F. J. Hans

Sequential visualization of brain and fiber tract deformation during intracranial surgery with three-dimensional ultrasound: an approach to evaluate the effect of brain shift.

OBJECTIVE: We present a technique that allows intraoperative display of brain shift and its effects on fiber tracts. METHODS: Three patients had intracranial lesions (one malignant glioma, one metastasis, and one cavernoma) in contact with either the corticospinal or the geniculostriate tract that were removed microneurosurgically. Preoperatively, magnetic resonance diffusion-weighted imaging (DWI) was performed to visualize the fiber tract at risk. DWI data were fused with those obtained from anatomic T1-weighted magnetic resonance imaging. A single-rack three-dimensional ultrasound neuronavigation system, which simultaneously displays the MRI scan and the corresponding ultrasound image, was used intraoperatively for 1) navigation; 2) definition of fixed and potentially shifting ultrasound landmarks near the fiber tract; and 3) sequential image updating at different steps of resection. The result was time-dependent brain deformation data. With a standard personal computer equipped with standard image software, the brain shift-associated fiber tract deformation was assessed by use of sequential landmark registration. After surgery, DWI was performed to confirm the predicted fiber tract deformation. RESULTS: The lesions were removed without morbidity. Comparison of three-dimensional ultrasound with DWI and T1-weighted magnetic resonance imaging data allowed us to define fixed and potentially shifting landmarks close to the respective fiber tract. Postoperative DWI confirmed that the actual fiber tract position at the conclusion of surgery corresponded to the sonographically predicted fiber tract position. CONCLUSION: By definition and sequential intraoperative registration of ultrasound landmarks near the fiber tract, brain shift-associated deformation of a tract that is not visible sonographically can be assessed correctly. This approach seems to help identify and avoid eloquent brain areas during intracranial surgery.

Partial “targeted” embolisation of brain arteriovenous malformations

The treatment of pial arteriovenous brain malformations is controversial. Little is yet known about their natural history, their pathomechanisms and the efficacy and risks of respective proposed treatments. It is known that only complete occlusion of the AVM can exclude future risk of haemorrhage and that the rates of curative embolisation of AVMs with an acceptable periprocedural risk are around 20 to 50%. As outlined in the present article, however, partial, targeted embolisation also plays a role. In acutely ruptured AVMs where the source of bleeding can be identified, targeted embolisation of this compartment may be able to secure the AVM prior to definitive treatment. In unruptured symptomatic AVMs targeted treatment may be employed if a defined pathomechanism can be identified that is related to the clinical symptoms and that can be cured with an acceptable risk via an endovascular approach depending on the individual AVM angioarchitecture. This review article gives examples of pathomechanisms and angioarchitectures that are amenable to this kind of treatment strategy.

Functional MRI and 18F FDG-Positron Emission Tomography for Presurgical Planning: Comparison with Electrical Cortical Stimulation

Summary. Background: In patients with mass lesions near “eloquent” cortical areas different preoperative mapping techniques can be used. Two of the most widely used approaches include positron emission tomography (PET) and functional MRI (fMRI). We employed both methods in the same patients undergoing presurgical evaluation and compared the results to those obtained by direct electrical cortical stimulation (DECS). Method: 22 patients with tumours of different aetiology near the central region were investigated. FMRI was performed using a T2*-weighted gradient-echo BOLD sequence at 1.5 T, PET was performed after injection of 122–301 MBq 18F-Fluorodeoxyglucose (18-FDG) under rest and activation conditions. DECS was performed in all patients with recordings of muscles primarily involved in the investigated tasks. Findings: In 19 patients all three modalities could be compared, 1 patient demonstrated discordance between fMRI and PET with DECS speaking in favour of fMRI, 6 patients had neighbouring results of PET and fMRI (between 1–2 cm distance), 12 patients had overlapping results. Interpretation: The high incidence of neighbouring results is presumably related to fMRI specific artefacts. Advantages of fMRI are: Higher spatial and temporal resolution, more and different functional runs, shorter examination time, wider availability, longitudinal examinations, non-invasiveness and cost-effectiveness, easy registration to anatomical images. Advantages of PET are: higher signal-to-noise ratio, lesser susceptibility to artefacts (motion, draining veins), evaluation of tumour metabolism. It is our opinion that the neurosurgeon has to decide on a case-by-case basis which study suits his specific needs in the presurgical evaluation of his patient.

New developments in MRA: time-resolved MRA.

