Johann Scharf

Cerebral arteriovenous malformations: Improved nidus demarcation by means of dynamic tagging MR-angiography

Our purpose was to further improve the target volume definition for radiosurgical treatment of cerebral arteriovenous malformations (AVMs) by means of dynamic MRA (dMRA) using a blood bolus tagging sequence. We therefore compare this technique with 3D-TOF-MRA and transfemoral high resolution angiography in plain film technique. Twenty patients with angiographically proven cerebral AVMs were investigated by dMRA, TOF-MRA, and conventional angiography during the MR-assisted radiosurgical planning protocol. The patients head was fixed in an MR-compatible stereotactic device. The different angiography techniques were evaluated by consensus of two radiologists. AVMs were characterized by the number and origin of feeding arteries, the maximum diameter of the AVM nidus, and the venous drainage pattern. Dynamic MRA was able to demonstrate the complete AVM characteristics and hemodynamics in 12 out of 20 patients. In three patients with an AVM nidus smaller than 1 cm in diameter the technique could not reliably depict the malformation. Technical problems due to steel screws and pins in the initially used stereotactic frame occurred in five patients. Due to reduced vessel overlap and the lack of disturbances caused by formations with short T1 time, dMRA was superior to TOF-MRA in the detection and the exact localization of the AVM nidus in four patients. We conclude that dMRA is able to demonstrate reliably AVM characteristics and hemodynamics in AVMs with a nidus larger than 1 cm in diameter. Because of the improved demarcation of the AVM nidus, this technique may be a valuable adjunct to radiosurgery planning of cerebral AVMs.

Characterization of Direct and Indirect Cerebral Revascularization for the Treatment of European Patients with Moyamoya Disease

Background: The best revascularization strategy for moyamoya disease (MMD) remains unknown. Our aim was to characterize angiographic revascularization effects of a bilateral standardized revascularization approach, consisting of superficial temporal artery (STA)-middle cerebral artery (MCA) bypass and encephalomyosynangiosis (EMS) on one hemisphere and single EMS on the contralateral hemisphere of each patient, and to compare the effects of both revascularization strategies on cerebral hemodynamics. Methods: In 30 patients (18 females/12 males, age 8–63 years), standardized revascularization was performed. Digital subtraction angiography was performed preoperatively and at 7 days, 6 months and 12 months postoperatively. STA-MCA and EMS functions were graded I (poor), II (medium) or III (extensive) according to angiographic aspects. In 20 patients, cerebrovascular reserve capacity (CVRC) was assessed pre- and postoperatively (at 12 months) using xenon CT. Results: After 12 months, STA-MCA/EMS function was grade 1 in 40/40%, grade 2 in 27/26%, and grade 3 in 27/10% of hemispheres, respectively. Twelve months after surgery, single EMS showed grade I in 37%, grade II in 27%, and grade III in 20% of hemispheres. Combined revascularization improved CVRC significantly compared to preoperative measurement (preoperative: 16.5 ± 34.6% vs. postoperative: 60.8 ± 64.22%; p < 0.05). Single EMS did not improve CVRC significantly (preoperative: 21.8 ± 35.9% vs. postoperative: 34.8 ± 63.0%; p < 0.05). Conclusions: Combined and indirect revascularization may be successfully applied in a bilateral standardized approach. STA-MCA/EMS is superior to single EMS in restoring CVRC in adult MMD patients.

Cerebral Sinus Thrombosis in a Trauma Patient after Recombinant Activated Factor VII Infusion

SEVERAL investigators have reported the astonishing effect of recombinant activated factor VII (rFVIIa) in trauma patients with diffuse bleeding. Currently, rFVIIa is approved for the treatment of patients with hemophilia with inhibitors to factors VIII and IX. Conditions with increased thromboembolic risk, including trauma, extensive tissue damage, sepsis, arteriosclerosis, and disseminated intravascular coagulation, may be considered contraindications for the drug. Thrombotic complications in trauma patients are rarely observed. To our knowledge, this is the first report of a patient who experienced a cerebral sinus thrombosis in the posttraumatic period after rFVIIa administration.

Assessment of hepatic perfusion in pigs by pharmacokinetic analysis of dynamic MR images

The purpose of this study was to evaluate a new method based on magnetic resonance imaging for the characterization of hepatic perfusion. In nine pigs dynamic MRI was performed before and after partial occlusion of the portal vein. The pharmacokinetic analysis of the contrast enhancement resulted in a set of parameters (amplitude, A; perfusion rate, kp; elimination rate, kel; lag time, tlag) of which kp was expected to correlate with hepatic perfusion. Reference measurements were done with ultrasound flowmeters and with a thermal diffusion probe (TDP). MR perfusion rate kp significantly dropped under partial portal vein occlusion from an average of 11.3 to 4.9 min−1 (P < 0.001), while the difference in amplitude A was not significant. The correlation between kp and the TDP measurement was r = 0.89 (P < 0.001). Pharmacokinetic analysis of MRI contrast enhancement provides a non‐invasive assessment of hepatic perfusion.J. Magn. Reson. Imaging 1999;9:568–572.

