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Mehmet Volkan Harput and Uğur Türe

This is the case of a 14-year-old female who presented with headache and seizures. Cranial magnetic resonance imaging revealed an arteriovenous malformation (AVM) located at the posterior portion of the right-sided fusiform gyrus. Cerebral angiography showed that the AVM was fed mainly by branches from the inferior temporal trunk of the posterior cerebral artery. The main venous drainage was to the right transverse sinus through the tentorial vein. The AVM was totally excised through the paramedian supracerebellar-transtentorial approach with the patient in a semisitting position. Postoperative MRI and cerebral angiography confirmed the total resection. The patient was discharged on the 5th postoperative day without neurological deficit.

The video can be found here: https://youtu.be/QPrUl8AP7G8.

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Uğur Türe and M. Necmettin Pamir

Object. Various approaches have been described for resection of the dens of the axis, each of which has potential advantages and disadvantages. Anterior approaches such as the transoral route or its modifications are the most commonly used for resection of this structure. The transcondylar approach, however, which allows the surgeon to view the craniovertebral junction (CVJ) from a lateral perspective, has been introduced by Al-Mefty, et al., as an alternative approach. In this report, the authors describe the surgical technique of the extreme lateral—transatlas approach and their clinical experiences.

Methods. The authors first examined the surgical approach to the dens from a lateral perspective in five cadaveric heads. They found that removal of the lateral mass of the atlas provided adequate exposure for resection of the dens. Following this cadaveric study, the extreme lateral—transatlas approach was successfully performed at the authors' institution over a 1-year period (September 1998–August 1999) in five patients with basilar invagination due to congenital anomaly of the CVJ and rheumatoid arthritis. Furthermore, during the same procedure, unilateral occipitocervical fusion was performed following resection of the dens.

In all cases complete resection of the dens was achieved using the extreme—lateral transatlas approach. This procedure provides a sterile operative field and the ability to perform occipitocervical fusion immediately following the resection. No postoperative complications or craniocervical instability were observed. The mean follow-up period was 17.2 months (range 13–24 months).

Conclusions. The extreme lateral—transatlas approach for resection of the dens was found to be safe and effective. Knowledge of the anatomy of this region, especially of the V3 segment of the vertebral artery, is essential for the success of this procedure.

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Cristina Goga and Uğur Türe

OBJECT

The goal in this study was to explore and further refine comprehension of the anatomical features of the temporal loop, known as Meyer's loop.

METHODS

The lateral and inferior aspects of 20 previously frozen, formalin-fixed human brains were dissected under the operating microscope by using fiber microdissection.

RESULTS

A loop of the fibers in the anterior temporal region was clearly demonstrated in all dissections. This temporal loop, or Meyer's loop, is commonly known as the anterior portion of the optic radiation. Fiber microdissection in this study, however, revealed that various projection fibers that emerge from the sublentiform portion of the internal capsule (IC-SL), which are the temporopontine fibers, occipitopontine fibers, and the posterior thalamic peduncle (which includes the optic radiation), participate in this temporal loop and become a part of the sagittal stratum. No individual optic radiation fibers could be differentiated in the temporal loop. The dissections also disclosed that the anterior extension and angulation of the temporal loop vary significantly.

CONCLUSIONS

The fiber microdissection technique provides clear evidence that a loop in the anterior temporal region exists, but that this temporal loop is not formed exclusively by the optic radiation. Various projection fibers of the IC-SL, of which the optic radiation is only one of the several components, display this common course. The inherent limitations of the fiber dissection technique preclude accurate differentiation among individual fibers of the temporal loop, such as the optic radiation fibers.

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Abdullah Keleş, Mehmet Volkan Harput and Uğur Türe

This video demonstrates resection of a left pontine cavernous malformation that is abutting the floor of the fourth ventricle (f4V). Even though accessing the lesion through the f4V seems to be reasonable, we used a lateral supracerebellar approach through the middle cerebellar peduncle to preserve especially the abducens and facial nuclei. After total resection the patient was neurologically intact at the 3-month follow-up. Postoperative MRI revealed 3.5-mm pontine tissue between the cavity and f4V that appeared to be absent in preoperative MRI. Approaching pontine lesions through the f4V is not the first choice. In our opinion, the philosophy of safe entry zones is a concept to be reassessed.

The video can be found here: https://youtu.be/1Jh6giZc-48.

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Uğur Türe, M. Gazi Yaşargil and Ossama Al-Mefty

✓ 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.

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M. Gazi Yaşargil, Uğur Türe and Dianne C. H. Yaşargil ¸

Object

In this paper the authors correlate the surgical aspects of deep median and paramedian supratentorial lesions with the connective fiber systems of the white matter of the brain.

Methods

The cerebral hemispheres of 10 cadaveric brains were dissected in a mediolateral direction by using the fiber dissection technique, corresponding to the surgical approach.

