Dual-Layer Detector Cone-Beam CT Angiography for Stroke Assessment: First-in-Human Results (the Next Generation X-ray Imaging System Trial)

BACKGROUND AND PURPOSE

In patients with stroke, IV cone-beam CTA in the angiography suite could be an alternative to CTA to shorten the door-to-thrombectomy time. However, image quality in cone-beam CTA is typically limited by artifacts. This study evaluated a prototype dual-layer detector cone-beam CT angiography versus CTA in patients with stroke.

MATERIALS AND METHODS

A prospective, single-center trial enrolled consecutive patients with ischemic or hemorrhagic stroke on initial CT. Intracranial arterial segment vessel conspicuity and artifact presence were evaluated on dual-layer cone-beam CTA 70-keV virtual monoenergetic images and CTA. Eleven predetermined vessel segments were matched for every patient. Twelve patients were necessary to show noninferiority to CTA. Noninferiority was determined by the exact binomial test; the 1-sided lower performance boundary was prospectively set to 80% (98.75% CI).

RESULTS

Twenty-one patients had matched image sets (mean age, 72 years). After excluding examinations with movement or contrast media injection issues, all readers individually considered dual-layer cone-beam CT angiography noninferior to CTA (CI boundary, 93%, 84%, 80%, respectively) when evaluating arteries relevant in candidates for intracranial thrombectomy. Artifacts were more prevalent compared with CTA. The majority assessment rated each individual segment except M1 as having noninferior conspicuity compared with CTA.

CONCLUSIONS

In a single-center stroke setting, dual-layer detector cone-beam CTA virtual monoenergetic images are noninferior to CTA under certain conditions. Notably, the prototype is hampered by a long scan time and is not capable of contrast media bolus tracking. After excluding examinations with such scan issues, readers considered dual-layer detector cone-beam CTA noninferior to CTA, despite more artifacts.

Experiences of positive encounters with healthcare professionals among women on long-term sickness absence due to breast cancer or due to other diagnoses: a nationwide survey

Background

Experiences of encounters with professionals have been shown to influence return to work (RTW) among sickness absentees in general. The aim was to gain knowledge on experiences of encounters with healthcare professionals and the ability to RTW among women on long-term sickness absence (SA) due to breast cancer (BC) compared to among women on long-term SA due to other diagnoses.

Methods

Analyses of questionnaire data about experiences of encounters with healthcare professionals among 6197 women aged 19–65 years and on a SA spell lasting 4–8 months. Of those, 187 were on SA due to BC. Descriptive statistics and adjusted (for age, birth country, educational level, depressive symptoms) logistic regression analyses with 95% confidence intervals (CI) were conducted.

Results

About 95% in both groups of women stated that they had experienced positive encounters with healthcare, and a minority, about 20%, had experienced negative encounters. Four specific types of positive encounters had been experienced to a lesser extent by women with BC: “allowed me to take own responsibility” (odds ratio (OR) 0.6; 95% CI 0.4–0.8), “encouraged me to carry through my own solutions” (OR 0.5; 95% CI 0.4–0.7), “made reasonably high demands” (OR 0.6; 95% CI 0.4–0.9), and “sided with me/stood on my side” (OR 0.6; 95% CI 0.4–0.8). Among the women with BC, 46% stated that positive encounters promoted their ability to RTW compared to 56% among the others. Conclusion: Most of the women had experienced positive encounters and about half stated that positive encounters promoted their ability to RTW, although a slightly smaller proportion of the women with BC stated that. This study emphasizes that not only medical treatment but also encounters may influence the ability to RTW, something that is of clinical importance.

