Hypofractionated stereotactic radiotherapy in Spetzler Martin grades 4 and 5 arteriovenous malformations in the pediatric population: Is it a viable alternative?

OBJECTIVE: To analyze the outcomes of hypofractionated stereotactic radiotherapy (HFSRT) for Spetzler Martin grades 4 and 5 arteriovenous malformations (AVMs) in a pediatric population. METHODS: Fourteen patients with Spetzler Martin (SM) grades IV and V large AVMs who underwent HFSRT between January 2013 and July 2019 were retrospectively reviewed. All patients received HFSRT at a dose of 30-36 Gy in 5 to 6 fractions. They were followed up annually with clinical and imaging assessments to evaluate obliteration rates. RESULTS: The median age at presentation was 15 years (range 8-21 years). Ten (71%) were SM grade 4 AVMs and the rest were SM grade 5 AVMs. The majority presented with headache (8 [57%]), and 3 (21%) presented with bleeding. The median nidus volume was 39.4 cc (IQR, 31.4-52.4). Two (14%) patients had infratentorial AVMs. All of them had deep venous drainage. The median clinical follow-up duration was 75 months (range 31-107 months). There was complete obliteration of the nidus in 3 (21%) patients with a median time to obliteration of 39 months. HFSRT resulted in a reduction of the AVM volume to 12 cc or less in nearly 70% of patients. None of the patients experienced re-bleeding. 79% reported an improvement in their symptoms. CONCLUSION: HFSRT is a highly effective treatment for high-grade AVMs in children, which can result in either complete elimination or significant reduction of the nidus volume or make it suitable for additional treatment, such as single-session stereotactic radiosurgery (SRS).

Comprehensive neurosurgical treatment of right occipital arteriovenous malformation with advanced angiographic techniques.

/Summary. A 39-year-old female with a notable medical history of smoking and a familial predisposition to unruptured aneurysms presented with clinical symptoms of intermittent right-sided headaches, flashes of light, and pulsatile tinnitus in the right ear. Diagnostic evaluations, including advanced angiographic techniques, identified a right occipital arteriovenous malformation (AVM). The angiogram revealed significant venous flow voids, emphasizing the need for a comprehensive treatment approach. The Spetzler-Martin grading system classified the AVM as Grade 2, indicating a moderate risk profile. A strategic decision was made to undergo partial embolization of two primary arterial feeders from the right posterior cerebral artery (PCA). Subsequent post-embolization angiograms confirmed a marked reduction in arteriovenous shunting, validating the efficacy of the intervention. The surgical approach encompassed an occipital craniotomy, meticulous subarachnoid dissection, and intraoperative angiography to ensure complete resection. Post-operative assessments showcased a successful and complete AVM resection. The patient experienced a brief, transient headache post-surgery, which resolved on its own. She was discharged on the third post-operative day and has since reintegrated into her professional life. However, she reported a minor visual field deficit, which, while noticeable, did not impede her daily activities. This case underscores the importance of a holistic, patient-centric approach in managing AVMs [1-3]. It challenges the conventional wisdom from the ARUBA trial, advocating for a more nuanced, individualized treatment paradigm, especially for young patients with low-grade AVMs [4].

Stereotactic radiosurgery outcome for deep-seated cerebral arteriovenous malformations in the brainstem and thalamus/basal ganglia: systematic review and meta-analysis.

Deep-seated unruptured AVMs located in the thalamus, basal ganglia, or brainstem have a higher risk of hemorrhage compared to superficial AVMs and surgical resection is more challenging. Our systematic review and meta-analysis provide a comprehensive summary of the stereotactic radiosurgery (SRS) outcomes for deep-seated AVMs. This study follows the guidelines set forth by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) Statement. We conducted a systematic search in December 2022 for all reports of deep-seated arteriovenous malformations treated with SRS. Thirty-four studies (2508 patients) were included. The mean obliteration rate in brainstem AVM was 67% (95% CI: 0.60-0.73), with significant inter-study heterogeneity (tau2 = 0.0113, I2 = 67%, chi2 = 55.33, df = 16, p-value < 0.01). The mean obliteration rate in basal ganglia/thalamus AVM was 65% (95% CI: 0.58-0.72) with significant inter-study heterogeneity (tau2 = 0.0150, I2 = 78%, chi2 = 81.79, df = 15, p-value < 0.01). The presence of deep draining veins (p-value: 0.02) and marginal radiation dose (p-value: 0.04) were positively correlated with obliteration rate in brainstem AVMs. The mean incidence of hemorrhage after treatment was 7% for the brainstem and 9% for basal ganglia/thalamus AVMs (95% CI: 0.05-0.09 and 95% CI: 0.05-0.12, respectively). The meta-regression analysis demonstrated a significant positive correlation (p-value < 0.001) between post-operative hemorrhagic events and several factors, including ruptured lesion, previous surgery, and Ponce C classification in basal ganglia/thalamus AVMs. The present study found that radiosurgery appears to be a safe and effective modality in treating brainstem, thalamus, and basal ganglia AVMs, as evidenced by satisfactory rates of lesion obliteration and post-surgical hemorrhage.

