Clinical introduction of an adjustable rigid instrument holder for frameless stereotactic interventions

Interactive image guidance is now in routine use for open neurosurgical procedures and has demonstrated patient benefits. However, freehand interactive guidance is not an appropriate replacement for the traditional frame-based stereotactic procedures of biopsy, electrode placement, and functional lesioning. These point-based procedures require precise target localization and direct instrument guidance to avoid collateral brain injury. To perform true frameless stereotactic procedures requires a guide that is also adjustable for positioning, lockable, and adaptable to multiple instruments. We describe such a device, which is employed for the guidance of biopsy needles, shunts, electrodes, and endoscopes during neuronavigation. The method of frameless stereotactic biopsy retrieval with an infrared-based neuronavigation system is described, clinical results are given, and further areas of application discussed.

Consent to surgery in a high risk specialty: a prospective audit

A prospective audit was performed to assess how well patients were being consented for neurosurgery. Sixty patients with various neurosurgical conditions were included in the study. Audit was performed firstly by means of a questionnaire to examine the type of information given to patients, and their understanding of such information. Secondly, the patient's medical notes were reviewed to analyse any written evidence by the consenting doctor for the consenting procedure. 100% of the patients felt that they had been informed satisfactorily about the nature of their condition and the nature of the operation. 92% understood the specific risks of their proposed operation. However, only 25% were informed about the general risks of surgery and anaesthesia. Only 33% felt that they were informed fully about alternative treatment options. 97% of the patients felt that they had reached an informed decision regarding surgery. 67% of the case notes contained information on the nature and specific risks of the operation, while information on general risks of surgery and anaesthesia was documented in only 17% of the case notes. 33% of the case notes contained no information for the consenting procedure. Our audit showed that the patients had a good understanding of the nature and aim of the operation and the specific risks. Areas that require improvement are explaining the general risks of surgery and alternative treatment. For the consenting doctor, there should be more documentation in the notes, and there should be mention of the doctor's satisfaction that the patient was deemed to be competent and had made an informed decision.

Generalised cerebral atrophy following temporal lobectomy for intractable epilepsy associated with mesial temporal sclerosis

Studies of post-operative imaging data have mainly concentrated on brain atrophy following radiotherapy and/or chemotherapy. We have investigated the effect of conventional surgery on the unresected brain tissue based on the comparison of magnetic resonance images acquired pre- and post-operatively in 13 subjects with a history of mesio-temporal epilepsy. The pre- and post-operative scans were co-registered prior to volumetric analysis. The total brain volume (TBV) was calculated by semi-automated segmentation, and the total volume loss was the difference between the post-operative and pre-operative TBV. The total volume of resection was determined by manual delineation in the post-operative scan. The atrophy volume in the post-operative scan was calculated as the difference between the total volume loss and the resection volume. In 6 cases, there was generalised cerebral atrophy of the order 4-5% of the total brain volume. In addition to the automated volumetric technique, the images were assessed by two expert neuroradiologists. There was complete correspondence between their assessment and the automated technique. The causes and significance of this phenomenon are unknown but it requires further investigation as it may be related to seizure control and neuropsychological changes following epilepsy surgery.

Results of posterior cervical foraminotomy for treatment of cervical spondylitic radiculopathy

We evaluated the results of posterior cervical foraminotomy for spondylitic radiculopathy using a questionnaire sent to all 77 patients who had undergone surgery between 1990 and 1995 at our institution. Sixty-two patients (40 male) returned their questionnaires, one of whom had undergone two procedures (dealt with as separate events). Sixty patients complained of pre-operative arm pain; of these 42 (70%) had complete or > 75% resolution of their pain, 14 (23%) had < 75% improvement in their pain and four (7%) had the same or worsened pain at the time of the questionnaire. Sixteen patients (27%) reported initial improvement in symptoms with subsequent deterioration. The mean patient satisfaction score using a linear analogue scale from 0 to 10 was 7.5. Main postoperative complaints were neck pain (22%), persisting motor deficit (6%) and persisting sensory deficit (9%). One patient suffered nerve root damage at surgery. For unilateral and, in some cases, multi-level degenerative disease causing cervical radiculopathy, posterior cervical foraminotomy is a useful technique with the advantage of avoiding fusion, immobilization and the long-term risk of instability.