Improvement of sensitivity and interrater reliability to detect acute stroke by dynamic perfusion computed tomography and computed tomography angiography.

Objective: To assess the benefits of additional computed tomography perfusion (CTP) and computed tomography angiography (CTA) on the detection of early stroke, vessel occlusion, estimated infarct size, and interrater reliability. Methods: Sixty-seven consecutive patients underwent nonenhanced computed tomography (CT) imaging, CTA, and CTP. The final diagnosis of stroke was made from follow-up neuroimaging. A first diagnosis was made on-site by the physician on duty. Three experienced neuroradiologists blinded to follow-up findings analyzed the data set off-line, evaluated CT for signs of acute stroke, and subsequently evaluated CTP and CTA for infarction-related perfusion deficits and vessel abnormalities. Results: Computed tomography perfusion and CTA increased the time from CT start to diagnosis from 2 minutes to 10 minutes. Sensitivity to detect acute stroke increased significantly in all investigators from 0.46-0.58 to 0.79-0.90 compared with CT (<0.005). The interrater weighted kappa value increased from 0.35 to 0.64. Estimation of infarct size was not improved. Conclusion: Computed tomography perfusion and CTA provide an effective add-on to standard CT in acute stroke imaging by significantly increasing the sensitivity and reliability of infarct detection.

Risk of intraoperative ischemia due to temporary vessel occlusion during standard extracranial-intracranial arterial bypass surgery.

OBJECT Standard extracranial-intracranial (EC-IC) arterial bypass surgery represents a well-recognized procedure in which the aim is to augment distal cerebral circulation. The creation of the bypass requires temporary occlusion of the recipient vessel. Thus, there exists controversy about the risk of standard EC-IC arterial bypass surgery causing ischemic complications due to temporary vessel occlusion. In this prospective study, the incidence of intraoperative ischemia was investigated in symptomatic patients with steno-occlusive cerebrovascular disease and existing hemodynamic insufficiency. METHODS Twenty consecutive patients (14 women and 6 men; mean age 46 +/- 11 years) suffering from recurrent transient ischemic attacks due to occlusive cerebrovascular disease and proven hemodynamic compromise in functional blood flow studies were enrolled in this study. The underlying pathological condition was internal carotid artery (ICA) or middle cerebral artery (MCA) occlusion in 6 cases and ICA or MCA stenosis in 3 cases, whereas 11 patients presented with moyamoya syndrome or moyamoya disease. The surgical procedure consisted of the establishment of a standard superficial temporal artery (STA)-MCA bypass, and was performed while a strict intraoperative management protocol was applied. Patients underwent clinical examination and magnetic resonance (MR) imaging within 48 hours before and after surgery. RESULTS The incidence of reversible clinical signs of ischemia was 2 (10%) of 20 patients. Postoperative MR imaging revealed signs of diffusion disturbances in 2 (10%) of 20 cases. The observed diffusion-weighted imaging changes, however, were situated within the dependent vascular territory at risk for ischemia in 1 patient only. No permanent neurological deficit occurred. The temporary vessel occlusion time ranged between 25 and 42 minutes (mean 33 +/- 7 minutes). All means are expressed +/- the standard deviation. CONCLUSIONS Temporary vessel occlusion during standard STA-MCA arterial bypass surgery carries a low risk of intraoperative ischemia when a strict perioperative management protocol is applied.

High prevalence of heterotopic ossification after cervical disc arthroplasty: outcome and intraoperative findings following explantation of 22 cervical disc prostheses

OBJECT Cervical disc arthroplasty (CDA) has been increasingly used for the treatment of cervical disc herniations. However, the impact of CDA on adjacent-segment degeneration and the degree of heterotopic ossification (HO) of the treated segment remain a subject of controversy. Due to a product failure of the Galileo-type disc prosthesis, 22 of these devices were explanted. The radiological and clinical course in each case was investigated in detail with an emphasis on the incidence of HO and facet joint degeneration 18 months following the operation. Intraoperative findings regarding ossification and implant fixation were documented. Thus, the authors were able to describe the true rate of adjacent-segment degeneration and HO following CDA and the clinical relevance thereof. METHODS In all 22 patients, functional radiographic imaging was performed prior to surgery, 3 and 12 months after surgery, and prior to disc prosthesis explantation. At all time points, the range of motion (ROM) in the operated and adjacent segments was determined. A motion index was calculated using the preoperative and all postoperative ROMs (preoperative ROM/postoperative ROM). Computed tomography was used preoperatively to measure the height of the index segment, extent of HO, and the degree of the progression of facet arthrosis, and was used postoperatively prior to prosthesis explantation. Patients completed clinical questionnaires that included a visual analog scale and the Neck Disability Index. RESULTS The motion index of the index segment declined gradually from 1.4 at 3 months postoperative to 1.2 prior to explantation, while the motion index of the adjacent upper segment increased from 0.9 to 1.3. The mean ROM of the index segment was 10.4° ± 6.7°, and fusion was observed in 2 (9%) of the 22 patients. Prosthesis migration was present in 3 patients (13.6%). Severe HO (Grades 3 and 4) was present in 17.4%. Computed tomography showed a significant increase of segmental height of the index segment (1.6 ± 1.1 mm, p = 0.035), and a significant increase of left-sided lateral osteophytes (1.7 ± 2.1 mm, p = 0.009). The incidence of severe osteophyte formation (> 2 mm) occurred in 40%. Intraoperative findings reflected the results from CT, with primary lateral proliferation of osteophytes found in approximately 25% of patients. The mean visual analog scale scores were 3.8 ± 2.7 (neck) and 2.4 ± 2.5 (arms), and the mean Neck Disability Index score was 30 ± 22. No correlation was found between radiological and clinical parameters. CONCLUSIONS In this study, a higher incidence of HO after CDA could be demonstrated using CT, compared with studies using fluoroscopy only. However, patient selection and/or the operative technique might have contributed to the high prevalence of osteophyte formation. Thus, the exact indication for CDA has to be reconsidered. Because implant migration was detected, using fixation in the present CDA model appears suboptimal.

