eMedicine创建于1996年，由近万名临床医师作为作者或编辑参与此临床医学知识库的建设，其中编辑均是来自美国哈佛、耶鲁、斯坦福、芝加哥、德克萨斯、加州大学等各分校医学院的教授或副教授。

eMedicine

Pathological perturbations of the brain are rarely confined to a single locus; instead, they often spread via axonal pathways to influence other regions. Patterns of such disease propagation are constrained by the extraordinarily complex, yet highly organized, topology of the underlying neural architecture; the so-called connectome. Thus, network organization fundamentally influences brain disease, and a connectomic approach grounded in network science is integral to understanding neuropathology. Here, we consider how brain-network topology shapes neural responses to damage, highlighting key maladaptive processes (such as diaschisis, transneuronal degeneration and dedifferentiation), and the resources (including degeneracy and reserve) and processes (such as compensation) that enable adaptation. We then show how knowledge of network topology allows us not only to describe pathological processes but also to generate predictive models of the spread and functional consequences of brain disease.

The connectomics of brain disorders

Tractography based on non-invasive diffusion imaging is central to the study of human brain connectivity. To date, the approach has not been systematically validated in ground truth studies. Based on a simulated human brain data set with ground truth tracts, we organized an open international tractography challenge, which resulted in 96 distinct submissions from 20 research groups. Here, we report the encouraging finding that most state-of-the-art algorithms produce tractograms containing 90% of the ground truth bundles (to at least some extent). However, the same tractograms contain many more invalid than valid bundles, and half of these invalid bundles occur systematically across research groups. Taken together, our results demonstrate and confirm fundamental ambiguities inherent in tract reconstruction based on orientation information alone, which need to be considered when interpreting tractography and connectivity results. Our approach provides a novel framework for estimating reliability of tractography and encourages innovation to address its current limitations.

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The challenge of mapping the human connectome based on diffusion tractography

While traditional models of language comprehension have focused on the left posterior temporal cortex as the neurological basis for language comprehension, lesion and functional imaging studies indicate the involvement of an extensive network of cortical regions. However, the full extent of this network and the white matter pathways that contribute to it remain to be characterized. In an earlier voxel-based lesion-symptom mapping analysis of data from aphasic patients (Dronkers et al., 2004), several brain regions in the left hemisphere were found to be critical for language comprehension: the left posterior middle temporal gyrus (MTG), the anterior part of Brodmann’s area 22 in the superior temporal gyrus (anterior STG/BA22), the posterior superior temporal sulcus (STS) extending into Brodmann’s area 39 (STS/BA39), the orbital part of the inferior frontal gyrus (BA47) and the middle frontal gyrus (BA46). Here, we investigated the white matter pathways associated with these regions using diffusion tensor imaging from healthy subjects. We also used resting-state functional magnetic resonance imaging data to assess the functional connectivity profiles of these regions. Fiber tractography and functional connectivity analyses indicated that the left MTG, anterior STG/BA22, STS/BA39 and BA47 are part of a richly interconnected network that extends to additional frontal, parietal and temporal regions in the two hemispheres. The inferior occipito-frontal fasciculus, the arcuate fasciculus and the middle and inferior longitudinal fasciculi, as well as transcallosal projections via the tapetum were found to be the most prominent white matter pathways bridging the regions important for language comprehension. The left posterior MTG showed a particularly extensive structural and functional connectivity pattern which is consistent with the severity of the impairments associated with MTG lesions and which suggests a central role for this region in language comprehension.

