Arteries of the insula

Surgical anatomy of the insula

The insula is the only cortical part of the brain which is not visible on the surface of the hemisphere. This is due to the fact that it is totally covered by the fronto-parietal and temporal opercula. The insula has a triangular shape, and is separated from the opercula by the anterior, superior, and inferior periinsular sulci. The limen insulae is the antero-inferiorly located insular cortical surface which conjoins the inferior insular point, the anterior perforated surface, and the temporo-mesial surface. The insula is morphologically divided into two parts by the central insular sulcus. The anterior part of the insula bears 3 gyri: the anterior, middle, and posterior short insular gyri, separated by the anterior and precentral insular sulcus. The posterior part of the insula contains the anterior and posterior long insular gyri, separated by the postcentral insular sulcus. The vascular supply of the insula is mainly provided by the M2 segment of the middle cerebral artery, which constitutes a substantial obstacle to any open or stereotactic procedure aiming at the insular region. Histologically, the insula is a part of the paralimbic cortex, as it bears in its antero-inferior part an allo and mesocortical area. The insula is functionally involved in cardiac rhythm and arterial blood pressure control, as well as in viscero-motor control and in viscero-sensitive functions. There is considerable evidence for the involvement of the insula as a somesthetic area, including a major role in the processing of nociceptive inputs. Its possible role in some epilepsies may explain some failures of temporal lobe resection. Surgery of the insular lobe is a technical challenge, whose risks can be minimized by the use of intra-operative direct cerebral stimulation.

Variaciones del sector anterior del polígono de Willis. Correlación anatomo-angiográfica y su implicancia en la cirugía de aneurismas intracraneanos (Arterias: ácigos cerebral anterior, mediana del cuerpo calloso y cerebral media accesoria)

It is worlwide accepted that in almost 60% of cases, anatomical variants in the Circle of Willis can be found. Some of them are associated with vascular malformations such as aneurysms. The knowledge of these anatomical variants is of vital importance when facing surgery, being the aims to preserve arteries in unusual localisations, which when injured can determine invalidating sequelae. The authors have reviewed 192 cerebral hemispheres, finding three variants in the anterior Circle of Willis: Azigos anterior cerebral artery; Median artery of the corpus callosum and accessory middle cerebral artery. The authors make an anatomical description of the findings, their angiographical correlation, and describe the influence of these changes during surgery of aneurysms in the involved regions.

Microsurgical anatomy of the early branches of the middle cerebral artery: morphometric analysis and classification with angiographic correlation

OBJECT

The cortical arteries arising from the main trunk of the middle cerebral artery, proximal to its bifurcation or trifurcation, are called "early branches." The purpose of this study was to characterize these early branches.

METHODS

The early branches were characterized according to their sites and patterns of origin, diameters, and relative proximity to the internal carotid artery bifurcation, as well as the course and area of supply of their cortical branches based on an examination of 50 hemispheres. Special attention was directed to the perforating arteries that arose from the early branches and entered the anterior perforated substance. The anatomical findings were compared with data obtained from 109 angiograms.

CONCLUSIONS

Early branches directed to the temporal and frontal lobes were found in 90 and 32% of the hemispheres, respectively. The early branches that arose more proximally from the M1 segment were larger than those arising distally. Lenticulostriate arteries arose from 81% of the early frontal branches (EFBs) and from 48% of the early temporal branches (ETBs). An average of two cortical arteries arose from the EFBs and 1.3 from the ETBs, the most common of which supplied the temporopolar and orbitofrontal areas. Although the microsurgical anatomy of the early branches demonstrates abundant diversity, they can be classified into clearly defined patterns based on anatomical features. These patterns can prove helpful in evaluating angiographic data and in planning an operative procedure.

The insula (Island of Reil) and its role in auditory processing. Literature review

The insular cortex is a complex structure which contains areas that subserve visceral sensory, motor, vestibular, and somatosensory functions. The role of the insular cortex in auditory processing was poorly understood until recently. However, recent case studies indicate that bilateral damage to the insulae may result in total auditory agnosia. Functional imaging studies demonstrate that the insulae participate in several key auditory processes, such as allocating auditory attention and tuning in to novel auditory stimuli, temporal processing, phonological processing and visual-auditory integration. These studies do not clarify the issue of further specialisation within the insular cortex, e.g. whether the posterior insulae are primarily sensory areas, while the anterior insulae serve mainly as integration/association auditory areas, two hypotheses that would be compatible with the cytoarchitectonic structure and connectivity of the insulae. The functional characterisation of the insulae remains incomplete, underlining the need for further studies.

