Posterior fossa stereotaxic biopsy using the Brown-Roberts-Wells stereotaxic system. Technical note

Posterior Fossa Approaches Using the Leksell Vantage Frame with a Virtual Planning Approach in a Series of 10 Patients-Feasibility, Accuracy, and Pitfalls

The open-face design of the Leksell Vantage frame provides many advantages. However, its more rigid, contoured design offers less flexibility than other frames. This is especially true for posterior fossa approaches. This study explores whether these limitations can be overcome by tailored frame placement using a virtual planning approach. The posterior fossa was accessed in ten patients using the Leksell Vantage frame. Frame placement was planned with the Brainlab Elements software, including a phantom-based (virtual) pre-operative planning approach. A biopsy was performed in all patients; in four, additional laser ablation surgery was performed. The accuracy of virtual frame placement was compared to actual frame placement. The posterior approach was feasible in all patients. In one case, the trajectory had to be adjusted; in another, the trajectory was switched from a right- to a left-sided approach. Both cases showed large deviations from the initially planned frame placement. A histopathological diagnosis was achieved in all patients. The new Leksell Vantage frame can be used to safely target the posterior fossa with a high diagnostic success rate and accuracy. Frame placement needs to be well-planned and executed. This can be facilitated using specific software solutions as demonstrated.

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.

Stereotactic brain biopsy: evaluation of robot-assisted procedure in 60 patients

BACKGROUND

Frameless stereotactic biopsies, particularly robot-assisted procedures are increasing in neurosurgery centers. Results of these procedures should be at least equal to or greater than frame-based reference procedure. Evaluate robot-assisted technology is necessary in particular, when a team has chosen to switch from one to another method.

OBJECTIVE

The objective of our prospective work was (i) to evaluate the success rate of contributive robotic-assisted biopsy in 60 patients, to report the morbidity and mortality associated with the procedure and (ii) to compare it with literature data.

METHODS

We performed a prospective and descriptive study including 60 consecutive patients having had robotic-assisted stereotactic biopsy at the Rouen University Hospital, France. All patients had presurgical imaging before the procedure included Magnetic Resonance Imaging merged with Computed Tomography scan acquisition. Registration was mostly performed with a touch-free laser (57/60). A control Computed Tomography scan was always realized at day 0 or day 1 after surgery. Data collected were success rate, bleeding, clinical worsening, infection, and mortality.

RESULTS

All the biopsies were considered as contributive and lead to the final diagnosis. In 41/60 patients (68%), the lesion was glial. Six in 60 patients (10%) had visible bleeding without clinical worsening related, 5/60 patients (8.5%) showed clinical impairment following surgery, which was permanent in 2 patients, and 1/60 patient presented generalized seizures. We did not report any infection and mortality.

CONCLUSION

Robot-assisted frameless surgery is efficient and provides a reasonable alternative to frame-based procedure. The operating time can be reduced, without increasing morbidity and mortality rates.

How is stereotactic brain biopsy evolving? A multicentric analysis of a series of 421 cases treated in Rome over the last sixteen years

OBJECTIVE

In recent decades, frame-based (FBB) and frame-less stereotactic brain biopsy (FLB) have played a crucial role in defining the diagnosis and management of expanding intracranial lesions in critical areas. During the same period, there have been significant advances in diagnostic imaging, a shift in surgical strategies towards extensive resection in gliomas and new molecular classification of brain tumors. Taking these advances into account, we have evaluated whether significant changes have occurred over the last sixteen years of our clinical practice in terms of frequency, indications, target selection, and the histologic results of stereotactic brain biopsy (SBB) procedures.

PATIENTS AND METHODS

We analyzed a series of 421 SBB cases treated between January 2002 and June 2017 in three major neurosurgical institutes in Rome, serving a total of 1.5 million people. Within this series, 94.8% of patients underwent FBB, while, more recently, FLB was performed in 5.2% of cases. The entire period under consideration, running from 2002 to 2017, has been further stratified into four-year time-frames (2002-2005, 2006-2009, 2010-2013, 2014-2017) for the purpose of analysis.