The Medina Embolic Device: Karolinska experience

Background The aim of this study was to report our single centre experience with the Medina Embolic Device (MED). Methods We performed a retrospective analysis of prospectively collected data to identify all patients treated with the MED. A total of 14 aneurysms (non-consecutive), in 13 patients, were treated including one ruptured and one partially thrombosed aneurysm. Fundus diameter was ≥5 mm in all cases. We evaluated the angiographic appearances, the clinical status, complications, and the need for adjunctive devices or repeat treatments. Results Aneurysm location was cavernous internal carotid artery (ICA; n = 1), supraclinoid ICA ( n = 1), terminal ICA ( n = 2), anterior communicating artery (AComA; n = 4), A2-3 ( n = 1), M1-2 junction ( n = 1), posterior communicating artery (PComA; n = 1), superior cerebellar artery (SCA; n = 1), and basilar tip ( n = 2). The average aneurysm fundus size was 8.6 mm (range 7-10 mm) and average neck size 3.75 mm (range 1.9-6.9 mm). Immediate angiographic results were modified Raymond-Roy occlusion classification (mRRC) I n = 2, mRRC II n = 1, mRRC IIIa n = 2, mRRC IIIb n = 2, the remaining 7 aneurysms showed complete opacification. At follow-up angiography (mean 5 months) mRRC I n = 5, mRRC II n = 5, mRRC IIIa n = 3, and persistent filling was seen in 1 aneurysm. Overall, four patients had repeat treatment and one is pending further treatment. Of the aneurysms treated with more than one MED, 75% showed complete occlusion at 6-month follow up whereas only one aneurysm treated with a single device showed complete occlusion. Overall, three patients had temporary complications and there were no deaths. Conclusions The MED is an intra-saccular flow-diverting device with satisfactory angiographic results and an acceptable safety profile. Use of a single MED cannot be recommended and further longer term studies are needed prior to widespread clinical use.

Cerebral air emboli from angiography in a patient with stroke: A case report

A 42-year-old woman with subarachnoid and intracerebral hemorrhage was investigated with diagnostic angiography, disclosing an occlusion of the left internal carotid artery and the middle cerebral artery. CT examination immediately after the angiography revealed a 12-h-old infarct of the left middle cerebral artery territory. There was also gas in the arteries supplying the infarcted part of the brain, but not in other vessels. Air had most probably been introduced during the angiography and had consequently been “trapped” in the cortical arteries of the ischemic brain. In the non-ischemic parts of the brain air may have passed through the vessels leaving no trace.

Target Delineation in Radiosurgery for Cerebral Arteriovenous Malformations

A study of 6 selected arteriovenous malformation (AVM) patients was performed to investigate the feasibility of delineating an AVM on MR images and to compare the AVM volume outlined on different images. Conventional stereotaxic angiograms, stereotaxic MR images and MR angiograms using several different pulse sequences were obtained prior to radiosurgery. Treatment plans were made from the conventional stereotaxic angiograms. These plans were then transferred to a separate dose planning computer which displayed the MR images with the superimposed isodose lines. The radiated volumes of AVM and brain tissue were measured from these MR images. Last, an assessment was made of the radiation volume needed for an appropriate treatment of the AVM if the treatment plan was made from the MR images rather than from the conventional stereotaxic angiogram. It was possible to delineate medium and large size AVM nidi on stereotaxic MR images based on an integration of information obtained from various pulse sequences. The estimated volumes of the AVM nidi were found to be larger on the conventional stereotaxic angiograms than on the stereotaxic MR images. Consequently, a dose plan based on a conventional stereotaxic angiogram would result in a higher integral dose to the brain with the same target dose. By using reliable MR information it is expected that the volume of brain exposed to radiation could be decreased and the adverse effects of stereotactic radiosurgery for AVM thereby minimized.

Computer Independent Sidemarker for CT Scanners

In performing a CT examination the user has to inform the apparatus about the position of the patient. This is a potential source of error. Right and left do sometimes get mixed up because of mistakes when programming the CT scanner. This is very treacherous when examining a symmetrical organ like the brain. To avoid this kind of accident some hospitals use a radiopaque catheter in the head support as a sidemarker. However, there is no general convention or rule as to the position of the catheter. It usually has a small cross sectional area and therefore has to have a rather high attenuation to be seen with the ordinary window settings used when evaluating the brain. This does sometimes give disturbing artifacts. The need for a good computer independent sidemarker for CT scanners is therefore obvious.

