White matter fiber dissection of the optic radiations of the temporal lobe and implications for surgical approaches to the temporal horn

OBJECT: The aim of this anatomical study was to define more fully the three-dimensional (3D) relationships between the optic radiations and the temporal horn and superficial anatomy of the temporal lobe by using the Klingler white matter fiber dissection technique. These findings were correlated with established surgical trajectories to the temporal horn. Such surgical trajectories have implications for amygdalohippocampectomy and other procedures that involve entering the temporal horn for the resection of tumors or vascular lesions. METHODS: Ten human cadaveric hemispheres were prepared with several cycles of freezing and thawing by using a modification of the method described by Klingler. Wooden spatulas were used to strip away the deeper layers of white matter progressively in a lateromedial direction, and various association, projection, and commissural fibers were demonstrated. As the dissection progressed, photographs of each progressive layer were obtained. Special attention was given to the optic radiation and to the sagittal stratum of which the optic radiation is a part. The trajectories of fibers in the optic radiation were specifically studied in relation to the lateral, medial, superior, and inferior walls of the temporal horn as well as to the superficial anatomy of the temporal lobe. In three of the hemispheres coronal sections were made so that the relationship between the optic radiation and the temporal horn could be studied more fully. In all 10 hemispheres that were dissected the following observations were made. 1) The optic radiation covered the entire lateral aspect of the temporal horn as it extends to the occipital horn. 2) The anterior tip of the temporal horn was covered by the anterior optic radiation along its lateral half. 3) The entire medial wall of the temporal horn was free from optic radiation fibers, except at the level at which these fibers arise from the lateral geniculate body to ascend over the roof of the temporal horn. 4) The superior wall of the temporal horn was covered by optic radiation fibers. 5) The entire inferior wall of the temporal horn was free from optic radiation fibers anterior to the level of the lateral geniculate body. CONCLUSIONS: Fiber dissections of the temporal lobe and horn demonstrated the complex 3D relationships between the optic radiations and the temporal horn and superficial anatomy of the temporal lobe. Based on the results of this study, the authors define two anatomical surgical trajectories to the temporal horn that would avoid the optic radiations. The first of these involves a transsylvian anterior medial approach and the second a pure inferior trajectory through a fusiform gyrus. Lateral approaches to the temporal horn through the superior and middle gyri, based on the authors' findings, would traverse the optic radiations.     

Diffusion tensor tractography of the temporal stem on the inferior limiting sulcus

OBJECT: The aim of this study was to use diffusion tensor tractography (DTT) to define the 3D relationships of the uncinate fasciculus, anterior commissure, inferior occipitofrontal fasciculus, inferior thalamic peduncle, and optic radiation and to determine the positioning landmarks of these white matter tracts. METHODS: The anatomy was studied in 10 adult human brain specimens. Brain DTT was performed in 10 healthy volunteers. Diffusion tensor tractography images of the white matter tracts in the temporal stem were obtained using the simple single region of interest (ROI) and multi-ROIs based on the anatomical knowledge. RESULTS: The posteroinferior insular point is the anterior extremity of intersection of the Heschl gyrus and the inferior limiting sulcus. On the inferior limiting sulcus, this point is the posterior limit of the optic radiation, and the temporal stem begins at the limen insulae and ends at the posteroinferior insular point. The distance from the limen insulae to the tip of the temporal horn is just one third the length of the temporal stem. The uncinate fasciculus comprises the core of the anterior temporal stem, behind which the anterior commissure and the inferior thalamic peduncle are located, and they occupy the anterior third of the temporal stem. The inferior occipitofrontal fasciculus passes through the entire temporal stem. The most anterior extent of the Meyer loop is located between the anterior tip of the temporal horn and the limen insulae. Most of the optic radiation crosses the postmedian two thirds of the temporal stem. CONCLUSIONS: On the inferior limiting sulcus, the posteroinferior insular point is a reliable landmark of the posterior limit of the optic radiations. The limen insulae, anterior tip of the temporal horn, and posteroinferior insular point may be used to localize the white matter fibers of the temporal stem in analyzing magnetic resonance imaging or during surgery.     

