Clinical Anesthesia in Neurosurgery

By Elizabeth A. M. Frost

Clinical Anesthesia in Neurosurgery, Second Edition, integrates the evolution of the field of neuroanesthesia with the major areas of neurosurgical activity to give the reader the required perspective and requisite information to help in laying the foundation for future advances as well as describing the current state of the art. The book contains 25 chapters organized into five parts. Part I presents studies on cerebral physiology and evaluation. Topics covered include cerebral circulation and metabolism, intraoperative neurophysiologic monitoring, and central nervous system effects of anesthetic agents. Part II covers neurosurgical and related procedures, such as posterior cranial fossa surgery, surgery of the spine, and peripheral nerve surgery. Part III examines central nervous system trauma including spinal cord trauma and cardiovascular effects of severe head injury. Part IV takes up postoperative and intensive care, including postanesthetic care, neurosurgical intensive care, and parenteral nutrition while Part V deals with the medical criteria and legal aspects of brain death.

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 22, 2013
• ISBN: 9781483164786

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M.D.

Preface to Second Edition

Six years have passed since the appearance of the first edition of this book. In considering the broad field of anesthesiology, one might note that over this relatively short period of time, there have been no major new discoveries of anesthetic agents or techniques. Thus, one might rationally assume that there are probably few changes in a subspecialty area such as neuroanesthesia. Nothing could be further from the truth. In preparing this second edition, not only have several chapters been added, but preexisting chapters have often been completely rewritten and major thrusts redirected.

Much new information has emerged concerning cerebral hemodynamics and metabolism. With the now widespread use of exciting radiologic techniques incorporating magnetic imaging and isotopes, our understanding of cranial function is expanding rapidly. The blood-brain barrier, now defined, is affected by many chemical situations and anesthetic techniques.

Electrophysiologic monitoring, in its infancy in 1984, is now standard technique in most operating suites, with rapidly expanding uses in neurosurgery. So much has been learned of the effects of the anesthetic agents on intracranial dynamics over the past few years that discussion of this topic now requires its own chapter. Deleterious effects of nitrous oxide on the injured brain have been confirmed. Sufentanil may also be contraindicated in specific situations and alfentanil indicated.

Recently, the importance of appropriate and adequate fluid management of the neurosurgical patient in ensuring optimal outcome has been emphasized. A new chapter, written by a neurosurgeon, addresses these pertinent issues.

In the arena of cerebrovascular disease, results of multi-institutional studies have required that we revise our previous approach to therapy of ischemic cerebral disorders. No longer are extracranial to intracranial bypasses and carotid endarterectomies routine procedures. Rather, much more vigorous standards must be applied.

Whereas lesions in the posterior fossa were commonly operated with the patient in the sitting position, the present trend is toward a prone or lateral position, thus preventing or minimizing complications.

Brain tumors, once thought to be synonymous with death, are now often successfully treated with several different therapies. A new chapter has been assigned to this topic.

New frontiers are being forged in the care of children with congenital neurologic abnormalities. Teams of specialists are forming to better understand and care for these babies. In this edition, a pediatric anesthesiologist and a pediatric neurosurgeon have collaborated to present a state-of-the-art view of the exciting subspecialty of pediatric neuroanesthesia.

Seizure surgery and stereotactic surgery remain important aspects of neurosurgical care. An anesthesiologist has joined with a neurosurgeon to present an updated view of these areas.

Pain therapy requires a team approach. A new, expansive chapter has been added in this edition to review the therapeutic options and outline the roles of the several specialists.

Central nervous system trauma remains one of the most devastating medico-socio-economic problems of our society. Again updated neurosurgical and anesthetic views are presented.

I received several requests after the first edition of this book appeared: What do you do with the head-injured patient, cleared for abdominal surgery? How do you manage the patient with a stroke for hip replacement? Thus, yet another chapter was added on the care of the patient with neurologic disease who presents for non-neurosurgical surgery.

One of the major exciting advances in postoperative and intensive care has involved hyperalimentation. Although many new drugs and techniques have been advanced to improve outcome after brain insult, no clear therapeutic approaches have been established. However, our understanding of the changes caused by hypoxic and ischemic insults are much clearer, and with understanding may come healing.

Finally, the latest court rulings applying to the definition of cerebral death are summarized.

Again, as in the first edition, this book is presented by anesthesiologists and neurosurgeons, most of whom work together on a daily basis. Even as pathologic processes become more clearly defined, rigid management plans are still not delineated. Rather, rational approaches to prudent anesthetic care are presented — bearing in mind that there are many different situations in this world, and strict adherence to a single technique is unfeasible, unrealistic, and usually not necessary.

I am proud to see the advances that the specialty of neuroanesthesia has made in these six years. Neuroanesthesiologists are not as yet resting on their laurels, but rather, with remarkable intensity, striving to further define neurologic, pathophysiologic, and appropriate anesthetic management

As before, I thank the contributors for all their hard work and the secretarial staff of Montefiore Medical Center and Bronx Municipal Hospital, who worked long hours to complete manuscripts. My gratitude is also extended to the staff at Butterworth-Heinemann for help and encouragement through both editions.

Elizabeth A.M. Frost

Preface to First Edition

Just as there is no standard central nervous system lesion, there is no single best choice in neuroanesthesia. Rather, over the years, there has been a gradual evolution, albeit rather peripatetic, in neuroanesthetic care, dictated in part by neurosurgical advances. Early craniotomies were performed without any anesthesia. Subsequent local anesthetic techniques employed ice, ether as a spray jet, and cocaine. Toward the end of the nineteenth century, a balanced technique using an inhalation anesthetic (chloroform) and a narcotic (morphine) was in vogue. Increased understanding of intracranial dynamics led to the adoption of intravenous anesthesia, a technique that was less likely to increase intracranial pressure. More recently, with the growing awareness of the possible deleterious effects of nitrous oxide and the development of better agents, the trend again is to use an inhalational agent (isoflurane) combined with a narcotic (sufentanil).

The state of the art in neurosurgery is such that operative intervention of many more and complex disease processes is possible. Intracranial function is influenced not only by anesthetic agents and techniques but is also acutely sensitive to abnormalities of other organ systems. Thus, optimal outcome after any neurosurgical procedure must depend on a team approach. Careful preoperative evaluation and stabilization of multisystem disease are essential. With a knowledge of the pathology involved and the operative approach and requirements, the anesthesiologist can then make a rational and appropriate choice of technique.

This book is a collaborative effort by anesthesiologists and neurosurgeons to collate their experiences and survey the extensive literature that has flooded the academic scene of the neurosciences over the past few years. The intent has not been to advocate rigid management plans for each situation but rather to present the pathology involved and suggest rational approaches to anesthetic care. Both anesthesiologist and neurosurgeon should be aware, for example, of the hazards of anesthesia in the patient with peripheral nerve trauma who has just eaten, or the difficulty of intubating a patient with cervical spine injury. The chapters describing seizure surgery, percutaneous ablative procedures, and stereotactic techniques might suggest a limited role for the anesthesiologist. These topics have been included, however, since in many parts of the world, many of these procedures are either done under general anesthesia or actually performed by the anesthesiologist.