Acute-Sinus Thrombosis in a Child with Antibodies against Cardiolipins

A case of thrombosis of the straight sinus and the left transverse sinus in an 11 year old boy is described. The patient had a history of slight trauma followed by infection of the upper airways and presented with severe impressive and expressive dysphasia and stupor.

He was treated with in situ fibrinolysis. Despite successful local fibrinolysis and thrombectomy with a balloon catheter the patient rethrombosed his left transverse sinus several times and had a late thrombosis of his jugular vein.

Nevertheless, flow in the left sigmoid sinus was facilitated and focal brain oedema was significantly reduced.

Serum levels of antibodies against cardiolipins, associated with venous thrombosis, were elevated and interfered with reagents used for measuring the activated partial tromboplastin time, causing it to be falsely prolonged with subsequent underdosage of heparin. He was treated with oral anticoagulants for one year after the episode and recovered completely.

Otorrhagia from the “Aberrant Internal Carotid” Artery in the Middle Ear

Agenesis of the cervical portion of the internal carotid artery (ICA) may result in blood supply to the ipsilateral cerebral hemisphere being provided by an enlarged inferior tympanic branch of the ascending pharyngeal artery. This enlarged vessel, passing through Jacobson's canal and anastomosing with the likewise enlarged caroticotympanic branch of the ICA in front of the promontorium, may simulate a middle ear mass.

We present five patients with this unusual anatomical variant, three of which underwent biopsy of what was believed to be a middle ear tumour.

One patient experienced rupture of an arterial aneurysm in the middle ear successfully treated with endovascular application of detachable platinum coils.

It is mandatory for ENT-surgeons and radiologists who perform head-and-neck examinations to recognize this anatomical variant, not mistaking it for a tumour, since biopsy of a large artery supplying the brain may have disastrous consequences.

In patients with otorrhagia, an arterial aneurysm must be considered as a possible source of bleeding, in some cases amenable for treatment with an endovascular technique.

The diagnosis of “aberrant internal carotid artery” is usually made with CT of the temporal bone or MR of the skull base. Cerebral angiography is in most cases not necessary, unless an endovascular procedure is planned.

Radiation Dose and Image Quality in Neuroangiography: Effects of Increased Tube Voltage, Added X-Ray Filtration and Antiscatter Grid Removal

During endovascular treatment the patient may be subject to fluoroscopy for long periods as well as multiple x-ray exposures. The radiation dose to the patient can be considerable, and cause local deterministic effects such as alopecia or even skin burn. The potential carcinogenic effects should also be noted, being especially important in the paediatric population.

We measured radiation doses to patients and personnel during neuroendovascular procedures and diagnostic neuroangiography. We also tried to reduce the radiation dose to the patient utilising increased tube voltage, additional primary X-ray filtration and by removing the antiscatter grid in front of the image intensifier, employing air gap technique.

We investigated radiation doses to patient and personnel during neuroangiographic procedures and optimized the examination technique with regard to radiation dose with maintained image quality.

Radiation exposure to patients and personnel was measured with thermoluminescent dosimeters and permanently mounted KermaDose-Area-Product meters in front of the X-ray tubes during 13 cerebral angiographies and six neuroendovascular procedures. We performed experiments with radiation dose measurements and evaluation of image quality with 80 and 90 kV tube voltage during image acquisition and 75 and 85 kV during fluoroscopy, as well as with different primary X-ray filtration.

Images from patient studies acquired with the original grid in front of the image intensifier were compared with images from patient studies acquired with the grid removed and air gap technique (30 cm).

Images from patient studies acquired with the original examination technique were compared to images from patient studies acquired with increased x-ray tube voltage, increased x-ray filtering and with the antiscatter grid removed using an airgap as scatter reduction method.

Radiation exposure to personnel was very low using standard protective devices. Measurable doses were recorded only on the hands and forehead of the neuroradiologist.

Maximum entrance skin dose was about 1 Gy on the side of the patientspatient's forehead during an endovascular procedure.

