Frontiers in Neurosurgery

This introductory chapter provides the readers with an insight into the history of neuroendovascular surgery. Acknowledging the past is of the utmost importance to understanding and interpreting present dynamics and future directions in such a young, yet quickly evolving medical field. Starting from ancient history with the first descriptions of cerebral aneurysms, we describe the era of the extravascular approach to cerebrovascular disease with a focus on the main techniques conceived such as arterial ligation, aneurysm wrapping, trapping and packing. With the invention of the aneurysmal clip, the direct surgical approach to cerebral aneurysms gained a privileged place in the management of intracranial vascular disease which it retained throughout most of the second half of the 20th century. Nevertheless, marked by the invention of cerebral angiography, the endovascular era symbolically began in 1927. Ingenious, sometimes bizarre and hazardous, endovascular approaches to cerebrovascular disease are recounted, touching the history of the evolution of endovascular techniques, embolic materials and navigation devices. Modern neuroendovascular surgery is described with a focus on the development of coil technology which represents an essential milestone as it gave a massive impulse toward the birth of a new subspecialty in neurosurgery. At the end of the chapter we discuss how the training of young neurosurgeons is changing and should cope with these new acquisitions. The role of neuroendovascular surgery in neurosurgical residency programs is summarized for the United States, Japan and Europe. Should this be part of the neurosurgeon’s armamentarium? Could it be delegated completely to the neurointerventional radiologist or might it be best part of a completely new specialty?

Arteriovenous fistulas, both pial and dural, are neurovascular malformations which frequently have a poor natural history. Their treatment can be either endovascular or neurosurgical. The evolution of neurointerventional materials and techniques extended the indication for endovascular treatment to most of the arteriovenous fistulas.

A clear understanding of the vascular anatomy of arteriovenous fistulas is essential in order to be able to treat them. Familiarity with neurovascular techniques and devices is also important for choosing the proper treatment strategy in each case.

In this chapter the different types of fistulas are discussed with the most appropriate treatment strategies in each situation, also taking into consideration the neurovascular materials now available.

Arteriovenous malformations of the brain are one of neurosurgery's most fascinating and challenging pathologies. These malformations were initially described in 1854 by Luschka and in 1863 by Virchow; subsequently several other scientists including Giordano, Spetzler and Martin, Ponce and Lawton described the pathogenesis, clinical presentation and medical treatments of cerebral arteriovenous malformations in detail. The clinical presentation of these malformations is extremely varied: they can present with hemorrhage, seizures or focal neurological deficits with a close correlation between the anatomical location of the malformation and its presenting symptoms. Unruptured and ruptured malformations are distinct pathological entities with different natural histories and multimodal treatment risks. The estimated generic bleeding risk of an unruptured arteriovenous malformation is between 3% and 4% per year; this risk of bleeding increases to 6% in the first year after a hemorrhagic episode and returns, after 5 years, to the same value as that of a corresponding unruptured malformation. Cerebral arteriovenous malformations are very complex entities and for this reason the first and major clinical dilemma is whether or not to treat a patient with such a malformation; the second issue is how to treat them. Each treatment is tailored to the individual patient, drawing a careful balance between efficacy and risks. In brief, a variable combination of three methods of treatment, endovascular, surgical and radiosurgical, can be considered. Each has specific indications and contraindications but all have the same aim: complete elimination of the malformation.

Large aneurysms (more than 25 mm in diameter) or aneurysms in particular positions inside the skull base are defined complex. They are associated with a high risk of subarachnoid or intracranial hemorrhage and neurological deficits. We discuss this particular class of aneurysms which, given their peculiar characteristics, require a complex therapeutic approach, including synergistic treatment with surgical and endovascular modalities.

Spinal cord vascular malformations are vessel disorders involving, directly or indirectly, the spinal cord tissue. Their management and treatment remain complex and require a deep knowledge of the “lesional” and regional anatomy. The object of this chapter is to explain the vascular embryology, the anatomy of the spinal cord and the treatment of vascular malformations such as arteriovenous malformations, dural arteriovenous fistulas and aneurysms.