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The Neural Architecture of the Language Comprehension Network: Converging Evidence from Lesion and Connectivity Analyses

Subarachnoid hemorrhage (SAH) is an acute cerebrovascular event which can have devastating effects on the central nervous system as well as a profound impact on several other organs SAH patients are routinely admitted to an intensive care unit and are cared for by a multidisciplinary team A lack of high quality data has led to numerous approaches to management and limited guidance on choosing among them Existing guidelines emphasize risk factors, prevention, natural history, and prevention of rebleeding, but provide limited discussion of the complex critical care issues involved in the care of SAH patients The Neurocritical Care Society organized an international, multidisciplinary consensus conference on the critical care management of SAH to address this need Experts from neurocritical care, neurosurgery, neurology, interventional neuroradiology, and neuroanesthesiology from Europe and North America were recruited based on their publications and expertise A jury of four experienced neurointensivists was selected for their experience in clinical investigations and development of practice guidelines Recommendations were developed based on literature review using the GRADE system, discussion integrating the literature with the collective experience of the participants and critical review by an impartial jury Recommendations were developed using the GRADE system Emphasis was placed on the principle that recommendations should be based not only on the quality of the data but also tradeoffs and translation into practice Strong consideration was given to providing guidance and recommendations for all issues faced in the daily management of SAH patients, even in the absence of high quality data

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Critical Care Management of Patients Following Aneurysmal Subarachnoid Hemorrhage: Recommendations from the Neurocritical Care Society’s Multidisciplinary Consensus Conference

The orbit is a paired, transversely oval, and cone-shaped osseous cavity bounded and formed by the anterior and middle cranial base as well as the viscerocranium. Its main contents are the anterior part of the visual system, globe and optic nerve, and the associated neural, vascular, muscular, glandular, and ligamentous structures required for oculomotion, lacrimation, accommodation, and sensation. A complex stream of afferent and efferent information passes through the orbit, which necessitates a direct communication with the anterior and middle cranial fossae, the pterygopalatine and infratemporal fossae, as well as the aerated adjacent frontal, sphenoidal, and maxillary sinuses and the nasal cavity. This article provides a detailed illustration and description of the microsurgical anatomy of the orbit, with a focus on the intrinsically complex spatial relationships around the annular tendon and the superior orbital fissure, the transition from cavernous sinus to the orbital apex. Sparse reference will be made to surgical approaches, their indications or limitations, since they are addressed elsewhere in this special issue. Instead, an attempt has been made to highlight anatomical structures and elucidate concepts most relevant to safe and effective transcranial, transfacial, transorbital, or transnasal surgery of orbital, periorbital, and skull base pathologies.

Anatomy of the Orbit.

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Petrous Apex Cholesterol Granulomas: Endonasal versus Infracochlear Approach

High-Definition Fiber Tractography in Evaluation and Surgical Planning of Thalamopeduncular Pilocytic Astrocytomas in Pediatric Population: Case Series and Review of Literature.

Dear Editor, We read with great interest the well-written review article by Michael Powell, Microscopic and endoscopic pituitary surgery, published in the July 2009 issue of Acta Neurochirurgica [5]. The author is to be particularly commended for completing a comprehensive overview of pituitary surgery based on a literature review and personal experience. The article nicely details common pituitary lesions, indications, and options for treatment. While we agree with most of the described concepts, we are concerned about the final statement of the “review” article: “No-one should change their style simply because of fashion.” As written by Powell, pituitary adenomas are “one of the most benign tumours to be found anywhere in the body,” and therefore outcome will not be dramatically changed depending upon the visualization tool used for their removal. Although not explicated by Powell, the key for increasing remission rates on the more challenging secreting pituitary adenomas (e.g., ACTH secreting) is to successfully perform an extracapsular dissection and removal of the lesion, as described by Oldfield and Vortmeyer [4], disregarding the use of the endoscope or the microscope. The dramatic difference between the endoscope and the microscope as surgical tools is related to the expanded endonasal approach. The expanded endonasal endoscopic approach is a new paradigm in skull base surgery that allows for more effective removal of ventrally located skull base lesions [3]. As an example, chordomas and chondrosarcomas can be completely removed by performing bilateral paraclival carotid mobilization with carotid canal resection, retrocarotid tumor removal, medial petrous apex drilling, abducens nerve decompression, and extradural posterior clinoid removal, if needed [2]. Craniopharyngiomas as well as diaphragmatic, tuberculum sellae and planum meningiomas can be removed with accurate preservation of vital arterial perforators, branches of the ICA, superior hypophyseal artery, and posterior communicating artery, which supply the optic apparatus and diencephalic structures [1]. Complex and invasive pituitary adenomas can spread away from the sella turcica and behave as the tumors cited above. The endoscopic approaches are far superior to microscopic ones when removing pituitary adenomas in the cavernous sinus, superior orbital fissure, Meckel’s cave, and other parasellar locations. The learning curve for such demanding surgical procedures should follow a clear pathway: intense endoscopic, microsurgical, and neuroanatomy laboratory training, dedicated observation of experienced surgeons, and progressive surgical experience. Mastering endoscopic pituitary surgery represents the mandatory requirement for pursuing expanded endonasal approaches. Is this a matter of fashion? We are convinced it is a matter of offering patients the safest and more effective surgical treatment for such challenging lesions. J. C. Fernandez-Miranda :D. M. Prevedello : P. Gardner : R. Carrau :C. H. Snyderman :A. B. Kassam Department of Neurosurgery, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA

