| Backgroud and purpose:The island or insula of Reil is named after the German anatomist, physiologist and phychiatrist, Johann Christian Reil, who in 1809 first described this anatomically and functionally complex structure situated in the depth of the sylvian fissure. The insula, forming the base of the sylvian fissure, totally encased within the brain and covered by the frontoorbital, frontoparietal, and temporal opercula. A detailed and discerning account of the topographic anatomy of the insula region and the relationships with overlying opercula and adjacent structures will be beneficial. The purpose of this study is to describe the anatomy of this region concisely, to present detailed anatomical relationships of the sylvian fissure, opercula, the middle cerebral artery, the basal ganglia, the internal capsule, the lateral ventricle and the insula. Offering sound basic anatomical knowledge and related parameters that will contribute to preoperative planning and to subsequent successful realization of surgical strategy.The insula can be affected by either low-grade or high-grade glioma. Currently improved diagnostic, neurophysiological and surgical allow the neurosurgeon to perform surgery of insular gliomas in a safe way. In th present clinical study, We provide our own preliminary experience of microsurgical management of insular gliomas according to the microsurgical anatomy of this region, and draw some conclusions about the present feasibility and limitations of insular surgery.Materials and methodsThe microsurgical anatomical features of the insular were studied in 12 formalin-fixed adult human brain specimens(24 hemispheres). To maintain the true anatomical contours and the vascular characteristics of the specimens, each was suspended in the solution from the basilar artery, and the vascular was perfused with colored latex(arteries with red and venous with blue) to facilitate dissection and improve photographic detail.We began our dissections by examining the overlying opercular anatomic features, the sylvian fissures were carefully opened under the operating microscope with the magnification×6 to×25. and then checking for the relationships with the sylvian fissure, the opercula, the middle cerebral artery and the underlying insular cortex. After removal of the frontoorbital, frontopatietal and temporal opercula, anatomic features were labeled and the method of measurement was depicted, and the relationships with the basal ganglia, the internal capsule, and the lateral ventricle were analized. Results:1.The relationship between the sylvian fissure and the insularThe human adult insular is completely enclosed and concealed within the sylvian fissure. The insular forms the sylvian fissures floor. The aperture of the sylvian fissure is slight wider at the sylvian point, exploration and splitting of the fissure at this location usually commences has the advantage of first exposing the insular apex.Opening specific portions of the sylvian fissure can expose different parts of the insula.Opening the posterior ramus below the apex of the pars triangularis exposed the anterior and middle short gyri and the anteroinferior portion of the insula. Opening the anterior horizontal rumas exposed the upper portion of the anterior short gyrus and the adjacent junction of the superior and anterior limiting sulci. Opening the anterior ascending ramus exposed the anterior short gyrus and the adjacent portion of the superior limiting sulcus. When the frontoorbital ramus presented, opening it provided access to the most anteroinferior portion of the insula, including the anterior limiting sulcus.2. The relationship between the opercula and the insularRemoval of the frontoorbital, frontoparietal,nd temporal opercula reveals the entire insular in the shape of a pyramid. Using opercula landmarks at the cerebral surface can be used to localize deeper structures in the insula area. Following the opercular suface of pars orbitalis to its deep edge exposed the upper part of the anterior short gyrus and adjacent part of the anterior limiting sulcus. Following the cortical surface of the pars opercularis exposed the superior portion of the anterior or middle short gyri and the adjacent portion of the superior limiting sulcus. Following the upper edge of the pars triangularis exposed the upper portion of anterior short gyrus in most hemispheres. The inferior limiting sulcus is located medial to the superior temporal sulcus. The supramarginal gyrus lies superficial to the junction of the superior and inferior limiting sulci at the posterior end of the insula. The transverse gyri extend obliquely backward and medially from the cortical surface toward the posterosuperior angle of the insula. The inferior end of the central sulcus on the convexity is located less than5.0mm anterior and 5.5mm posterior to the central insular sulcus.3.The relationship between the middle cerebral artery and the insularThe M2 segment included the trucks and the branches that lies on and supply the insula. It began at the genu of the MCA where the trucks of the MCA passed over the limen insular and terminated at the periisular sulci of the insula. The main furcation of the MCA occurred at the genu in 17 cases (71%),before the genu in 2 cases (8%),after the genu in 5 cases (21%).Bifurcation were found in 15 cases (64%).Distance between the most lateral lenticulostriate artery and the apex of the insula was not more than 20mm.The long perforating artery of the insula could reach the corona radiata. The superior trunk of the middle cerebral artery and its branches supply the anterior, the middle, and posterior short gyri, the anterior limiting sulcus, the short sulci, and the insular apex. The inferior trunk supplys the posterior long gyrus,inferior limiting sulcus, and limen area in most hemispheres.4.The relationship between the basal ganglia and the insularIsular cortex and the extreme capsule cover the claustrum, external capsule, putamen, globus pallidus, and the internal capsule. The insular is surrounded by the superior longitudinal fasciculus, A C-shaped association fiber system of the brain connecting the temporal region to the parietal and frontal regions. The uncinate