Migration of lipiodol into lateral ventricles after embolization of cerebral arteriovenous malformation: a case report.

N-butyl cyanoacrylate (NBCA) has been used to embolise brain arteriovenous malformations (AVMs) for over 30 years. It is a mixed with lipiodol in varying proportions. We report a 22-year-old male with intraventricular hemorrhage from a ruptured intranidal AVM aneurysm in the left temporal lobe. The intranidal aneurysm and the nidus were successfully embolized using a 20% NBCA and lipiodol mixture without any complications according to computed tomography (CT) immediately after treatment. Scattered high-density spots were observed in both lateral ventricles on CT 5 days after embolization, suggesting migration of lipiodol. We speculated that the aneurysm was a pseudoaneurysm whose wall protruded into the inferior horn of the left lateral ventricle, and the lipiodol in the NBCA migrated into the ventricles after the thin part of the wall ruptured. The patient developed pyrexia due to chemical meningitis, which responded to steroid treatment for one month.

De novo brain AVM following radiotherapy for cerebral cavernous malformation in a child: A 15-year clinical course.

Multiple de novo brain arteriovenous malformations (bAVM) have been reported in the literature, raising questions about the contended purely congenital nature of these lesions. We present the 15-year course of a pediatric patient, who initially presented at age 5 with a thalamic cavernous malformation and was treated with radiosurgery, and then subsequently developed a thalamic de novo bAVM immediately adjacent to the initial lesion location, discovered 2 years later. Treatment of the bAVM entailed two transarterial embolizations and one radiosurgery session which ultimately led to complete angiographic resolution. Finally, this patient's course was complicated by intraparenchymal hemorrhage and acute obstructive hydrocephalus, and further imaging revealed two newly formed cavernous malformations, also associated with the initial lesion's location, that have remained stable since their formation. This case likely represents the second-hit model for the formation of vascular malformations, as sparsely supported by the current literature. According to this, genetically aberrant, yet quiescent, brain areas might promote the de novo formation of vascular malformations after brain injury, including radiation.

The Thalamic Arteriovenous Malformations Have Better Prognosis than Basal Ganglia Malformations Regarding Obliteration: Prognostic Factors Analysis.

BACKGROUND: Arteriovenous malformations (AVMs) are rare vascular congenital lesions that affect mainly patients during their productive years of life. In order to obtain a better quality of life for patients with this disease, a multidisciplinary approach is recommended. Radiosurgery is one of the treatment modalities available for AVMs, but many factors may influence the effectiveness of this strategy. Classically, it has been said that deep-seated lesions have a particular behavior compared with AVMs in other regions, but a differentiation between thalamic lesions and those located in the basal ganglia has not been made. METHODS: Institutional records for central core AVMs treated with radiosurgery between January 2004 and January 2014 were retrospectively analyzed. Brainstem lesions were excluded from the analysis. RESULTS: Forty-nine patients with deep-seated AVMs were included. Forty-three (87.8%) were located in the thalamus and 6 (12.2%) in the area of basal ganglia. The nidus mean volume was 4.1 cm3 (SD: 4.1), the maximum diameter mean was of 19.5 mm (SD: 8.0). The prescription dose was 18.2 Gy (SD: 2.1), and the follow-up time was 75.8 months (SD: 32.5). There was a greater obliteration rate in thalamic AVMs compared with those located in the basal ganglia: 81.4% versus 33.3% (P = 0.026), respectively. There was no association between categorical variables and obliteration rate. CONCLUSIONS: Stereotactic radiosurgery is a good option for patients with thalamic and basal ganglia AVMs, but a multidisciplinary approach to decision-making is mandatory in order to achieve the best results.

Hyperbaric oxygen therapy in the treatment of malign edema complication after arteriovenous malformation radiosurgery.