Artefact on MRA following aneurysm clipping: an in vitro study and prospective comparison with conventional angiography

Using both an experimental model and clinical cases, we looked at the artefact produced by Aesculap titanium-alloy aneurysm clips on MRA. Experimentally, the volume affected by artefact was 50 % less when the clip was imaged lying parallel to the main ferromagnetic field than when lying perpendicular to it. Clinically, MRA was prospectively compared with digital subtraction angiography (DSA) in nine patients who had undergone aneurysm clipping. One patient with a non-diagnostic MRA due to movement artefact was excluded. In all other cases there was an area of signal loss surrounding the clips, obscuring the immediately adjacent vessel segments. There was good demonstration of the adjacent bifurcations in five cases and the contralateral circulation was seen well in all patients. In three cases in which the adjacent bifurcations were not seen, considerable vasospasm was suggested by MRA and confirmed with DSA. In one patient an unclipped contralateral ophthalmic artery aneurysm was identified using both modalities. In this series there were no adverse events relating to clips in either static or time-varying magnetic fields.

Analysis of temporal lobe resections in MR images

PURPOSE

The nature of the resection in surgery for intractable medial temporal lobe epilepsy is likely to be a principal factor determining seizure and neuropsychological outcome. However, there is no universally accepted system for describing the characteristics of individual resections to allow comparison between patients and patient groups treated at different institutions. We therefore developed a technique of volumetric analysis of temporal lobe resections.

METHODS

With comparison of coregistered pre- and postoperative, volumetric magnetic resonance imaging (MRI) scans in 10 subjects, the volumes of six temporal lobe substructures were determined by manual delineation in the pre- and post-operative images for each case, allowing the extent of resection to be determined.

RESULTS

The substructures and their extent of resection were measured with acceptable repeatability in each case.

CONCLUSIONS

We developed a reliable method for the quantitative description of temporal lobe resections. This will be of application in determining the relation between the anatomic nature of the resection in intractable epilepsy and the seizure and neuropsychological outcome.

Accuracy of true frameless stereotaxy: in vivo measurement and laboratory phantom studies. Technical note

The authors present the results of accuracy measurements, obtained in both laboratory phantom studies and an in vivo assessment, for a technique of frameless stereotaxy. An instrument holder was developed to facilitate stereotactic guidance and enable introduction of frameless methods to traditional frame-based procedures. The accuracy of frameless stereotaxy was assessed for images acquired using 0.5-tesla or 1.5-tesla magnetic resonance (MR) imaging or 2-mm axial, 3-mm axial, or 3-mm helical computerized tomography (CT) scanning. A clinical series is reported in which biopsy samples were obtained using a frameless stereotactic procedure, and the accuracy of these procedures was assessed using postoperative MR images and image fusion. The overall mean error of phantom frameless stereotaxy was found to be 1.3 mm (standard deviation [SD] 0.6 mm). The mean error for CT-directed frameless stereotaxy was 1.1 mm (SD 0.5 mm) and that for MR image-directed procedures was 1.4 mm (SD 0.7 mm). The CT-guided frameless stereotaxy was significantly more accurate than MR image-directed stereotaxy (p = 0.0001). In addition, 2-mm axial CT-guided stereotaxy was significantly more accurate than 3-mm axial CT-guided stereotaxy (p = 0.025). In the clinical series of 21 frameless stereotactically obtained biopsies, all specimens yielded the appropriate diagnosis and no complications ensued. Early postoperative MR images were obtained in 16 of these cases and displacement of the biopsy site from the intraoperative target was determined by fusion of pre- and postoperative image data sets. The mean in vivo linear error of frameless stereotactic biopsy sampling was 2.3 mm (SD 1.9 mm). The mean in vivo Euclidean error was 4.8 mm (SD 2 mm). The implications of these accuracy measurements and of error in stereotaxy are discussed.