For the most part, neurosurgical disease processes have been considered in separate chapters. Supratentorial tumors and adult hydrocephalus are characterized mainly by raised intracranial pressure; since the anesthetic management involves principles rather than specific care, these diseases have been covered in Chapter 3, Physiology of Intracranial Pressure.

The section on intensive care is not intended as a reference for the intensivist but rather as a guide for the practitioner who, as part of a team, must see the patient through a critical period following trauma or surgery.

Finally, from two disciplines, neither of which allows room for compromise, the views from both sides of the ether screen have been presented in the belief (to paraphrase Antoine de Saint Exupéry) that Progress does not consist in gazing at each other but in looking outward together in the same direction.

The editor thanks the contributors for their patience, Carolyn Burke Giles for her secretarial help, and Nancy Megley of Butterworth-Heinemann for her advice and encouragement.

Elizabeth A.M. Frost

1

Introduction

Elizabeth A.M. Frost

Publisher Summary

This chapter presents an overview of the role of anesthesia in neurosurgery. Neurosurgery, like anesthesia, has an active and productive history of little more than 100 years. Remarkable advances in both specialties over the past century have made treatment possible for a broad range of disorders involving the delicate central nervous system. All anesthesia concerns itself with the interruption of pain perception by higher cortical centers within the central nervous system. In that sense, it might be argued that all anesthesia is neuroanesthesia, although, in fact, the subspecialty of neuroanesthesia has become firmly established as the anesthetic care of patients with central nervous system disease. The chapter presents an historical background of the use of anesthesia in surgical procedures. The principles and practice of neuroanesthesia must rest on three factors: the use of rapid and reversible agents, the maintenance of a stable environment, and the control of intracranial pressure. The chapter also describes the ancillary roles of the neuroanesthesiologist.

All anesthesia concerns itself with the interruption of pain perception by higher cortical centers within the central nervous system. In that sense, it might be argued that all anesthesia is neuroanesthesia, although in fact the subspecialty of neuroanesthesia has become firmly established as the anesthetic care of patients with central nervous system disease.

REQUIREMENTS OF THE DISCIPLINE

Anesthesia for neurologic surgery occupies a unique place within the larger field of anesthesiology. Admittedly, overlap exists, as for example in the anesthetic management of a patient with head injury who is having emergency splenectomy. In essence, though, a patient with preexisting neurologic disease is undergoing neurosurgical intervention under the influence of centrally acting depressant anesthetic drugs. A clear understanding of the situation and the ability to balance all three factors are essential for the successful outcome of any neurosurgical procedure. Thus, it is apparent that major problems unique to neurosurgery must be fully understood and solved by anesthesiologists.

The brain appears to have a certain redundancy of circuitry and plasticity of function that become lost as the organ matures. Perhaps it is because the brain has so little capability for repair that it is so uniquely protected, both physically and physiologically: it has its own container, the skull, and is biochemically isolated by the blood-brain barrier; the brain also most probably has its own waste disposal system in the cerebrospinal fluid circulation. Sometimes these protective features are a mixed blessing, as when the skull is confining the swollen brain and intracranial pressure increases, or the cerebrospinal fluid passages are blocked and hydrocephalus results. But this uniquely controlled environment permits the central nervous system to function and, in turn, to monitor and control the environment for the rest of the organ system. Responsibility for maintaining this stable environment during operation and resuscitation from any neurosurgical experience and well into the postoperative period rests with the anesthesiologist.

The primary problem in neuroanesthesia is to regulate brain volume and pressure. Whether it is done by controlling respiratory patterns and blood gas tensions, administering diuretic or hypotensive agents, draining cerebrospinal fluid, or any other means, changes critical to the successful outcome of a case will be realized immediately. The second major problem is to control hemorrhage. The anesthesiologist profoundly influences blood loss through choice of anesthetics and control of blood pressure and ventilation. The third critical task is to protect nervous tissue from ischemic and surgical injury. Regeneration of the central nervous system is slow and limited: apart from Purkinje cells, no new cells are formed; minimal repair facilities are available; existing neurons do not hypertrophy. Whereas skin, bone, or liver will regenerate, the central nervous system cannot, and extreme efforts must be made to protect existing tissue.

Of course, numerous lesser problems also arise during neurosurgical anesthesia. Access to the head is difficult; the positioning required tends to obstruct the airway; temperature, fluid, and electrolyte control are essential. Matters are complicated by the uncommonly painstaking techniques, initiated by Halsted and widely practiced by Cushing, that often result in very lengthy operations and, thus, greatly prolonged anesthetic time. Inevitably, neuroanesthesia appeals to a relatively small number of anesthesiologists of unusual patience who possess an almost pathologic adherence to meticulous detail in technique, for there is no room for compromise.

Ancillary Roles of the Neuroanesthesiologist

With the introduction of diathermy, the operating microscope, ultrasonic devices to detect and remove lesions, high-speed drills, LASER probes to act as bloodless knives, and neurophysiologic mapping of nervous tissue, numerous procedures that were not previously feasible are now commonplace. Many of these operations result in real but reversible brain damage, and meticulous care and maintenance of a stable environment are required during the operation and postoperatively.

A growing number of head trauma and spinal cord injury victims now survive because of increased public awareness and availability of resuscitation and transport mechanisms. As only about 20% of these patients require surgical intervention, the emphasis in neurologic surgery has been shifting away from the operating room alone and into the realm of neurologic supportive care. Success in such an area clearly depends on a team approach, but anesthesiologists—with their detailed knowledge of respiratory and cardiac physiology, fluid and electrolyte balance, and intracranial dynamics—are the logical physicians to lead, or even to pioneer, the neurosurgical intensive care unit.

Finally, new neuroradiologic techniques—including magnetic resonance and computed tomography for diagnosis, and therapeutic procedures for tumors and arteriovenous malformations—require that anesthetic care be available in radiology suites.

Neuroanesthesia Societies

To initiate research and teaching in the field of neuroanesthesia, the Commission of Neuroanesthesia, comprising anesthesiologists from nine countries, was founded on July 9, 1960, in Antwerp, Belgium (1). Since then, societies have been established in the United Kingdom and Germany as well as other parts of the world. Among them is the Society of Neuroanesthesia and Neurologic Supportive Care, founded in the United States in 1973. Headquartered in Richmond, Virginia, it maintains a file of locations and availability of neuroanesthesia fellowships and a neuroanesthesia bibliography. The society is recognized by the American Society of Anesthesiologists and the American Association of Neurological Surgeons, and participates actively in their annual meetings as well as sponsoring two meetings of its own each year.

HISTORICAL BACKGROUND

Earliest Times

Understanding of the central nervous system and of anesthesia dates from at least ancient Egypt and Greece. The early Egyptians (circa 3000 BC) apparently had knowledge of the function of the brain and spinal cord. Carotid artery is derived from the Greek word meaning the artery of sleep, and pressure or even ligation of this vessel may have been used as a means of producing insensibility (2); on the other hand, the Greeks may have simply observed that cutting the carotid artery usually resulted in unconsciousness and death from hemorrhage.