Increasing the tube voltage from 75 to 85 – 85 and 90 kV, exchanging the original 0.5 mm aluminium primary filtration for 0.2 mm copper and removing the antiscatter grid allowed us to reduce entrance skin dose to the patient by 70% with unchanged or slightly improved image quality.

Negative CT angiography findings in patients with spontaneous subarachnoid hemorrhage: When is digital subtraction angiography still needed?

BACKGROUND AND PURPOSE

CTA is becoming the frontline modality to reveal aneurysms in patients with SAH. However, in about 20% of SAH patients no aneurysm is found. In these cases, intra-arterial DSA is still performed. Our aim was to evaluate whether negative findings on CTA can reliably exclude aneurysms in patients with acute SAH.

MATERIALS AND METHODS

We conducted a retrospective analysis of all negative findings on CTAs performed from 2005 to 2009 in patients with spontaneous SAH. Findings were compared with DSA. CTAs were performed with a 64-section multidetector row CT scanner.

RESULTS

One hundred ninety-three patients with SAH and negative findings on CTA who underwent subsequent DSA were identified. The distribution of blood on unenhanced CT was the following: PMH in 93 patients, diffuse aneurysmal pattern in 50, no blood on CT (xanthochromic LP) in 32, and peripheral sulcal distribution in 18. All patients with PMH had negative findings on DSA. One patient with no blood on CT had vasculitis on DSA. Six of 18 (33%) patients with peripheral blood had vasculitis on DSA. Three of these were also diagnosed by CTA. All except 1 patient with diffuse aneurysmal blood had negative findings on DSA. One patient was diagnosed with an aneurysm on DSA (1/50, 0.5%). Repeat delayed DSA performed in 28 of these patients revealed a small aneurysm in 4 (14%). Five patients had a complication of DSA (2.6%); 1 was a clinical stroke (0.5%).

CONCLUSIONS

In patients with SAH, negative CTA findings are reliable in ruling out aneurysms in the PMH pattern or no blood on CT. DSA is indicated in the diffuse aneurysmal pattern of SAH, and repeat delayed DSA is required if the initial DSA findings are negative. When the blood is peripheral, CTA should be scrutinized for vasculitis and DSA is recommended for confirmation.

Vertebrobasilar Dissection with Pseudo-aneurysm or Subarachnoid Hemorrhage: Intracranial Stenting as the Only Treatment. A Report of Three Cases

SUMMARY

Vertebrobasilar dissection may cause ischaemia or subarachnoid haemorrhage and can pose a significant treatment challenge. Endovascular treatment using stents alone has been described but there are few reports of its clinical application. We here report our experiences from three cases of vertebrobasilar dissection and pseudo-aneurysm or subarachnoid hemorrhage treated with stents alone.

Neurovascular radiosurgery

SUMMARY

This article focuses on the treatment of neurovascular diseases, in particular brain arteriovenous malformations (BAVMs), with radiosurgery. The target group for this review is physicians who manage patients with neurovascular diseases, but are not actively engaged in radiosurgery. Radiosurgery for BAVMs is an established treatment with clearly defined risks and benefits. The efficacy of radiosurgery for dural arteriovenous shunts (DAVSs) is probably similar but the treatment has not yet gained the same acceptance. Radiosurgical treatment of cavernomas (cavernous hemangiomas) remains controversial. Well founded predictive models for BAVM radiosurgery show: * The probability of obliteration depends on the dose of radiation given to the periphery of the BAVM. * The risk of adverse radiation effects depends on the total dose of radiation, i.e. the amount of energy imparted into the tissue. The risk is greater in centrally located lesions. The risk of damage to brainstem nucleii and cranial nerves must be added to the risk predicted from current outcome models. * The risk of hemorrhage during the time span before obliteration depends on the BAVM volume, the dose of radiation to the periphery of the lesion and the age of the patient. Central location is a probably also a risk factor.