RESULTS

The diagnostic yield was 97%. Final diagnoses revealed tumors in 90% of cases and non-neoplastic masses in 7%, while 3% of cases were not conclusive. The morbidity rate was 3% (12 cases) and mortality was 0.7% (3 cases). Intra-operative frozen sections were made in 78% of biopsies. In our three institutes, the number of SBBs decreased steadily throughout the time-frames under consideration. We have also observed a statistically significant reduction in biopsy procedures in lobar lesions, while those performed on the basal ganglia increased and the number of SBBs of multiple masses and lesions of the corpus callosum remained stable. Primary central nervous system diagnosis of lymphomas (PCNSL) was the sole diagnosis whose incidence increased significantly.

CONCLUSIONS

Over the last sixteen years, we have witnessed a significant decrease in SBB procedures and a modification in target selection and histologic results. Despite the significant evolution of neuroimaging, an accurate non-invasive diagnosis of intracranial expanding lesions has not yet been achieved. Furthermore, the most recent WHO classification of brain tumors (2016), which incorporates molecular and morphological features, has boosted the need for molecular processing of tissue samples in all expanding brain lesions. For these reasons, it is likely that SBBs will continue to be performed in specific cases, playing a significant role in diagnostic confirmation by providing tissue samples, so as to better assess the biology and the prognosis of cerebral lesions, as well as their sensitivity to standard radio-chemotherapy or to new molecular target therapies.

The stereotactic suboccipitaltranscerebellar approach to lesions of the brainstem and the cerebellum

OBJECTIVE

The stereotactic suboccipital-transcerebellar approach is widely regarded as technically demanding requiring substantial modifications of the standard stereotactic methods thus often making a transfrontal approach preferable. In this comprehensive series we aim to present our experience with the stereotactic suboccipital-transcerebellar approach to lesions of the brainstem or cerebellum using two standard stereotactic systems.

PATIENTS AND METHODS

In the period of 2000-2015 overall 80 patients (mean age 43.95 ± 23.76 years) with lesions of the brainstem or cerebellum underwent stereotactic surgery for diagnostic or therapeutic purposes via a suboccipital approach. In 59 patients stereotactic surgery was performed using the Riechert-Mundinger Stereotactic Frame, the Leksell Stereotactic Frame was used in 21 patients. For both frames standard systems were used without modification. Retrospective analysis of intraoperative stereotactic technique, achievement of the predefined surgical objectives and perioperative complications was carried out.

RESULTS

In this series, the stereotactic suboccipital-transcerebellar approach proved to be feasible with two standard stereotactic systems. Using either frame the predefined surgical objective was achieved in 90.0%. A verified neuropathological diagnosis was obtained in 89.6%. Minor transient perioperative complications occurred in 8.75%. There was no surgery-related permanent morbidity or mortality.

CONCLUSION

In this comprehensive series the stereotactic suboccipital-transcerebellar approach using a standard stereotactic system proved to be a favorable stereotactic approach with a high diagnostic success rate and no surgery-related permanent morbidity.

Validation of a magnetic resonance imaging guided stereotactic access to the ovine brainstem

Background

Anatomical differences between humans and domestic mammals preclude the use of reported stereotactic approaches to the brainstem in animals. In animals, brainstem biopsies are required both for histopathological diagnosis of neurological disorders and for research purposes. Sheep are used as a translational model for various types of brain disease and therefore a species-specific approach needs to be developed. The aim of the present study was to establish a minimally invasive, accurate and reproducible stereotactic approach to the brainstem of sheep, using the magnetic resonance imaging guided Brainsight^TM frameless stereotactic system.

Results

A transoccipital transcerebellar approach with an entry point in the occipital bone above the vermis between the transverse sinus and the external occipital protuberance was chosen. This approach provided access to the target site in all heads. The overall mean needle placement error was 1.85 ± 1.22 mm.

Conclusions

The developed transoccipital transcerebellar route is short, provides accurate access to the ovine caudal cranial fossa and is a promising approach to be further assessed in live animals.