DTI tractography of the human brain's language pathways

Diffusion Tensor Imaging (DTI) tractography has been used to detect leftward asymmetries in the arcuate fasciculus, a pathway that links temporal and inferior frontal language cortices. In this study, we more specifically define this asymmetry with respect to both anatomy and function. Twenty right-handed male subjects were scanned with DTI, and the arcuate fasciculus was reconstructed using deterministic tractography. The arcuate was divided into 2 segments with different hypothesized functions, one terminating in the posterior superior temporal gyrus (STG) and another terminating in the middle temporal gyrus (MTG). Tractography results were compared with peak activation coordinates from prior functional neuroimaging studies of phonology, lexical-semantic processing, and prosodic processing to assign putative functions to these pathways. STG terminations were strongly left lateralized and overlapped with phonological activations in the left but not the right hemisphere, suggesting that only the left hemisphere phonological cortex is directly connected with the frontal lobe via the arcuate fasciculus. MTG terminations were also strongly left lateralized, overlapping with left lateralized lexical-semantic activations. Smaller right hemisphere MTG terminations overlapped with right lateralized prosodic activations. We combine our findings with a recent model of brain language processing to explain 6 aphasia syndromes.     

Optic radiations: a microsurgical anatomical study

OBJECT: In this study, the authors used a fiber-dissection technique to describe the optic radiation. They focused on the morphological characteristics (length and breadth) of this structure, its course, and its relationships with neighboring fasciculi and the lateral ventricle. METHODS: The authors dissected 10 previously frozen, formalin-fixed human brains with the aid of an operating microscope by following the fiber dissection technique described by Klingler in 1960. Lateral, inferior, and medial approaches were made. The optic radiation, also known as the Gratiolet radiation, extended from the lateral geniculate body to the calcarine fissure. The average distance from the tip of the anterior Meyer loop to the calcarine sulcus was 105 mm (range 95-114 mm). The breadth of the optic radiations, one on each side of the brain, averaged 17 mm at the level of the inferior horn (range 15-18 mm). This tract could be divided into three main segments: the anterior or Meyer loop, the body, and the end of the optic radiation. Adjacent anatomical structures included: laterally, the inferior longitudinal fasciculi; medially, the tapetum of the corpus callosum; and the ependyma of the inferior horn of the lateral ventricle. CONCLUSIONS: Various practical surgical approaches are discussed. The knowledge gained by studying this particular anatomy will help prevent injury to the optic radiations during neurosurgery.     

Surgical anatomy of the lateral ventricles

The lateral ventricle is a deep-seated cavity, overlayed by a cortical mantle which contains eloquent areas, especially on the dominant hemisphere, and surrounded by the optic radiations. The surgical approach requires a thorough preoperative reflexion based on magnetic resonance imaging, in order to understand the site of origin and the vascular pedicles of the tumor. Surgical approaches to the frontal horn, temporal horn and atrium are successively described.     

Quantitative diffusion tensor tractography of association and projection fibers in normally developing children and adolescents

Whole-brain diffusion tensor tractography (DTT) at high signal-to-noise ratio and angular and spatial resolutions were utilized to study the effects of age, sex differences, and lateral asymmetries of 6 white matter pathways (arcuate fasciculus [AF], inferior longitudinal fasciculus, inferior fronto-occipital fasciculus [IFOF], uncinate fasciculus [UF], corticospinal tract [CST], and somatosensory pathway [SS]) in 31 right-handed children (6-17 years). Fractional anisotropy (FA), a measure of the orientational variance in water molecular diffusivity, and the magnitude of water diffusivity (parallel, perpendicular, and mean diffusivity) along the pathways were quantified. Three major patterns of maturation were observed: 1) significant increase in FA with age, accompanied by significant decreases in all 3 diffusivities (e.g., left IFOF); 2) significant decreases in all three diffusivities with age without significant changes in FA (e.g., left CST); and 3) no significant age-related changes in FA or diffusivity (e.g., SS). Sex differences were minimal. Many pathways showed lateral asymmetries. In the right hemisphere, the frontotemporal (FT) segment of AF was not visualized in a substantial (29%) number of participants. FA was higher in the left hemisphere in the FT segment of AF, UF, and CST, whereas it was lower in the frontoparietal segment of AF. This study provides normative data essential for the interpretation of pediatric brain DTT measurements in both health and disease.     

Surgical indications and microsurgical anatomy of the transchoroidal fissure approach for lesions in and around the ambient cistern