Measurement of changes in opioid receptor binding in vivo during trigeminal neuralgic pain using [11C] diprenorphine and positron emission tomography

The binding of [11C]diprenorphine to mu, kappa, and delta subsites in cortical and subcortical structures was measured by positron emission tomography in vivo in six patients before and after surgical relief of trigeminal neuralgia pain. The volume of distribution of [11C]diprenorphine binding was significantly increased after thermocoagulation of the relevant trigeminal division in the following areas: prefrontal, insular, perigenual, mid-cingulate and inferior parietal cortices, basal ganglia, and thalamus bilaterally. In addition to the pain relief associated with the surgical procedure, there also was an improvement in anxiety and depression scores. In the context of other studies, these changes in binding most likely resulted from the change in the pain state. The results suggest an increased occupancy by endogenous opioid peptides during trigeminal pain but cannot exclude coexistent down-regulation of binding sites.

Disproportion in the distribution of gray and white matter: neuropsychological correlates

OBJECTIVE

To examine the relationship between measures of disproportion in the regional distribution of gray and white matter and preoperative neuropsychological function in temporal lobe epilepsy patients with proved hippocampal sclerosis (HS).

BACKGROUND

Subtle cerebral structural disruption, not evident on routine inspection of high-resolution MRI, is associated with poor surgical outcome in patients with histologically proved HS. Preoperative global memory dysfunction is also associated with poor postoperative seizure control. The authors hypothesize that patients with HS and abnormal regional distributions of gray and white matter would show more diffuse neuropsychological deficits preoperatively than patients with isolated HS alone.

METHODS

A total of 28 adults with lateralized temporal lobe epilepsy and hippocampal volume loss measured on MRI were assessed preoperatively on neuropsychological tests of general intellect and the learning and recall of both verbal and nonverbal material. Quantitative MRI analysis of the regional distribution of gray and white matter was performed. Chi-square analyses were used to examine the relation between the presence or absence of cerebral abnormalities and preoperative performance on the neuropsychological tests.

RESULTS

A total of 15 of 28 patients had extrahippocampal abnormalities on quantitative MRI analysis. Thirteen patients had global memory impairment. Bilateral memory deficits were significantly associated with both the presence of cerebral abnormalities (p < 0.02) and poor postoperative seizure control (p < 0.05).

CONCLUSIONS

Disproportion in the regional distribution of gray and white matter in patients with HS may form the structural basis of global memory disturbance in a distinct group of patients with temporal lobe epilepsy.

Accuracy of true frameless stereotaxy: in vivo measurement and laboratory phantom studies. Technical note

The authors present the results of accuracy measurements, obtained in both laboratory phantom studies and an in vivo assessment, for a technique of frameless stereotaxy. An instrument holder was developed to facilitate stereotactic guidance and enable introduction of frameless methods to traditional frame-based procedures. The accuracy of frameless stereotaxy was assessed for images acquired using 0.5-tesla or 1.5-tesla magnetic resonance (MR) imaging or 2-mm axial, 3-mm axial, or 3-mm helical computerized tomography (CT) scanning. A clinical series is reported in which biopsy samples were obtained using a frameless stereotactic procedure, and the accuracy of these procedures was assessed using postoperative MR images and image fusion. The overall mean error of phantom frameless stereotaxy was found to be 1.3 mm (standard deviation [SD] 0.6 mm). The mean error for CT-directed frameless stereotaxy was 1.1 mm (SD 0.5 mm) and that for MR image-directed procedures was 1.4 mm (SD 0.7 mm). The CT-guided frameless stereotaxy was significantly more accurate than MR image-directed stereotaxy (p = 0.0001). In addition, 2-mm axial CT-guided stereotaxy was significantly more accurate than 3-mm axial CT-guided stereotaxy (p = 0.025). In the clinical series of 21 frameless stereotactically obtained biopsies, all specimens yielded the appropriate diagnosis and no complications ensued. Early postoperative MR images were obtained in 16 of these cases and displacement of the biopsy site from the intraoperative target was determined by fusion of pre- and postoperative image data sets. The mean in vivo linear error of frameless stereotactic biopsy sampling was 2.3 mm (SD 1.9 mm). The mean in vivo Euclidean error was 4.8 mm (SD 2 mm). The implications of these accuracy measurements and of error in stereotaxy are discussed.

