The role of image-directed biopsy in the diagnosis and management of brainstem lesions

[Primary tumors of the brain stem. State of the problem]

Primary brainstem gliomas are still poorly studied in neurooncology. This concept includes tumors with different histological and genetic features, as well as variable clinical course and outcomes. Nevertheless, treatment implies radiotherapy without a clear idea of morphological substrate of disease in 80% of cases. Small number of studies and insufficient data on histological and genetic nature of brainstem tumors complicate clear diagnostic and treatment algorithms. This review provides current information regarding primary glial brainstem tumors. Appropriate problems and objectives are highlighted. The purpose of the review is to provide a comprehensive and updated understanding of the current state of brainstem glial tumors and to identify areas requiring further study for improvement of diagnosis and treatment of these diseases. Brainstem tumors are an understudied problem with small amount of data that complicates optimal treatment strategies. Further researches and histological verification are required to develop new methods of therapy, especially for diffuse forms of neoplasms.

Primary midbrain germinomas: Report of a rare case with an updated review of the literature

Intracranial germinomas are most commonly extra-axial germ cell tumors that are predominantly found in the pineal and suprasellar regions. Primary intra-axial midbrain germinomas are extremely rare, with only eight reported cases. Here we present a 30-year-old man who presented with severe neurological deficits, with an MRI that showed a heterogeneously enhancing mass with ill-defined margins in the midbrain, and with surrounding vasogenic edema extending to the thalamus. The presumptive preoperative differential diagnosis included glial tumors and lymphoma. The patient underwent a right paramedian suboccipital craniotomy and biopsy obtained through the supracerebellar infratentorial transcollicular approach. The histopathological diagnosis was reported as pure germinoma. After patient discharge, he received chemotherapy with carboplatin and etoposide, followed by radiotherapy. Follow-up MRI at up to 26 months showed no contrast-enhancing lesions but a mild T2 FLAIR hyperintensity adjacent to the resection cavity. Differential diagnosis of midbrain lesions can be challenging and should include glial tumors, primary central nervous system lymphoma, germ cell tumors, and metastasis. Accurate diagnosis requires adequate tissue sampling. In this report, we present a very rare case of a primary intra-axial germinoma of the midbrain which is biopsied via a transcollicular approach. This report is also unique as it provides the first surgical video of an open biopsy and the microscopic appearance of an intra-axial primary midbrain germinoma via a transcollicular approach.

Stereotactic Brainstem Biopsy: Technical Aspects with Emphasis on Role of Awake Craniotomy

Introduction The role of frame-based stereotactic biopsy in brainstem lesions has been well established in literature. Transfrontal, transtentorial, and transcerebellar routes are used to access various targets within the brainstem. While the transfrontal approach is preferable in midbrain lesions, a transcerebellar approach via the middle cerebellar peduncle forms the shortest possible trajectory for pontine and medullary lesions.

Objective Authors to describe the technical nuances of frame-based stereotactic biopsy of lower brainstem lesions to increase the procedural safety and efficacy.

Materials and Methods Technical modifications in frame fixation were done to acheive the desired trajectory to the target. In adult cases biopsy was performed with patient awake during the procedure.

Results Total of five patients underwent biopsy with the technical modifications. Three patients were adults and two were in pediatric age group. Their age ranged from 12 to 50 years. No complications were encountered. Two of the biopsies showed demyelination and the other three turned out to be low-grade glioma, pilocytic astrocytoma, and lymphoma, respectively.

Conclusion Despite obvious inherent risks, the transcerebellar biopsy in semi-sitting position is a well-tolerated and effective method of obtaining a diagnostic tissue sample in brainstem lesions. We have noted that adoption of the technical modifications described in this article has aided in improving the safety and ease of the procedure.

Usefulness of Ultrasound-Guided Microsurgery in Cavernous Angioma Removal

BACKGROUND

Primary elements of surgical treatment of cavernous angiomas (CAs) are precise lesion identification and optimal trajectory determination. Navigation techniques allow for better results compared to microsurgery alone. In this study, we examined the benefits of intraoperative ultrasound (IOUS) use as an adjunct to standard localization systems.