OBJECTIVE: Opening the temporal part of the choroidal fissure (CF) makes it possible to expose the crural cistern, the ambient cistern, and the medial temporal lobe. We examined the microsurgical anatomy and the surgical indications for use of the trans-CF approach. METHODS: The microsurgical anatomy encountered in the trans-CF approach for lesions in and around the ambient cistern was studied in three cadavers. On the basis of these cadaveric studies, the trans-CF approach was used during surgery in three live patients with such lesions. RESULTS: The angiographic "plexal point," which indicates the entrance of the anterior choroidal artery as it enters the temporal horn of the lateral ventricle, was thought to be a key anatomic landmark of the trans-CF approach. A cortical incision for entry into the temporal horn should be made in the inferior temporal gyrus to minimize the potential damage to the optic radiations and to the speech centers. After the CF is opened posteriorly to the plexal point between the tenia fimbria and the choroid plexus, the posterior cerebral artery (PCA) in the ambient cistern can be observed with minimal caudal retraction of the hippocampus. In this study, surgical procedures using the trans-CF approach were successfully performed on patients with high-positioned P2 aneurysms whose PCA ran close to the plexal point or higher, whose medial temporal arteriovenous malformations were fed mainly by the PCA, and whose tentorial hiatus meningiomas protruded into the temporal horn through the CF, with no resulting postoperative visual or memory disturbances. CONCLUSION: The trans-CF approach is especially useful in surgery for lesions in and around the ambient cistern.     

利用扩散张量成像及纤维跟踪技术分析 胼胝体发育不良脑内主要纤维束

目的 利用扩散张量成像(DTI)和纤维跟踪技术显示胼胝体发育不良状态下脑内纤维结构的变化。方法患者，男，9岁，头痛1周。采用SIEMENS Trio2003T完成全脑MRI和DTI数据收集和后处理。结果常规MRI显示胼胝体体中部以后缺如，半球间蛛网膜囊肿，右侧向上延伸。纤维跟踪技术显示左侧弓状纤维柬、下纵行纤维柬、扣带柬、海马及外囊等主要的连合、联合纤维走行方向与正常发育不同，有左右侧相互支援的趋势。结论DTI纤维跟踪技术能精确、直观显示先天性发育畸形的脑内白质纤维柬，有助于预后的评估。     

Arteries and veins of the lateral ventricle

Tumors of the frontal horn of the lateral ventricle (LV) are only supplied by the posteromedial choroidal artery. Tumors of the body of the LV are supplied by the same artery. Tumors of the atrium of the LV with anterior extension are supplied by both posteromedial choroidal and posterolateral arteries. Tumors of the atrium with inferior extension are supplied by both anterior choroidal artery and posterolateral choroidal arteries. Tumors of the inferior horn are only supplied by anterior choroidal artery. The tumoral venous drainage is organized with three main groups of veins: a medial group, a lateral group and a choroidal group.     

Microsurgical anatomy of the choroidal fissure

The microsurgical anatomy of the choroidal fissure was examined in 25 cadaveric heads. The choroidal fissure, the site of attachment of the choroid plexus in the lateral ventricle, is located between the fornix and thalamus in the medial part of the lateral ventricle. The choroidal fissure is divided into three parts: (a) a body portion situated in the body of the lateral ventricle between the body of the fornix and the thalamus, (b) an atrial part located in the atrium of the lateral ventricle between the crus of the fornix and the pulvinar, and (c) a temporal part situated in the temporal horn between the fimbria of the fornix and the lower surface of the thalamus. The three parts of the fissure are the thinnest sites in the wall of the lateral ventricle bordering the basal cisterns and the roof of the third ventricle. Opening through the body portion of the choroidal fissure from the lateral ventricle exposes the velum interpositum and third ventricle. Opening through the temporal portion of the choroidal fissure from the temporal horn exposes the structures in the ambient and crural cisterns. Opening through the atrial portion of the fissure from the atrium exposes the quadrigeminal cistern, the pineal region, and the posterior portion of the ambient cistern. The neural, arterial, and venous relationships of each part of the fissure are reviewed. The operative approaches directed through each part of the fissure are also reviewed.     

Asymmetry of the uncinate fasciculus: a post-mortem study of normal subjects and patients with schizophrenia

The uncinate fasciculus interconnects the anterior temporal and inferior frontal lobes. The temporal lobes show a number of anatomical asymmetries, some of which are altered in schizophrenia. This study was performed to assess the size and symmetry of the uncinate fasciculus in normal subjects and in patients with the disorder. The area, fibre density and total fibre number of left and right uncinate fasciculi were estimated using stereological methods in 21 control subjects and 17 schizophrenics. The uncinate fasciculus was found to be asymmetrical in both sexes, being 27% larger and containing 33% more fibres in the right than the left hemisphere. Of the 25 brains from which both hemispheres were available, the size asymmetry was seen in 20 subjects and the greater number of fibres in 21 subjects. There was no significant effect of schizophrenia upon the uncinate fasiculus, nor interactions of diagnosis with side or sex. We conclude that the uncinate fasciculus is larger in the right hemisphere, perhaps indicating greater right-sided fronto-temporal connectivity. The unchanged size of the fasciculus in schizophrenia contrasts with commissural tracts, which are affected in this brain series in a sex-specific manner.     