Conclusions

This study illuminates the delicacy of the intertwined and stratified fiber laminae of the white matter, and establishes that these structures can be preserved at surgical exploration in patients.

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Sait Naderi, Uğur Türe and T. Glenn Pait

The first reference to spinal cord injury is recorded in the Edwin Smith papyrus. Little was known of the function of the cord before Galen's experiments conducted in the second century AD. Galen described the protective coverings of the spinal cord: the bone, posterior longitudinal ligament, dura mater, and pia mater. He gave a detailed account of the gross anatomy of the spinal cord. During the medieval period (AD 700–1500) almost nothing of note was added to Galen's account of spinal cord structure. The first significant work on the spinal cord was that of Blasius in 1666. He was the first to differentiate the gray and white matter of the cord and demonstrated for the first time the origin of the anterior and posterior spinal nerve roots. The elucidation of the various tracts in the spinal cord actually began with demonstrations of pyramidal decussation by Mistichelli (1709) and Pourfoir du Petit (1710). Huber (1739) recorded the first detailed account of spinal roots and the denticulate ligaments. In 1809, Rolando described the substantia gelati-nosa. The microtome, invented in 1824 by Stilling, proved to be one of the fundamental tools for the study of spinal cord anatomy. Stilling's technique involved slicing frozen or alcohol-hardened spinal cord into very thin sections and examining them unstained by using the naked eye or a microscope. With improvements in histological and experimental techniques, modern studies of spinal cord anatomy and function were initiated by Brown-Séquard. In 1846, he gave the first demonstration of the decussation of the sensory tracts. The location and direction of fiber tracts were uncovered by the experimental studies of Burdach (1826), Türck (1849), Clarke (1851), Lissauer (1855), Goll (1860), Flechsig (1876), and Gowers (1880). Bastian (1890) demonstrated that in complete transverse lesions of the spinal cord, reflexes below the level of the lesion are lost and muscle tone is abolished. Flatau (1894) observed the laminar nature of spinal pathways.

The 20th century ushered in a new era in the evaluation of spinal cord function and localization; however, the total understanding of this remarkable organ remains elusive. Perhaps the next century will provide the answers to today's questions about spinal cord localization.

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Hatice Türe, M. Volkan Harput, Nural Bekiroğlu, Özgül Keskin, Özge Köner and Uğur Türe

OBJECTIVE

The semisitting position of a patient confers numerous advantages in various neurosurgical procedures, but venous air embolism is one of the associated complications of this position. To date, no prospective studies of the relationship between the degree of head elevation and the rate and severity of venous air embolism for patients undergoing a procedure in this position have been performed. In this study, the authors compared changes in the severity of venous air embolism according to the degree of head elevation (30° or 45°) in patients undergoing an elective cranial neurosurgical procedure in the semisitting position.

METHODS

One hundred patients undergoing an elective infratentorial craniotomy in the semisitting position were included, and each patient was assigned to 1 of 2 groups. In Group 1, each patient’s head was elevated 30° during surgery, and in Group 2, each patient’s head elevation was 45°. Patients were assigned to their group according to the location of their lesion. During surgery, the standard anesthetic protocol was used with total intravenous anesthesia, and transesophageal echocardiography was used to detect air in the blood circulation. Any air embolism seen on the echocardiography screen was classified as Grade 0 to 4. If multiple events occurred, the worst graded attack was used for statistical analysis. During hemodynamic changes caused by emboli, fluid and vasopressor requirements were recorded. Surgical and anesthetic complications were recorded also. All results were compared statistically, and a p value of < 0.05 was considered statistically significant.

RESULTS

There was a statistically significant difference between groups for the total rates of venous air emboli detected on transesophageal echocardiography (22.0% [n = 11] in Group 1 and 62.5% [n = 30] in Group 2; p < 0.0001). The rate and severity of air embolism were significantly lower in Group 1 than in Group 2 (p < 0.001). The rates of clinically important venous air embolism (Grade 2, 3, or 4, venous air embolism with decreased end-tidal carbon dioxide levels and/or hemodynamic changes) were 8.0% (n = 4) in Group 1 and 50.0% (n = 24) in Group 2 (p < 0.0001). There was no association between the rate and severity of venous air embolism with patient demographics (p > 0.05). An association was found, however, between the rate of venous air embolism and the type of surgical pathology (p < 0.001); venous embolism occurred more frequently in patients with a meningioma. There were no major surgical or anesthetic complications related to patient position during the postoperative period.

CONCLUSIONS

For patients in the semisitting position, an increase in the degree of head elevation is related directly to a higher rate of venous air embolism. With a 30° head elevation and our standardized technique of positioning, the semisitting position can be used safely in neurosurgical practice.

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Uğur Türe, M. Gazi Yaşargil, Ossama Al-Mefty and Dianne C. H. Yaşargil

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.

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Uğur Türe, Dianne C. H. Yaşargil, Ossama Al-Mefty and M. Gazi Yaşargil

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.