Subarachnoid Haemorrhage from a Large Cerebral Aneurysm Visible only on Repeat Angiography

SUMMARY

We report the case of a 49-year-old woman with a massive subarachnoid haemorrhage in conjunction with trauma. The initial cerebral angiography was normal. Three weeks later she had a second subarachnoid haemorrhage. A repeat angiography demonstrated an eight mm aneurysm of the internal carotid artery bifurcation, a region clearly normal in the previous angiography.

Regression of a Flow-Related Ophthalmic Artery Aneurysm After Treatment of a Frontal DAVS. A Case Report

SUMMARY

We report a case of a frontal dural arteriovenous shunt or fistula (DAVS) adjacent to the left side of the cribriform plate, with bilateral supply from multiple arteries, the most prominent being the dural branches originating from the anterior ethmoidal artery coming from the left ophthalmic artery. Before treatment there was an eight mm flow-related arterial aneurysm proximally on the left ophthalmic artery. After transarterial embolization of the DAVS with N-butyl cyanoacrylate and polyvinyl alcohol, minimal shunting still remained. At follow-up angiography six months after the treatment, the shunt was obliterated and the ophthalmic artery aneurysm had regressed completely. Our case illustrates that complete obliteration of a DAVS may be achieved even though arteriovenous shunting remains at the end of the procedure. Furthermore, a flow-related arterial aneurysm, may not warrant any specific treatment. Elimination of the high flow situation can lead to complete regression of these aneurysms.

Gamma knife outcome models as a reference standard in the embolisation of cerebral arteriovenous malformations

BACKGROUND

We sought to utilise outcome models from Gamma Knife radiosurgery (GKRS) to cerebral arteriovenous malformations (AVM) as a reference standard in assessing the clinical outcome of embolisation, thus comparing the outcomes of two different management alternatives, in the same patients.

METHODS

87 consecutive patients with 88 AVM were admitted during 1997-1999 for initial embolisation of an AVM. The clinical outcomes were recorded prospectively. Angiography under stereotactic conditions with measurement of AVM volume was performed before and after embolisation. GKRS outcome models were used to predict obliteration rate, complication rate and risk of haemorrhage before and after embolisation. The clinical outcome of embolisation followed by predicted outcome of adjunct GKRS was then compared with the predicted outcome of GKRS as the only treatment.

FINDINGS

Eight patients were subjected to microcatheterisation but not to embolisation. By the end of the study period, embolisation had been terminated in 55 patients out of 80 (69%). The predicted outcome of GKRS alone was 58 obliterations and 12 complications while that of the combined management was 58 obliterations and 15 complications. The difference was not significant on the p < 0.1 level.

INTERPRETATION

Volume measurement from angiography and outcome models from Gamma Knife radiosurgery are useful as a reference standard in the management of AVM. Absolute volume reduction from embolisation is most prominent for AVM > 10 ml and thus facilitates subsequent radiosurgery. For AVM < or = 10 ml, GKRS as the only treatment can be an alternative to primary embolisation, particularly if no significant volume reduction or obviously beneficial effect of targeted embolisation is expected. Further prospective studies are needed to identify subgroups in which one treatment has advantages over the other.

Risk for hemorrhage during the 2-year latency period following gamma knife radiosurgery for arteriovenous malformations

PURPOSE

Radiosurgery does not immediately obliterate an arteriovenous malformation (AVM), and the risk for hemorrhage still persists until the AVM is occluded. There is controversy about whether this risk is altered after as compared to before radiosurgery. The aim of this paper is to study this topic further and to suggest a model to predict the risk for posttreatment hemorrhage.

METHODS AND MATERIALS

The incidence of hemorrhages within the first 24 months following Gamma Knife radiosurgery was studied retrospectively among 1593 AVM patients, and was related to patient, AVM, and treatment parameters.

RESULTS

Fifty-six patients experienced a hemorrhage in the latency period, representing an average annual incidence of 1.8%. The incidence of posttreatment hemorrhage was related to the patient's age, AVM volume, minimum dose, and average dose delivered to the AVM nidus. Based on these observations, an equation was defined that could quantify the probability for a posttreatment hemorrhage to occur.