Wrapping of solitary ruptured intracranial aneurysms, outcome at five years

Previous follow up studies of patients who have had ruptured intracranial aneurysms treated by a wrapping technique have largely been in the pre-microsurgical era. Our objective was to ascertain whether wrapping aneurysms with the aid of the operating microscope provides protection against rebleeding in the short and long term. The study involved retrospective analysis of patients with ruptured aneurysms treated by wrapping over a six-year period. Twenty-nine patients were identified with wrapped aneurysms, of these 15 had wrapping of a solitary ruptured aneurysm, the remainder were excluded because of clip/wrap combination, multiple aneurysms, and unruptured aneurysms. Of the 15 patients who had a solitary ruptured aneurysm wrapped, none had rebled at one year follow up. One patient died of a myocardial infarction at 4 years, the remaining 14 patients had no episodes of rebleeding with all patients achieving Glasgow outcome scores of four or five at 5 years follow-up. Although surgical clipping of intracranial aneurysms is the definitive method of treatment, our findings suggest that wrapping of ruptured intracranial aneurysms with the aid of the operating microscope confers good protection against both early and late rebleeding in those cases considered 'unclippable'.

Intracranial osteosarcomas: report of four cases and review of the literature

Four cases of intracranial osteosarcoma are reported. In three cases the tumors were primary neoplasms arising from the sellar region, base of the occiput and the parieto-occipital area. One case represented osteosarcoma metastatic to the cerebellum, a site not previously described, from a primary tumor at the femur. In addition, the current literature on intracranial osteosarcoma is reviewed.

The EASI project--improving the effectiveness and quality of image-guided surgery

In recent years, advances in computer technology and a significant increase in the accuracy of medical imaging have made it possible to develop systems that can assist the clinician in diagnosis, planning, and treatment. This paper deals with an area that is generally referred to as computer-assisted surgery, image-directed surgery, or image-guided surgery. We report the research, development, and clinical validation performed since January 1996 in the European Applications in Surgical Interventions (EASI) project, which is funded by the European Commission in their "4th Framework Telematics Applications for Health" program. The goal of this project is the improvement of the effectiveness and quality of image-guided neurosurgery of the brain and image-guided vascular surgery of abdominal aortic aneurysms, while at the same time reducing patient risks and overall cost. We have developed advanced prototype systems for preoperative surgical planning and intraoperative surgical navigation, and we have extensively clinically validated these systems. The prototype systems and the clinical validation results are described in this paper.

Neuronavigation--impact on operating time

It is uncertain whether the use of image-guided surgery has an influence on operating time. We prospectively studied the time requirements which have to be invested for using image-guided surgery and performed a comparison of operating room times from 125 matched pairs of image-guided and conventional operations. Our study revealed that neuronavigation has to be regarded as time neutral in general neurosurgery, whereas in stereotactic surgery, namely biopsy retrival, a significant reduction of anaesthetic time can be achieved through the complete separation of imaging and operation in the frameless approach.

Infective and traumatic aneurysms

Traumatic intracranial aneurysms are rare lesions but should be considered in penetrating head injury, particularly in cases of low-velocity gunshot wounds or stab wounds to the head. Because most of these aneurysms are false aneurysms, treatment may require excision or trapping procedures.

Posterior communicating artery aneurysm presenting with haemorrhage into an arachnoid cyst

A patient is reported on with a subarachnoid haemorrhage (SAH) from an aneurysm of the posterior communicating artery, who initially presented with a sentinel bleed into an arachnoid cyst and normal magnetic resonance angiography (MRA) of the intracranial vasculature which led to a delay in diagnosis. Although this is a very rare presentation of a relatively common condition, it is important to recognise the importance of intracystic haemorrhage in such circumstances as well as the limitations of MRA, as a delay in diagnosis may have serious clinical consequences.

Postimaging brain distortion: magnitude, correlates, and impact on neuronavigation

OBJECT

This prospective study was conducted to quantify brain shifts during open cranial surgery, to determine correlations between these shifts and image characteristics, and to assess the impact of postimaging brain distortion on neuronavigation.

