VOLUMEVOLUME 3636 •• NUMBERNUMBER 122 JanuaryNovember 31, 1,2014 2014 A BIWEEKLY PUBLICATION FOR CLINICAL NEUROSURGICAL CONTINUING MEDICAL EDUCATION Aneurysms Associated With Arteriovenous Malformations Beatrice Gardenghi, MD, Carlo Bortolotti, MD, and Giuseppe Lanzino, MD Learning Objectives: After participating in this CME activity, the neurosurgeon should be better able to: 1. Assess the various classifi cations of cerebral aneurysms associated with arteriovenous malformations (AVMs). 2. Compare the various hypotheses about the pathogenesis of the cerebral aneurysms associated with AVMs. 3. Evaluate the role of surgery, endovascular therapy, and radiosurgery in the treatment of intracranial aneurysms associated with AVMs. Intracranial aneurysms can occur in patients with brain Classifi cation arteriovenous malformations (AVMs), and this not uncom- A clear understanding of the various types of aneurysms mon association poses important therapeutic challenges. In and aneurysm-like dilations that occur in patients with AVMs patients presenting with intracranial hemorrhage, the AVM is paramount to clarify their pathophysiology and clinical is responsible for bleeding in 93% of cases, with the remaining signifi cance. These aneurysms can be classifi ed on the basis 7% related to associated intracranial aneurysms. The inci- of location, histopathologic characteristics, and hemodynamic dence of aneurysms in patients with AVMs is higher than features. expected on the basis of the frequency of each lesion indi- vidually. This observation suggests that factors such as Location increased regional fl ow (hence hemodynamic stress) may Aneurysms associated with AVMs can occur on the arterial play a causative role in the formation of aneurysms associated side (arterial aneurysms) or the venous side (venous aneurysms). with AVMs, although other causative factors such as genetic In relation to the nidus of the AVM, aneurysms and aneurysm- predisposition cannot be excluded. In this article, we review like dilations are categorized as either extranidal (arterial or the various types of aneurysms and aneurismal-like dilations venous) or intranidal. Intranidal aneurysms are within the seen in patients with AVMs and discuss their clinical signifi - nidus and fi ll “early” during angiography, before substantial cance and therapeutic implications. venous fi lling has occurred. Intranidal aneurysms are usually venous aneurysms. Arterial aneurysms can be localized on vessels that do not contribute to the vascular supply of the AVM (unrelated Dr. Gardenghi is Research Fellow, Department of Neurologic Sur- aneurysms, Figure 1A) or arise from vessels that participate gery, Mayo Clinic, Rochester, Minnesota; Dr. Bortolotti is Attending Physician, Division of Neurosurgery, IRCCS Institute of Neuro- in the vascular supply of the AVM (Figures 1A–C) and as logical Science, Bologna, Italy; and Dr. Lanzino is Professor, Depart- such are related to fl ow dynamics (fl ow-related aneurysms). ment of Neurologic Surgery, Mayo Clinic, 200 SW First St, Rochester, MN 55905; E-mail: [email protected]. All faculty and staff in a position to control the content of this CME Category: Cerebrovascular activity, and their spouses/life partners (if any), have disclosed that they have no fi nancial relationships with, or fi nancial interests in, Key Words: Intracranial aneurysms, Cerebral arteriovenous malformations, any commercial organizations related to this CME activity. Risk of hemorrhage, Multidisciplinary treatment Lippincott Continuing Medical Education Institute, Inc. is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. Lippincott Continuing Medical Education Institute, Inc. designates this enduring material for a maximum of 1.5 AMA PRA Category 1 Credits™. Physicians should only claim credit commensurate with the extent of their participation in the activity. To earn CME credit, you must read the CME article and complete the quiz and evaluation on the enclosed form, answering at least 70% of the quiz questions correctly. This activity expires on October 31, 2015. CCNEv36n22.inddNEv36n22.indd 1 112/1/142/1/14 33:47:47 PPMM Figure 1. A 57-year-old woman had undergone fractioned radiotherapy for a left frontal AVM at another institution 20 years previously. She was referred for evaluation of multiple aneurysms. A, Catheter angiography, right internal carotid artery (ICA) injection, anteropos- terior view showing multiple proximal fl ow-related aneurysms (white arrows) and an unrelated middle cerebral artery aneurysm (red arrow). B, Anteroposterior view and C, lateral view of left ICA injection showing multiple proximal fl ow-related aneurysms (arrows) and the per- sistent large AVM. Flow-related arterial aneurysms can occur away from the usually are close to the nidus, with irregular shape. They nidus (proximal flow-related aneurysms, Figures 1A–C) or often originate from small or perforating arteries, very close originate from feeding vessels adjacent to the nidus (distal to the ependymal surfaces. Defi nitive diagnosis can be flow-related aneurysms). Although proximal flow-related made on histologic analysis, but their nature is often aneurysms usually occur at bifurcation points (a result of the implied by progressive growth on serial early angiograms. combined effects of hemodynamic stress and intrinsic The term venous aneurysm is a misnomer, because the weakness of the vessel wall at bifurcation points), distal fl ow- venous aneurysm does not contain the typical wall related aneurysms often occur along the feeding pedicle not components of the aneurysm wall, but this term is established related to branching points. in the terminology of aneurysms associated with AVMs and A different subcategory of arterial aneurysm-like dilation will be maintained in this article. Intranidal aneurysms are a is the arterial pseudoaneurysm, which is thought to be the subtype of venous aneurysms. Venous pseudoaneurysms can result of rupture of thin-walled small perforating arteries be seen at the periphery of the nidus and can be identifi ed if that supply the AVM. A pseudoaneurysm results from the surgery is performed shortly after a parenchymal bleed as unclotted portion of the hematoma still in communication areas of venous dilation at the periphery of the nidus partially with vessel lumen and as such can show rapid interval fi lled with clotted blood. The draining veins of the AVM often growth on subsequent imaging studies. Pseudoaneurysms present dilations and varices (Table 1). EDITOR: Ali F. Krisht, MD The continuing education activity in Contemporary Neurosurgery is intended for neurosurgeons, neurologists, Director, Arkansas Neuroscience Institute neuroradiologists, and neuropathologists. 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