METHODS

We retrospectively analyzed 59 CAs, comparing outcomes in 2 groups of patients: 34 who underwent frame-based or frameless navigation-assisted microsurgery (no-IOUS group) and 25 who underwent IOUS-guided microsurgery associated with these techniques (IOUS group).

RESULTS

The use of IOUS did not significantly increase the surgery time (mean, 172 ± 1.7 minutes in the IOUS group and 192.6 ± 11.5 in no-IOUS group; P = 0.08). In all 25 patients in the IOUS group, IOUS allowed for ready identification of CA as a hyperechoic mass. At the last follow-up (mean, 41.7 ± 3.5 months postsurgery), 95.2% of the IOUS group and 80.8% of the no-IOUS group had a modified Rankin Scale score of 0-1 and an Extended Glasgow Outcome Scale score of 7-8 (P = 0.2), with 100% and 64%, respectively, included in Engel outcome scale class IA (P = 0.006). Complete removal, as confirmed on postoperative magnetic resonance imaging, was achieved in all patients in the IOUS group and in almost all (97.1%; P = 0.4) patients in the no-IOUS group.

CONCLUSIONS

IOUS is a valid tool for the intraoperative identification of CAs. Implementation of standard localization methods with IOUS guidance was associated with complete resection in all cases, without increasing surgical time. Compared with microsurgery without IOUS guidance, long-term functional outcomes showed better trends, and the epilepsy-free rate was significantly higher.

Update on the diagnostic value and safety of stereotactic biopsy for pediatric brainstem tumors: a systematic review and meta-analysis of 735 cases

OBJECTIVE Recent studies have shed light on the molecular makeup of diffuse intrinsic pontine gliomas and led to the identification of potential treatment targets for these lesions, which account for the majority of pediatric brainstem tumors (pedBSTs). Therefore, stereotactic biopsy-driven molecular characterization of pedBSTs may become an important prerequisite for the management of these fatal brain tumors. The authors conducted a systemic review and meta-analysis to precisely determine the safety and diagnostic success of stereotactic biopsy of pedBSTs. METHODS A systematic search of PubMed, EMBASE, and the Web of Science yielded 944 potentially eligible abstracts. Meta-analysis was conducted on 18 studies (including the authors' own institutional series), describing a total of 735 biopsy procedures for pedBSTs. The primary outcome measures were diagnostic success and procedure-related complications. Pooled estimates were calculated based on the Freeman-Tukey double-arcsine transformation and DerSimonian-Laird random-effects model. Heterogeneity, sensitivity, and meta-regression analyses were also conducted. RESULTS The weighted average proportions across the analyzed studies were 96.1% (95% CI 93.5%-98.1%) for diagnostic success, 6.7% (95% CI 4.2%-9.6%) for overall morbidity, 0.6% (95% CI 0.2%-1.4%) for permanent morbidity, and 0.6% (95% CI 0.2%-1.3%) for mortality. Subgroup analyses at the study level identified no significant correlation between the outcome measures and the distribution of the chosen biopsy trajectories (transfrontal vs transcerebellar), age, year of publication, or the number of biopsy procedures annually performed in each center. CONCLUSION Stereotactic biopsy of pedBSTs is safe and allows successful tissue sampling as a prerequisite for the molecular characterization and the identification of potentially druggable targets toward more individualized treatment concepts to improve the outcome for children harboring such lesions.

Application of stereotactic biopsy for diagnosing intracranial lesions in patients with AIDS in China: Report of 7 cases

RATIONALE

The aim of the study was to evaluate stereotactic biopsy for diagnosing intracranial lesions in patients with AIDS.

PATIENT CONCERNS

Seven AIDS patients with an intracranial lesion who underwent stereotactic biopsy were included in this retrospective study (4 males and 3 females, 15 to 49 years old). The patients' disease history ranged from 1 month to 1 year. The samples were examined by hematoxylin-eosin (HE) staining and immunohistochemical examination.