A 16-year-old female patient with headache was admitted to our hospital. Radiological examination showed a Spetzler-Martin Grade III arteriovenous malformation (AVM) located at the left frontal lobe. Volume-staged stereotactic radiosurgery (SRS) treatment performed in two fractions at three-month intervals and post-procedural period were uneventful. Eight months later the patient was admitted to our hospital with headache, vomiting, right-sided facial palsy and right upper extremity paresthesia. Radiological examination demonstrated severe vasogenic edema in the left centrum semiovale and temporal region. Due to severe and steroid-resistant malign edema, hyperbaric oxygen (HBO2) therapy was performed as an alternative treatment option. Neurological symptoms resolved completely after HBO2. Radiological examination demonstrated serious improvement of brain edema and mass effect.

Thalamus Cavernous Malformation Resection of via Contralateral Anterior Interhemispheric Transcallosal Approach: Two-Dimensional Operative Video.

Thalamic cavernous malformations (CM) are highly challenging surgically. In this illustrative video (Video 1), we present the case of a 36-year-old man with a CM at the left medial thalamus, which was successfully treated by a contralateral anterior interhemispheric transcallosal approach. Informed consent was obtained from the patient. Preoperative imaging demonstrated that the CM appeared to have reached the pial surface superiorly and medially, and diffusion tensor imaging showed the pyramidal tracts to be traveling laterally to the CM. Based on the "Two-point" principle and to avoid pyramidal tract impingement, an anterior interhemispheric transcallosal approach was chosen. Furthermore, to avoid excessive retraction on the ipsilateral hemisphere, we selected the contralateral trajectory over the ipsilateral trajectory. The head was positioned with the right side down; thus, the space between the right hemisphere and the falx could expand because of gravity autoretraction, which could minimize the need of retraction during the interhemispheric dissection. A small incision on the corpus callosum was performed under the guidance of neuronavigation, and the left ventricle was subsequently entered. After a thin layer of hemosiderin-stained pia was opened on the superior surface of the left thalamus, some sandlike old hemorrhagic component was removed for decompression, and the lesion was carefully dissected away from the normal parenchyma within the surrounding gliosis boundary. The CM was removed en bloc, and the deep venous anomaly was well protected. The patient did not experience any intraoperative changes shown by electrophysiologic monitoring, and he recovered well postoperatively.

Left Thalamus Arteriovenous Malformation Secondary to Radiation Therapy of Original Vermian Arteriovenous Malformation: Case Report.

A 70-year-old gentleman with history of hypothyroidism, hyperlipidemia, hypertension, and right superior cerebellar aneurysm presented to the neurosurgery service in 2008 with vertigo. Diagnostic cerebral angiography performed that year demonstrated a vermian arteriovenous malformations (AVM). The patient underwent stereotactic proton beam radiosurgery, which resulted in a decrease in flow and size of the lesion, and the patient was lost to follow-up. Now at the age of 80, the patient presented with acute gait instability. Cerebral angiogram demonstrated his stable vermian AVM and a new 1.1 cm AVM nidus in the region of the left posterior thalamus. Although AVMs are often described as congenital lesions, there is a growing body of literature suggesting that AVMs can grow, spontaneously regress, and even arise de novo in response to some insult. Understanding what leads to the growth, remodeling, regression, and hemorrhage of AVMs is crucial in order to better direct therapeutic endeavors. We would argue that this patient's AVM is secondary to endothelial cell damage from radiation therapy. Radiation can cause endothelial cell injury and upregulation of factors, such as vascular endothelial growth factor and transforming growth factor beta expression, which are implicated in AVM development pathways. We believe that this patient's new AVM is secondary to entrance radiation dosing affecting the thalamus during radiation therapy for the original vermian AVM.

Transvenous embolization of thalamic arteriovenous malformation under transient cardiac standstill.

Transvenous embolization (TE) has been increasingly applied for arteriovenous malformation (AVM) treatment. Transient cardiac standstill (TCS) has been described in cerebrovascular surgery but is uncommon for endovascular embolization. The authors present a patient with a ruptured thalamic AVM in whom both techniques were applied simultaneously. Surgery was considered, but the patient refused. Transarterial embolization was performed with an incomplete result. The deep-seated draining vein provided sole access to the AVM. A microcatheter was advanced into the draining vein. Under TCS, achieved with rapid ventricular pacing, complete AVM embolization was obtained. One-year magnetic resonance imaging and cerebral angiography demonstrated no residual AVM.The video can be found here: https://youtu.be/CAzb9md_xBU.

