RECENT TRENDS IN MANAGEMENT OF CEREBRAL ARTERIOVENOUS MALFORMATIONS

Abstract

The intracranial arteriovenous malformations (AVMs) represent abnormalities of vascular development with tangles of tortuous abnormal arteries and veins that permit single or multiple direct connections and high-flow shunting between them without intervening capillary beds. These AVMs look like a ball of worms that contains conspicuous gliotic nonfunctional neural tissue and vascular or interstitial calcification. The aetiology of intracranial arteriovenous malformations remains unknown, but recent studies suggested a role for genetic factors in both susceptibility and disease progression. Nevertheless, sporadic AVMs are supposed to be most likely determined by the interaction between genetic and environmental factors, and are capable of expanding by angiogenesis and rupture. The prevalence of AVMs varies between 10 and 18 per 100,000 adults, with an annual incidence of 1.1 to 1.3 AVMs per 100,000 person-years. They are responsible for 2% of all hemorrhagic strokes and usually present before the age of 40 years, affecting men and women equally. The most common presenting symptom of AVMs is hemorrhage, ranging from 42% to 72%. Other symptoms include seizures (focal or generalized), headache, progressive neurological deficit, and pulsatile tinnitus. The annual risk of hemorrhage ranges from 1.3% to 4% per year, with an increase up to 6% to 7% in the first year after the previous hemorrhage. The morbidity resulting from hemorrhage ranges from 53% to 81%, whereas mortality ranges from 10% to 30%, although some data suggest that the mortality rate may be lower. Associated arteriovenous fistulas and prenidal, intranidal, or flow-related aneurysms have demonstrated to increase the risk of rupture of AVMs as well as small AVM size, feeding artery pressures, lesions located in a periventricular or intraventricular locations, presence of deep venous drainage, intranidal or multiple aneurysms, arterial supply via perforators, vertebrobasilar supply, and basal ganglia location. Overall, deep-seated lesions have demonstrated to have an early clinical onset, higher bleeding rates, and increased morbidity and mortality (50%) rather than superficial lesions. Since there are no reliable data regarding the natural history of AVMs and presumably ruptured brain AVMs have a higher hemorrhagic risk (4.5%–34%) than previously unruptured ones (0.9%–8%), interventional treatment of ruptured brain AVMs is advisable. Three dimensional computerized tomography angiography (3D-CTA) imaging provided excellent visualization of intracranial AVMs. The details of arterial supply (numerical measure, orientation, caliber and routing) and vascular nidus (size, morphosis and location) provided by 3D-CTA images were the same as Digital subtraction angiography (DSA) and the details of venous drainage were an approximate match. Additionally, 3D-CTA can depict tridimensional anatomical information for AVMs and their relationship to adjacent structures, a function not possible with DSA. This assisted the surgeons in making better surgical planning and reduced trauma. As a non-invasive course, there are no related-complications in the course of 3D-CTA processing. Magnetic resonance digital subtraction angiography (MR DSA) however, can show the hemodynamics of AVMs and may serve as a supplement to conventional MR imaging in the diagnosis of cerebral AVMs. Conventional intra-arterial digital subtraction angiography (DSA) used to be regarded as the gold standard for diagnosis of intracranial arteriovenous malformations. it is strongly recommended that an MRI study and a 4-vessel angiogram be obtained to delineate the anatomy of an AVM. Recently intracranial 4D Flow MRI for assessment of Arteriovenous Malformation Hemodynamics and Treatment-Induced Changes has been established. The treatment of cerebral AVMs requires a multidisciplinary approach that includes microsurgery, endovascular embolization, and stereotactic radiosurgery (SRS). Surgical resection remains the gold standard for the radical and definitive eradication of most of these lesions. Endovascular embolization and SRS are increasingly used for the management of nonsurgical AVMs. For small lesions that are usually deep and/or in eloquent locations, SRS represents a safe and efficacious primary treatment option. If the AVM has bled, targeted endovascular embolization of the AVM is recommended in selected cases because it may decrease the risk of hemorrhage and eradicate radioresistant spots of the lesion during the latency period following SRS . Spetzler-Martin AVM grading system The Spetzler and Martin classification was established to grade AVMs according to their degree of surgical difficulty and the risk of surgical morbidity and mortality. Lesions are typically excised by standard microsurgical techniques with the operating microscope. The arterial feeders are generally attacked first, followed by excision of the nidus of the lesion and finally resection of the draining vein. Recently Intraoperative functional MRI (fMRI) is technically feasible allowing a real-time identification of eloquent brain areas despite brain shift. Awake craniotomy intraoperative functional MRI (ai-fMRI) for the localization of sensorimotor areas in awake patients confirmed that ai-fMRI is feasible and reliable in identifying functional areas during awake craniotomy. Intraoperative three-dimensional ultrasound and navigation, provides a mean to adapt resection strategies, define dissection planes, and interpret intraoperative findings. It added confidence and the improved mental image of the lesion that improved the quality and flow of surgery.

Endovascular Embolization is an invasive technique, The most commonly used embolic agent is Ethylene vinyl alcohol co-polymer (Onyx) which is less adhesive, more slowly polymerizing and accordingly much more advantageous than n-butyl Cyanoacrylate n-BCA as the The use of rapidly polymerizing liquid adhesive (n-BCA) for brain AVMs requires experience and skill, Since the intra-nidal flow and polymerization of n-BCA are both quick and largely unpredictable.