DIAGNOSES, INTERVENTIONS AND OUTCOMES

All patients were successfully sampled, and the histological results showed inflammation in 4 cases, toxoplasma gondii infection in 1 case, astrocytoma in 1 case, and abscess in 1 case. The clinical diagnosis included toxoplasma encephalitis (TE) in 2 cases, cryptococcus encephalitis in 2 cases, cytomegalovirus (CMV) encephalitis in 2 case, tubercular abscess in 1 case, astrocytoma in 1 case, and co-infection of TE with Cryptococcus infection in 1 patient. The clinical diagnosis was made according to the plasma and cerebrospinal fluid (CSF) laboratory testing, the imaging data and the histological findings. The diagnostic yield was 100%, and the post-operation morbidity was 14.3% (1/7) with an asymptomatic haemorrhage and seizure in 1 case. There was no operation-related mortality. Patients were followed up for 6 months to 6 years; 1 case fully recovered, 4 cases significantly improved in symptoms, and 2 died.

LESSONS

Stereotactic biopsy is a safe and effective way of diagnosing intracranial lesions in patient with AIDS. It is helpful for the differential diagnosis and for choosing a suitable therapy. Due to the broad spectrum of nervous system abnormalities in AIDS, histological findings are very valuable. However, histology is not a unique tool for making a definite diagnosis, whereas the combination of molecular pathology and stereotactic biopsy should play a more important role in the future.

Diagnostic value and safety of stereotactic biopsy for brainstem tumors: a systematic review and meta-analysis of 1480 cases

BACKGROUND

The feasibility and safety of stereotactic biopsy for brainstem tumors (BSTs) are controversial. Although magnetic resonance imaging (MRI) has been reported as the preferred diagnostic tool, histopathological analysis is frequently necessary to establish a definitive diagnosis. Recent advances in molecular characterization of brainstem gliomas-accounting for the majority of BSTs-have revealed several potential targets for molecular-based therapies. Hence, a molecular stereotactic biopsy that combines histopathological diagnosis with molecular-genetic analysis will become increasingly important for patients with BSTs.

OBJECTIVE

We conducted a systemic review and meta-analysis to determine the risks and benefits of stereotactic biopsy for BSTs.

METHODS

A systematic search in PubMed, Embase, and the Web of Science yielded 3766 potentially eligible abstracts. Meta-analysis was conducted on 38 studies describing 1480 biopsy procedures for BSTs. Primary outcome measures were diagnostic success and procedure-related complications. Data were analyzed according to standard meta-analytic techniques.

RESULTS

The weighted average proportions across the analyzed studies were: 96.2% (95% confidence interval [CI]: 94.5%-97.6%) for diagnostic success, 7.8% (95% CI: 5.6%-10.2%) for overall morbidity, 1.7% (95% CI: 0.9%-2.7%) for permanent morbidity, and 0.9% (95% CI: 0.5%-1.4%) for mortality. Meta-regression revealed a significant correlation between diagnostic success rates and the number of biopsy procedures performed annually in each center (P = .011). Other factors did not affect the outcome measures.

CONCLUSION

Stereotactic biopsy of BSTs is safe. It allows exact histopathological diagnosis as a prerequisite for adequate treatment and opens new perspectives for the molecular characterization of these tumors as a crucial first step toward more individualized treatment concepts.

ABBREVIATIONS

: BST, brainstem tumorCI, confidence intervalD-BSG, diffuse brainstem gliomaHGG, high-grade gliomaLGG, low-grade gliomasTC, transcerebellarTF, transfrontal.

Transcerebellar stereotactic biopsy for lesions of the brainstem and peduncles under local anesthesia

OBJECTIVE

For certain brainstem lesions, a diagnostic biopsy is required for treatment planning. We reviewed the indications, safety, and diagnostic effectiveness of a transcerebellar stereotactic biopsy using local anesthesia and sedation.

METHODS

We retrospectively reviewed hospital records for all adult patients with symptomatic lesions of the pons and/or cerebellar peduncle who underwent an awake transcerebellar stereotactic biopsy at our institution over a 7-year period. Our technique features several modifications from the standard method and was performed under local anesthesia with patients in the semi-sitting position.

