"Triple cross" of the hypoglossal nerve and its microsurgical impact to entrapment disorders.

OBJECTIVE: Cadaveric dissections were performed to review the intracranial and extracranial course of the hypoglossal nerve. The neurological significance of a newly defined "triple cross" of the hypoglossal nerve is discussed. MATERIALS AND METHODS: 10 cadaveric heads (left and right; 20 sides) were dissected using microsurgical techniques. RESULTS: In the cisternal segment of hypoglossal nerve, the diameter of the rostral trunk amounted to 155-680 microm (mean 435 microm), and the caudal trunk to 210-820 microm (mean 482 microm). The roots formed three trunks in 20% of the hypoglossal nerves and two trunks in the rest. As a first cross, the anterior medullary segment of the vertebral artery crossed the hypoglossal nerve roots in 14 of 20 sides (70%). As a rare variation, the vertebral artery extended medial to the nerve (25%) or between its roots (5%). The second cross was found between the descendens hypoglossus and the occipital artery (75%), sternocleidomastoid artery and vein complex (15%) and external carotid artery (10%). The third cross was shown in the submandibular triangle between the lingual hypoglossus and its drainage vein; vena committans nervus hypoglossus. CONCLUSION: Throughout its way, the hypoglossal nerve passes over vascular structures in three crossing points which may serve as a probable cause of hypoglossal nerve entrapment disorders.

Fiber dissection technique: lateral aspect of the brain.

OBJECTIVE: The fiber dissection technique involves peeling away the white matter tracts of the brain to display its three-dimensional anatomic organization. Early anatomists demonstrated many tracts and fasciculi of the brain using this technique. The complexities of the preparation of the brain and the execution of fiber dissection have led to the neglect of this method, particularly since the development of the microtome and histological techniques. Nevertheless, the fiber dissection technique is a very relevant and reliable method for neurosurgeons to study the details of brain anatomic features. METHODS: Twenty previously frozen, formalin-fixed human brains were dissected from the lateral surface to the medial surface, using the operating microscope. Each stage of the process is described. The primary dissection tools were handmade, thin, wooden spatulas with tips of various sizes. RESULTS: We exposed and studied the myelinated fiber bundles of the brain and acquired a comprehensive understanding of their configurations and locations. CONCLUSION: The complex structures of the brain can be more clearly defined and understood when the fiber dissection technique is used. This knowledge can be incorporated into the preoperative planning process and applied to surgical strategies. Fiber dissection is time-consuming and complex, but it greatly adds to our knowledge of brain anatomic features and thus helps improve the quality of microneurosurgery. Because other anatomic techniques fail to provide a true understanding of the complex internal structures of the brain, the reestablishment of fiber dissection of white matter as a standard study method is recommended.

Arteries of the insula.

OBJECT: The insula is located at the base of the sylvian fissure and is a potential site for pathological processes such as tumors and vascular malformations. Knowledge of insular anatomy and vascularization is essential to perform accurate microsurgical procedures in this region. METHODS: Arterial vascularization of the insula was studied in 20 human cadaver brains (40 hemispheres). The cerebral arteries were perfused with red latex to enhance their visibility, and they were dissected with the aid of an operating microscope. Arteries supplying the insula numbered an average of 96 (range 77-112). Their mean diameter measured 0.23 mm (range 0.1-0.8 mm), and the origin of each artery could be traced to the middle cerebral artery (MCA), predominantly the M2 segment. In 22 hemispheres (55%), one to six insular arteries arose from the M1 segment of the MCA and supplied the region of the limen insulae. In an additional 10 hemispheres (25%), one or two insular arteries arose from the M3 segment of the MCA and supplied the region of either the superior or inferior periinsular sulcus. The insular arteries primarily supply the insular cortex, extreme capsule, and, occasionally, the claustrum and external capsule, but not the putamen, globus pallidus, or internal capsule, which are vascularized by the lateral lenticulostriate arteries (LLAs). However, an average of 9.9 (range four-14) insular arteries in each hemisphere, mostly in the posterior insular region, were similar to perforating arteries and some of these supplied the corona radiata. Larger, more prominent insular arteries (insuloopercular arteries) were also observed (an average of 3.5 per hemisphere, range one-seven). These coursed across the surface of the insula and then looped laterally, extending branches to the medial surfaces of the opercula. CONCLUSIONS: Complete comprehension of the intricate vascularization patterns associated with the insula, as well as proficiency in insular anatomy, are prerequisites to accomplishing appropriate surgical planning and, ultimately, to completing successful exploration and removal of pathological lesions in this region.