Access to the posterior medial temporal lobe structures in the surgical treatment of temporal lobe epilepsy

The authors describe a surgical technique that allows access to the posterior temporal horn of the lateral ventricle with preservation of the most functional lateral temporal cortex. Development of the technique was stimulated by the need to resect posteromedial temporal lobe structures in patients with intractable complex partial epilepsy and well-identified unilateral posterior hippocampal foci. This technique has also been of value in the resection of some lateral ventricular and posteromedial temporal lobe masses. The operation consists of three steps. No more than 4.5 cm of the anterolateral temporal lobe is removed en bloc such that the most anterior aspect of the temporal horn is entered. An incision is carried from the floor of the temporal horn through the inferior longitudinal fasciculus to the middle fossa dura mater and posteriorally into the lateral ventricular atrium. The lateral temporal cortex and white matter are then elevated with a self-retaining retractor. This exposes the posteromedial temporal horn or intraaxial mass for excision or allows en bloc resection of the entire hippocampus and medial temporal lobe structures while preserving the functional association areas of the lateral temporal cortex, including speech and visual spatial function.     

Intraoperative subcortical stimulation mapping of language pathways in a consecutive series of 115 patients with Grade II glioma in the left dominant hemisphere

OBJECT: Despite better knowledge of cortical language organization, its subcortical anatomofunctional connectivity remains poorly understood. The authors used intraoperative subcortical stimulation in awake patients undergoing operation for a glioma in the left dominant hemisphere to map the language pathways and to determine the contribution of such a method to surgical results. METHODS: One hundred fifteen patients harboring a World Health Organization Grade II glioma within language areas underwent operation after induction of local anesthesia, using direct electrical stimulation to perform online cortical and subcortical language mapping throughout the resection. RESULTS: After detection of cortical language sites, the authors identified 1 or several of the following subcortical language pathways in all patients: 1) arcuate fasciculus, eliciting phonemic paraphasia when stimulated; 2) inferior frontooccipital fasciculus, generating semantic paraphasia when stimulated; 3) subcallosal fasciculus, inducing transcortical motor aphasia during stimulation; 4) frontoparietal phonological loop, eliciting speech apraxia during stimulation; and 5) fibers coming from the ventral premotor cortex, inducing anarthria when stimulated. These structures were preserved, representing the limits of the resection. Despite a transient immediate postoperative worsening, all but 2 patients (98%) returned to baseline or better. On control MR imaging, 83% of resections were total or subtotal. CONCLUSIONS: These results represent the largest experience with human subcortical language mapping ever reported. The use of intraoperative cortical and subcortical stimulation gives a unique opportunity to perform an accurate and reliable real-time anatomofunctional study of language connectivity. Such knowledge of the individual organization of language networks enables practitioners to optimize the benefit-to-risk ratio of surgery for Grade II glioma within the left dominant hemisphere.     

Surgical approaches to tumours of the lateral ventricles in the dominant hemisphere

BACKGROUND: Intraventricular neoplasms are rare tumours (1% of the tumours of the central nervous system). The surgical approach sometimes is quite difficult, particularly in the dominant hemisphere. The best choice of surgical approach is discussed. METHODS: The authors describe a series of 25 patients who underwent surgical treatment for tumours situated in the lateral ventricles of the dominant hemisphere. They discuss the most influential factors in the choice of surgical approach, which must allow maximum exposure of the lesion and vascular feeding branches without damaging highly functional areas (motor, visual and language areas). In particular, they report their experience using a low transtemporal route, between the middle and inferior gyri, for removing tumours localized in the temporal horn and/or trigone which made it possible to keep postoperative visual and phasic deficits to a minimum. RESULTS: In 5 patients the approach was transfrontal, in 10 temporal, in 6 superior parieto-occipital and in 4 transcallosal. Three patients died. Only 5 patients presented permanent deficits (anomia, apraxia and visual fields alterations). CONCLUSIONS: The size, site, hemisphere and vascularization of intraventricular tumours influence the choice of surgical approach. The basal transtemporal approach is particularly indicated to remove tumours of the temporal horn and trigone and it seems to reduce the risk of speech disturbances and alterations of posture.     

Neurosurgical topography of the optic radiation in the temporal lobe

Summary Damage to the optic radiation during surgery in the temporal lobe results in more or less severe visual field defects. In the present study, the optic radiation was represented by either Klingler's fibre dissection technique or by consecutive frontal sections respectively in 25 formalin-fixed human hemispheres. This enabled one to gain exact data on the three-dimensional course, the length and other measurements of this important fibre system. In addition, its relations to the temporal horn, the trigonum and the occipital horn of the lateral ventricle were determined. The results of these measurements are discussed with respect to various surgical interventions involving the temporal lobe.     