The Edwin Smith Surgical Papyrus, named for an American Egyptologist who purchased the document in Luxor in 1862, is a copy prepared about 1700 BC. It describes 48 cases that may originally have been patients of Imhotep, Egypt’s great architect-physician and advisor to Pharaoh Yoser, who lived about 3000 BC. Indeed, this document might well represent the original neurosurgical text, as of the 48 cases, 15 concern head injury; 12, facial wounds and fractures; and 7, vertebral injuries. The other 14 cases involve pathology of the upper thorax. Although pain is recognized as a sensation caused by the injury and by movements a patient made on instruction from the physician, the latter is exhorted to palpate his wound, although he shudders exceedingly and cause him to lift his face if it is painful for him to open his mouth, his heart beats feebly (3) (from case 7, a depressed skull fracture). It is as though pain, associated only with the injury, was not intensified by anything the physician did and therefore could not be alleviated by him. Wound approximations are encouraged but no mention is made of surgical intervention of any means of inducing anesthesia. In the Ebers Papyrus too, a much larger document attributed to the period of 1600 BC, a need for anesthesia is not acknowledged.

Perhaps rather obviously, the development of neuroanesthesia is closely linked to that of neurosurgery itself. Certain neurosurgical procedures have been performed for thousands of years. The initial discovery of trephined neolithic skulls estimated to be between 4000 and 5000 years old was received with considerable skepticism. After Prunières first found ancient skulls with human-made holes at Lozeres in 1873 (4), however, neolithic trephined skulls were eventually discovered throughout most of Europe, Asia, and the Americas (Figure 1.1). Although trephining is not mentioned in The Edwin Smith Papyrus, a single trephined skull was found in the pits at Lisht, which probably belonged to one of the noble families of the XII Dynasty (5).

FIGURE 1.1. Trephined skull found in Peru. Note large opening cut in the cranium with a hand tool. (Reproduced with permission of the Division of Medical Sciences, Museum of American History, Smithsonian Institution.)

These subsequent discoveries confirmed that making holes in the skull was a relatively frequent practice among ancient peoples. The holes were usually solitary but could be multiple, and were placed on any part of the skull convexity. The bony defects were made by sharp cutting stones (Figure 1.2) and occasionally were filled with gold. These procedures may have been done in the treatment of headache or head injury, to release evil spirits (to cure epilepsy, insanity, or idiocy), for ritualistic purposes, or after death to obtain amulets or allow suspension for embalming (6).

FIGURE 1.2. Hand trephine.

It probably took about half an hour to operate, and how the patient was controlled is unknown. Coca leaves, from which Nieman purified cocaine in 1860, were used for centuries in Peru. Early writings suggest that local anesthesia could be induced by an assistant who chewed the leaves and spat into the wound. Also, the patient (or victim) was encouraged to inhale the fumes of burning herbs (7). That early Peruvians used antiseptics is likely, as wound healing was good with little evidence of suppuration or osteomyelitis.

Aretaeus, outlining the treatment of seizures in the second century AD, recommended perforating the skull with a trepan when the meninx there is found black, combined with surface cooling, sedation, and catharsis. If the putrefaction could be cleansed (i.e., subdural clot could be released), cure was to be expected. Apparently he recognized little need for anesthesia, as the habit of such persons renders them tolerant of pains and their goodness of spirits and good hopes render them strong in endurance (8).

Elsewhere, no mention is made in early writings of other kinds of intracranial surgery. The great medical work of ancient China, The Yellow Emperor’s Classic of Internal Medicine, was started about 2697 BC and rewritten several times between then and the Sui Dynasty (589–618 AD) (9). It consisted of two parts, the Huang Ti Nei Ching Su Wen, which is simple discussions between the emperor and his chief physician, Ch’i Po; and the Nei Ching Ling Shu Ching, a 91-chapter treatise on acupuncture. Surgery is barely mentioned. The Chinese felt that the superiority of internal therapy made operations, and even knowledge of anatomy, unnecessary. Probably more important in countering any tendency to the practice of surgery were Confucian tenets about the sacredness of the body. Epilepsy, palsies, and many mental derangements were graphically described, but the therapy was herbal or needling of appropriate points to reestablish the balance of the meridians.

Chinese medical history does record two eminent surgeons. Pien Ch’iao is said to have been so skillful in his use of anesthesia that he was able to operate completely painlessly. The first heart transplant is ascribed to him during the second century BC. The other surgeon, Hua T’o, became famous for his writings on surgery and anesthesia about 200 AD. He achieved general anesthesia by means of a drug dissolved in wine. The components of this drug, ma-fei-san (literally, bubbling drug medicine) are not known, but Dr. Erich Hauer, the Sinologist, believed that ma-fei referred to opium (9).

The Middle Ages

With the fall of the Roman Empire, the Catholic Church became more influential in the practice of medicine. Headaches, often attributed to punishment or the presence of evil, were treated by trephination. The first report of any other type of neurosurgical procedure appeared in Hindu writings. In 927 AD two surgeons anesthetized the King of Dhar with a drug called samohini. They opened the skull, removed a tumor, and closed the wound with sutures. A reversal agent described only as a stimulant was also used (1). During the early Middle Ages, with the exception perhaps of Avicenna in Isfahan, anatomical dissection of the dead was forbidden, and few advances were made in understanding the physiology of the central nervous system.

In the fourteenth century, Roland de Parme gave a detailed description of the use of the trephine in his book La Chirurgia. An elderly patient, head shaven, is shown sitting placidly, hands crossed in his lap, while a man of the Church drills a hole in his head (Figure 1.3). A pre-Columbian instrument called a tumi, dating from 1300 AD, was also used for trephination (Figure 1.4). The figures on the handle depict its use: while one man holds the patient, the other trephines the skull. A century later, Charaf-ed Din in his book La Chirurgie des llkhani (1465 AD) shows the treatment of a child with hydrocephalus (Figure 1.5). The child is held by an assistant while the surgeon, using a bistoury, cuts off the excess head. Somewhat earlier, in the thirteenth century, Theodoric recommended that anesthesia be induced by a spongia somnifera, a sponge impregnated with spirituous extracts of various narcotic substances held to the patient’s nostrils until sleep was induced. After operation the patient was aroused by application of a second sponge containing vinegar and other nasal irritants such as fenugreek (10).

FIGURE 1.3. Skull operation performed by means of a trephine. From La Chirurgia by Roland de Parme, fourteenth century. (Biblioteca Casanatense, Rome.) (Courtesy of Richardson-Merrill, Inc.)

FIGURE 1.4. Pre-Columbian tumi used for trephination. Sculpture on the handle end depicts its use. Made of champi, an alloy of copper, gold, and silver. Northern coast of Peru, Chimu period (about 1300–1500 AD). (Courtesy of Richardson-Merrill, Inc.)

FIGURE 1.5. Treatment of a child’s hydrocephalus. From La Chirurgie des Ilkhani by Charaf-ed Din, 1465. (Biblothèque Nationale, Paris.) (Courtesy of Richardson-Merrill, Inc.)