RESULTS

Our rate of diagnostic success (92%) was comparable to those in other published reports. However, only 5 (42%) of 12 biopsy-derived diagnoses were consistent with those predicted from preoperative magnetic resonance imaging. There were no deaths, and the only neurological complication was a cranial nerve palsy. Diagnoses in the 13 cases included infiltrative glioma (), metastases (), lymphoma (), encephalitis (), and reactive astrogliosis ().

CONCLUSION

Tissue diagnosis of lesions in the brainstem and cerebellar peduncles continues to be a significant challenge, with the potential for major morbidity. With appropriate patient selection, however, awake transcerebellar biopsy is a safe and effective procedure that can change clinical management and provide important prognostic information.

Stereotactic biopsy of brain stem masses: decision analysis and literature review

BACKGROUND

Adult brain stem tumors are rare, and diverse pathology can be found in this location. Stereotactic biopsy of lesions in the brain stem has been performed since the 1960s with high diagnostic and low complication rates. Advances in imaging technology have raised questions regarding the utility of biopsy. We perform decision analysis to aid clinicians in their approach to management of adult brain stem lesions.

METHODS

A structured literature search revealed 20 publications with 457 patients who had undergone brain stem lesion biopsy. These publications were reviewed to determine diagnostic rates and the incidence of complications. Standard decision analytic techniques were applied to the case of a virtual adult patient with a lesion in the brain stem.

RESULTS

A 1-way sensitivity analysis revealed the likelihood that the preoperative diagnosis was correct and the rate at which incorrect treatment was based on faulty empirical diagnosis as the 2 factors with the greatest effects on patient outcome. The diagnostic rate and complication rate of biopsy, within the ranges reported in the literature, had lesser effects. A threshold analysis was constructed to compare outcomes from stereotactic biopsy vs empiric therapy for a brain stem lesion. The probability that the preoperative diagnosis is correct is plotted vs the probability that empirical treatment based on an incorrect diagnosis will have adverse effect.

CONCLUSIONS

Management of lesions in the adult brain stem requires careful consideration of multiple preoperative factors including clinical and radiographic diagnostic certainty, consequences of empiric therapy, and the surgeon's complication rate.

Accuracy and diagnostic yield of stereotactic biopsy in the diagnosis of brain masses: Comparison of results of biopsy and resected surgical specimens

The aim of this retrospective study was to investigate the diagnostic yield and accuracy of stereotactic biopsy in patients harboring brain mass. Stereotactic biopsy was performed in 130 patients between 1995 and 2000 in an educational and research hospital in Turkey. The results of histological analysis were compared to the resected specimens in 23 patients. The lesions were lobar in 62% of cases and deep-seated in 38% of cases. During the biopsy procedures, the pathologist was in the operating theatre and a very small fragment was used for cytological examination. No frozen section was used in any of the cases. Samples were diagnostic in 122 cases. The overall diagnostic yield of the procedure was 94%. A definitive histological diagnosis was not made in eight patients. The histological diagnoses of the two procedures were identical (complete agreement) in 16 cases. In three cases, the histological diagnoses between the two procedures were slightly different without impact on patient care (minor disagreement). The diagnosis of the stereotactic biopsy was completely changed after craniotomy in four cases (major disagreement). The accuracy of the histological diagnosis was 83%. There was only one major complication, which involved intracerebral hemorrhage. Despite the limited number of patients who underwent resection, our data suggest that stereotactic biopsy of brain masses is a safe and accurate technique that can obtain adequate tissue for histological diagnosis, thus providing the best avaible treatment for patients. Cytological evaluation of the streotactic biopsy also is a highly effective tool for obtaining sufficient material during the procedure in many cases.

Pontine malignant astrocytoma with hemorrhagic onset--case report

A 7-year-old boy presented with acute onset of left hemiparesis and headache, followed by disturbance of consciousness. Neuroimaging studies showed pontine hemorrhage. Surgery was performed to remove a massive hematoma. Histological examination of the wall revealed anaplastic astrocytoma. Postoperative radiation therapy and several types of chemotherapy were administered. However, the tumor recurred and he died 9 months after onset. Hemorrhagic onset of pontine glioma is rare and carries an extremely poor prognosis.

