumes give a good delineation of metastases and the solid part of gliomas before starting the resection. Navigated 3D US is at least as reliable as navigated 3D MR to delineate gliomas and metastases.

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.

Functional Imaging with Intraoperative Ultrasound: Detection of Somatosensory Cortex in Dogs with Color-duplex Sonography

OBJECTIVE

To evaluate the capability of intraoperative color-duplex sonography to detect eloquent flow-activated areas and their anatomic relationship in dogs.

METHODS

After craniotomy, the sensory cortex of eight dogs was identified by recording the highest amplitude detected with a grid electrode evoked with somatosensory evoked potential stimulation of the nervus ischiadicus. A 7.5-MHz linear array transducer was placed on the dura, and eight images were taken in color-coded capture mode during baseline and somatosensory evoked potential stimulation of the ipsilateral (nonevoked) and contralateral (evoked) sensory cortex. The differences in flow velocity intensities were statistically compared (Wilcoxon test) in three arbitrary velocity ranges and across all colored pixels in a region of interest between baseline and stimulation in both hemispheres.

RESULTS

Comparing both hemispheres during stimulation, the evoked sensory cortex demonstrated an increase of 10% in the number of counted colored pixels during stimulation, whereas the number of counted colored pixels in the ipsilateral sensory cortex decreased by 2% (P < 0.05), indicating an overall increase in measured flow during stimulation. Comparing differences during nonstimulation and stimulation in single hemispheres, the lowest of the three velocity ranges (approximately 10-20 mm/s) demonstrated a statistically significant (P = 0.01) increase during stimulation, whereas no change was observed during stimulation in the ipsilateral hemisphere. This increase has been confirmed by regional cerebral blood flow measurement with colored microspheres.

CONCLUSION

This study indicates, for the first time, the capability of intraoperative ultrasound to detect functionally important areas during evoked stimulation.

Brain Shift Estimation in Image-Guided Neurosurgery Using 3-D Ultrasound

Intraoperative brain deformation is one of the most important causes affecting the overall accuracy of image-guided neurosurgical procedures. One option for correcting for this deformation is to acquire three-dimensional (3-D) ultrasound data during the operation and use this data to update the information provided by the preoperatively acquired MR data. For 12 patients 3-D ultrasound images have been reconstructed from freehand sweeps acquired during neurosurgical procedures. Ultrasound data acquired prior to and after opening the dura, but prior to surgery, have been quantitatively compared to the preoperatively acquired MR data to estimate the rigid component of brain shift at the first stages of surgery. Prior to opening the dura the average brain shift measured was 3.0 mm parallel to the direction of gravity, with a maximum of 7.5 mm, and 3.9 mm perpendicular to the direction of gravity, with a maximum of 8.2 mm. After opening the dura the shift increased on average 0.2 mm parallel to the direction of gravity and 1.4 mm perpendicular to the direction of gravity. Brain shift can be detected by acquiring 3-D ultrasound data during image-guided neurosurgery. Therefore, it can be used as a basis for correcting image data and preoperative planning for intraoperative deformations.

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.

Neuronavigation by intraoperative three-dimensional ultrasound: initial experience during brain tumor resection

OBJECTIVE

Three-dimensional (3-D) ultrasound is an intraoperative imaging modality used in neuronavigation as an alternative to magnetic resonance imaging (MRI). This article summarizes 4 years of clinical experience in the use of intraoperative 3-D ultrasound integrated into neuronavigation for guidance in brain tumor resection.

METHODS

Patients were selected for inclusion in the study on the basis of the size and location of their lesion. Preoperative 3-D MRI data were registered and used for planning as in other conventional neuronavigation systems. Intraoperative 3-D ultrasound images were acquired three to six times, and tumor resection was guided on the basis of these updated 3-D images.

