Ultrasound(US) is a longitudinal mechanical wave characterized by a frequency higher than 20,000 Hz. US generation is possible because of the discovery of the piezoelectric effect by the Curie brothers in 1880 and the inverse effect by Gabriel Lippmann one year later. The first concrete application for piezoelectric technology was during World War I, when, in 1917, Paul Langevin developed an ultrasonic submarine detector. Progress has led to the introduction of piezoelectric technology in all sectors. Concerning medical applications, the most significant is represented by US-based imaging and treatment.

The human spine consists of 33 vertebrae grouped into five regions. From superior to inferior there are seven cervical, 12 thoracic, five lumbar, five fused sacral, and four small fused coccygeal vertebrae. The spine is a functionally complex and significant component of the human body that not only provides bony protection to the spinal cord but also provides an incredible amount of flexibility to the trunk and serves as the mechanical linkage between the upper and lower extremities, allowing movement in all three planes. Biomechanics, the application of mechanical principles to living organisms, is crucial in understanding how the bony and soft spinal components interact to ensure spinal stability, and how this is affected by degenerative disorders, trauma, and tumors.

The adoption of magnetic resonance imaging(MRI) into clinical practice brought about a revolution in the diagnosis and treatment of neurological illness, and has dramatically advanced the study of brain anatomy. Early MRI resolved structures in the brain with comparatively poor resolution on the order of 2.5 mm, with limited methods of amplifying contrast between different tissues. Advances in imaging sequences and analytical methods, combined with improvements in spatial resolution and contrast modalities, have dramatically increased the diagnostic and treatment utility of MRI in neurosurgery. Over time, MRI has been used to study and diagnose nervous system diseases of all kinds, from brain tumors, to stroke, to multiple sclerosis. Today, MRI techniques enable the in-vivo study of brain microstructure, connectivity, functional activity, tissue composition, and blood flow; supports surgical planning; and provides critical feedback during selected neurosurgical interventions.

Maximizing extent of resection while minimizing neurological morbidity is a key tenet of glioma and epilepsy surgery. Numerous intraoperative and preoperative techniques exist to assess functional domains including motor and language. In this chapter, we describe the primary methods used to map brain function, with a focus on highlighting the neuroscience principles behind common language tasks used for language mapping.

Due to improvements in population health, systemic cancer therapies and screening tools, the incidence of brain cancer metastases has continued to rise. The constituent cells possess unique characteristics that allow them to penetrate the blood–brain barrier, colonize the central nervous system, and co-opt their surroundings to thrive while evading surveillance by the immune system. This presents a unique challenge both to the multidisciplinary teams that care for these patients and the investigators striving to leverage these tumors’ distinctive attributes into novel treatments. In this chapter, we outline the pathways and mechanisms underlying the development and survival of brain metastases, and how they inform current and emerging treatment strategies.

Tumors of the spine are a heterogeneous group of neoplasms involving the spinal column and spinal cord. They can be distinguished based on their location within the spine into three groups: intradural–intramedullary, intradural–extramedullary, and extradural. Another classification seeks to separate out these tumors based on their cell of origin, with primary spine tumors arising from either the spinal cord itself, its surrounding coverings including the leptomeninges, bone, cartilage, and soft tissue, or as secondary tumors arising from spinal involvement of a systemic neoplasm such as myeloma or as a metastasis from a distant site. This chapter seeks to discuss current evidence on the genetic, epigenetic, and cellular underpinnings of spine tumors with emphasis on the pathobiology and mechanisms underlying these neoplasms.

We discuss the fundamental units of the nervous system: neurons and supporting cells, which are formed from radial glial cells, progenitor cells that divide to generate new neurons, which then migrate to their destination. An understanding of the anatomy of neurons and their function enables us to decipher how information travels within the nervous system and how neurons communicate with each other through synapses to form networks capable of performing sophisticated and complex tasks. We then discuss how ions traverse the cell membrane and the critical role ion channels play in establishing resting membrane potential, and how action potentials are generated and propagated along the axon.

Spondylolisthesis is defined as the slippage of one vertebra over another. When the posterior bony elements are dissociated from the anterior column, high shear forces on the disc can lead to slippage of the vertebral bodies on one another. There are five types: dysplastic isthmic, degenerative, traumatic, and pathological. Biomechanical models are limited and attempt to replicate on isthmic and degenerative etiologies. From a clinical standpoint, several studies have explored the relative efficacy of surgical versus non-operative treatment and among surgical treatments, the need for decompression and fusion vs decompression alone. While several landmark studies have established several guides to surgical treatment, the lack of consensus on the use of different surgical approaches leaves room for future work.