fasciculus supplies the major source of interconnection between limbic and paralimbic structures. The claustrum is the gray matter located between the fibers that form the extreme and external capsules. The occipitofrontal fasciculus passes beneath the inferior portion of the insular cortex, within the extreme and external capsules, to connect the frontal, insular, temporal,and occipital regions. The putamen is located media to the external capsule, adjacebt to the central portion of the insular. The average length of the putamen was 44mm(range42-47mm) and the average height of 41mm(range 38-44mm). Dissection directed medially, in the region of the periinsular sulci, leads directly to the internal capsule, whereas dissection through the central portion of the insular leads to the putamen. The anterior insular point is the landmark that can be readily identified and will indicate the direction that exploration should follow to approach the anterior limb of the internal capsule. The posterior insular point can likewise be readily identified and will indicate the direction that exploration should follow to approach the posterior limb of the internal capsule and the artrial portion of the lateral ventricle.5.The relationship between the lateral ventricle and the insularWith the exception of the insular stem, the insular is located adjacent to the lateral ventricle. The internal capsule separates the periinsular sulci from the lateral ventricle. The superior periinsular sulcus follows a course adjacent the frontal horn, body, and atrial portions of the lateral ventricle. Approximately four fifths of the posterior portion of the inferior periinsular sulcus follows a course adjacent to the temporal horn and atrial portions of the lateral ventricle. An average of 10.8mm(range 9-14mm) of the anterior portion of the inferior or periinsular sulcus is formed by the temporal stem. Approximately two thirds of the inferior portion of the anterior periinsular sulcus is surrounded by the anterior limb of the internal capsule. An average of 11.2mm(rang 9.8-10.5mm) of the superior portion of the anterior periinsular sulcus is located adjacent to the frontal horn. The anterior portion of the superior periinsular sulcus is separated from the frontal horn by the anterior isthmus, and the posterior portion of the periinsular sulcus is separated from the atrium by the posterior isthmus. Vertical distance between the anterior insular point and the frontal horn is approximately 11.4mm. Distance between the posterior insular point and the atrium is 10.9mm.Distance between the mid inferior periinsular sulcus and the temporal horn is 10mm.The foramen of Monro is located deep to the posterior short gyrus at the midpoint level of the middle short gyrus.6.The relationship between the cerebral fiber system and the insularRemoval of the cortical gray matter of the long and short insular gyri exposes the extreme capsule,which is composed of multiple short association fibers that connect the insular gyri with each other, and with the adjacent frontal, parietal, and temporal operculae. Some of these short fibers emerge from the gray matter digitations of the claustrum, which conform to the shape of the overlying posterior short and long insular gyri. Removal of the fibers of the extreme capsule exposes the gray matter of the dorsal claustrum located above and posterior to the limen insular, posterior to the insular apex, and beneath the proximal part of the posterior short and long insular gyri. The central insular sulcus crosses at or near to the center of the dorsal claustrum. Removal of the cortical gray matter overlying the limen insular exposes the thick uncinate fascicle, with its characteristic hooklike shape, connecting the temporal pole with the orbitofrontal area and forming the anterior part of limen insular. The posterior-most fibers at the level of the limen insular belong to the inferior occipitofrontal fascicle, which is located deep with respect to the insular apex, and to the anterior and middle short gyri.Conclusions1. Understand concisely the detailed anatomical relationships of the sylvian fissure, opercula, the middle cerebral artery and the insula, with sound basic anatomical knowledge and related parameters that will contribute to preoperative planning and to subsequent successful realization of surgical strategy.2.The superior trunk of the middle cerebral artery and its branches supply the anterior, the middle, and posterior short gyri, the anterior limiting sulcus, the short sulci, and the insular apex. The inferior trunk supplys the posterior long gyrus,inferior limiting sulcus, and limen area in most hemispheres. the most lateral lenticulostriate artery arises from Ml or M2 and the long perforating arteries distribute in the junction region of the superior and the inferior limiting sulcus that could reach the corona radiata should avoid to be injured.3. Isular cortex and the extreme capsule cover the claustrum, external capsule, putamen, globus pallidus, and the internal capsule. The anterior insular point is the landmark that can be readily identified and will indicate the direction that exploration should follow to approach the anterior limb of the internal capsule. The posterior insular point can likewise be readily identified and will indicate the direction that exploration should follow to approach the posterior limb of the internal capsule and the artrial portion of the lateral ventricle.4. A transsylvian approach suits gliomas limited in the insular local region. A transcortical approach respecting a subpial plane of dissection avoids any injury or iatrogenic spasm of the MCA and its branches and remains most suitable when opercula extension of the tumour has occurred. Transient or permanent paresis and hemisphere was the most commen postoperative deficit. Indentification of the primary motor area of the face and hand, and the perisylvian language sites, lightly retraction of the opercula cortex, avoiding injury to the most lateral lenticulostriate artery and the large perforating artery, and intraoperative ultrasound or subcortical electrical stimulation mapping will helpful. |
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