Assessment of hepatic perfusion in transplanted livers by pharmacokinetic analysis of dynamic magnetic resonance measurements

Objective:The purpose of this study was to validate the assessment of hepatic perfusion by pharmacokinetic analysis of dynamic contrast-enhanced magnetic resonance image series. Materials and Methods:Dynamic measurements were performed with a saturation recovery turbo fast low angle shot (ie, FLASH) sequence over the course of approximately 4 minutes in 17 patients with transplanted livers. By pharmacokinetic analysis using an open 2-compartment model, we estimated and correlated an amplitude of signal enhancement, A, and the perfusion rate, kp, with invasive perfusion measurements from implanted thermo-diffusion probes (FTDP). Results:Data analysis for segment IV of the transplanted livers yielded a mean blood flow of 81 ± 19 mL/min/100g and a mean perfusion rate of 13 ± 6 minutes−1. There was a significant correlation between FTDP and kp (rS = 0.64, P = 0.01) but not with A. Conclusions:Although our open 2-compartment model oversimplifies the complexity of hepatic perfusion, it allows a numerically robust estimation of regional blood flow per unit of blood volume. Thus, dynamic magnetic resonance imaging represents a noninvasive method to assess hepatic perfusion rate which can be visualized in color coded images.

A comparison of magnetization prepared 3D gradientecho (MP-RAGE) sequences for imaging of intracranial lesions

In a pilot study including 64 patients with different types of brain tumors we investigated four types of MP-RAGE sequences. The sequences differ in the length of the recovery period and the data acquisition mode (sequential vs. centric phase-encoding). The sequence with sequential encoding and a short recovery period provided images that reached the quality and reliability of spin-echo images. The other MP-RAGE sequences failed in providing equivalent information. In particular, a considerable number of small lesions identified in spin-echo images were not detected in MP-RAGE images. The impact of the evolving magnetization on the point spread function was analyzed by performing simulation calculations. It was found that lesions with short T1 times are rendered with low spatial resolution when sequence parameters are not set appropriately. The low overall quality of images obtained by sequences applying centric encoding may be explained by eddy current effects as reported in other recently published studies.

TrueFISP imaging of the pineal gland: More cysts and more abnormalities

INTRODUCTION Although pineal cysts are found with a frequency of over one third in autopsy series, prevalences reported in standard magnetic resonance imaging (MRI) studies only range between 0.14% and 4.9%. With the advances in scanner technology and more sensitive high-resolution 3D-sequences, pineal cysts with atypical appearance are more frequently encountered as an incidental finding. In order to help the radiologist and the clinician to correctly interpret these incidental findings and to avoid follow-up MRI or even surgical intervention, we analysed the frequency of typical and atypical pineal cysts using standard MRI-sequences and a high-resolution 3D-trueFISP-sequence (true-Fast-Imaging-with-Steady-State-Precession). METHODS In 111 patients undergoing MRI we analysed the prevalence of pineal cysts in relation to gender and age, as well as the frequency of atypical cysts defined by thickened rim, trabeculations, or asymmetric form using three standard MRI-sequences (T1-SE (T1 weighted spin echo), T2-TSE (T2 weighted turbo spin echo), FLAIR (fluid attenuated inversion recovery)) and compared the diagnostic certainty of these standard sequences with the sensitivity of a high-resolution trueFISP MRI sequence. RESULTS Using trueFISP pineal cysts were detected more frequently than in the standard sequences (35.1% vs. 9.0% (T1-SE), 4.5% (T2-TSE) and 9.0% (FLAIR)). Diagnostic uncertainty was least frequent in trueFISP. In trueFISP, 41.0% of the detected cysts showed one or more features of atypical cysts (standard sequences: 21.4%). Highest prevalence of cysts was detected in the group of 20-30-year-old patients and decreased with increasing age. CONCLUSION High-resolution 3D-sequences like trueFISP increase the detection rate of pineal cysts to levels reported in autoptic series while decreasing the diagnostic uncertainty. Atypically configurated pineal cysts are frequently detected as an incidental finding.