Surgical and Endovascular Management of Acutely Ruptured Arteriovenous Malformations

Introduction

A brain arteriovenous malformation (AVM) is a tangle of dysplastic blood vessels characterized by abnormal connections between arteries and veins. Dilated arteries and a nidus drained by arterialized veins without intervening capillaries form a high-flow, low-resistance shunt between the arterial and venous systems. High flow through the feeding arteries, nidus, and draining veins may lead to rupture and intracerebral hemorrhage. AVMs are a leading cause of intracerebral hemorrhage in young adults. Patients with AVM rupture and intracerebral hemorrhage may have better outcomes than patients with intracerebral hemorrhage from other causes, but AVM rupture is still associated with significant morbidity and mortality and long-term disability. While an increasing number of AVMs are now discovered incidentally due to widespread brain imaging, patients frequently present with hemorrhage, seizure, or progressive neurological deficits. Diagnosis mainly involves CT, MRI, and angiography.

Most AVMs are solitary and occur sporadically, while multiple AVMs are associated with syndromes, such as hereditary hemorrhagic telangiectasia (HHT). AVMs have long been considered congenital; however, their pathogenesis is still not well understood, and a growing body of evidence suggests that AVMs can form de novo after a variety of insults associated with trauma, treatment of dural arteriovenous fistulas, tumors, cavernous malformations, and other AVMs. The overall incidence of ruptured and unruptured AVMs is about 1 per 100,000 person years.

There is controversy whether patients with unruptured AVMs should be treated or observed . There is no primary medical therapy. The overall risk of hemorrhage is about 1–2% per year, however the risk of additional hemorrhage increases significantly once rupture occurs . Deep locations, deep venous drainage, increasing age, and the presence of flow-related aneurysms may also increase the risk of additional hemorrhage. Seizures or progressive neurological deficits are other important indications for consideration of treatment, as they may result from silent AVM microhemorrhages associated with increased risk of more significant hemorrhage and frank rupture.

Acutely ruptured AVMs often present with an intracerebral hematoma, mass effect, and increased intracranial pressure causing neurological deterioration, and are operated upon immediately to relieve mass effect. The hematoma creates a corridor of exposure to the AVM and facilitates resection.

Selection of AVM patients for treatment requires balancing risk of treatment complications against the risk of hemorrhage in the natural history course. Modern treatment of AVMs is multimodal and includes microsurgical resection along with endovascular embolization and stereotactic radiosurgery, either as surgical adjuncts or as alternatives. Microsurgical resection has superior cure rates compared to endovascular embolization and stereotactic radiosurgery, however not all patients are good candidates for surgery. Resection of large and complex AVMs in eloquent brain is associated with poor neurological outcomes. Grading systems are used to predict neurological outcomes after AVM surgery and develop management plans. Patients with high surgical risk are considered for endovascular embolization, embolization of flow-related aneurysms, or palliative embolization to eliminate functional steal. Single-session stereotactic radiosurgery or volume-staged radiosurgery can also be used to “downgrade” an AVM, or reduce its volume and make it more favorable for embolization and microsurgical resection.

AVM Grading Systems

Grading systems are used to describe AVMs as well as develop management plans. The Spetzler–Martin and Lawton–Young supplementary grading systems were developed to predict neurological outcomes after AVM surgery. The Spetzler–Martin scale is the predominant classification scheme, and includes AVM size, eloquence of surrounding brain, and venous drainage patterns . The Lawton–Young supplementary grading system supplements the traditional Spetzler–Martin system by incorporating additional factors important to surgical selection and outcome, including patient age, hemorrhagic presentation, and compactness . A patient with a supplemented grade ≤6 is a viable candidate for surgery, while patients with grades >6 have a high risk for surgical complications and poor outcomes. Patients with grades >6 are then considered for radiosurgery, or observed. Incompletely obliterated AVMs are reconsidered for surgery when downgraded to a more manageable size. Judicious patient selection is essential to avoid complications and poor neurological outcomes.

AVMs are also classified by their location in the brain: frontal, temporal, and parieto-occipital lobes, ventricles, deep central core, brainstem, and cerebellum. Frontal AVMs are the most common and include the lateral frontal ( Fig. 159.1 ), medial frontal, paramedian frontal, basal frontal, and Sylvian frontal subtypes. Temporal AVM subtypes include one for each surface of the temporal lobe: lateral temporal ( Fig. 159.2 ), basal temporal, Sylvian temporal, and medial temporal. Parieto-occipital AVMs often have a more robust arterial supply than frontal and temporal AVMs and include four subtypes: lateral parieto-occipital ( Fig. 159.3 ), medial parieto-occipital, paramedian parieto-occipital, and basal occipital. Ventricular and periventricular AVMs “float” in cerebrospinal fluid (CSF) and are easier to circumdissect than parenchymal and deep AVMs. Ventricular and periventricular subtypes include callosal ( Fig. 159.4 ), ventricular body, atrial, and temporal horn AVMs. Deep AVMs require a high selection threshold, but favorable results can be expected with surgery. Subtypes include the pure Sylvian, insular, basal ganglial, and thalamic AVMs ( Fig. 159.5 ). Similarly to deep AVMs, brainstem AVMs are often considered inoperable, but maybe located entirely on the pial surface, have higher hemorrhage rate than supratentorial AVMs, and may not be amenable to radiosurgery or embolization. Lateral brainstem AVMs in particular have adequate surgical exposures and are often surgically resectable. Subtypes include anterior midbrain, posterior midbrain, anterior pontine, lateral pontine ( Fig. 159.6 ), anterior medullary, and lateral medullary. Finally, the cerebellar AVMs include five subtypes: suboccipital, tentorial, vermian ( Fig. 159.7 ), tonsillar, and petrosal. Cerebellar AVMs are more likely to present with hemorrhage than supratentorial AVMs. Each subtype is characterized by unique arterial supply, draining veins, eloquent surrounding structures, surgical approach, and management strategy.