A legacy of microneurosurgery: memoirs, lessons, and axioms.

This article is written at the request of the editor. It contains my autobiographical sketch, professional memories, lessons, axioms, and reflections on the present problems in neurodiagnosis and neurotherapy. The combination of microsurgical techniques, the bipolar coagulation technique, the concept of arachnoidal exploration, and the concept of segmental and compartmental occurrence of vascular and neoplastic lesions of the central nervous system, with their predilection sites, allowed microneurosurgery to gradually unfold and proceed within the last 30 years as a continuation of conventional neurosurgical principles established by the founder generation. Today, the lesions in each region of the central nervous system can be accessed without using computer-assisted targeting and navigation technology and can be selectively eliminated ("pure lesionectomy") with acceptable outcomes; the mortality and morbidity rates have been reduced remarkably. Further scientific and technological advances will promote the ongoing evolution in neurodiagnosis and neurotherapy. Competitive neurospecialties are welcomed in the interest of patients, medical sciences, and surgical advances. The younger generation of neurosurgeons will have spent more time in laboratory training, deepening their knowledge of neuroanatomy and gaining experience in surgical techniques. The achievements, limits, and problems of neurosurgery in relation to technology, medical and surgical standards, and controversial treatment options have been presented thoroughly in numerous professional publications. However, the relationship of neurosurgery to the evolution of integral neurophysiology and biochemistry has hitherto been inadequately evaluated. The advances in microbiology, anesthesiology, and topographic neurology have been viewed as essential components of neurosurgery's foundations. A critical analysis proves that this is only partially true. The turning point in the development from craniospinal surgery to physiological neurosurgery began with the research of Th. Kocher, V. Horsley, H. Cushing, and W. Dandy concerning the importance of the cerebrospinal fluid system. This was the first step in a trend toward integral neurophysiology, which initiated neurosurgical procedures on a routine basis. The intensive research on the hypothalamus by R.W. Hess and associates led to intensified studies on the autoregulated integral functional units of the central nervous system ("dynamic homeostasis," in the words of W.B. Cannon). This slowly developing but exciting history of neurophysiology requires patient study to seek out solutions for the present difficulties in neurodiagnosis and neurotherapy, which constitute a similar situation to that encountered by the pioneer surgeons at the end of the last century. In pertinent sections, my personal opinions relating to observations and experiences with a large number of operated patients with vascular and neoplastic lesions are presented. The predilection sites of brain tumors in the neopallial and paleopallial (limbic-paralimbic) areas and brainstem, and their expansive but usually not infiltrative growth, are discussed and documented. The current hypothesis of infiltrative growth of gliomas is opposed. The microsurgical technique for the treatment of various types of lesions is summarized. The principal microsurgical instruments and apparatus are presented with some remarks relating to their conception and manufacture.

A case history of glioma progression.