An analysis of the respective risks of hematoma formation in 361 consecutive morphological and functional stereotactic procedures

OBJECTIVE

The risk of hematoma formation in stereotactic procedures is generally considered to range between 1 and 4%, and it has been speculated that morphological procedures may have a higher risk of bleeding than functional procedures.

METHODS

Between 1989 and 1999, all patients who underwent a stereotactic procedure performed by the same surgeon were enrolled sequentially onto the study. All patients had normal preoperative prothrombin time, partial thromboplastin time, and platelet count. High-resolution computed tomography or magnetic resonance imaging with a 1.5-T machine were used for the target definition. None of the patients had an angiogram before surgery.

RESULTS

A total of 361 procedures was performed comprising 175 morphological procedures (139 biopsies, 18 lesion evacuations [cysts, abscesses, and hematomas], and 18 drain implantations) and 186 functional procedures (137 lesions [thalamotomy or pallidotomy], 47 deep brain electrode implantations, and two physiological explorations without lesions or implantations). There were no infections or seizures in either group. Three hematomas (1.7%) occurred in the morphological group, two of them in inflammatory lesions in immunocompromised patients (one death) and one in a pineal tumor. Three hematomas (1.6%) occurred in the functional group (no mortality). There was no statistically significant difference (P > 0.05; Fisher's exact test) in the risk of hematoma formation between morphological and functional stereotactic procedures. The morbidity and mortality related to bleeding also were not statistically different (P > 0.05; Fisher's exact test) between these two groups.

CONCLUSION

In this series, the risk of bleeding was not higher for morphological procedures than for functional procedures. This suggests that the risk of bleeding for stereotactic procedures is related more to the patient than to the type of procedure performed. Our study confirms an overall risk of bleeding of 1.7% for any type of stereotactic procedure, resulting in a mortality of 0.3% and a morbidity of 1.4%.

Combined magnetic resonance imaging- and positron emission tomography-guided stereotactic biopsy in brainstem mass lesions: diagnostic yield in a series of 30 patients

OBJECT

In the management of brainstem lesions, the place of stereotactic biopsy sampling remains debatable. The authors compared the results of magnetic resonance (MR) imaging, positron emission tomography (PET) scanning, and histological studies obtained in 30 patients who underwent MR imaging- and PET-guided stereotactic biopsy procedures for a brainstem mass lesion.

METHODS

Between July 1991 and December 1998, 30 patients harboring brainstem mass lesions underwent a stereotactic procedure in which combined MR imaging and PET scanning guidance were used. Positron emission tomography scanning was performed using [18F]fluorodeoxyglucose in 16 patients, methionine in two patients, and both tracers in 12 patients. Definite diagnosis was established on histological examination of the biopsy samples. Interpretation of MR imaging findings only or PET findings only was in agreement with the histological diagnosis in 63% and 73% of cases, respectively. Magnetic resonance imaging and PET findings were concordant in 19 of the 30 cases; in those cases, imaging data correlated with histological findings in 79%. Treatment based on information derived from MR imaging was concordant with therapy based on histological findings in only 17 patients (57%). Combining MR imaging and PET scanning data, the concordance between the neuroimaging-based treatment and treatments based on histological findings increased to 19 patients (63%). In seven patients who underwent biopsy procedures with one PET-defined and one MR imaging-defined trajectory, at histological examination the PET-guided samples were more representative of the tumor's nature and grade than the MR imaging-guided samples in four cases (57%). In 18 patients PET scanning was used to define a biopsy target and provided a diagnostic yield in 100% of the cases.