The arcuate eminence of the petrous portion of the temporal bone. Descriptive features

The superior semicircular canal is an important landmark in the middle cranial fossa approach to the temporal bone and the internal acoustic meatus. This mark is frequently located by its topographic association to the arcuate eminence, a bony prominence located on the anterior surface of petrous portion of the temporal bone. In recent studies, otolaryngologists described that the arcuate eminence lies more posterior and laterally than the superior semicircular canal and stated that some eminences corresponded to sulci of the temporal lobe, of which most were traces of the occipitotemporal sulcus. Our work examines by dissection the relationship of the arcuate eminence to the superior semicircular canal, demonstrating a third origin of the arcuate eminence: well pneumatized temporal bones in the region of the epi-tympanic recess.     

高定义角度纤维追踪技术重建人脑颞顶枕区短纤维束连接

目的观察人脑颞顶枕区短纤维束连接的空间走行、皮质连接及三维空间关系。方法对10名健康志愿者进行MR扫描。下载90名健康志愿者的弥散谱成像(DSI)综合数据模板(NTU-90)。应用高定义角度纤维束追踪技术(HDFT)对所收集数据进行人脑颞顶枕区3条短纤维束连接[上纵束的垂直部(SLF-V)、枕纵束(VOF)和颞顶束(TP)]重建,并分析其纤维走行、皮质连接、空间三维关系及左右侧别差异。结果 3条纤维束在10名志愿者和NTU-90中均重建成功。SLF-V纤维束起源于颞中回和颞下回后部,终止于角回和缘上回;VOF纤维束起源于下枕叶和梭状回,少量纤维来源于颞下回的后部和枕极前部,终止点位于角回和上枕叶外侧部;TP纤维束主要起源于颞中回、颞下回、梭状回和下颞-下枕结合部,连接于顶上小叶;左右侧SLF-V、VOF和TP的纤维束体积差异无统计学意义(P均0.05)。结论应用HDFT纤维束成像技术成功重建了SLF-V、VOF和TP,可为脑功能研究和神经外科手术提供解剖学依据。     

下睑囊性睑板筋膜弓状扩张部的解剖结构研究及应用

目的：研究下睑囊性睑板筋膜弓状扩张部及其周围组织的解剖结构,为相关的下睑部老化及其临床治疗提供理论依据。方法：通过对10具（20侧）尸颅的解剖,阐明下睑囊性睑板筋膜弓状扩张部及其周围组织的解剖结构,结合文献复习,对下睑皱襞的形成及下睑部老化的治疗方法提出意见。结果：弓状扩张部是一个立体结构,其与眶下缘骨膜、眶隔、囊性睑板筋膜及Lockwood韧带均有连接。结论：弓状扩张部与下睑皱襞的形成及下睑部眶隔脂肪的疝出密切相关,是下睑部重要的支持结构。     

Inferior temporal sulcus as a site of corticotomy: magnetic resonance imaging analysis of individual sulcus patterns

OBJECTIVE: Transcortical approaches to the inferior horn often result in quadrant hemianopsia attributable to the injury to the optic radiation. The inferior temporal sulcus (ITS) has received little attention as an entrance point for the transsulcal approach. We used the method of detecting the ITS with magnetic resonance imaging (MRI) scans and investigated the sulcus pattern of ITS, its incidence rate, and the availability of the ITS to the corticotomy for selective amygdalohippocampectomy. METHODS: The sulcus patterns of the ITS of 100 temporal lobes in 50 healthy individuals were classified according to the number of interruptions by gyral bridges, and the localization of the ITS was characterized in relation to the outer surface by means of the surface anatomy scan of MRI. RESULTS: Most of the ITS was interrupted by one to three gyral bridges (0 bridges, 8%; one bridge, 27%: two bridges, 37%; three bridges, 20%; more than four bridges or no apparent ITS, 8%). When the ITS was present, it was located 15 mm above the orbitotragus line at a point 20 mm anterior to the tragus. The number of gyral bridges was significantly larger in the left temporal lobes than in the right temporal lobes, regardless of the sex of the subject. CONCLUSION: The ITS was clearly identified in 72% of the temporal lobes by the oblique sagittal view of MRI scans; thus, in such cases, the ITS was considered to be a candidate for an entrance point of a small temporal corticotomy. The preoperative observation of the ITS in relation to the orbitotragus line by means of MRI may improve the planning of the transsulcal approaches to deeply seated mesial temporal lesions, such as hippocampal sclerosis.