For many clinical questions, less invasive angiography methods have at least in part already replaced digital subtraction angiography (DSA) as a routine diagnostic procedure. However, temporal resolution achievable with DSA is still indispensable in some patients. Recent advances in MR hardware performance and imaging techniques permit sub-second frame rate MR angiographies to be performed using a rapidly repeated fast T1 weighted gradient echo sequence during administration of a contrast bolus, and subsequent complex subtraction in k-space to emphasise the difference in phase between stationary tissue and contrast-enhanced blood. This technique allows two-dimensional projection angiograms to be obtained at a temporal frame rate of three images per second and with a spatial in-plane resolution of about one square millimetre. This time-resolved information is important for (a) the detection and follow-up of arteriovenous malformations, including their arterial feeders, the size of the nidus and their venous drainage patterns, (b) the demonstration of dural arteriovenous fistulas, recognised as an early filling of a dural sinus during the early arterial phase, and (c) the characterization of the vascularisation of brain tumours. With regards to vascular malformations, the direction of venous drainage and therefore the most pressing clinical questions concerning the need for therapeutic intervention can be ascertained. This technique is the only MR imaging method able to provide dynamic information on the cerebral vasculature. It therefore constitutes a helpful adjunct to the imaging armentarium in many clinical situations.

Time-of-flight-, phase contrast and contrast enhanced magnetic resonance angiography for pre-interventional determination of aneurysm size, configuration, and neck morphology in an aneurysm model in rabbits.

We describe three different magnetic resonance (MR)-angiography techniques to evaluate aneurysm size, configuration, and neck morphology of experimentally created aneurysms in a rabbit model. In five New Zealand White rabbits an aneurysm was created by endovascular occlusion of the right common carotid artery (CCA) using a pliable balloon and subsequent endoluminal incubation of elastase within the proximal CCA above the balloon and distal ligation of the vessel. In all animals, time-of-flight (TOF), phase contrast and contrast enhanced (CE) MR angiographies (MRA) were performed and compared to conventional digital subtraction angiography results. We found, that aneurysms are best visualized employing CE MRA, however, neck morphology was also found to demonstrate interpretable results when evaluating the axial source data of the TOF MRA. The animal model we used can be employed for testing endovascular devices such as new coil material, or covered stents. The described MRA techniques might then be helpful for pre-interventional planning and maybe even for the follow-up of the thus treated aneurysms.

Endovascular treatment of experimentally induced aneurysms in rabbits using stents: a feasibility study

Although Guglielmi detachable coil (GDC) systems have been generally accepted for treatment of intracranial aneurysms, primary stenting of aneurysms using porous stents or implantation of coils after stent placement remains experimental. Testing of these new methods requires an animal model which imitates human aneurysms in size, configuration and neck morphology. We assessed in detail the technical requirements of and steps for transfemoral stent treatment of experimentally induced aneurysms at the top of the brachiocephalic trunk in rabbits. We created aneurysms in ten rabbits by distal ligation and intraluminal digestion of the right common carotid artery with elastase. We treated five animals with porous stents alone, and five with stents plus coiling via the meshes of the stent, which permitted dense packing of coils. No complications related to the procedures occurred. In all animals, even in those treated solely with porous stents, total occlusion of the aneurysm was achieved. Our animal model can be suitable for testing the biocompatibility and occlusion rate of new methods and devices for the treatment of experimental aneurysms.

Movement artefacts and MR BOLD signal increase during different paradigms for mapping the sensorimotor cortex.

Summary.Summary. Background: The authors evaluated the impact of motion artefacts on presurgical mapping of the sensorimotor cortex with functional magnetic resonance imaging (fMRI). Different mapping paradigms were compared with regard to the frequency of motion artefacts and the resulting signal increase. Method: 94 surgical candidates with mass lesions near the central region were investigated using BOLD1-contrast T2* weighted multislice multi-echo EPI gradient echo sequences on a 1,5 T Philips Gyroscan. Three functional paradigms were performed: a) repetitive self-paced clenching of the hand to a fist (68 runs); b) repetitive finger-to-thumb opposition (46 runs); c) sensory stimulation by repetitive brushing of the palm (15 runs). Task-related haemodynamic changes were identified by statistical analysis with the Kolmogorov-Smirnov-test. MR signal increase in percent was calculated for each of the paradigms. Motion artefacts were rated on a scale from 1 to 3. Findings: Severe motion artefacts occurred in 8 hand clenching runs and in 2 finger opposition runs. Artefacts were more pronounced in hand clenching than in finger opposition. There were no motion artefacts in any of the sensory stimulation runs. Concerning the percent MR signal change there was no significant difference between hand clenching and finger opposition (T-test: p>0,5) but a highly significant difference (p<0,0001) between both motor tasks and the sensory paradigm (hand clenching: 2.68±0.75; finger opposition: 2.76±0.79; sensory stimulation: 1.72±0.65). Interpretation: Sensory stimulation causes by far less artefacts than motor paradigms but it also has to be considered less sensitive as it produces a smaller MR signal increase. Therefore in presurgical evaluation sensory stimulation should be kept in reserve for cases in whom motion artefacts are very likely to occur, i.e. patients with severe forms of paresis.