The Renaissance

During the great revival of art, literature, and learning that began in Italy in the fourteenth century and spread throughout Europe over the next 200 years, the ban on human dissection was lifted. Outstanding work was accomplished by such great anatomists as Vesalius, Eustachius, and Sylvius. Morgagni demonstrated remarkable developments in the understanding of the central nervous system. Despite all this activity, no further intracranial surgery was described.

That neurosurgery was practiced widely in the sixteenth century is evidenced by the surgeon’s case of Ambroise Paré, surgeon to the King of France during the 1560s: of 13 surgical instruments, 5 are trephines (Figure 1.6).

FIGURE 1.6. A surgeon’s case, attributed to Ambroise Paré. Bottom to top: hand levator, bistoury, two retractors, four trephines, a punch, two double-curved levators, a brace with a fifth trephine, and a key. (Museum in Laval, France.) (Courtesy of Richardson-Merrill, Inc.)

At the beginning of the seventeenth century, one of the first medical textbooks written in English appeared: The Physician’s Practice, wherein are contained all inward Diseases from the Head to the Foot by that famous and worthy Physician, Walter Bruel. The book describes in great anatomic detail headaches, palsies, paralyses, brain inflammations, and all the causes thereof. Surgery was not recommended. Instead, the reader was advised to bleed the nose to let the evil out, and to use rosemary flowers and the roots of elecampany as an opiate (11). Bathing the patient in water prepared from flayed foxes and their whelps was guaranteed to produce results. Horse leeches applied to the temporal artery, diuretics, and cathartics were strongly recommended as means of reducing increased intracranial pressure. Gross humors could be abated and turned into vapors by holding a red-hot frying pan over the patient’s shaven head.

Throughout the eighteenth century, much anatomic dissection and further understanding of human anatomy and physiology were accomplished. By 1765, Cotugno had described the cerebrospinal fluid and outlined its composition and some of its function (12), but still no surgical advances were reported.

The Nineteenth Century

In 1829 Sir Astley Cooper, consulting surgeon to Guy’s Hospital in London, published a series of lectures he had delivered in the operating theater at St. Thomas’s Hospital on the principles and practice of surgery. He stated that trephining in concussion is now so completely abandoned that in the last four years I do not know that I have performed it once, whilst 35 years ago I would have performed it five or six times a year. Instead, he recommended frequent bleeding, calomel purges, and leeches (13). The leeches again were to be applied to the temporal arteries. Undoubtedly, the many successes recounted in his lectures could only have been due to a brinksmanship reduction of intracranial pressure by hypovolemia. Anesthesia was achieved with liberal doses of wine if it was needed at all. The surgeon gaily noted that the wine was rarely necessary, as either the patients were already in an obtunded state or the surgery was not painful enough (cf. Aretæus).

In 1846, Dr. J.F. Malgaigne from the Faculté de Médicine in Paris wrote a manual of operative surgery that included descriptions of puncture operations for hydrocephalus and various types of nerve divisions for pain relief (frontal, infraorbital, facial, and inferior dental and sciatic). A chapter on the means of diminishing pain during surgery was included. Although four years had elapsed since Crawford Long had performed the first operation under ether anesthesia, Malgaigne mentioned only the use of narcotics, animal magnetism, or cutting the nerve supply to the area (14). He also outlined James Moore’s experiments using a Dupuytren compressor to produce sufficient pressure on the nerve supplying the area to render the incised part analgesic. Other methods suggested were excessive venesection, as described by Wardrop, or insensibility by mesmerism.

The Discovery of General Anesthesia

Sir Humphry Davy at the end of the eighteenth century had discovered the remarkable properties exercised on the nervous system by the inhalation of nitrous oxide. Experiments were made with the gas in the hope of relieving pain during surgical operation, but they did not prove satisfactory and were abandoned except as a means of amusement (15).

However, in 1844 Horace Wells, a dentist from Hartford, Connecticut, inhaled nitrous oxide to render himself insensible during a tooth extraction. The experiment succeeded and Wells repeated it on some of his patients. He failed on several occasions, however, and it was left to his pupil and colleague, W.T.G. Morton, to make the first convincing demonstration of anesthesia. Morton was a dentist who had followed the work of Crawford Long of Danielsville, Georgia. In 1847 Morton applied to the Massachusetts General Hospital for permission to administer sulfuric ether during Dr. J.C. Warren’s operation to remove a tumor of the neck. Thus was modern anesthesia born (2).

Dr. James Simpson of Edinburgh introduced chloroform as an anesthetic agent in 1848. The drug had been simultaneously prepared by Guthrie in the United States and Soubeiran in France in 1831 and by Liebig in Germany a year later. Flourens first described chloroform’s anesthetic properties in 1847, and Alexander Dumas gave the drug its name. When Queen Victoria received chloroform during the birth of one of her children, the agent’s widespread acceptance in Great Britain was assured.

By 1860, several means of local anesthesia had been developed. Dr. J. Arnott described a frigorific mixture of ice, snow, and salt. Dr. Richardson used a fine spray jet of ether with a low specific gravity to freeze an area of skin before making the incision (10).

In 1869, John Erichsen of University College Hospital in London wrote a textbook on the science and art of surgery. His summary after twenty years of general use of anesthetic techniques is as current now as it was then (10):

The employment of anaesthetics in surgery is undoubtedly one of the greatest boons ever conferred upon mankind. To the patient it is invaluable in preventing the occurrence of pain and to the surgeon in relieving him of the stress of inflicting it. Anaesthesia is not, however, an unmixed good. Every agent by which it can be induced produces a powerful impression on the system and may occasion dangerous consequences when too freely or carelessly given; and even with every possible care, it appears certain that the inhalation of any anaesthetic agent is in some cases almost inevitably fatal. We cannot purchase immunity from suffering without incurring a certain degree of danger. There can, however, be little doubt that many of the deaths that have followed the inhalation of anaesthetics have resulted from want of knowledge or of due care on the part of the administrators. Yet, whatever precautions be taken, there is reason to fear that a fatal result must occasionally happen. This immediate result, which is but very small, is more than counterbalanced by the immunity from other dangers during operations which used formerly to occur.

The Origins of Neuroanesthesia

On the state of the neurosurgical art at this time, Dr. Erichsen wrote that the safest practice (for concussion) is to wrap the patient up warmly in blankets; to put hot bottles around him. Alcoholic stimulants of all kinds should be avoided (10). Should deterioration in the general condition occur, however, purging, bleeding, and leeches were still the principal therapy. He did note a beneficial effect of opiates in general cerebral irritation to quiet the patient and induce sleep, although great care was to be taken, especially if tachycardia was apparent. In summary, he wrote: In the treatment of injuries of the brain, little can be done after the system has rallied from the shock, beyond attention to strict antiphlogistic treatment, though this need not be of a very active kind. As much should be left to nature as possible, the surgeon merely removing all sources of irritation and excitement from his patient and applying simple local dressings. He described the operation of trephining as important but not used as much as previously. Indications for such intervention were compression and inflammation. Results were not favorable: of 45 patients described by Lente at New York Hospital, 11 recovered. Of 17 patients that Erichsen himself, along with Cooper and Liston, had treated at University College Hospital, only 6 recovered (10).