CONCLUSIONS

Although the use of combined PET and MR imaging improves radiological interpretation of a mass lesion in the brainstem, it does not accurately replace histological diagnosis that is provided by a stereotactically obtained biopsy sample. Combining information provided by MR imaging and PET scanning in stereotactic conditions improves the accuracy of targeting and the diagnostic yield of the biopsy sample; an MR imaging- and PET-guided stereotactic biopsy procedure is a safe and efficient modality for the management of mass lesions of the brainstem.

Combined magnetic resonance imaging– and positron emission tomography–guided stereotactic biopsy in brainstem mass lesions: diagnostic yield in a series of 30 patients

In the management of brainstem lesions, the place of stereotactic biopsy sampling remains debatable. The authors compared the results of magnetic resonance (MR) imaging, positron emission tomography (PET), and histological findings obtained in 30 patients who underwent an MR image– and PET-guided stereotactic biopsy procedure for a brainstem mass lesion.

Between July 1991 and December 1998, 30 patients harboring a brainstem mass lesion underwent a stereotactic procedure in which combined MR imaging and PET guidance was used. Positron emission tomography scanning was performed using [18F]-fluorodeoxyglucose in 16 patients, methionine in two patients, and with both tracers in 12 patients. Definite diagnosis was established on histological examination of the biopsy samples. Interpretation of MR imaging findings only or PET findings only were in agreement with the histological diagnosis in 63% and 73% of cases, respectively. Magnetic resonance imaging and PET findings were concordant in 19 of the 30 cases; in those cases, imaging data correlated with histological findings in 79%. In seven patients who underwent one PET-defined and one MR imaging–defined trajectory, at histological examination the PET-guided samples were more representative of the tumor's nature and grade than the MR imaging–guided samples in four cases (57%). In 18 patients PET scanning was used to define a biopsy target and provided a diagnostic yield in 100% of the cases.

Although the use of combined PET and MR imaging improves radiological interpretation of a mass lesion in the brainstem, it does not accurately replace histological diagnosis that is provided by a stereotactically obtained biopsy sample. Combined information provided by MR imaging and PET in stereotactic conditions improves the accuracy of targeting and the diagnostic yield of the stereotactically biopsy sample; an MR imaging– and PET-guided stereotactic biopsy procedure is a safe and efficient modality for the management of mass lesions of the brainstem.

A brainstem stereotactic atlas in a three-dimensional magnetic resonance imaging navigation system: first experiences with atlas-to-patient registration

OBJECT

The authors describe a computer-resident digital representation of a stereotactic atlas of the human brainstem, its semiautomated registration to sagittal fast low-angle shot three-dimensional (3-D) magnetic resonance (MR) imaging data sets in 27 healthy volunteers and 24 neurosurgical patients, and an analysis of the subsequent transforms needed to refine the initial registration.

METHODS

Contour drawings from the atlas, which offer the 70th percentile of variation of anatomical structures, were interpolated into an isotropic 3-D representation. Initial atlas-to-patient registration was based on the fastigium/ventricular floor plane reference system. The quality of the fit was evaluated using superimposition of the atlas and MR images. If necessary, the atlas was tailored to the individual anatomy by using additional transforms. On average, the atlas had to be stretched by 2 to 6% in the three directions of space. Scale factors varied over a broad range from -8 to +19% and the benefit of visual interactive control of the atlas-to-patient registration was evident. Analysis of distances within the pons measured in the midsagittal MR imaging slices and the required scale factors revealed significant correlations that may be used to reduce the amount of user interaction in the coregistration substantially. In 70.6% of the cases, the atlas had to be shifted in a cranial direction along the brainstem axis (in 25.5% of cases 3-4 mm, in 45.1% of cases 1-2 mm). This was due to a more caudal position of the fastigium cerebelli on the MR images compared with the atlas.

CONCLUSIONS

This observation, in conjunction with the variability of the height of the fourth ventricle in our MR imaging data (range 6.1-15.2 mm, mean 10.1 mm, standard deviation 1.8 mm) calls into question the role of the fastigium cerebelli as an anatomical landmark for localization within the brainstem.