Stereotactic radiosurgery for arteriovenous malformations of the basal ganglia and thalamus: an international multicenter study.

OBJECTIVE: Arteriovenous malformations (AVMs) of the basal ganglia (BG) and thalamus are associated with elevated risks of both hemorrhage if left untreated and neurological morbidity after resection. Therefore, stereotactic radiosurgery (SRS) has become a mainstay in the management of these lesions, although its safety and efficacy remain incompletely understood. The aim of this retrospective multicenter cohort study was to evaluate the outcomes of SRS for BG and thalamic AVMs and determine predictors of successful endpoints and adverse radiation effects. METHODS: The authors retrospectively reviewed data on patients with BG or thalamic AVMs who had undergone SRS at eight institutions participating in the International Gamma Knife Research Foundation (IGKRF) from 1987 to 2014. Favorable outcome was defined as AVM obliteration, no post-SRS hemorrhage, and no permanently symptomatic radiation-induced changes (RICs). Multivariable models were developed to identify independent predictors of outcome. RESULTS: The study cohort comprised 363 patients with BG or thalamic AVMs. The mean AVM volume and SRS margin dose were 3.8 cm3 and 20.7 Gy, respectively. The mean follow-up duration was 86.5 months. Favorable outcome was achieved in 58.5% of patients, including obliteration in 64.8%, with rates of post-SRS hemorrhage and permanent RIC in 11.3% and 5.6% of patients, respectively. Independent predictors of favorable outcome were no prior AVM embolization (p = 0.011), a higher margin dose (p = 0.008), and fewer isocenters (p = 0.044). CONCLUSIONS: SRS is the preferred intervention for the majority of BG and thalamic AVMs. Patients with morphologically compact AVMs that have not been previously embolized are more likely to have a favorable outcome, which may be related to the use of a higher margin dose.

Intracranial stereotactic radiosurgery.

Stereotactic radiosurgery (SRS) is the use of a single high dose of radiation, stereotactically directed to an intracranial region of interest, in order to create a lesion or obliterate a preexisting one. This technology has evolved over the years into the use of multiple radiation sources oriented at a variety of angles, thus permitting the creation of various treatment target shapes. This allows for non-open surgical treatment of intracranial pathologies, which significantly decreases the risk of morbidity. The destruction of pathological tissue following radiosurgery is a stepwise process that involves a number of different stages, beginning with the necrotic stage, followed by the resorption stage, and concluding with the glial scar formation stage. There are currently a number of different delivery methods of SRS, including linear accelerators, Gamma Knife units, and charged particle methods (Bragg-peak and plateau-beam). Various intracranial lesions exhibit different responses to radiosurgery; however, most lesions of appropriate size tend to respond favorably. Radiosurgery is used today in the treatment of brain metastases, meningiomas, vestibular schwannomas, sellar and suprasellar lesions, and arteriovenous malformations. SRS is widely used to treat functional conditions, such as trigeminal neuralgia and intractable tremor. The treatment of intracranial lesions with radiosurgery can result in undesirable effects on the adjacent normal brain, resulting in adverse radiation effects. The distinction between tumor progression and adverse radiation effects can be challenging but is aided by various imaging modalities. Treatment options for this condition include observation, corticosteroids, pentoxifylline and vitamin E, bevacizumab, laser-interstitial thermal therapy, and surgical resection.

Multimodal management of arteriovenous malformations of the basal ganglia and thalamus: factors affecting obliteration and outcome.

OBJECTIVE: Arteriovenous malformations (AVMs) of the basal ganglia and thalamus are particularly difficult lesions to treat, accounting for 3%-13% of all AVMs in surgical series and 23%-44% of malformations in radiosurgery series. The goal of this study was to report the results of multimodal management of basal ganglia and thalamic AVMs and investigate the factors that influence radiographic cure and good clinical outcomes. METHODS: This study was a retrospective analysis of a prospectively maintained database of all patients treated at the authors' institution. Clinical, radiological, follow-up, and outcome data were analyzed. Univariate and multivariate analyses were conducted to explore the influence of various factors on outcome. RESULTS: The results and data analysis pertaining to 123 patients treated over 32 years are presented. In this cohort, radiographic cure was achieved in 50.9% of the patients. Seventy-five percent of patients had good clinical outcomes (stable or improved performance scores), whereas 25% worsened after treatment. Inclusion of surgery and radiosurgery independently predicted obliteration, whereas nidus diameter and volume predicted clinical outcomes. Nidus volume/diameter and inclusion of surgery predicted the optimal outcome, i.e., good clinical outcomes with lesion obliteration. CONCLUSIONS: Good outcomes are possible with multimodal treatment in these complex patients. Increasing size and, by extension, higher Spetzler-Martin grade are associated with worse outcomes. Inclusion of multiple modalities of treatment as indicated could improve the chances of radiographic cure and good outcomes.