Endonasal endoscopic pituitary surgery: is it a matter of fashion?

To The ediTor: We read with great the interest the recent article by Maruyama et al. (Maruyama K, Koga T, Kamada K, et al: Arcuate fasciculus tractography integrated into Gamma Knife surgery. Clinical article. J Neu-rosurg 111:520–526, September, 2009). The authors are to be particularly commended for pioneering the integration of diffusion tensor–based tractography into Gamma Knife surgery (GKS). 6,7 In this article, the authors reported their results with the retrospective integration of the left arcuate fascicle tractography in 12 right-handed patients with left perisylvian arteriovenous malformations that were treated with GKS. As a conclusion, the authors stated that the administration of a 10-Gy radiation dose was tolerated in the frontal but not in the temporal fibers of the arcuate fascicle. Fiber tractography is already an established imaging technique with multiple applications in neurosurgery and neuroscience. 3 However, diffusion tensor–based tractog-raphy has several limitations including poor detailing of fiber tracts, fibers ending in white matter before contacting the cortical mantle, an inability to solve fiber crossings , excessive false continuity, and the inability to follow bundles within fiber tracts. High-definition fiber tractography (HDFT) has been recently developed by the application of novel pulse sequences and processing algorithms , such as high-angular resolution diffusion imaging and diffusion spectrum imaging (DSI). High-definition fiber tractography is characterized by high detailing of fiber tracts, the fact that fibers can be followed to the end point, the ability to follow fibers through crossings, reduced false continuity, and the ability to follow bundles within fiber tracts (Fig. 1 upper). At our institution, we have been using HDFT for precise neuroanatomical studies of the white matter connectivity and for meticulous presurgical planning of selected neurosurgical cases. The connectivity of language cortical areas (Broca and Wernicke) through the language pathways has been one of our primary research focuses. Based on the results of subcortical intraoperative stimulation studies, Duffau et al. 2 described the ventral and dorsal language pathways. The dorsal or phonological pathway corresponds to the arcuate fascicle, while the ventral or semantic pathway corresponds to the inferior occipitofrontal fascicle. Recently , investigators have tried to demonstrate the ven-tral language pathway using HDFT with partial success. They were not able to show the cortical terminations of the fibers that connect the Broca and Wernicke areas, and they have considered this ventral pathway as equivalent to the so-called extreme capsule. 5 In our surgical planning laboratory, we have been …

Juan C. Fernandez-Miranda

Papers

Anatomy of the Orbit.

Petrous Apex Cholesterol Granulomas: Endonasal versus Infracochlear Approach

High-Definition Fiber Tractography in Evaluation and Surgical Planning of Thalamopeduncular Pilocytic Astrocytomas in Pediatric Population: Case Series and Review of Literature.

Endonasal endoscopic pituitary surgery: is it a matter of fashion?

High-definition fiber tractography and language.