RESULTS

Intraoperative 3-D ultrasound represents a good solution to the problem of brain shift in neuronavigation because it easily provides an updated, and hence more accurate, map of the patient's true anatomy in all phases of the operation. Ultrasound makes it possible to follow the progression of the operation, and it improves the radicality of tumor resection by detecting tumor tissue that would remain if the imaging technology had not been used (in 53% of the cases). Integration of 3-D ultrasound with navigation technology solves the orientation problem experienced previously with two-dimensional ultrasound in neurosurgery. The technology makes it possible to directly compare intraoperative ultrasound and MRI data regarding visualization of the lesion. Ultrasound image quality is useful for guiding surgical procedures.

CONCLUSION

Intraoperative 3-D ultrasound seems to provide a time- and cost-effective way to update high-quality 3-D maps used in neuronavigation.

Comparison of intraoperative MR imaging and 3D-navigated ultrasonography in the detection and resection control of lesions

Object

The authors undertook a study to compare two intraoperative imaging modalities, low-field magnetic resonance (MR) imaging and a prototype of a three-dimensional (3D)–navigated ultrasonography in terms of imaging quality in lesion detection and intraoperative resection control.

Methods

Low-field MR imaging was used for intraoperative resection control and update of navigational data in 101 patients with supratentorial gliomas. Thirty-five patients with different lesions underwent surgery in which the prototype of a 3D-navigated ultrasonography system was used. A prospective comparative study of both intraoperative imaging modalities was initiated with the first seven cases presented here.

In 35 patients (70%) in whom ultrasonography was performed, accurate tumor delineation was demonstrated prior to tumor resection. In the remaining 30% comparison of preoperative MR imaging data and ultrasonography data allowed sufficient anatomical localization to be achieved. Detection of metastases and high-grade gliomas and intra-operative delineation of tumor remnants were comparable between both imaging modalities. In one case of a low-grade glioma better visibility was achieved with ultrasonography. However, intraoperative findings after resection were still difficult to interpret with ultrasonography alone most likely due to the beginning of a learning curve.

Conclusions

Based on these preliminary results, intraoperative MR imaging remains superior to intraoperative ultrasonography in terms of resection control in glioma surgery. Nevertheless, the different features (different planes of slices, any-plane slicing, and creation of a 3D volume and matching of images) of this new ultrasonography system make this tool a very attractive alternative. The intended study of both imaging modalities will hopefully allow a comparison regarding sensitivity and specificity of intraoperative tumor remnant detection, as well as cost effectiveness.

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.

Intraoperative color duplex sonography of basal arteries during aneurysm surgery

This prospective study aimed at (1) characterizing the duplex sonographic appearance of cerebral aneurysms, (2) visualizing their location, and (3) ensuring the complete occlusion of the aneurysm as well as the patency of the basal arteries during aneurysm surgery. During 9 months 30 craniotomies for aneurysm clipping in 29 patients were monitored intraoperatively by B-mode and color-coded duplex sonography. Following craniotomy the aneurysm and the preaneurysmatic and postaneurysmatic arteries were sonographically visualized before and after clipping and removal of the spatulas. Twenty-seven (90%) of 30 aneurysms appeared as a hypoechoic structure. Together with the typical dichromatic picture in the color mode and the characteristic bidirectional flow pattern in the duplex mode, 29 (97%) of 30 aneurysms were identified and localized anatomically correctly. Eighty (99%) of 81 relevant vessels were visualized and measured with the Doppler mode. After clipping, flow was detectable in all major arteries except 3 middle cerebral artery (MCA) branches. In 1, occlusion was confirmed by postoperative angiography. In the other 2, early postoperative computed tomography showed an infarction of the corresponding MCA territories. This study demonstrated the potential of color duplex sonography to visualize and characterize cerebral aneurysms and adjacent basal arteries before and after clipping. It offers a noninvasive intraoperative method to control the patency of basal arteries and complete occlusion of the aneurysm.

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.