MR-guided procedures using contemporaneous imaging frameless stereotaxis in an open-configuration system

Frameless MR-guided procedures have had limited application using conventional closed magnets, due largely to the technical difficulties involved. As a result of in-room MR image-monitoring capabilities, new open-design magnets now allow frameless stereotaxis using contemporaneous imaging to guide more invasive procedures. We evaluate our clinical experience with this new technique. An open-design 0.2 T magnet (Siemens OPEN) combined with an in-room monitor was used for 33 frameless MR-guided procedures (aspiration cytology, biopsy, and/or treatment) in a variety of locations in the head, neck, spine, brain, pelvis, and abdomen. Success of the procedure was based on the ability to accurately position the instrument in the target region to allow biopsy and/or treatment. The open-design magnet allowed the physician to directly access the patient for frameless stereotaxis as the procedure was performed. The in-room monitor provided contemporaneous imaging feedback during the procedure for successful placement of the instrument in the target region. Twenty-eight biopsy and five treatment procedures were performed. In all cases the technique resulted in successful placement of the instrument within the target tissue to complete the procedure. MR-guided procedures using contemporaneous imaging frameless stereotaxis are possible in an open-design magnet with in-room image monitoring and offer exciting possibilities for further development.

Computerized tomography-guided stereotactic surgery for brainstem masses: a risk-benefit analysis in 71 patients

The benefits of the use of computerized tomography (CT)-guided stereotactic surgical techniques for the management of intrinsic brainstem masses diagnosed from clinical evaluation and imaging studies were evaluated vis-à-vis the risks involved in 71 consecutive patients. Seventy-two procedures were performed. The masses were diffuse, involving two or three contiguous brainstem segments, in 60 patients and focal in 11 patients. On the CT scans, 25 patients had hypodense nonenhancing masses, two had isodense nonenhancing masses, 19 had ring-enhancing masses, and 25 had heterogeneously enhancing masses. A positive biopsy was obtained in 68 of 69 patients (98.5%) undergoing a biopsy procedure. In nine patients (12.6%) with suspected malignant masses a benign pathology was diagnosed (four tuberculomas, two epidermoid cysts, one pyogenic abscess, one epidermal cyst, and one case of encephalitis). Additionally, fluid from cystic masses could be aspirated in eight cases, providing benefit in six (four patients had benign lesions and two had neoplastic lesions). Thereby, a total of 13 patients (18.3%) were deemed to have benefited from the surgery (two patients were included in both categories). Patients with focal masses and ring-enhancing masses had the highest proportion of benign lesions (60% and 36.8%, respectively) and therefore derived the most benefit from histological verification. There was no procedure-related mortality. One patient (1.4%) suffered permanent morbidity and four others (5.6%) had transient worsening attributable to the procedure. The authors conclude that CT-guided stereotactic surgery of the brainstem is safe and reliable. Histological verification of all enhancing (especially ring-enhancing) and focal brainstem masses should be undertaken to identify patients with benign nonneoplastic lesions. Selected patients with diffuse hypodense nonenhancing masses with atypical clinical or imaging features may also benefit from stereotactic biopsy. Even in these patients the lack of enhancement on a contrast-enhanced magnetic resonance image, rather than the diffuse location of the tumor alone, should form the basis for diagnosing a malignant glioma. The main value of stereotactic surgery lies in the identification of benign masses in a significant proportion of patients with intrinsic brainstem masses and in providing a rapid and safe method for evacuation of the contents of cystic masses.

Frameless stereotaxy and interactive neurosurgery with the ISG viewing wand

Preliminary experience with the ISG wand for frameless stereotaxy is presented. The wand is a multijointed mechanical arm with a range of 25 inch radius sphere. The arm has a analog/digital hybrid transducers to locate the spatial position of the probe tip. The real time displays of triplanar 2D images with an optional 2D/3D image helps in surgical planning and interactive surgery. Seventeen patients underwent neurosurgical procedures with the help of wand. The wand was used to place minimal craniotomies, localise the brain-tumour interface and excise the lesions. The wand had an accuracy of 1.8 mm (SEM +/- 0.36 mm) in localising the lesions. Thus, the use of frameless stereotaxy has made easier and more precise surgical planning in several applications.