Low-grade diffuse astrocytomas have an intrinsic tendency for malignant progression but the factors determining the kinetics of this process are still poorly understood. We report here the case of a male patient who developed a fibrillary astrocytoma at the age of 33 years and who underwent six surgical interventions over a period of 17 years without radiotherapy or chemotherapy. The first three biopsies spanned a period of 11 years and led to the diagnosis of low-grade, diffuse astrocytoma (WHO grade II), with a growth fraction (MIB-1 labeling index) of 2.3-3.7%. The fourth to sixth biopsies showed histological features of anaplastic astrocytoma (WHO grade III), with growth fractions between 5.0 and 10.5%. The fraction of gemistocytic neoplastic astrocytes also increased, from 0.3% in the first biopsy to 17.5% in the last biopsy and preceded the increase in proliferative activity and transition to anaplastic astrocytoma. The fraction of tumor cells immunoreactive to BCL-2 increased from 0.3% to 8.2%. A p53 mutation in codon 273 (CGT-->TGT, Arg-->Cys) was identified in the first biopsy and persisted throughout the course of the disease. However, the fraction of cells with p53 protein accumulation increased significantly during progression, from 3.2% in the first biopsy to 13.7% in the last. The absence of additional genetic alterations (PTEN mutations, loss of chromosome 10 and 19q) may be responsible for the slow progression and lack of glioblastoma features even after a 17-year disease duration.

Topographic anatomy of the insular region.

OBJECT: The insula is one of the paralimbic structures and constitutes the invaginated portion of the cerebral cortex, forming the base of the sylvian fissure. The authors provide a detailed anatomical study of the insular region to assist in the process of conceptualizing a reliable surgical approach to allow for a successful course of surgery. METHODS: The topographic anatomy of the insular region was studied in 25 formalin-fixed brain specimens (50 hemispheres). The periinsular sulci (anterior, superior, and inferior) define the limits of the frontoorbital, frontoparietal, and temporal opercula, respectively. The opercula cover and enclose the insula. The limen insula is located in the depths of the sylvian fissure and constitutes the anterobasal portion of the insula. A central insular sulcus divides the insula into two portions, the anterior insula (larger) and the posterior insula (smaller). The anterior insula is composed of three principal short insular gyri (anterior, middle, and posterior) as well as the accessory and transverse insular gyri. All five gyri converge at the insular apex, which represents the most superficial aspect of the insula. The posterior insula is composed of the anterior and posterior long insular gyri and the postcentral insular sulcus, which separates them. The anterior insula was found to be connected exclusively to the frontal lobe, whereas the posterior insula was connected to both the parietal and temporal lobes. Opercular gyri and sulci were observed to interdigitate within the opercula and to interdigitate the gyri and sulci of the insula. Using the fiber dissection technique, various unique anatomical features and relationships of the insula were determined. CONCLUSIONS: The topographic anatomy of the insular region is described in this article, and a practical terminology for gyral and sulcal patterns of surgical significance is presented. This study clarifies and supplements the information presently available to help develop a more coherent surgical concept.

The endovascular treatment of brain arteriovenous malformations.