The role of adjuvant radiation and multiple resection within the surgical management of brain metastases

Cerebral metastases occur in 25% to 35% of all cancer patients. The advances in systemic and topical treatment as well as the rising incidence of lung cancer and melanomas are associated with an increasing incidence of cerebral metastases. More than 20,000 patients die every year in the Federal Republic of Germany of this disease. This retrospective analysis covers 145 patients who underwent surgery. Survival analysis of different subgroups was performed. The patients were grouped according to their clinical status and the different therapeutical procedures which were performed. Group A, consisting of all those patients where a gross total resection could be performed and where no systemic disease was apparent at the time of craniotomy showed the best results, having the highest portion of long term survivors. Group B, consisting of those patients who underwent a subtotal resection and who had no systemic disease at the time of craniotomy, had a worse outcome. Group C patients (gross total resection and systemic disease) as well as Group D (subtotal resection and systemic disease) presented the poorest results with respect to survival. A benefit was mediated by adjuvant radiation as well as multiple resections. Surgery is the method of choice for the treatment of a single metastasis. Advances in microsurgery nowadays sometimes justify even the removal of multiple metastases, depending on their location, on the general condition of the patient and on prognosis.

Correlation of intra-operative ultrasound with histopathologic findings after tumour resection in supratentorial gliomas. A method to improve gross total tumour resection

The aim of this study was to evaluate whether intra-operative ultrasound (= IOUS) is a suitable tool to detect residual tumour tissue after gross total resection in supratentorial gliomas. During a period of 18 months 45 patients with supratentorial gliomas (38 high-grade and 9 low-grade, according to the WHO-grading system [42]) were operated on. A series of 78 biopsies was taken from the resection cavity under continuous sonographic control at the end of surgery. Gross total tumour resection was intended in 34 patients (= 76%). The biopsy specimens were matched with the sonographic features at each biopsy site. The sonographic appearance of the resection margins were classified into 2 groups: (1) Irregular hyperechoic areas extending from the cavity into the iso-echogenic brain tissue and (2) a dense small (< or = 3 mm in diameter) rather regular hyperechoic rim surrounding the resection cavity. 47 out of 53 biopsies taken from hyperechoic areas (group I) (36 high-grade/11 low-grade) revealed solid tumour tissue (= 89%). 34 (= 72%) of these 47 areas were microscopically assessed as inconspicuous by the surgeon. 6 samples (4 high-grade/2 low-grade) contained tumour infiltration zone. 25 biopsies (23 high-grade/2 low-grade) taken from the hyperechoic rim [group 2] were diagnosed as follows: Normal brain tissue in 11, tumour infiltration zone in 8 and solid tumour tissue in 6 cases. Of 34 cases with "gross total removal" according to the surgeon's assessment 25 showed sonographic signs of residual tumour tissue, which was confirmed histologically as solid tumour tissue in 22 of these cases. It is concluded, that IOUS following resection of supratentorial gliomas can detect residual tumour tissue with high specificity and thus improve gross total resection. However, a thin hyperechoic rim surrounding the resection cavity (less than 3 mm in diameter) is a non-specific finding, which can mask thin residual tumour layers and therefore needs further evaluation of its nature.

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 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.

Practical application of intraoperative ultrasound imaging

Intraoperative real-time ultrasound imaging (US) was used in over 500 patients to investigate which of the previously considered applications are of practical use in everyday neurosurgery. During all intraoperative applications for a wide variety of pathological conditions, small deep-seated as well as subcortically located lesions were detected with accuracy; in many instances they could be approached through smaller surgical exposures. US guidance was accurate in 209 cases for the stereotactic introduction of needles or endoscopes into various lesions: thus burrhole evacuation was performed on 148 intracerebral haematomas; in 16 patients endoscopic biopsy and resection of ventricular tumours was performed as well as biopsies of 39 hemispheric brain tumours and aspiration of a brain abscess in 6 instances. Seventy six gliomas were investigated by US imaging; the frequently unclear boundary between tumour and surrounding oedema was not better visualized than with CT or MRI. Moreover, US imaging for the detection of residual tumour towards the end of operation was unreliable. Postoperative imaging through burrholes or other cranial defects was mostly of unacceptably low quality for therapeutic decision making.