CONCLUSION

A model that can predict the probability for a hemorrhage within the first 24 months after radiosurgery is presented. The risk is higher for larger AVMs and for older patients, and it is lower when higher doses of radiation are used.

Cerebral air emboli from angiography in a patient with stroke. A case report

A 42-year-old woman with subarachnoid and intracerebral hemorrhage was investigated with diagnostic angiography, disclosing an occlusion of the left internal carotid artery and the middle cerebral artery. CT examination immediately after the angiography revealed a 12-h-old infarct of the left middle cerebral artery territory. There was also gas in the arteries supplying the infarcted part of the brain, but not in other vessels. Air had most probably been introduced during the angiography and had consequently been "trapped" in the cortical arteries of the ischemic brain. In the non-ischemic parts of the brain air may have passed through the vessels leaving no trace.

Volume measurement of cerebral arteriovenous malformations from angiography

We designed software for measuring the volume of cerebral arteriovenous malformations from angiography and validated it against prescription volumes in radiosurgery. We aimed to create a model for the risk for complications as a function of volume, based on established outcome prediction models for Gamma Knife radiosurgery, but without the need for dose planning. We created an application for computing the volume of cerebral arteriovenous malformations from the intersection of two X-ray cones in stereotactic space. Volume measurements were compared with prescription volumes from dose planning, in phantoms and in patients treated with Gamma Knife radiosurgery for cerebral arteriovenous malformations. Previous studies of 1128 treated patients were used to calculate the risk for complication as a function of the nidus volume. In 63 patients volumes measured with either method correlated, R2 = 0.85. Volume as measured with the intersecting cone model (ICM) correlated with predicted Gamma Knife radiosurgery complication rate, R2 = 0.84. The ICM can thus be used for measurement of AVM volumes less than 10 cm3 from angiography. Outcome models from Gamma Knife radiosurgery may be applied, but with reduced exactness. Standardised AVM volume measurement is valuable for comparing outcome and for quantification of volume reduction after therapy, notably embolisation. Thus the optimal management plan may be selected in conjunction with diagnostic or therapeutic angiography.

Can the probability for obliteration after radiosurgery for arteriovenous malformations be accurately predicted?

PURPOSE

To investigate how accurate different models predict the probability for obliteration following radiosurgery for an arteriovenous malformation (AVM).

METHODS AND MATERIALS

The probability for obliteration was calculated for all 838 AVMs with a known treatment outcome and treated at the Karolinska Hospital with Gamma Knife surgery 1970-1993. Four different models were used for the calculation, resulting in four different values of the probability for obliteration. The calculated prediction values were added for each model, and the total number of predicted obliteration compared to that observed in the whole patient material as well as in different subgroups.

RESULTS

Three of the four models predicted the total number of obliterations accurately. In two of those three models, the accuracy of the prediction was dependent on AVM volume and treatment dose. In one model only, the prediction was accurate and independent of all investigated parameters.

CONCLUSIONS

The probability for obliteration was accurately predicted by one of the models analyzed. In this model, the probability for obliteration was related to the dose to the AVM periphery only. The AVM volume had no independent impact on the probability for obliteration. There was a trend that AVMs with a central location had a better obliteration rate than predicted.

X-ray angiography in stereotactic conditions: techniques and interest for interventional neuroradiology

This paper reports work in progress on X-ray angiography acquired under stereotactic conditions. The objective is to be able to match multimodality images (typically MRI and X-ray) without a stereotactic frame but with stereotactic precision. We have identified potential problems and have studied them in detail. We conclude that, although the overall application is feasible, much work remains to be done on the estimation of the X-ray system conic projection and on automatic matching based on vascular structures.

