Neriman Özkan

Evaluation of Hardware-related Geometrical Distortion in Structural MRI at 7 Tesla for Image-guided Applications in Neurosurgery

RATIONALE AND OBJECTIVES Geometrical distortion is a well-known problem in structural magnetic resonance imaging (MRI), leading to pixel shifts with variations up to several millimeters. Because the main factors of geometrical distortion are proportional to B(0), MRI spatial encoding distortions tend to increase with higher magnetic field strength. With the increasing prospects of utilizing ultra-high-field MRI (B(0) ≥ 7 Tesla) for neuroimaging and subsequently for image-guided neurosurgical therapy, the evaluation and correction of geometrical distortions occurring in ultra-high-field MRI are essential preconditions for the integration of these data. Hence, we conducted a phantom study to determine hardware-related geometrical distortion in clinically relevant sequences for structural imaging at 7 T MRI and compared the findings to 1.5 T MRI. MATERIAL AND METHODS Hardware-related geometrical distortion was evaluated using a MRI phantom (Elekta, Sweden). Both applied scanner systems (Magnetom Avanto 1.5 T and Magnetom 7 T, Siemens Healthcare, Erlangen, Germany) were equipped with similar gradient coils capable of delivering 45 mT/m of maximum amplitude and a slew rate of 220 mT/m/ms. Distortion analysis was performed for various clinically relevant gradient echo and spin echo sequences. RESULTS Overall, we found very low mean geometrical distortions at both 7 T and 1.5 T, although single values of up to 1.6 mm were detected. No major differences in mean distortion between the sequences could be found, except significantly higher distortions in turbo spin-echo sequences at 7 T, mainly caused by B(1) inhomogeneities. CONCLUSION Hardware-related geometrical distortions at 7 T MRI are relatively small, which may be acceptable for image coregistration or for direct tissue-targeting procedures. Using a subject-specific correction of object-related distortions, an integration of 7 T MRI data into image-guided applications may be feasible.

Non-enhanced MR imaging of cerebral aneurysms: 7 Tesla versus 1.5 Tesla.

Purpose To prospectively evaluate 7 Tesla time-of-flight (TOF) magnetic resonance angiography (MRA) in comparison to 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced magnetization-prepared rapid acquisition gradient-echo (MPRAGE) for delineation of unruptured intracranial aneurysms (UIA). Material and Methods Sixteen neurosurgical patients (male n = 5, female n = 11) with single or multiple UIA were enrolled in this trial. All patients were accordingly examined at 7 Tesla and 1.5 Tesla MRI utilizing dedicated head coils. The following sequences were obtained: 7 Tesla TOF MRA, 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced MPRAGE. Image analysis was performed by two radiologists with regard to delineation of aneurysm features (dome, neck, parent vessel), presence of artifacts, vessel-tissue-contrast and overall image quality. Interobserver accordance and intermethod comparisons were calculated by kappa coefficient and Lins concordance correlation coefficient. Results A total of 20 intracranial aneurysms were detected in 16 patients, with two patients showing multiple aneurysms (n = 2, n = 4). Out of 20 intracranial aneurysms, 14 aneurysms were located in the anterior circulation and 6 aneurysms in the posterior circulation. 7 Tesla MPRAGE imaging was superior over 1.5 and 7 Tesla TOF MRA in the assessment of all considered aneurysm and image quality features (e.g. image quality: mean MPRAGE7T: 5.0; mean TOF7T: 4.3; mean TOF1.5T: 4.3). Ratings for 7 Tesla TOF MRA were equal or higher over 1.5 Tesla TOF MRA for all assessed features except for artifact delineation (mean TOF7T: 4.3; mean TOF1.5T 4.4). Interobserver accordance was good to excellent for most ratings. Conclusion 7 Tesla MPRAGE imaging demonstrated its superiority in the detection and assessment of UIA as well as overall imaging features, offering excellent interobserver accordance and highest scores for all ratings. Hence, it may bear the potential to serve as a high-quality diagnostic tool for pretherapeutic assessment and follow-up of untreated UIA.

The CHESS score: a simple tool for early prediction of shunt dependency after aneurysmal subarachnoid hemorrhage

Acute hydrocephalus is an early and common complication of aneurysmal subarachnoid hemorrhage (SAH). However, considerably fewer patients develop chronic hydrocephalus requiring shunt placement. Our aim was to develop a risk score for early identification of patients with shunt dependency after SAH.

Improved cerebral time-of-flight magnetic resonance angiography at 7 Tesla--feasibility study and preliminary results using optimized venous saturation pulses.