In the United States, the influence of Long and Morton remained. An extremely detailed record is preserved in Lumberton, New Jersey, of Mary Catherine Anderson, age 17, shot in the head on February 7, 1887 (16). On February 22, four notable physicians, Pancoast, Spitzka, Girdner, and Spiller, crowded together in a tiny cottage and used a telephonic probe in an unsuccessful attempt to locate the bullet. Under ether anesthesia the girl’s condition rapidly deteriorated, and the procedure was abandoned. Unfortunately, she died some two weeks later without regaining consciousness, and the case was referred to the judicial system.

The realization that anesthesia for neurosurgery requires special consideration was established independently by four neurosurgeons: Victor Horsley, William Macewen, Harvey Cushing, and Fedor Krause.

Victor Horsley

Sir Victor Horsley (Figure 1.7) is acknowledged as the father of neurosurgery in England. In 1880, as a house surgeon to John Marshall at University College Hospital, London, he began a long series of experiments on his own brain. He or a friend anesthetized him some 50 times, and Horsley devised ways of recording and signaling his experiences. It is reported that the hospital authorities noted an increased consumption of gas (17)— undoubtedly today such behavior would mandate instant suspension and drug rehabilitation.

FIGURE 1.7. Sir Victor Horsley.

Horsley’s observations on nitrous oxide anesthesia were published in the October issue of Brain: experimenting on myself … the anaesthesia was complete and pushed until rigidity and sometimes cyanosis resulted. The recovery of consciousness was very frequently attended with considerable muscular spasm and semi-coordinated convulsive struggles and excitement (18). It was to be many years before these detrimental effects of nitrous oxide on the central nervous system were again recognized (19).

Between 1883 and 1885, Horsley investigated the different intracranial effects during surgery of chloroform, ether, and morphine sulfate. He concluded that ether caused blood pressure to rise, increased blood viscosity, and prompted excessive bleeding, dangerous postoperative vomiting, and excitement; thus, he concluded that it should not be used in neurosurgery. He found morphine valuable because of the apparent decrease in cerebral blood flow and more readily controlled hemorrhage in the surgical field (20). His preference was for chloroform, though, and he advised the judicious use of chloroform to control haemorrhage.

His first operation at Queen Square Hospital was on May 25, 1886. The patient, a 22-year-old man identified as James B, suffered from intermittent status epilepticus due to head trauma sustained as a child (21). Under chloroform anesthesia, Horsley removed the scar in the brain and the surrounding brain substance to a depth of 2 cm. The outcome was most successful except for an omission noted by Dr. Hughlings Jackson, physician of record: Here’s the first operation of this kind that we ever had at the Hospital; the patient is a Scotsman. We had the chance of getting a joke into his head and we failed to take advantage of it (22).

Horsley believed major intracranial surgery should be performed in two stages to minimize shock. He recognized the value of hypotension, which he achieved by increasing the depth of anesthesia (22). In his earlier operations he combined morphine with chloroform, but later he used only chloroform because of its respiratory depressant effects (17).

Death under chloroform was not uncommon, however. Between 1864 and 1912, eight committees and commissions were convened to study the drug. In 1901, the British Medical Association appointed a Special Chloroform Committee including Doctors Wallers, Sherrington, Harcourt, Buxton, and Horsley. It had already been shown that rather less than 2% chloroform vapor in air was sufficient to induce anesthesia, and much less was required for maintenance. Debate centered around the need for an apparatus to determine the percentage of vapor exactly, as opposed to simply sprinkling the drug on a fold of cloth.

The issue was that of science dictating to practice. Horsley insisted that the percentage should be controlled. He used a vaporizer designed by Vernon Harcourt, a physical chemist, which delivered 2% as a maximum (Figure 1.8). During craniotomy, Horsley ruled that chloroform administration should be reduced to 0.5% or less after removal of the bone (23). He considered that an exact determination of the percentage delivered was particularly important in patients with raised intracranial pressure, thinking that a concentration safe under normal circumstances might be fatal in these patients (Figure 1.9). A cylinder of oxygen was adjusted to the inhaler in the belief that giving oxygen instead of chloroform might reduce capillary bleeding. Dr. Mannell, his anesthetist from 1904 to 1914, noted that Horsley’s demand for reduced concentrations often made it necessary for assistants to restrain patients intraoperatively (24).

FIGURE 1.8. The Vernon Harcourt vaporizer arranged with a cylinder of compressed oxygen.

FIGURE 1.9. Sir Victor Horsley’s pain graph.

William Macewen

In Scotland, Sir William Macewen (Figure 1.10) introduced a flexible metal tube, passed through the mouth, instead of tracheotomy or laryngotomy during operations on the head and neck (25,26). He also insisted that anesthetics be administered only by trained individuals and instituted formal lectures and certification (27,28). He was noted for his clinical acumen and tenacity in reporting physical signs. After a long series of observations, he mapped out pupillary changes in response to anesthetics, cerebral injuries, and intoxication.

FIGURE 1.10. Sir William Macewen.

Macewen disliked ether because of its stimulant action on the heart and salivary glands (29). He preferred chloroform, believing its cardiac depressant effect was of no importance and even advantageous, and could be reversed by ether if necessary. He cautioned that anesthetics must be used with care in acute inflammatory cerebral disease, as prolonged or deep anesthesia could increase fluid retention in an already edematous brain. Chloroform was to be given gradually and could be supplemented with a 1/8 g morphine suppository. However, because even small doses of morphine can have very long-lasting effects, that drug could be omitted.

Harvey Cushing

Harvey Cushing (Figure 1.11), a great pioneer of American neurosurgery, was less successful as an anesthesiologist. While a second-year medical student at the Massachusetts General Hospital in 1893, he anesthetized a young woman with a strangulated hernia. Cushing recorded that he used 1/60 g atropine, subcutaneous brandy, 1/60 g strychnine, and 1/100 g nitroglycerine prior to etherization with the sponge. The patient died during induction (30), and Cushing’s future writings frequently reflected his discontent with the inadequacies of anesthesia administered by unskilled students.

FIGURE 1.11. Dr. Harvey Cushing.

Cushing is credited with several important contributions to the development of neuroanesthesia. In 1897, working on a principle introduced by William S. Halsted (31), he began to experiment with block anesthesia produced by cocaine infiltration. At about this time, he and a classmate, Amory Coleman, introduced ether charts, which were quickly developed into the anesthetic record (Figure 1.12). Cushing also championed the Riva-Rocci pneumatic device for continuous recording of blood pressure during surgery after seeing the instrument at Padua in 1901. He attached great importance to continuous auscultation of the heart and lungs, a technique he learned from his anesthesiologist, Dr. S. Griffith Davis (32).

FIGURE 1.12. One of the ether charts introduced by Cushing and Coleman in 1895 to increase safety in surgical procedures.