Recurring Thalamic Symptoms Due to Intracranial Dural Arteriovenous Fistula: Report of Unusual Case and Treatment Outcome.

BACKGROUND: Initial clinical presentation of dural arteriovenous fistula (DAVF) with predominantly thalamic symptoms is rare and has not been reported until now. CASE DESCRIPTION: A young child presenting with complaints of tinnitus and mild right hemiparesis was evaluated with an initial magnetic resonance imaging, which revealed a Borden type 2 DAVF in the right transverse sinus with retrograde venous drainage and cortical venous reflux. Flow-related small aneurysms were also noted in the left basal vein of Rosenthal (BVR). Two days later, his motor power deteriorated and he developed right hemisensory loss and severe thalamic pain. Aphasia was atypical and mimicked the transcortical type. Repeat imaging revealed expanding thrombosed aneurysm of BVR with mass effect and edema on thalamocapsular region. Initial antiedema measures reversed the neurologic deficits; however, they recurred, necessitating an urgent endovascular intervention. Angiogram revealed an extensive high-flow DAVF in the right transverse-sigmoid sinus and torcula with preferential retrograde venous drainage into deep veins and left BVR. He underwent staged embolization of DAVF, resulting in significant obliteration of shunt. Neurologic deficits improved in the postoperative period, and the patient remained clinically asymptomatic at 6 months of follow-up. CONCLUSIONS: DAVF presenting with recurrent predominantly thalamic symptoms is rare. Atypical transcortical aphasia rather than fluent aphasia is an unusual clinical manifestation of thalamic pathology and could result from the involvement of specific thalamic nuclei. Preferential high flow into BVR in the presence of venous anomalies could potentially induce architectural weakness of the venous wall and precipitate aneurysm formation. Embolization of the DAVF can potentially reverse this unusual neurologic condition.

Transarterial Balloon-Assisted Glue Embolization of Pial Arteriovenous Fistulas.

OBJECTIVE: Endovascular disconnection of pial arteriovenous fistulas (AVFs) is challenging. The aim of this study was to evaluate safety and effectiveness of transarterial balloon-assisted glue embolization for treating pial AVFs. METHODS: We retrospectively reviewed medical and imaging records of 8 patients with high-flow pial AVFs treated by transarterial balloon-assisted glue embolization from August 2011 to July 2017. RESULTS: There were 6 male patients and 2 female patients with age range of 1-48 years. Presentation was seizure in 4 patients, headache in 3 patients, and subarachnoid hemorrhage in 1 patient. Seven lesions were located in the supratentorial region. All lesions were single-channel fistulas associated with venous varix. Five lesions had a single feeder, and 3 had multiple feeders. All lesions were obliterated completely in single-session embolization with no procedure-related complications. Two patients experienced symptomatic thrombosis of drainage venous system after embolization. One patient fully recovered on discharge, and another patient fully recovered after 8 months. With a mean clinical follow-up of 12.1 months, all patients were free of pretreatment symptoms. Follow-up angiograms revealed durable occlusion of fistulas. CONCLUSIONS: Transarterial balloon-assisted glue embolization is a feasible and effective option for treatment of high-flow pial AVFs.

Evaluation of a novel liquid embolic agent (precipitating hydrophobic injectable liquid (PHIL)) in an animal endovascular embolization model.

BACKGROUND: The choice of the embolic agent and the embolization technique can have a significant impact on the success of endovascular embolization. OBJECTIVE: To evaluate a novel iodinated copolymer-based liquid embolic agent (precipitating hydrophobic injectable liquid (PHIL)) in the porcine rete mirabile (RM), serving as an endovascular embolization model. Onyx, as an established liquid embolic agent, served as comparator. MATERIALS AND METHODS: Sixteen embolization procedures were performed using PHIL (n=8) or Onyx (n=8) as liquid embolic agent. Waiting time between injections was set to 30 or 60 s (n=4 per study group). Survival time after intervention was 2 hours or 7 days. Embolization characteristics (eg, procedure times, number of injections and volume of embolic agent) and embolization extent (percentage of embolized RM in post-interventional x-ray) were assessed. Post-interventional CT and histopathological analyses were performed. RESULTS: Embolization characteristics and embolization extent were not significantly different for PHIL and Onyx, including subgroups (eg, embolization extent 44% vs 69% (medians); p=0.101). For PHIL, extension of the waiting time from 30 to 60 s led to a significantly higher embolization extent (24% vs 72% (medians); p=0.035). Moderate disintegration and mild inflammation of the embolized blood vessels were present for both embolic agents. CONCLUSION: PHIL is feasible for transarterial embolization in an acute and subacute endovascular embolization model. In this preliminary experimental in vivo study, embolization characteristics, embolization extent, and biocompatibility seem to be similar to those of Onyx.