Cortisol dynamics in the acute phase of aneurysmal subarachnoid hemorrhage: associations with disease severity and outcome.

The purpose of this study was to assess cortisol dynamics in the acute phase after aneurysmal subarachnoid hemorrhage (SAH) and to set the parameters of cortisol release in relation to the severity of illness and outcome. In 22 consecutive patients with aneurysmal SAH, cortisol, corticosteroid binding globulin, interleukin-6, and adrenocorticotrophic hormone were measured immediately after hospital admission (t(0)), 7 days (t(1)) later, and at least 14 days later (t(2)). Additionally, diurnal profiles of cortisol secretion were assessed at t(1) and t(2), and area under the curve (AUC) was computed for calculated free serum cortisol (CFSC). In this study, normal diurnal CFSC profiles were associated with a significantly shorter ICU-stay, less complications, and a more favorable outcome than abnormal diurnal profiles. AUC and 8 a.m. cortisol were not related to clinical course or outcome. It is concluded that cortisol secretion patterns are associated with the severity and outcome of SAH. For an appraisal of the hypothalamo-pituitary-adrenal axis in SAH patients, single cortisol measurements are insufficient.

A less invasive surgical concept for the resection of spinal meningiomas.

SummaryBackground. The surgical strategy for spinal meningiomas usually consists of laminectomy, initial tumour debulking, identification of the interface between tumour and spinal cord, resection of the dura including the matrix of the tumour, and duroplasty. The objective of this study was to investigate whether a less invasive surgical strategy consisting of hemilaminectomy or laminectomy, tumour removal and coagulation of the tumour matrix allows comparable surgical and cinical results to be obtained, especially without an increase of the recurrence rate as reported in the literature. Patients and methods. Between 1990 and 2005, 61 patients (11 men, 50 women) underwent surgery for spinal meningioma. All patients were treated microsurgically by a posterior approach. In 56 of the 61 patients, the above outlined – less invasive – surgical technique with tumour removal and coagulation of the tumour matrix was performed. In 5 patients, dura resection and duroplasty was additionally performed. Electrophysiological monitoring was routinely used since 1996. Recurrence was defined as new onset or worsening of symptoms and radiological confirmation of tumour growth. The pre-and post-operative clinical status was measured by the Frankel grading system. Results. Pre-operatively, 40 patients were in Frankel grade D, 13 patients in grade C, 6 patients in grade E and 1 patient each in grade A and B. Following surgery no patient presented a permanent worsening of clinical symptoms. All patients who initially presented with a Frankel grades A–C (n = 15) recovered to a better grade at the time of follow-up. Patients who presented with Frankel grade D remained in stable condition (n = 27) or recovered to a better neurological status (n = 13). Two patients experienced a temporary worsening of their symptoms, but subsequently improved to a better state than pre-operatively. Two (3.3%) complications (pseudomeningocele, wound infection) requiring surgery, were encountered. The pseudomeningocele developed in a patient who underwent durotomy. During the follow-up period of 2 months to 10 years (mean 31.3 months), 3 patients (5%) required surgery for symptomatic recurrence: 1 patient had 2 recurrences that occured 4 and 7 years after first tumour removal and matrix coagulation, 1 recurrence occurred 1 year after tumour removal that was accompanied by matrix coagulation in a patient with a diffuse anterocranial tumour extension and 1 occured 3 years after tumour removal and durotomy. Two patients showed a small recurrence on MRI during follow-up after 2 and 5 years, respectively, without any symptoms requiring surgery. Conclusions. The high rate of favourable clinical results combined with the low rate of recurrences supports our less invasive surgical concept, which does not aim for resection of the dural matrix of the spinal meningioma.

The Aneurysmal Wall: The Key to a Subclassification of Intracranial Arterial Aneurysm Vasculopathies?

The pathogenesis of intracranial arterial aneurysms (AA) has been debated for many years and still remains unclear, although these entities might pose life-threatening risks to the patient and understanding the disease is of utmost importance for choosing treatment concepts. Apart from the “classical” berry-type aneurysm, there are different other types of intracranial AA such as infectious, dissecting or giant, partially thrombosed aneurysms. From the clinicians perspective, the hypothesis that some of these intracranial aneurysms might be due to abluminal factors has been put forward for many years. Alterations of the vessel wall, either due to luminal or abluminal factors may be employed for an etiological classification of aneurysmal vasculopathies as will be discussed in this article. Moreover, regarding certain aneurysmal vasculopathies as an abluminal disease might alter current therapeutic strategies since therapy should not only aim at the intraluminal repair of the artery but may also target the vessel wall.