Cushing remained skeptical about the safety of ether for neurosurgical anesthesia mainly because of the continued intraoperative mortality. Students at the Johns Hopkins Medical School were permitted to administer ether just as had been the case at Harvard, and Cushing, as assistant resident under Halsted, could not change the practice. Thus he began his experiments with block anesthesia by cocaine infiltration (30). He popularized various local anesthetic techniques and coined the term regional anesthesia. In 1929, a patient from whom he had removed a large intracranial cyst as a demonstration for Pavlov reported: One of the secrets of Dr. Cushing’s success is that he uses nothing except a local anaesthetic which permits the normal functioning of the heart and other organs during the operation (32). Cushing’s preference was shared by DeMartel, who in 1913 adopted local infiltration for all types of neurosurgery (Figure 1.13).

FIGURE 1.13. During the early part of the twentieth century, local infiltration was used frequently for craniotomy, especially in the United States.

Fedor Krause

Fedor Krause (Figure 1.14), born in Friedland in 1857, founded German neurological surgery. After working as assistant to Richard Volkman at the Surgical University Hospital at Halle from 1883 to 1892, he went to Altona and then to Berlin (33,34). During his time with Volkman, he saw a morphine/chloroform combination in use but was not convinced it was advantageous for neurosurgical procedures.

FIGURE 1.14. Professor Fedor Krause.

Starting in 1889 his preference was for chloroform alone (35), but he recognized the value of morphine in small doses for postoperative pain relief in adults. Although he appreciated the greater overall safety of ether, he recommended against its use because of venous bleeding. Rarely, he conceded, ether might have a place in the care of patients with noncompensated heart lesions being operated on for removal of the Gasserian ganglion.

Like Horsley, Krause suggested increasing the concentration of chloroform to cause hypotension and decrease bleeding. He noted a tendency with intracranial tumors for respiration to cease suddenly and cause death. He considered oxygenation especially important for patients with respiratory problems and favored a Roth-Dräger oxygen/chloroform apparatus, which allowed administration of 100% oxygen. Like Horsley and Macewen, Krause emphasized that the brain is not sensitive to pain and only very light narcosis is needed. Anesthetic concentrations need to be increased during surgery of the scalp, periosteum, and dura, however (35).

When some surgeons began to advocate local anesthesia, Kraus questioned the technique. He considered that pain was not the only problem: preparation for surgery, a positive attitude, and psychological status must all be carefully controlled. In particular, he noted that death might be caused by severe mental disturbance prior to anesthesia. He concluded that a rapid, aseptic surgical technique, minimal blood loss, maintenance of normothermia (especially avoidance of hypothermia), and general narcosis were essential to a good outcome.

In some circumstances, however, local anesthesia—particularly novacain 0.5% with 1% epinephrin (15 drops per 100 cc)—could be used for spinal surgery; Braun had recommended the technique (36). Krause injected the solution above and below the spinous processes in four aliquots of 5 ml. Anesthesia was satisfactory until the dura had to be detached from the inner surface of the vertebral arch. The laminectome caused less pain; however, the technique is only effective in patients who can exercise a certain degree of self control (35). Krause felt that spinal anesthesia as described by Augustus Bier (37) was rarely necessary, especially if the cord was not compressed.

The Twentieth Century

Willstaetter and Duisburg synthesized tribromethanol in 1923, and Butzengeiger and Eichholtz used it that same year as the sole anesthetic agent for their neurosurgical procedures. At the Johns Hopkins Hospital in 1931, Walter Dandy administered the agent rectally to reduce elevated intracranial pressure (38). Leo Davidoff (Figure 1.15), finding that the effects wore off too quickly, used tribromethanol in combination with local infiltration (39).

FIGURE 1.15. Professor Leo Davidoff, First Professor and Chairman, Department of Neurological Surgery, Albert Einstein College of Medicine and Montefiore Medicai Center.

Trichlorethylene with nitrous oxide as a neuroanesthetic technique gained considerable popularity in the British Commonwealth. After D.E. Jackson described it in 1934 (40), Hewer published several successful case reports. Hershenson used low concentrations of closed-circuit cyclopropane and reported on his method in 1942 (41). The cyclopropane technique never became popular, however, undoubtedly because of the danger of explosion.

Volwiler and Tabern synthesized thiopental in 1930, and Lundy and Waters introduced it into clinical practice four years later. A report by Shannon and Gardner in 1946 describes the use of thiopental for all types of neurosurgery (42), but its popularity was short-lived. Halothane was synthesized by Raventos and Suckling in 1956 and introduced into clinical anethesia by Johnstone in the same year (43–45). It became one of the most frequently used anesthetics in neurosurgery and paved the way for isoflurane.

Besides anesthetic agents, many techniques developed over the past century have greatly accelerated the growth of neurosurgery and neuroanesthesia. The cautery and the operating microscope were breakthroughs for neurosurgery. In anesthesia the most important innovation was endotracheal intubation, introduced by Macewen (25,26) and adopted routinely for surgery by Magill and Rowbotham in 1916. At last ventilation could be controlled, and the importance of the partial pressure of arterial blood gases in controlling cerebral blood flow was apparent.

All degrees of hypothermia from minimal to profound have been paraded in the neurosurgical arena. Hypothermia using cardiopulmonary bypass techniques has been largely abandoned, although interest in the technique has recently been rekindled for therapy of basilar artery aneurysms.

Minute control over blood pressure can be accomplished through a microinfusion of some potent hypotensive agent such as nitroprusside. The effects can be monitored by continuous recording from an arterial cannula and transducer. Similarly, arterial blood gas and gas chromatography analyses may be continuously obtained using an on-line sensor. Other ongoing measurements may be made of intracranial pressure, cerebral perfusion pressure, cerebral blood flow, evoked potentials, brain retractor pressures, and electroencephalographic changes. With the possible exception of cardiac surgery, neuroanesthesia may be unique among the anesthetic subspecialties in the degree of precision monitoring that it affords.

CONCLUSIONS

Neurosurgery, like anesthesia, has an active and productive history of little more than 100 years. Remarkable advances in both specialties over the past century have made treatment possible for a broad range of disorders involving the delicate central nervous system.

The principles and practice of neuroanesthesia must rest on three factors: use of rapid and reversible agents, maintenance of a stable environment, and control of intracranial pressure. The inescapable verity is that the brain remains irreplaceable. While renal and cardiac transplantation have become commonplace, and lung, liver, and pancreas replacement noteworthy but not unusual, the brain is still unsupplantable. A goal of this book is to clarify how the anesthesiologist and neurosurgeon can work as a team to protect and preserve this extraordinary computer.

REFERENCES

1. Schapira, M. Evolution of anesthesia for neurosurgery. NY State J Med. 1964; 64:1301–1305. [June 1].

2. Raper, HR.Man against pain, the epic of anesthesia. New York: Prentice-Hall, 1945.

3. The Edwin Smith Surgical PapyrusBreasted, JH, eds. University of Chicago Oriental Institute Pub.; 177. University of Chicago Press, Chicago, 1930:596.

4. Prunièrés, D. Sur les crânes artificiellement perforés à l’époque des Dolmens. Bull Mem Soc Anthrop (Paris). 1874; 9:185–205.

5. Broca, P., Remarques sur le siège de la faculté du langage articulé suivies d’une observation d’aphémie. Bull Soc Anat. 1861; S.2:330–357.