Feasibility, safety, and indications for surgical biopsy of intrinsic brainstem tumors in children

PURPOSE

Diffuse intrinsic pontine gliomas (DIPGs) are rapidly progressive and aggressive tumors that usually arise in children. Their anatomic location makes gross total surgical resection impossible, and fewer than 10% of patients survive more than 2 years after diagnosis. Often, these lesions are treated based on imaging characteristics alone. However, despite aggressive chemotherapy and radiation treatments available, prognosis remains poor. There is therefore a need for new therapies directed by biologic profiling. This necessitates a tissue diagnosis and, therefore, surgical biopsy. We have reviewed the results of biopsy for DIPGs in children at a single institution and compared our results to those available in the literature to elucidate the utility of biopsy for DIPGs.

METHODS

A historical cohort study was performed using medical records of patients under the age of 18 who underwent surgical biopsy of a DIPG at a single institution.

RESULTS

Nine patients were included, four males and five females. Age at presentation ranged from 8 months to 10 years (average 5.7 years). Pathologic diagnoses included five high grade (WHO grade III or IV) gliomas and four low grade (WHO grade II) astrocytomas. There were no intraoperative complications, and only one patient developed a new postoperative neurologic deficit.

CONCLUSIONS

Stereotactic biopsy of DIPGs is essential to obtain a pathologic diagnosis and is associated with low morbidity. This technique is important to elucidate biological characteristics of these tumors in order to direct multidisciplinary treatment plans possibly involving chemotherapy, radiation therapy, or other future clinical trial interventions for children with DIPGs.

Pitfalls in precision stereotactic surgery

Precision is the ultimate aim of stereotactic technique. Demands on stereotactic precision reach a pinnacle in stereotactic functional neurosurgery. Pitfalls are best avoided by possessing in-depth knowledge of the techniques employed and the equipment used. The engineering principles of arc-centered stereotactic frames maximize surgical precision at the target, irrespective of the surgical trajectory, and provide the greatest degree of surgical precision in current clinical practice. Stereotactic magnetic resonance imaging (MRI) provides a method of visualizing intracranial structures and fiducial markers on the same image without introducing significant errors during an image fusion process. Although image distortion may potentially limit the utility of stereotactic MRI, near-complete distortion correction can be reliably achieved with modern machines. Precision is dependent on minimizing errors at every step of the stereotactic procedure. These steps are considered in turn and include frame application, image acquisition, image manipulation, surgical planning of target and trajectory, patient positioning and the surgical procedure itself. Audit is essential to monitor and improve performance in clinical practice. The level of stereotactic precision is best analyzed by routine postoperative stereotactic MRI. This allows the stereotactic and anatomical location of the intervention to be compared with the anatomy and coordinates of the intended target, avoiding significant image fusion errors.

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.

Stereotactic computed tomography–guided brain biopsy: diagnostic yield based on a series of 170 patients

BACKGROUND

Stereotactic CT-guided biopsy is a valuable and safe procedure for diagnosing intracranial lesions. The objectives of this article are to analyze the diagnostic yield in a series of stereotactic CT-guided brain biopsies and to evaluate whether predictive factors may influence diagnostic yield.

METHODS

The medical records of a series of patients who underwent stereotactic CT-guided brain biopsy from 1993 to 2005 in a neurosurgical center were reviewed. Clinical data were stored and analyzed with Microsoft Access (Microsoft Corp, Seattle, WA) and SPSS V11.0 software (SPSS, Inc, Chicago, IL). The following variables were analyzed: age, sex, anatomopathologic diagnosis, lesion topography and volume, postsurgical complications, and predictive factors that may affect diagnostic yield.

RESULTS

One hundred seventy patients (102 males, 68 females; average age, 48.5 years) were analyzed. Stereotactic CT-guided biopsies allowed diagnosis in 157 cases (92%). The most frequent anatomopathologic diagnoses were high-grade glioma (n = 45), low-grade glioma (n = 31), nonspecific inflammatory lesions (n = 19), metastasis (n = 10), and lymphoma (n = 10). The most frequent topographies were frontal (n = 42), basal ganglia (n = 40), and parietal (n = 27) and front-parietal lobes (n = 9). Complications occurred in 5 patients (2.9%). Mortality rate was 1.2% (2 patients). Age had a positive impact, whereas female sex negatively affected diagnostic yield. All other predictive factors analyzed were not significant.