Purpose Conventional saturation pulses cannot be used for 7 Tesla ultra-high-resolution time-of-flight magnetic resonance angiography (TOF MRA) due to specific absorption rate (SAR) limitations. We overcome these limitations by utilizing low flip angle, variable rate selective excitation (VERSE) algorithm saturation pulses. Material and Methods Twenty-five neurosurgical patients (male n = 8, female n = 17; average age 49.64 years; range 26–70 years) with different intracranial vascular pathologies were enrolled in this trial. All patients were examined with a 7 Tesla (Magnetom 7 T, Siemens) whole body scanner system utilizing a dedicated 32-channel head coil. For venous saturation pulses a 35° flip angle was applied. Two neuroradiologists evaluated the delineation of arterial vessels in the Circle of Willis, delineation of vascular pathologies, presence of artifacts, vessel-tissue contrast and overall image quality of TOF MRA scans in consensus on a five-point scale. Normalized signal intensities in the confluence of venous sinuses, M1 segment of left middle cerebral artery and adjacent gray matter were measured and vessel-tissue contrasts were calculated. Results Ratings for the majority of patients ranged between good and excellent for most of the evaluated features. Venous saturation was sufficient for all cases with minor artifacts in arteriovenous malformations and arteriovenous fistulas. Quantitative signal intensity measurements showed high vessel-tissue contrast for confluence of venous sinuses, M1 segment of left middle cerebral artery and adjacent gray matter. Conclusion The use of novel low flip angle VERSE algorithm pulses for saturation of venous vessels can overcome SAR limitations in 7 Tesla ultra-high-resolution TOF MRA. Our protocol is suitable for clinical application with excellent image quality for delineation of various intracranial vascular pathologies.

Outcome after conservative management or surgical treatment for new-onset epilepsy in cerebral cavernous malformation

OBJECTIVE The aim of this study was to determine seizure outcome, functional outcome, and the withdrawal of antiepileptic drugs (AEDs) after conservative or surgical treatment of patients with new-onset cavernoma-related epilepsy (CRE). METHODS The authors conducted a retrospective comparative observational study of 79 consecutive patients, each with a single sporadic cerebral cavernous malformation (CCM) and new-onset CRE. RESULTS Forty-one patients underwent initial surgery (IS), and 38 patients underwent initial conservative (IC) treatment. Of those in the latter group, 19 underwent delayed surgical (DS) treatment. At the last follow-up, 88%, 32%, and 79% of patients in the respective groups had been seizure free for at least 2 years (International League Against Epilepsy [ILAE] Class 1; IS vs IC, p < 0.0001) and 78%, 8%, and 58%, respectively, had been off AEDs (IS vs IC, p < 0.0001). The cumulative probability of staying seizure free (ILAE Class 1) during a 5-year period was 73% (mean seizure-free follow-up 49.8 ± 2.7 months, 95% CI 44.4-55.1 months) for the IS group, 22% (mean 31.8 ± 3.6 months, 95% CI 24.8-38.8 months) for the IC group, and 68% (mean 48.6 ± 4.3 months, 95% CI 40.1-57.1 months) for the DS group (IS vs IC p < 0.001). Long-term operative morbidity was 3%, and long-term morbidity in the conservatively treated group was also 3%. CONCLUSIONS Patients with CCM and new-onset CRE who underwent IS treatment showed better results in seizure control and the discontinuation of AEDs than the conservatively treated patients. Operative morbidity was comparable to the morbidity from symptomatic CCM hemorrhage in the conservative group. Half of the patients who started with conservative treatment underwent subsequent surgical treatment; however, a longer duration of epilepsy prior to surgery did not worsen postoperative seizure outcome.

Outcome After Clipping of Unruptured Intracranial Aneurysms Depends on Caseload

OBJECTIVE Although most neurovascular centers currently have a coil first policy, the percentage of coiled versus clipped aneurysms, as well as treatment outcomes, varies strongly between these centers. This study evaluates the impact of an increase in clipping caseload on treatment outcome in a large single-center series. METHODS All consecutive patients who underwent microsurgical clipping of unruptured intracranial aneurysms between January 2003 and April 2014 in our department were analyzed retrospectively. According to the change of the chairman in the neurosurgical department (1 September 2008) with a subsequent increase in the clipping volume, the entire cohort was divided into 2 groups with equal time intervals (historic and current cohorts). RESULTS There were 94 clipped unruptured intracranial aneurysms in the historic cohort and 252 in the current cohort. Unfavorable outcome at 6 months postoperatively (defined as modified Rankin Score >2) was observed in 8 cases (8.5%) in the historic cohort and 7 cases (2.8%) in the current cohort (P < 0.0001). The surgical mortality decreased from 3.2% to 0%. Cerebral infarction on postoperative computed tomography scan was observed in 25 cases (26.6%) in the historic cohort and 19 cases (7.5%) in the current cohort (P < 0.0001). Within the current cohort, there was a progressive improvement of surgical outcome over the time. CONCLUSIONS The improvement of the surgical outcome after increasing the clipping caseload underlines the importance of sufficient surgical volume for maintenance of competitive treatment results.

Value of DSA in the diagnostic workup of pulsatile tinnitus.