6. Walker, AE. A history of neurological surgery. New York: Hafner, 1951; 6.

7. Lastres, JB, Cabieses, F. La trepanacion del craneo en el antiiguo Peru. Lima: Universidád Nacional Mayor de San Marcos, 1960; 146.

8. Aretæus, the CappodocianF Adams, ed. Extant works. Syndenham Society: London, 1856:469.

9. Veith I, ed. The yellow emperor’s classic of internal medicine. Baltimore: Williams & Wilkins, 1949.

10. Erichsen, JE. Science and art of surgery. Philadelphia: Henry C Lea, 1869; 40–47. [335–337].

11. Bruel, W. 2nd Ed.. The physician’s practice; 10. John Warton for William Sheares, London, 1639:76–89.

12. Cotugno, D.De ischiade nervosa commentarius. Naples: Simoniana, 1762.

13. Cooper, A. Lectures in the principles and practice of surgery. London: Westley, 1829; 119–129.

14. Malgaigne, JF. Manual of operative surgery. London: Henry Renshaw, 1846; 42–43. [109–116].

15. Davy, H. Researches chemical and philosophical chiefly concerning nitrous oxide. Bristol: Biggs and Cottle, 1800; 333–343.

16. Henderson, AR. Prominent medicine convenes at Lumberton, 1887. J Med Soc NJ. 1976; 73(1):18–22.

17. Paget, S. Sir Victory Horsley, a study of his life and work. London: Constable, 1919; 40–41.

18. Frost, EAM. Central nervous system effects of nitrous oxide. In: El Eger II, ed. Nitrous Oxide N2O. New York: Elsevier; 1985:157–176.

19. Shapira, M. Evolution of anesthesia for neurosurgery. NY State J Med. 1964; 64:1301–1305.

20. Horsley, V. On the technique of operations on the central nervous system. Br Med J. 1906; 2:411–423.

21. Horsley, V. Brain surgery. Br Med J. 1886; 2:670–675.

22. Lyons, JB. Citizen surgeon. London: Peter Downay, 1966; 85–86.

23. Horsley, V. On the technique of operations on the central nervous system. Address in Surgery, Toronto: Lancet, 1906; 484. [ii].

24. Mannell, Z. Anaesthesia in intracranial surgery. Am J Surg (Anesth Supp). 1924; 38:44.

25. Macewen, W. The introduction of tubes into the larynx through the mouth instead of tracheotomy and laryngotomy. Glasgow Med J. 1879; 9:72–74. [and 12;218–221].

26. Macewen, W. Clinical observations on the introduction of tracheal tubes by the mouth instead of performing tracheotomy or laryngotomy. Br Med J. 1880; 2:122–124. [(July 24), 163–265 (July 25)].

27. Board of Managers Reports. Glasgow Royal Infirmary 1882–83, Archives; University of Glasgow.

28. Watt, OM. Glasgow anaesthetics 1846–1946. Clydebank: James Pender, 1962; 21.

29. Macewen, W. Introduction to a discussion on anaesthetics. Glasgow Med J. 1890; 34:321–332.

30. Fulton, JF. Harvey Cushing. Springfield, IL: Charles C Thomas, 1946; 69–70. [120, 578.].

31. Halsted, WS. Surgical papers; Vol 1. Johns Hopkins Press, Baltimore, 1924:167–178.

32. Cushing, HW. Some principles of cerebral surgery. JAMA. 1909; 52:184–192.

33. Behrend, CM. Fedor Krause und die Anfänge der Neurochirugie in Deutschland. Dtsch Med Wochenschrift. 1957; 82(15):519–520.

34. Jefferson, G. Fedor Krause und die neurologische Chirurgie: Fedor Krause Gedächtnisvorlesung. Acta Neurochir Wein. Vienna: Springer-Verlag. 1960; 9(1):661–664.

35. Krause, F.Haubold, H, Thorek, M, eds. Surgery of the brain and spinal cord based on personal experiences; vol 1. Rebman, New York, 1912:137–138.

36. Braun, H. Uber die Lokalanästhesie im Krankenhaus nebst Bemerkung ü die Technik der örtlichen Anästhesierung. Beitr Klin Chir. 1909; 62:641–685.

37. Bier, A. Versuche über Cocainisirung des Rückenmarkes. Dtsch Chir. 1899; 51:361–369.

38. Dandy, WE. Avertin anesthesia in neurologic surgery. JAMA. 1931; 96:1860–1864. (May 30)

39. Davidoff, LM. Avertin as a basal anesthetic for craniotomy. Bull Neurol Inst. 1934; 3:544–550.

40. Jackson, DE. A study of analgesia and anesthesia with special reference to such substances as trichlorethylene and vinesthene together with apparatus for their administration. Anesth Analg (Cleve) Current Researches. 1934; 13:198–203.

41. Hershenson, BB. Some observations on anesthesia for neurosurgery. NY State J Med. 1942; 42:2111–2118.

42. Shannon, EW, Gardner, WJ. Pentothal sodium anesthesia in neurological surgery. N Engl J Med. 1946; 234:15–16.

43. Raventos J. 20th International Physiological Congress, Brussels. Abstracts of Communications. 1956:754.

44. Sadove, MS, Wallace, VE. Halothane. Philadelphia: FA Davis, 1962; A3–A16.

45. Johnstone, M. The human cardiovascular response to flurothane anaesthesia. Br J Anaesth. 1956; 28:392–410.

I

CEREBRAL PHYSIOLOGY AND EVALUATION

2

Cerebral Circulation and Metabolism

F. Harrison Boehm, Jr. and R.A. de Los Reyes

Publisher Summary

This chapter reviews the anatomy and physiology of the cerebral circulation in health and disease and intraoperative alterations of the circulation. The cerebral circulation is of obvious importance to an organ that comprises only 2% of body weight but demands 15% of the cardiac output and 20% of the inspired oxygen at rest. The cerebral circulation may be divided into the anterior (carotid) and posterior (vertebrobasilar) circulations. These are joined at the base of the brain by a variable anastomotic system, forming the circle of Willis. The right common carotid artery arises from the innominate artery, while the left common carotid has a direct origin from the aortic arch. Several features peculiar to the cerebral circulation are of interest to the physiologist as well as to the clinician for their implications in a variety of disease states. This is particularly applicable to the cerebrovascular system’s ability to regulate its own blood flow, the blood–brain barrier, and the consequences of perfusing a vital organ encased within a closed space.

The cerebral circulation is of obvious importance to an organ that comprises only 2% of body weight but demands 15% of the cardiac output and 20% of the inspired oxygen at rest (1). This chapter reviews the anatomy and physiology of the cerebral circulation in health and disease and intraoperative alterations of the circulation.

ANATOMY OF THE CEREBRAL CIRCULATION

The cerebral circulation may be divided into the anterior (carotid) and posterior (vertebrobasilar) circulations. These are joined at the base of the brain by a variable anastomotic system, forming the circle of Willis (Figure 2.1).