Advances in superselective microcatheterization techniques, which took place in the past decade, established superselective endovascular exploration as an integral and indispensable tool in the pretherapeutic evaluation of brain AVMs. The strict and routine application of superselective angiography furthered our knowledge on the angioarchitecture of brain AVMs, including vascular composition of the nidus, types of feeding arteries and types and patterns of venous drainage. In addition, various types of weak angioarchitectural elements, such as flow-related aneurysms, intranidal vascular cavities and varix formation proximal to high-grade stenosis of draining veins, could be identified as factors predisposing for AVM rupture. A wide spectrum of secondary angiomorphological changes induced by the arteriovenous shunt of the nidus and occurring up- and downstream of the nidus have been identified as manifestations of high-flow angiopathy. These data help to better predict the natural history, understand the widely variable clinical presentation and to define therapeutic targets of brain AVMs. Correlation of the topography of the AVM as demonstrated by MR with the angioarchitecture as demonstrated by superselective angiography provided a system for topographic-vascular classification of brain AVMs, which proved very useful for patient selection and definition of therapeutic goals. This study showed, that 40% of patients with brain AVMs can be cured by embolization alone with a severe morbidity of 1.3% and a mortality of 1.3%. Part of theses patients can, however, be cured equally effective by microsurgery or radiosurgery. Which modality will be chosen for a particular patient will mainly depend on the locally available expertise and experience, but also on the preference of the patient following its comprehensive information about the chances for cure and the risks associated with each of these therapeutic modalities. Embolization has a significant role in the multimodality treatment of brain AVMs, by either enabling or facilitating subsequent microsurgical or radiosurgical treatment. Appropriately targeted embolization in otherwise untreatable AVMs represents a reasonable form of palliative treatment of either ameliorating the clinical condition of the patient or reducing the potential risk of hemorrhage. Regarding the practical aspects of the endovascular treatment the following conclusions could be drawn from the experience obtained with this series of 387 patients with a brain AVM: (1) The goal of endovascular treatment should be defined prior to the procedure. This does not preclude a change in the goal, if additional information obtained during the procedure make this necessary. (2) The result of endovascular treatment of a brain AVM in terms of the degree of obliteration achieved and complication rate depends mainly on the endovascular strategy developed and the technique applied. These depend on the specific angioarchitecture and topography of the individual AVM, on the past history and clinical presentation of the patient and on the predefined goal of embolization. The strategy should include the definition of embolization targets, the selection of the most appropriate approach for endovascular navigation, the determination of the sequence of catheterization of individual feeding arteries, the selection of the type of catheters and microcatheters, the selection of the appropriate embolic materials as well as the site and mode of their delivery. Thereafter, every endovascular move should be, as in a chess game, the result of a logical plan. (3) Atraumatic superselective microcatheterization is a key point in the endovascular treatment of brain AVMs. It requires manual skills, knowledge of anatomy and respect for the vascular wall. (4) All locations of brain AVMs should be regarded as eloquent, and no distinction should be made between eloquent and non-eloquent areas of the brain when deciding on the execution of embolizatio

The transcallosal-transforaminal approach to the third ventricle with regard to the venous variations in this region.

Surgical approaches to lesions located in the anterior and middle portions of the third ventricle are challenging, even for experienced neurosurgeons. Various exposures involving the foramen of Monro, the choroidal fissure, the fornices, and the lamina terminalis have been advocated in numerous publications. The authors conducted a microsurgical anatomical study in 20 cadaveric brain specimens (40 hemispheres) to identify an exposure of the third ventricle that would avoid compromising vital structures. An investigation of the variations in the subependymal veins of the lateral ventricle in the region of the foramen of Monro was performed, as these structures are intimately associated with the surgical exposure of the third ventricle. In 16 (80%) of the brain specimens studied, 19 (47.5%) of the hemispheres displayed a posterior location of the anterior septal vein-internal cerebral vein (ASV-ICV) junction, 3 to 13 mm (average 6 mm) beyond the foramen of Monro within the velum interpositum, not adjacent to the posterior margin of the foramen of Monro (the classic description). Based on this finding, the authors advocate opening the choroidal fissure as far as the ASV-ICV junction to enlarge the foramen of Monro posteriorly. This technique achieves adequate access to the anterior and middle portions of the third ventricle without causing injury to vital neural or vascular structures. The high incidence of posteriorly located ASV-ICV junctions is a significant factor influencing the successful course of surgery. Precise planning of the surgical approach is possible, because the location of the junction is revealed on preoperative neuroradiological studies, in particular on magnetic resonance venography. It can therefore be determined in advance which foramen of Monro qualifies for posterior enlargement to gain the widest possible access to the third ventricle. This technique was applied in three patients with a third ventricular tumor, and knowledge of the venous variations in this region was an important resource in guiding the operative exposure.

Is there a superior occipitofrontal fasciculus? A microsurgical anatomic study.