A systematic characterization of the factors influencing polymerization and dynamic behavior of n-butyl cyanoacrylate.

INTRODUCTION: Brain arteriovenous malformations are abnormal connections between arteries and veins without an intervening capillary bed. Endovascular glue embolization with N-butyl cyanoacrylate (NBCA) is an accepted form of treatment. The reported complication rates vary widely from 2% to 15%, and timing of polymerization appears to play a major role. Additionally, the interaction between NBCA and vessel surface as well as the presence of biological catalysts are poorly understood. METHODS: Polymerization time was measured for mixtures of Lipiodol/NBCA of 50/50, 70/30, and 60/40. The influence of pH, temperature, and the presence of biological catalysts on polymerization time was investigated. Contact angles were measured on polyvinyl alcohol cryogel (PVA-C), silicone, and endothelial surfaces in a submerged aqueous environment to assess physical surface interactions. High speed video analysis of glue injection through a microcatheter was performed to characterize simulated coaxial flow. RESULTS: NBCA polymerization rate increased with pH and temperature. A hydrophilic surface such as PVA-C was better than silicone at mimicking the physical properties of endothelium. Live endothelium provided a catalytic surface that at least doubled the rate of polymerization. Blood products further increased the polymerization rate in the following order (slowest to fastest): plasma, platelets, red blood cells (RBCs), and lysed RBCs. These factors could explain the discrepancy between in vitro and in vivo results reported in the current literature. High speed video analysis of NBCA injection showed dripping to jetting transition with significant wall effect which deviated from previous ideal assumptions. CONCLUSIONS: The determinants of NBCA polymerization rate are multifactorial and dependent mainly on the presence of biological catalysts coupled with flow related wall interaction.

Bilateral Thalamic Edema from Coexisting Choroid Plexus Arteriovenous Malformation and Sinus Thrombosis: Case Report.

Bilateral thalamic dysfunction secondary to venous congestion may result from either venous sinus thrombosis or high flow arteriovenous malformations or a combination of both. We present a case of bilateral thalamic edema resulting from concomitant choroid plexus arteriovenous malformation (AVM) and straight sinus thrombosis and describe our treatment approach. The patient presented with several weeks of progressive confusion and memory deficits. Magnetic resonance imaging and venography (MRI/ MRV) showed bilateral thalamic T2 hyperintensities and straight sinus thrombosis. Subsequent cerebral angiography revealed a choroid plexus AVM within the right lateral ventricle. The patient underwent surgical resection of the AVM resulting in postoperative resolution of bilateral thalamic edema on MRI and improvement of his confusion and memory deficits. This case demonstrates a rare example of reversible bilateral thalamic edema secondary to venous hypertension from both an AVM and sinus occlusion after appropriate treatment of the AVM.

Delayed symptomatic haemorrhage from the remnants of a thalamic arteriovenous malformation after previous angiographic cure with radiotherapy.

In 1995 a 16-year old girl was diagnosed with a large left thalamic AVM that was considered unsuitable for microsurgical resection and was treated with radiotherapy twice, which led to angiographic cure. She re-presented 19 years after initial treatment with a symptomatic acute thalamic haemorrhage. Her digital subtraction angiography was negative for arterio-venous shunting. MRI/MRA showed cystic change with adjacent contrast enhancement in the region of the previously irradiated arteriovenous malformation. The patient underwent an interhemispheric transcallosal resection of the left thalamic haemorrhagic lesion via a contralateral craniotomy. Intra-operatively there was a cystic cavity filled with blood products in association with thrombosed, calcified vessels as well as actively filling vessels. Histologically there were aggregated abnormal blood vessels with a dilated lumen and surrounded by brain parenchyma. Some of the vessel walls were thickened with fibrosis and some were arterialised with presence of elastin fibres. Potential mechanisms for the delayed haemorrhage are discussed.