An algorithm for correction of distortion in stereotaxic digital subtraction angiography

An algorithm for correction of the geometrical distortion in digital subtraction angiography (DSA) images was developed. Originally invented for 3D X-ray angiography, the algorithm was implemented in a computer program designed to fulfil the specific needs of stereotaxic DSA. The algorithm is based on transformation of an image of a grid from a distorted image back into its original pattern. The same transformation is then applied pixel-by-pixel to the angiographic images, which are acquired in direct conjunction with the grid image, without moving the gantry. The algorithm was tested in phantom studies and in the clinical situation with seven patients in ten examinations. Comparisons were made between co-ordinate determinations made on conventional full-size cut film and those performed on uncorrected and corrected DSA images, using 30- and 23-cm fields of view. With our method of measurement we could not shown any remaining geometric distortion in the corrected DSA images. This distortion correction can, if properly applied, be used for high-precision stereotaxic DSA.

Factors influencing the risk for complications following Gamma Knife radiosurgery of cerebral arteriovenous malformations

BACKGROUND AND PURPOSE

We reported previously a model predicting the risk for radiation-induced complications following Gamma Knife radiosurgery for AVM. No factor other than the dose distribution was related to the risk. The aim of this study was to define if other parameters are of importance for the risk of complications.

MATERIAL AND METHODS

The model above was used to calculate the risk for complications in all 1128 AVM patients Gamma Knife-treated at the Karolinska Hospital 1970-1993. The number of predicted complications was compared to the number of observed ones for a number of different parameters.

RESULTS

The model underestimated the risk of complications for patients previously given radiation with multiple or single fractions. Neither age nor gender influenced the risk of complications. Centrally located AVM had a higher, and peripheral a lower incidence of complications as compared to the calculated risk, and a previous hemorrhage reduced the risk of complications. From the observed number of complications, parameters in the model were determined by a fitting procedure separately for three groups of AVM: central and peripheral with and without a previous hemorrhage. It is also shown that the assumption of a serial functional architecture is valid in the model. This was investigated by the use of a relative seriality model with a combined serial-parallel functional architecture.

CONCLUSIONS

The risk of complications following radiosurgical treatment of AVM is dependent on the clinical history, AVM location and whether the patient has received radiation earlier.

Volume Determination of Intracranial Arteriovenous Malformations Prior to Stereotactic Radiosurgical Treatment

Exact dose planning for stereotactic radiosurgery was enabled in connection with diagnostic angiography or at the end of an endovascular procedure by simply placing a stereotactic localizing box onto the head of the patient while acquiring PA and lateral angiographic views.

The fiducials engraved on the localizing box enabled the appropriate images to be scaled to the stereotactic space. Regular dose planning was then performed after estimating the size of the patient's head. A prediction of the chances of obliteration and the risks of complication could then be made immediately after the endovascular or diagnostic procedure, and further therapy could be selected much more confidently.

This technique may also be used at centres without facilities for radiosurgical treatment if only the localizing box is available. The images may then be sent for evaluation to a unit with dose planning equipment.

The technique is simple and involves little risk, significantly improving patient management. Digital subtraction angiography was used in this study. A correction algorithm was used to minimize the geometric distortion inherent to the digital technique.

Gamma knife radiosurgery in 11 hemangioblastomas

One suprasellar, one mesencephalic, and nine cerebellar hemangioblastomas were treated with the gamma knife in 10 patients (median age 48 years) in Stockholm between 1978 and 1993. Four patients had von Hippel-Lindau disease, a dominant inherited trait predisposing to multiple hemangioblastomas. Six hemangioblastomas were treated with radiotherapy at a median margin dose of 25 Gy (20-35 Gy) before 1990 and the next five with a median of 10 Gy (5-19 Gy). Computerized tomography or magnetic resonance images were available for 10 of the 11 hemangioblastomas at a median follow-up time of 26 months (4-68 months) after radiosurgery. The solid part of six hemangioblastomas shrank in a median of 30 months, whereas four hemangioblastomas were unchanged at a median of 14 months. Five hemangioblastomas had an adjoining cyst and three of these cysts had to be evacuated after radiosurgery. One solitary hemangioblastoma later developed a de novo cyst that also needed evacuation. One patient with two cerebellar hemangioblastomas (margin dose 25 Gy each) developed edema at 6 months and required a shunt and prolonged corticosteroid treatment. The combined follow-up data of the 23 hemangioblastomas in 15 patients from previous literature and the present series indicate that, first, a solitary small- or medium-sized hemangioblastoma usually shrinks or stops growing after radiosurgery. The recommended margin dose is 10 to 15 Gy. Second, the adjoining cyst often does not respond to radiosurgery but requires later, sometimes repeated evacuation.