CONCLUSION

Stereotactic CT-guided brain biopsies performed presented acceptable anatomopathologic diagnostic rate. Age had a positive impact, whereas female sex negatively affected diagnostic yield in this series.

A contralateral, transfrontal, extraventricular approach to stereotactic brainstem biopsy procedures. Technical note

The authors report on the technique and results of stereotactic biopsy for intrinsic lateral pontine and medial cerebellar lesions via a contralateral, transfrontal, extraventricular approach. Multiplanar stereotactic magnetic resonance imaging was used to plan an intraparenchymal approach, thus limiting the number of crossed pial surfaces to one and eliminating the need to cross ependymal surfaces. After the administration of a local anesthetic agent with light intravenous sedation, six patients harboring intrinsic lateral pontine lesions underwent biopsies via this intraparenchymal approach with 100% diagnostic yield and no operative morbidity. In comparison to the ipsilateral transfrontal approach, the contralateral approach laterally expands the infratentorial area accessible during biopsy to include the lateral pons and middle cerebellar peduncle. The contralateral, transfrontal, extraventricular approach is a useful, straightforward and safe alternative to the suboccipital transcerebellar and ipsilateral, transfrontal, transtentorial routes for reaching lesions of the lateral pons and middle cerebellar peduncle.

Stereotactic biopsies of focal brainstem lesions

BACKGROUND

Stereotactic biopsies of the brainstem (SBB) are a selected group of stereotactic operations owing to the lower incidence of brainstem lesions requiring biopsy, the greater complexity, and the higher risks of these procedures. Usually, the lower the lesion in the brainstem, the greater the risks involved. The approach of the different target locations by distinct routes, transcerebral and transcerebellar, is still a matter of debate. Moreover, pure medullary lesions are seldom biopsied, whereas diffuse brainstem lesions, typical of children's brainstem gliomas and rather frequent in most published series, depend less and less on the histopathological confirmation for treatment. In this study, the authors present their own experience on SBB aiming to discuss mainly their indications, approach routes choice, and procedure techniques.

METHODS

The authors reviewed a series of 30 SBB (27 adults and 3 children) out of 450 stereotactic biopsies of the central nervous system performed for the last 10 years. All cases but one presented as focal brainstem masses, 19 mainly in the pons and 10 in the midbrain. Eleven lesions (10 in the midbrain and one midbrain-pontine) were approached by a transfrontal route. All the others were approached by a suboccipital transcerebellar route.

RESULTS

Twenty-six (87%) out of the 28 cases (93%) where a positive histopathological result was obtained had a specific diagnosis: 18 tumors (14 astrocytomas, 2 primary brain lymphomas, 1 oligodendroglioma, and 1 ganglioglioma), 2 toxoplasmosis, 2 sarcoidosis, 1 aspergillus abscess, 1 vasculitis, 1 acute inflammatory demyelinating disease, and 1 progressive multifocal leucoencephalopathy. Four nontumoral lesions arose in patients with AIDS. Morbidity was restricted to 2 cases consisting of transient cranial nerve deficits.

CONCLUSIONS

Stereotactic biopsies are specially useful for the diagnosis of focal brainstem lesions. Midbrain and midline lesions should be approached through the cerebrum, whereas most of the pontine lesions through the cerebellum. Overall, this procedure should be performed with "functional-like" precision and require some technical refinements to reach maximal accuracy with minimal morbidity.

Results and expectations with image-integrated brainstem stereotactic biopsy

BACKGROUND

The histologic diagnosis of an intrinsic brainstem tumor remains problematic due to controversies in methods of biopsy. Despite the widespread use of biopsy techniques, stereotactic brain stem biopsy has received limited attention due to potential morbidity and limited sample size.