METHODS

During 48 operations, movements of the cortex on opening, the deep tumor margin, and the cortex at completion were measured relative to the preoperative image position with the aid of an image-guidance system. Bone surface offset was used to assess system accuracy and correct for registration errors. Preoperative images were examined for the presence of edema and to determine tumor volume, midline shift, and depth of the lesion below the skin surface. Results were analyzed for all cases together and separately for four tumor groups: 13 meningiomas, 18 gliomas, 11 nonglial intraaxial lesions, and six skull base lesions. For all 48 cases the mean shift of the cortex after dural opening was 4.6 mm, shift of the deep tumor margin was 5.1 mm, and shift of the cortex at completion was 6.7 mm. Each tumor group displayed unique patterns of shift, with significantly greater shift at depth in meningiomas than gliomas (p = 0.007) and significantly less shift in skull base cases than other groups (p = 0.003). Whereas the preoperative image characteristics correlating with shift of the cortex on opening were the presence of edema and depth of the tumor below skin surface, predictors of shift at depth were the presence of edema, the lesion volume, midline shift, and magnitude of shift of the cortex on opening.

CONCLUSIONS

This study quantified intraoperative brain distortion, determined the different behavior of tumors in four pathological groups, and identified preoperative predictors of shift with which the reliability of neuronavigation may be estimated.

Bitemporal hemianopia caused by metastatic carcinoma in a patient with Wegener's granulomatosis: an unexpected finding

Metastatic lesions in the suprasellar region are extremely rare. The differential diagnosis of a focal lesion at this site is wide ranging and lesions often have a similar radiological appearance. We present a woman with known Wegener's granulomatosis who lost vision while on medical treatment for a presumed granuloma at this site. Exploration revealed a metastatic carcinoma of unknown origin. Attention is drawn to the importance of making a histological diagnosis in cases of suprasellar lesions.

Intramedullary thoracic cord metastasis managed effectively without surgery

Spinal intramedullary metastases present with rapidly progressing neurological deficits and have an extremely poor prognosis. Prompt investigation and management are required. This case history illustrates that radiotherapy and steroids can be effective in returning motor function. The behaviour of the primary tumour and the stage of the disease influence whether surgery is appropriate.

Correlation of widespread preoperative magnetic resonance imaging changes with unsuccessful surgery for hippocampal sclerosis

Despite meticulous preoperative assessment, about 30% of patients with refractory partial epilepsy due to hippocampal sclerosis fail to become seizure free after appropriate temporal lobe surgery. Perioperative complications, hippocampal remnants, and bitemporal disease do not account for all failures; extrahippocampal epileptogenic tissue must persist in some patients. Such dual pathology is detected on routine visual inspection of magnetic resonance images in about 15% of patients with hippocampal sclerosis, but most such patients are excluded from surgery. We postulated that some patients have occult extrahippocampal cerebral structural abnormalities (i.e., subtle dual pathology) and that the presence of these abnormalities would be associated with a poor surgical outcome. Quantitative postprocessing of preoperative magnetic resonance images from 27 patients subsequently proved to have hippocampal sclerosis demonstrated extrahippocampal structural abnormalities in 14, 10 of whom did not become seizure free, while 11 of 13 patients without such changes did become seizure free (chi2, p < 0.005). Such structural information may supplement clinical decision making in some patients being evaluated for epilepsy surgery and help to explain the biological basis of poor outcome from such surgery.

Image-directed neurosurgery

Images

Juvenile xanthogranuloma of nerve root origin

A case of juvenile xanthogranuloma arising from the first sacral nerve root is reported together with a review of the literature. The patient presented with symptoms of low back pain and sciatica, and with S1 nerve root tensions signs. Computed tomography and magnetic resonance imaging revealed a mass arising from the right S1 nerve root. The tumour was resected, and the morphological and immunocytochemical appearances of the lesion confirmed the diagnosis of juvenile xanthogranuloma. Soft tissue juvenile xanthogranulomas have been described but are extremely rare. However, we believe this is the first reported case of such a tumour affecting a spinal nerve root.