Prediction of results following Gamma Knife surgery for brain stem and other centrally located arteriovenous malformations: relation to natural course

Two models for predicting the results of Gamma Knife surgery for brain stem and other centrally located arteriovenous malformations (AVMs) are presented. By using these models, the probability of total obliteration and the risk of complications can be predicted. The model to predict the probability for obliteration is based on the following two observations. First, there is a positive relationship between the minimum dose given to the AVM nidus and the incidence of obliteration. Second, there is a negative relationship between the AVM nidus volume and the minimum dose given in the obliterated cases. The risk estimation model is also based on two observations. First, centrally located AVMs carry a higher risk of complications than those located peripherally. Second, the average dose to volumes which are large for radiosurgery is related to the incidence of complications. The findings of this study may be used to estimate the consequences of Gamma Knife treatment for every individual case prior to the treatment. This makes a comparison between different treatment options and no treatment possible. The risk of hemorrhage without any treatment is also quantified.

Clinical experience with stereotactic digital subtraction angiography with distortion correction software

Recently developed software for correction of the geometric distortion in digital subtraction angiography was tested clinically. Localization and subsequent radiosurgical treatment of intracranial arteriovenous malformations was undertaken in 60 patients. During each angiographic series, a series of grid images was also acquired. All images were transferred to a workstation where the grid images were compared to a previously stored ideal image of the grid. A distortion correction was then performed on the grid images. The same pixel-by-pixel correction was applied to the respective angiographic images. The target was outlined on corrected subtracted images on the monitor. The outlined regions of interest and reference points were transferred to another workstation for dose planning, and the treatment was subsequently executed in the Gamma Knife unit. The clinical applicability of the distortion correction program was tested and possible sources of error examined. The experience gained is being used for further development of the software and for smoother data management and reduction of the processing time.

Multiple intracranial arteriovenous malformations: a case report

Multiple intracranial arteriovenous malformations are rare. There are a few cases in the literature with up to three malformations in one patient. A child with seven separate cerebral malformations is now described. There was no history of haemorrhage, but only of febrile seizures. The malformations were discovered at CT and verified at angiography. Six were selected for stereotaxic irradiation with the multi-cobalt unit. The seventh was considered too big for irradiation and suitable for surgery.

Target delineation in radiosurgery for cerebral arteriovenous malformations. Assessment of the value of stereotaxic MR imaging and MR angiography

A study of 6 selected arteriovenous malformation (AVM) patients was performed to investigate the feasibility of delineating an AVM on MR images and to compare the AVM volume outlined on different images. Conventional stereotaxic angiograms, stereotaxic MR images and MR angiograms using several different pulse sequences were obtained prior to radiosurgery. Treatment plans were made from the conventional stereotaxic angiograms. These plans were then transferred to a separate dose planning computer which displayed the MR images with the superimposed isodose lines. The radiated volumes of AVM and brain tissue were measured from these MR images. Last, an assessment was made of the radiation volume needed for an appropriate treatment of the AVM if the treatment plan was made from the MR images rather than from the conventional stereotaxic angiogram. It was possible to delineate medium and large size AVM nidi on stereotaxic MR images based on an integration of information obtained from various pulse sequences. The estimated volumes of the AVM nidi were found to be larger on the conventional stereotaxic angiograms than on the stereotaxic MR images. Consequently, a dose plan based on a conventional stereotaxic angiogram would result in a higher integral dose to the brain with the same target dose. By using reliable MR information it is expected that the volume of brain exposed to radiation could be decreased and the adverse effects of stereotactic radiosurgery for AVM thereby minimized.