METHODS

To evaluate the safety and efficacy of brain stem stereotactic biopsy using a dedicated computed tomography (CT)-stereotactic operating room suite, we reviewed our outcomes in 40 consecutive patients over a 13-year interval. This study included patients with midbrain lesions (n = 20), pontine lesions (n = 18), and medullary lesions (n = 2). Midline lesions were approached via a coronal, transthalamic trajectory; lateral brain stem lesions usually were approached via a transcerebellar route.

RESULTS

A histologic diagnosis was achieved in 38 patients (95%). All patients had an immediate, intraoperative, postbiopsy CT scan to check for hemorrhage (none occurred). Morbidity was limited to one patient (2.5%) who developed a transient diplopia; there was no mortality.

CONCLUSIONS

Stereotactic biopsy for intrinsic brain stem lesions proved as safe and effective as biopsy in the supratentorial compartment. Using high-resolution stereotactic imaging, an appropriate intraparenchymal trajectory, limited sampling, and specific neuropathologic tests, stereotactic techniques within the brain stem were performed with low risk and high accuracy. Biopsy results facilitated specific management strategies for each patient.

Stereotactic biopsy for intrinsic lesions of the medulla through the long-axis of the brainstem: technical considerations

The authors report the technique and results for stereotactic biopsy of intrinsic lesions of the medulla oblongata through the long-axis of the brainstem. Multi-planar stereotactic magnetic resonance imaging and/or reformatted computed tomography imaging is used for coordinate determination and trajectory selection and facilitates a completely intra-axial pathway through critical neural tissue. Two patients with small, solitary, enhancing lesions of the medulla had stereotactic sampling via this approach performed under local anesthesia. There was no morbidity and in both the patients a histologic diagnosis of lymphoma was obtained. We believe that with high-resolution, multi-planar stereotactic imaging, small lesions in the medulla can safely be biopsied, avoiding the need for either posterior fossa craniectomy and open biopsy, or for empiric management.

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

The appreciation that brainstem tumours do not comprise a homogeneous pathological group and that up to 20% of the preoperative radiological diagnoses of brainstem lesions prove at operation to be wrong, has established the need for a firm histological diagnosis prior to treatment. Current neuro-imaging modalities may have increased the diagnostic accuracy and the detection rate of intrinsic brainstem lesions, but open exploration in cases without an exophytic component is still associated with a low diagnostic yield and considerable morbidity. A series of 72 brainstem lesions approached stereotactically with CT or MRI guidance is presented. A transcortical frontal precoronal trajectory was used in 58 and a suboccipital transcerebellar route in 14. Haematoma was diagnosed preoperatively in 16 cases and therapeutic aspiration was planned. In 56 cases the diagnosis was uncertain, although intrinsic tumour was suspected. A histological diagnosis was established in 52 cases, although in the remaining four cases a tumour was excluded. Unexpected findings occurred in over 15% of the cases. There were no operative deaths and the morbidity was low. In no case was there a permanent neurological deterioration directly related to the procedure, although there was a transient deterioration in two patients and another patient required early re-aspiration of a haematoma.

Image directed stereotactic surgery for brain stem lesions

Advances in neurological imaging may have increased the diagnostic accuracy and the detection rate of intrinsic brain stem lesions, but a histological diagnosis is still an essential requirement for rational and appropriate management. Open exploration allows biopsy and resection in cases where an exophytic component is present. The surgical inaccessibility and the resultant morbidity of these approaches, however, associated with a low diagnostic yield in cases with no visible surface abnormality, are important limiting factors. A series of 45 brain stem lesions stereotactically approached with CT or MRI guidance is presented. A transcortical frontal pre-coronal trajectory was used in all of them. Haematoma was preoperatively diagnosed in 10 cases and the procedure was for therapeutic aspiration. Of 35 cases where the diagnosis was uncertain, although intrinsic tumour was suspected, positive results were obtained in 33, while unexpected findings of granuloma, lymphoma, angioma, leucoencephalopathy, vasculitis and radiation necrosis were found in over 10% of the cases. There were no operative deaths and the morbidity was low. In no case was there a permanent neurological deterioration directly related to the procedure, although there was a transient deterioration in two patients and one patient required early reaspiration of a haematoma. Image directed stereotactic approaches to brain stem lesions can combine a high degree of accuracy (offering positive histological diagnoses) with a low operative morbidity. MRI directed biopsies can complement CT guided ones thus increasing the number of suitable cases and improving the success rate. The frontal precoronal transcortical trajectory provides safe access to the majority of the brain stem targets.