OBJECTIVE: Using a fiber-dissection technique, our aim was to expose and study the myelinated fiber bundles of the brain to achieve a clearer conception of their configurations and locations. During the course of our study, the superior occipitofrontal fasciculus became the focus of our interest. Many publications have defined this as a bundle of association fibers, located between the corpus callosum and the caudate nucleus, that connects the frontal and occipital lobes. By examining this area using fiber dissection, we realized that the descriptions of the anatomy are inadequate; thus, we focused on the elucidation of the anatomic structures of this region and, in particular, that known as the superior occipitofrontal fasciculus. METHODS: Twenty previously frozen, formalin-fixed human brains were dissected under the operating microscope using the fiber-dissection technique. RESULTS: On coronal sections of the brain, a structure on the superolateral aspect of the caudate nucleus usually has been identified as the superior occipitofrontal fasciculus. However, our fiber dissections revealed that this structure is the superior thalamic peduncle, that it is composed of projection fibers rather than association fibers, and that it does not interconnect the occipital and frontal lobes. CONCLUSION: The structures of the brain are better understood when the fiber-dissection technique is used to explore their configurations and locations. The resulting information is especially beneficial for planning strategies and tactics of neurosurgical procedures.

The arteries of the corpus callosum: a microsurgical anatomic study.

OBJECTIVE: The corpus callosum is the major commissural pathway connecting the hemispheres of the human brain. It is particularly important, because various tumors and vascular lesions can be located in and around the corpus callosum, and it is a route through which pass several surgical approaches. Performing accurate surgery in this region and avoiding damage to normal structures require that the neurosurgeon have adequate knowledge of the anatomy of the intricate blood supply to this area. METHODS: In 20 cadaver brains, the arteries of the corpus callosum were examined under the operating microscope, with particular attention to the origin, course, anastomoses, number, and caliber of the arteries. RESULTS: In all specimens, the pericallosal and posterior pericallosal arteries were found to be the main sources of blood supply to the corpus callosum. In 80% of the specimens, the anterior communicating artery gave rise to either a subcallosal artery or a median callosal artery, each of which made a substantial contribution to the blood supply of the corpus callosum. A detailed examination of the anatomic features of all the main arteries of supply revealed anastomoses within the callosal sulcus that formed the pericallosal pial plexus. This network supplied the corpus callosum, the radiation of the corpus callosum, and the cingulate gyrus. CONCLUSION: Familiarity with the details of the vascularity of the corpus callosum is crucial when performing surgery in this region. The additional, significant data described expands the knowledge of this anatomy, which can enhance the surgeon's ability to accomplish a more accurate and successful exploration.

Neuropathological findings in 224 patients with temporal lobe epilepsy.

During the period between 1976 and 1990, 247 patients with pharmaco-resistant complex partial seizures and a documented unilateral epileptogenic area in the mediobasal temporal lobe underwent a selective amygdalo-hippocampectomy procedure at our institution. Biopsy specimens from 224 patients (91% of the total) were available for a retrospective histopathological and immunohistochemical review. The tissue specimens of 23 patients without evidence for a macroscopic lesion have been used for neurochemical studies and could not be evaluated histopathologically. The most common temporal lobe pathology were neoplasms in 126 patients, i.e. 56%. Tumor entities observed included 23 astrocytomas (18% of all tumors), 17 gangliogliomas (13%), 15 oligodendrogliomas (12%), 15 cases of glioblastoma multiforme (12%), 13 pilocytic astrocytomas (10%), 12 oligo-astrocytomas (10%), 11 anaplastic astrocytomas (9%) and 20 tumors of various other histologies. In 23 specimens (10%), small foci of oligodendroglia-like clear cells were found. The frequent association of these foci with low-grade gliomas or neural hamartomas raises the possibility that these structures may serve as precursor lesion for neuroepithelial tumors of the temporal lobe. In 98 cases, pathological changes of non-neoplastic origin were encountered. The most common diagnoses in this group included hippocampal gliosis/sclerosis (49 cases, 22%) and vascular malformations (20 cases, 9%). Hamartomas, i.e. focal accumulations of dysplastic neuro-glial cells were diagnosed in 14 patients (6%). In only four cases have we not been able to detect any microscopic pathology. These results indicate that a high proportion of pharmaco-therapy-resistant complex-partial seizures are caused by neoplasms of the temporal lobe, some of which appear to be strikingly overrepresented in this group of patients.