Objectives Pulsatile tinnitus (PT) is a rare complaint, but can be a symptom of life-threatening disease. It is often caused by vascular pathologies, e.g. dural arteriovenous fistula (dAVF), arteriovenous malformation (AVM) or vascularized tumors. The current diagnostic pathway includes clinical examination, cranial MRI and additional DSA. The aim of this study was to evaluate the diagnostic impact of DSA in the diagnostic workup of patients with PT in comparison to MRI alone. Methods Retrospectively, 54 consecutive patients with pulsatile tinnitus were evaluated. All patients had a diagnostic workup including cranial MRI and DSA. MRI examinations were blinded to the results of DSA and retrospectively analyzed in consensus by two experienced neuroradiologists. The MR-examinations were evaluated for each performed sequence separately: time-of-flight-angiography, ce-MRA, T2, ce-T1-sequence and ce-T1-sequence with fat saturation. Results 37 of the 54 patients revealed a pathology explaining PT on MRI, which was detected by the readers in 100% and proofed by means of DSA. 24 dAVF, four paraganglioma, two AVM and seven more pathologies were described. All patients without pathology on MRI did also not show any pathology in DSA. Conclusions MR imaging is sufficient to exclude pathology in patients with pulsatile tinnitus.

Surgical management of intradural spinal cord tumors in children and young adults: A single-center experience with 50 patients.

Background: Intradural spinal cord tumors (IDSCTs) in children and young adults are rare diseases. This present study is aimed to demonstrate our experience with a large series of children and young adults with IDSCT. Methods: A total of 50 patients aged <20 years with IDSCT treated in our department between 1990 and 2010 were included in the study. Clinical, histological, and radiological findings, treatment strategies, and clinical outcome were retrospectively assessed. Depending on the relation to the spinal cord, IDSCT were dichotomized into intramedullary SCT (IMSCT) and extramedullary SCT (EMSCT). The functional outcome was evaluated with the Frankel score assessing the longest available follow-up period. Results: Mean age was 10.3 years (range 6 months–19 years). IDSCT surgery was performed in 44 patients (88%). A common first symptom in patients with EMSCT was neck and back pain (41%), whereas monoparesis of arms (43%) were often seen in patients with IMSCT. The main duration of the symptoms was longer in patients with IMSCT. The postoperative functional outcome was generally comparable to the preoperative functional condition, while better for EMSCT (P < 0.01). The functional outcome at last follow-up correlated significantly with the preoperative Frankel score (P < 0.002). Conclusion: Due to the mostly mild impact of the surgery on the functional outcome, the surgical treatment of IDSCT in children and young patients can be uniquely advocated.

Cervical spondylodiscitis – A clinical analysis of surgically treated patients and review of the literature

OBJECTIVE The aim of this study was to analyze our clinical and neurological results of surgically treated patients suffering from cervical spondylodiscitis with focusing particularly on the surgical methods used and to review the literature. PATIENTS AND METHODS We present a series of 21 patients operated with cervical spondylodiscitis between 1998 and 2011. Basic demographic data, comorbidities, the radiological segments involved, the surgical strategy with special consideration of the material used and the clinical outcome were evaluated retrospectively. RESULTS The mean age of 6 female and 12 male patients was 65 years (range 28-89 years). The mean follow-up was 3.7 years ranging between 4 weeks and 9 years. The leading symptom was neurological deficits rather than pain. The segments C 5/6 (n=8) and C 6/7 (n=7) were most frequently involved. Different surgical methods depending on the location, anatomical and pathological condition and extension of the lesion were performed. CONCLUSION In conclusion, cervical spondylodiscitis could effectively be treated in the presented patient cohort by surgical decompression, debridement and PMMA or bone graft implants followed by long term antibiotic therapy. The presented surgical reconstruction technique with PMMA might be a feasible alternative to the use of bone graft or cages. The promising clinical results warrant future prospective studies to further investigate this technique.

Operative strategies in ventrally and ventrolaterally located spinal meningiomas and review of the literature

Meningiomas are usually benign tumors that arise from the meninges. They occur both intracranially and intraspinally. Spinal meningiomas account for 25–46 % of all spinal canal tumors [5, 7, 17, 21, 26]. Typically, these tumors are located in the intradural extramedullary space. Due to space occupying growth they become symptomatic over time. Initial clinical symptoms are not specific and comprise of pain, sensory deficits, motor weakness, and vegetative dysfunction, respectively [13, 14, 29]. If indicated, spinal meningiomas are usually treated by surgical resection only. Technological achievements such as preoperativemagnetic resonance imaging (MRI), intraoperative electrophysiological monitoring, and specialized microsurgical techniques have helped to improve the clinical outcome of patients suffering from spinal meningiomas in the last decades dramatically [9, 11, 17, 24, 26]. Similar to the treatment of dorsally attached tumors, the excision of ventrally attached tumors is usually performed via dorsal approaches as well, which is then hindered by the covering spinal cord [26]. Therefore, the surgical removal of such meningiomas is usually considered to be more difficult when compared to dorsally located tumors [21, 26]. In the present study, we thus investigate a large series of patients suffering from such ventrally located spinal meningiomas that were surgically treated in our department during a 20-year period.