Is peroperative smear cytology necessary for CT-guided stereotaxic biopsy?

Neuropathology is a relatively scarce resource with uneven geographical distribution, and some surgeons rely on macroscopic appearances of tissue and await later paraffin section histology for the final diagnosis. The effect of the introduction of a peroperative cytology service has been assessed in a 5-year series of CT-directed stereotaxic biopsies of intracranial mass lesions using a low cost adapted pre-CT stereotaxic frame. The technique has been mastered by 28 different surgeons with varying degrees of neurosurgical expertise and 259 procedures have been performed in 245 patients. Benign lesions were detected in 24 (9.8%) patients, confirming the importance of making a histological diagnosis prior to initiating treatment. Permanent morbidity was 6.5% and mortality 3.3% and morbidity was balanced by an improvement in 19.6% of the patients following the procedure. For the first 142 patients no peroperative histological diagnosis was available and a diagnostic rate of 86.6% was achieved. For the last 103 patients the availability of peroperative smears improved the diagnostic rate to 94.2% and reduced the number of second biopsies needed for diagnosis from seven to zero. Our series demonstrates the need for peroperative cytology in CT stereotaxic biopsies, and confirms that a complete neuropathology service is a prerequisite for neurosurgical patient care.

Stereotactic suboccipital transcerebellar biopsy under local anesthesia using the Cosman-Roberts-Wells frame. Technical note

Previously reported suboccipital transcerebellar stereotactic biopsy methods, performed with the patient in the prone position, have required general endotracheal anesthesia. A technique is described for performing such biopsies with the patient in the lateral decubitus position, under local anesthesia. Phantom planning and routine computerized tomography graphics allow the selection of a safe entry point and intra-axial trajectory to the lesion. The time required for data acquisition and the operative procedure itself compares well with that of more routine biopsy techniques.

Stereotactic anatomy of the posterior cranial fossa. A study of the transcerebellar approach to the brainstem

The stereotactic transcerebellar (suboccipital) approach to the brainstem is one of the most accessible routes to reach targets located in the pons or in the medulla oblongata. Its use requires a perfect knowledge of the stereotactic anatomy of the posterior cranial fossa, and a standard reference system related to structures of the brainstem itself which can easily be visualized by Nuclear Magnetic Resonance. The present work consists in a three-dimensional variability study of the human posterior cranial fossa with its main contents, based on the investigation of 30 normal specimens (hemifossae). A new stereotactic reference system is proposed for the pons and the medulla, comprising three orthogonal** planes: the midsagittal plane, the IVth ventricular floor plane and the pontomedullary junction plane. A standard "safety access tunnel" was defined for the transcerebellar approach to the pons and, with some limitations, to the medulla. A complementary investigation, based upon angiographic studies, was carried out to define a safe "entry zone" to the posterior cranial fossa of the occipital bone beneath the transverse venous sinus.

The stereotactic approach to brain stem lesions: a follow-up of 29 cases

Stereotactic biopsy is the safest and most reliable method for the histological diagnosis of intraaxial brain stem lesions. The definitive pathological diagnosis permits the selection of adequate therapy. No operative and/or adjuvant therapy must be proposed without a previous histological diagnosis. This approach avoids the complication of inappropriate therapy and provides valuable prognostic information.

Stereotactic craniotomy and intraoperative lesion localisation using the Brown-Robert-Wells frame. Technical note

A simple technique of stereotactic craniotomy and intraoperative lesion localisation that uses the Brown-Robert-Wells (BRW) stereotactic frame is presented. The method optimises craniotomy placement and facilitates localisation of small intracerebral lesions. Using the system, 16 patients have had resection of intracranial neoplasms from deep and/or eloquent areas of the brain with no neurological morbidity.