FIGURE 2.1. The circle of Willis, as it is situated in the base of the brain. (From: Pernkopf. Atlas of topographical and applied human anatomy. Baltimore and Munich: Urban & Schwarzenberg, 1980.)

Anterior Circulation

The right common carotid artery arises from the innominate artery, while the left common carotid has a direct origin from the aortic arch. At approximately the level of the fourth cervical vertebra (2,3), the common carotid bifurcates into the external carotid, which supplies the face and scalp, and the internal carotid, which supplies the intracranial circulation (Figure 2.2). Several potential sites for naturally occurring anastomoses between these two circulations exist. The most common is retrograde flow through the orbit by way of the ophthalmic artery (Figure 2.3).

FIGURE 2.2. Bifurcation of the common carotid artery. (From: Wood JH, ed. Cerebral blood flow. New York: McGraw-Hill, 1987:20. With permission of the author and publisher.)

FIGURE 2.3. The external carotid artery; external-internal and external vertebral communications. (From: Wood JH, ed. Cerebral blood flow. New York: McGraw-Hill, 1987:21. With permission of the author and publisher.)

The internal carotid artery (ICA) may be divided into the cervical (C1), petrous (C2), intracavernous (C3), and supraclinoid (C4) segments. The meningohypophyseal trunk arises from the intracavernous carotid and gives off branches that supply the pituitary gland and basal meninges (4).

The petrous carotid is occasionally involved in skull-base tumors, but direct operation on this portion of the artery, other than dissection of tumors away from the artery, is extremely rare. The cavernous carotid may be involved in cases of carotid-cavernous (C-C) fistulas, intracavernous aneurysms, or tumors. Although still in its infancy as an operative procedure, direct repair of these entities, with preservation of patency of the parent artery, is attempted with increasing frequency (5–7).

After emerging from the cavernous sinus the ICA pierces the inner layer of the dura to form the supraclinoid portion, which extends to the carotid bifurcation. The first intradural branch of the internal carotid is the ophthalmic artery. This artery supplies the majority of the blood flow to the orbit and, because of its extensive anastomoses with the external circulation, is a potential source of collateral circulation.

The next branch of the carotid, the posterior communicating artery (PCoA), provides a connection between the anterior and posterior circulations by joining the latter at the first portion of the posterior cerebral artery. On the average, seven branches arise from the medial aspect of this artery, supplying the lateral aspect of the brainstem and the inferior aspects of the basal ganglia (8). Clipping of this artery at either end is usually not associated with any neurological deficit as long as the above-mentioned branches are spared. However, if the artery is of the fetal configuration, with a substantial connection to the posterior circulation, marked by a large artery with substantial angiographic evidence of posterior circulation irrigation via the PCoA, then sacrificing the artery can also have deleterious effects. It is estimated that 22% of PCoA vessels are in the fetal category (9), so named because in fact these vessels are large in the fetal state but tend to regress during childhood.

The anterior choroidal artery (AChoA) usually arises 2 to 4 mm distal to the PCoA and is the last major branch before the carotid bifurcation. This artery supplies the visual pathways (optic tract, lateral geniculate body, optic radiations), parts of the basal ganglia, and the corticospinal pathways (posterior limb of the internal capsule, middle third of the cerebral peduncle). Occlusion of the AChoA may result in deficits ranging from hemiplegia and hemianopsia to no deficit at all (10).

The AChoA is most frequently occluded accidentally during clipping of a PCoA aneurysm or intentionally during clipping of a ruptured AChoA aneurysm when the parent artery arises from the dome of the aneurysm (11). The former complication can be avoided by careful microsurgical technique and knowledge of the anatomy, and awareness of this potential pitfall. The latter is a judgment call. The rate of permanent hemiparesis or hemiplegia in elective clipping of the AChoA (an outdated treatment for Parkinson’s disease) ranges from 6 to 20% (12). This complication must be weighed against the expected morbidity and mortality of wrapping (but not excluding from the circulation) a ruptured AChoA aneurysm.

After giving off the anterior choroidal artery, the ICA bifurcates to form the anterior cerebral artery (ACA) and the middle cerebral artery (MCA). The portion of the ACA between the ICA bifurcation and the anterior communicating artery (ACoA) is known as the Al segment of the ACA. This segment gives rise to perforators that perfuse the internal capsule, thalamus, and hypothalamus. Injury to these arteries may result in psychological and intellectual dysfunction, as well as motor deficits (13,14). The A1 segment has been found to be hypoplastic in approximately 10% of autopsies (15,16). This figure rises to approximately 50% in patients with ACoA aneurysms (17). In those patients with ACoA aneurysms who have hypoplastic A1 segments, the aneurysm is three times as likely to arise from the dominant A1 as from the hypoplastic side (18).

The ACoA connects the two ACAs and defines the point at which the Al becomes the distal anterior cerebral artery, A2. Perforators from the ACoA supply the anterior hypothalamus (19), and damage to these vessels can result in lethargy and vegetative disturbances. The largest of the branches in the ACA-ACoA region is the recurrent artery of Heubner (20). This vessel supplies the anterior portions of the basal ganglia and internal capsule, and its accidental occlusion in the course of surgery for clipping of an ACoA aneurysm may result in hemiparesis.

The distal anterior cerebral artery (A2) then courses from the ACoA superiorly and posteriorly, in the interhemispheric fissure, and divides to form the pericallosal and callosomarginal arteries near the genu of the corpus callosum. The A2 and its branches supply the medial aspects of the frontal and parietal lobes. Occlusions involving the A2 segment affect the lower extremities more than the upper, sometimes to the point of mimicking spinal cord disease (21).

The middle cerebral artery (MCA) is the largest branch of the ICA (22). The first segment (Ml) of the MCA extends from the ICA bifurcation to the MCA bifurcation in the sylvian fissure. It is from the Ml segment that the medial and lateral lenticulostriate arteries arise. These arteries, which take off at right angles from the dorsal aspect of the M1, supply the basal ganglia and especially the superior half of the internal capsule.

In the sylvian fissure the MCA divides into two to four branches, the M2 segments (23). It is at this point that most MCA aneurysms arise. The M2 segments (and their further M3 and M4 segments) course out of the sylvian fissure and spread over the convexity of the hemisphere to supply the lateral aspect of the frontal, parietal, occipital, and temporal lobes.

Posterior Circulation

The vertebral artery (VA) is the first branch from the subclavian artery. After arising at right angles from the subclavian, the VA courses for several centimeters before entering the intervertebral foramen of C6. It then runs through the foramina of C6 through C1 and courses over the superior aspect of the arch of C1 to pierce the atlanto-occipital membrane and enter the cranial cavity. Flowing ventrally and superiorly, it gives rise to the posterior inferior cerebellar artery (PICA) before joining the opposite VA at the midline on the ventral aspect of the pontomedullary junction to form the basilar artery (BA). The BA, after giving off several branches, bifurcates to form the two posterior cerebral arteries at the pontomesencephalic junction. Connection to the anterior circulation via the PCoAs completes the circle of Willis.

The PICA is the largest branch of the posterior (vertebrobasilar) circulation, and supplies the medulla, the inferior vermis, the tonsils, and the inferior aspect