Association of epidermal growth factor receptor gene amplification with loss of chromosome 10 in human glioblastoma multiforme.

Although the loss of tumor suppressor genes and the activation of oncogenes have been established as two of the fundamental mechanisms of tumorigenesis in human cancer, little is known about the possible interactions between these two mechanisms. Loss of genetic material on chromosome 10 and amplification of the epidermal growth factor receptor (EGFR) gene are the most frequently reported genetic abnormalities in glioblastoma multiforme. In order to examine a possible correlation between these two genetic aberrations, the authors studied 106 gliomas (58 glioblastomas, 14 anaplastic astrocytomas, five astrocytomas, nine pilocytic astrocytomas, seven mixed gliomas, six oligodendrogliomas, two ependymomas, one subependymoma, one subependymal giant-cell astrocytoma, and three gangliogliomas) with Southern blot analysis for loss of heterozygosity on both arms of chromosome 10 and for amplification of the EGFR gene. Both the loss of genetic material on chromosome 10 and EGFR gene amplification were restricted to the glioblastomas. Of the 58 glioblastoma patients, 72% showed loss of chromosome 10 and 38% showed EGFR gene amplification. The remaining 28% had neither loss of chromosome 10 nor EGFR gene amplification. Without exception, the glioblastomas that exhibited EGFR gene amplification had also lost genetic material on chromosome 10 (p less than 0.001). This invariable association suggests a relationship between the two genetic events. Moreover, the presence of 15 cases of glioblastoma with loss of chromosome 10 but without EGFR gene amplification may further imply that the loss of a tumor suppressor gene (or genes) on chromosome 10 precedes EGFR gene amplification in glioblastoma tumorigenesis.

Tumours of the limbic and paralimbic system.

240 patients with tumours of the limbic and paralimbic areas are presented. The following tumour growth patterns have been observed: they remain isolated to areas within the allocortex; they spread throughout allocortical regions; they spread from allocortical to mesocortical zones. With the exception of advanced malignant tumours there seems to be a tendency for tumours to spare the adjacent neocortical and medial structures. The tumours can be approached and extirpated using the trans-Sylvian approach and microneurosurgical technique. 56% have been histologically benign. 60% were below 40 years of age. Seizures were the leading manifestation (77%). In 95% the postoperative results were good. There was no peri-operative mortality.

Tumours of the limbic and paralimbic systems.

Clinical manifestations, findings, management and outcome of a series of 177 cases with tumours of the limbic and paralimbic systems are presented. There was no operative mortality. Postoperatively 95% of them had no or only minor neurological deficits. Most of them were able to resume work. Pre-operatively 77% of the patients had epilepsy, but 84% became seizure-free after tumour removal. All 77 cases with malignant tumours died within 1-5 years. In the past many neurosurgeons were reluctant to attempt complete tumour removal in these areas. This series demonstrates the efficacy of highly skilled microneurosurgery.

Central neurocytoma: histopathological variants and therapeutic approaches.

The central neurocytoma has recently been added to the differential diagnosis of intraventricular tumors. Histopathologically, this tumor is characterized by a uniform neoplastic cell population with features of neuronal differentiation. Central neurocytomas occur in young adults, develop in the area of the foramen of Monro, and are usually associated with the septum pellucidum. Initial reports appeared to indicate that these tumors are benign lesions with a favorable postoperative prognosis. The authors present clinical and neuropathological findings in a series of eight patients with central neurocytoma. An anterior transcallosal microneurosurgical approach yielded good outcomes. Postoperative radiation therapy was restricted to two patients with a malignant variant of central neurocytoma and one patient with a recurrent tumor. Observations of anaplastic variants of this neoplasm in two cases and local tumor recurrences in three indicate that the biological behavior and postoperative prognosis of central neurocytoma may not always be as favorable as previously assumed.