Pediatric vascular malformations are a heterogeneous group of disorders that can generally be categorized into structural lesions and arteriopathies. The most common structural lesions encountered in pediatric neurosurgery include high-flow malformations involving abnormal connections between arteries and veins and low-flow malformations of aberrant capillary development(cavernous malformations). The term “moyamoya” is used to encompass a diverse group of arteriopathies characterized by the shared finding of progressive stenosis of the intracranial internal carotid arteries resulting in stroke. Here we will define these lesions, discuss epidemiology to put the scope of the disease in context, and then review the pathobiology in detail, with current genetic screening recommendations.

Neurosurgeons have the privilege of peeking inside the most precious and the most mysterious device on earth: the human brain. The human brain is also the most expensive device on earth given that mental health problems constitute the largest health care cost. By deciphering the inner secrets of brain computations, scientists and engineers have taken inspiration to develop smart artificial intelligence(AI) algorithms. These AI algorithms in turn provide much help to understanding brain function and to multiple applications in brain disorders, including neurosurgery.

The peripheral nervous system(PNS) comprises spinal and cranial nerves, which include motor, sensory, and autonomic nerves, as well as their roots, trunks, plexuses, ganglia, and accompanying supportive connective tissue distal to the brain and spinal cord. It is located peripheral to the central nervous system(CNS), and has very little in the way of protection from injury. In contrast to the CNS, it has a much higher innate capacity for repair and recovery after injury. Despite its physiological diversity, the PNS has a highly organized and choreographed injury response mechanism partially explaining its improved outcomes post-injury. In this chapter, we discuss the pathophysiology of peripheral nerve injury(PNI) and its ensuing reparative response. Before delving into PNIs and their classifications, it is important to review the basic anatomic organization of the PNS, its key cellular components, and supporting connective tissue.

Spinal cord injury(SCI) is a debilitating problem with a global incidence of 8–246 cases per million and an associated significant increase in healthcare cost. Research generally focuses on two broad categories: minimizing initial insult via modulation of primary and secondary injury cascades, or on novel therapeutic strategies aimed at recovering function. To this end, numerous SCI preclinical models have been developed, and promising clinical trials have arisen as a result, highlighting the importance of choosing the optimal model in relation to one’s scientific question. We highlight relevant spinal cord anatomy, embryology, and the pathophysiology of SCI with a focus on how these factors relate to preclinical models of SCI and spinal cord trauma, and hope to highlight important factors necessary for future research.

The brain and the encased skull constitute an incompressible system that encloses a volume of approximately 1450 ml. Normally, the intracranial volume is made up of 80% brain tissue, 10% cerebrospinal fluid(CSF), and 10% intravascular blood. The basic principle of physics in relation to intracranial content is described by the Monroe–Kellie doctrine. This hypothesis states that the total volume of the brain, CSF, and intracranial blood should be constant. Any increases in the volume of one of the components must be at the expense of the other two to maintain adequate brain function.

Peripheral nerve injuries(PNIs) come in many varieties and their mechanism of injury can have a tremendous impact on a patient’s expected outcome. As discussed in Chapter 26, depending on the mechanism, PNIs have a relatively well-choreographed response to injury. However, much of this sequence will be influenced by both modifiable and non-modifiable prognostic factors. Furthermore, this mechanism of injury and its severity will also help dictate the appropriate treatment of the injury. In this chapter, basic science principles and models addressing PNIs are more specifically examined as they occur in the context of trauma, entrapment, tumors, and the changes occurring in acute and chronic pain states. Clinical case examples of such injuries will be discussed to conclude each section, including their respective management.

Radiculopathy refers to pathology at the nerve root level, manifest as positive symptoms such as pain, paresthesias and dysesthesias, and negative symptoms such as numbness and weakness. While a number of causes for radiculopathy exist, the archetypal etiology is lumbar disc herniation, leading to compression of the traversing or, less commonly, exiting nerve root. Such mechanical bases for radiculopathy were first recognized nearly a century ago, initially in the lumbar region by Mixter and Barr(1934),followed by the cervical spine by Semmes and Murphey in 1943.

Degenerative cervical myelopathy(DCM) is the most debilitating form of degenerative disc disease, and is the most common acquired cause of spinal cord dysfunction in adults. DCM is caused by progressive abnormalities of the vertebral column that result in spinal cord damage due to both primary mechanical and secondary biological injury. DCM pathohistology demonstrates a consistent pattern of deleterious changes including severe Wallerian degeneration cephalad and caudal to the level of compression, apoptotic oligodendrocyte cell loss, and anterior horn dropout. Spinal cord ischemia and hypoxia play a major role in DCM pathogenesis. Novel spinal cord imaging studies such as MR spectroscopy and diffusion tensor imaging have provided novel insights into the neurobiology of this disorder. The central nervous system effects of DCM not only involve the spinal cord, but also include upstream functional and structural alterations that can influence disease progression and response to surgical intervention.