Early recanalization of a thrombosed cerebral artery in a patient with acute ischemic stroke is related to better outcome and reduced mortality. Intravenous administration of rt-PA within 4.5 hours from stroke onset is the recommended therapy for acute ischemic stroke. However, several studies demonstrated improvements, in terms of anatomical and clinical results when intravenous therapy is associated with intra-arterial approach. Although improvement in outcome of patients treated by mechanical approach reported in various case series, three recent randomized controlled failed to demonstrate the superiority of mechanical thrombectomy over intravenous fibrinolysis. In the first part of this chapter we report the results of these randomized trials and discuss their biases and limitations. We then describe stentriever thrombectomy techniques and the mechanical approach to tandem occlusions.

In this chapter, we discuss the history of devices developed for neuroendovascular therapy, culminating with the state-of-the-art devices in each category. Innovative tools for intracranial access including guide catheters, intermediate catheters, microcatheters, and guidewires which were critical to the development of neurointerventional procedures are addressed first. With the introduction of coil embolization, aneurysms became amenable to minimally invasive treatment. Stents brought the strategy of parent vessel reconstruction to assist coiling of wide neck aneurysms, while disruption of flow at the aneurysm neck to enhance stagnation of blood in the sac enabled treatment of previously untreatable aneurysms, without sacrificing the parent vessel. For revascularization in acute ischemic stroke, mechanical thrombectomy devices were developed for clot removal. Subsequently, advances in polymer and materials technology and engineering breakthroughs in catheter design made it possible to deliver 5 French and 6 French catheters safely and reliably to the middle cerebral artery, thus allowing the promise of simple aspiration thrombectomy to be realized. The future of stent design and the exciting promise of neurointervention are also considered.

Neuroendovascular techniques have evolved rapidly during the last decades extending the range of treatment options available for neuroendovascular surgeons and creating new applications other than those in the field of cerebrovascular diseases. Endovascular approaches for the management of head and neck tumors date back to the 1970s when the French surgeon Manelfe described the first pre-surgical embolization for an intracranial meningioma. Thereafter, indications for such treatment widened to other intracranial hypervascular tumors such as hemangiopericytomas and hemangioblastomas or extra/intracranial neoplasms including paragangliomas and juvenile nasopharyngeal angiofibromas. Moreover, the possibility of reaching specific regions of the brain via the endovascular route made intra-arterial chemotherapy for brain tumors feasible, mitigating complications related to systemic exposure to toxic drugs. The indications, outcomes and complications of these relatively new techniques are discussed in depth.

Dual antiplatelet therapy is currently used in clinical practice to prevent thrombotic events during and after neuroendovascular procedures.

Despite antiplatelet therapy, a significant number of patients show insufficient platelet inhibition, as measured by laboratory tests. These patients are at greater risk of developing thrombotic events than are patients sensitive to the treatment. This phenomenon is known as "antiplatelet drug resistance". The mechanisms that influence the individual response to antiplatelet therapy are not completely understood and are likely to be multifactorial.

Several platelet function tests have been developed to monitor antiplatelet therapy and may assist in adjusting it to improve outcomes in patients with antiplatelet drug resistance. Nevertheless, the optimal management for these patients has not yet been established. This chapter summarizes information on the available antiplatelet drugs currently used in neuroendovascular procedures, the commonly used tools for platelet function testing and the potential mechanisms underlying suboptimal platelet inhibition by aspirin and clopidogrel.

Many intracranial vascular pathologies are now being successfully managed by interventional neuroradiology techniques. The procedures have become increasingly complex, requiring planning and coordination. Key roles are played by the anesthesiologist and close collaboration with neuroradiologist is crucial for successful results. The optimal conduct of anesthesia in a neuroradiology suite requires careful planning of each procedure and detailed evaluation of the individual patient. The basic principles of neuroanesthesia cannot be avoided: optimization of cerebral blood flow, perfusion pressure, control of intracranial pressure and close monitoring of hemodynamic values, respiratory patterns, fluid status and body temperature are all necessary. Rapid awakening must be ensured so that the patient’s neurological status can be assessed quickly. The provision of anesthesia outside the operating room has its own inherent risks. This chapter will focus on perioperative anesthesiologic care and strategies to avoid or deal with complications if they do occur.