The effects on prognosis of surgical treatment of hypertensive putaminal hematomas through transsylvian transinsular approach

OBJECTIVE

Hypertensive putaminal hematoma (HPH) is a devastating type of stroke that mostly results in death or severe neurologic deficit. There seems to be no general agreement on the selection of treatment modality for individual patients. In this study a comparison has been made between conservative treatment and the results of surgical treatment through the transsylvian transinsular approach of HPH with 30 cc or more.

METHODS

Sixty-six patients with 30 cc volume or over of HPH, who were admitted within 36 hours after ictus, have been included in this study. Selection of the patients was made primarily according to the computerized tomography scan (CT) findings on admission. Out of the 66 patients, 47 were operated for hematoma evacuation through transsylvian transinsular approach, and the remaining 19 were accepted as a control group to be treated conservatively after their relatives declined authorization for surgery. All patients' neurologic grades and CT findings on admission were classified according to the hypertensive intracerebral hemorrhage grading system, as proposed by the cooperative study in Japan. After 6 months the outcomes of both groups were assessed according to the Glasgow outcome scale (GOS).

RESULTS

The statistical difference between the mortality rates was considerable (p < 0.05) with ratios of 34% and 63.1% in the surgically and conservatively treated groups, respectively. Good recovery, that is GOS score 5, was not observed in either group. In the group of surgically treated patients, 27.7% was eventually moderately disabled (GOS score 4); whereas this ratio was 5.3% among the conservatively treated group, giving a statistically significant difference (p < 0.05). Our results indicate that neurologic grades and CT findings on admission are good predictors of outcome, as the grades increase the outcome worsens. Furthermore, ventricular spread of hematoma is not a good prognostic factor.

CONCLUSIONS

Surgical treatment via transsylvian transinsular approach of HPH with a volume of 30 cc or more results in improved outcome as compared to conservative treatment. Operation time within the first 36 hours after ictus did not affect the outcome.

Anatomy based research in neurosurgery

The Anatomy Based Research in Neurosurgery is an important part of Applied Neuroanatomy that mainly concerns neurosurgical procedures and related problems, namely neuroimaging, brain mapping and surgical techniques. This includes a wide variety of research fields such as 2-D and 3-D structure visualization and referencing (stereotaxy), intraoperative imaging cartography and targeting (neuronavigation), as well as microsurgical, functional and endoscopic anatomy. The methods involved in this investigation regard predominantly microsurgical proceedings and morphological variability studies, both on living or post-mortem material (the strict neuroimaging techniques remaining a main tool for radiologists). The present paper provides an overview of the main techniques of neuroanatomical research applied to neurosurgery. Their major indications and requirements are described and discussed. Special attention is paid to some anatomical techniques such as microdissection and serial sectioning as well as 2-D and 3-D image procedures that are explained in detail.

Surgical resection of intrinsic insular tumors: complication avoidance

OBJECT

Surgical resection of tumors located in the insular region is challenging for neurosurgeons, and few have published their surgical results. The authors report their experience with intrinsic tumors of the insula, with an emphasis on an objective determination of the extent of resection and neurological complications and on an analysis of the anatomical characteristics that can lead to suboptimal outcomes.

METHODS

Twenty-two patients who underwent surgical resection of intrinsic insular tumors were retrospectively identified. Eight tumors (36%) were purely insular, eight (36%) extended into the temporal pole, and six (27%) extended into the frontal operculum. A transsylvian surgical approach, combined with a frontal opercular resection or temporal lobectomy when necessary, was used in all cases. Five of 13 patients with tumors located in the dominant hemisphere underwent craniotomies while awake. The extent of tumor resection was determined using volumetric analyses. In 10 patients, more than 90% of the tumor was resected; in six patients, 75 to 90% was resected; and in six patients, less than 75% was resected. No patient died within 30 days after surgery. During the immediate postoperative period, the neurological conditions of 14 patients (64%) either improved or were unchanged, and in eight patients (36%) they worsened. Deficits included either motor or speech dysfunction. At the 3-month follow-up examination, only two patients (9%) displayed permanent deficits. Speech and motor dysfunction appeared to result most often from excessive opercular retraction and manipulation of the middle cerebral artery (MCA), interruption of the lateral lenticulostriate arteries (LLAs), interruption of the long perforating vessels of the second segment of the MCA (M2), or violation of the corona radiata at the superior aspect of the tumor. Specific methods used to avoid complications included widely splitting the sylvian fissure and identifying the bases of the periinsular sulci to define the superior and inferior resection planes, identifying early the most lateral LLA to define the medial resection plane, dissecting the MCA before tumor resection, removing the tumor subpially with preservation of all large perforating arteries arising from posterior M2 branches, and performing craniotomy with brain stimulation while the patient was awake.

CONCLUSIONS

A good understanding of the surgical anatomy and an awareness of potential pitfalls can help reduce neurological complications and maximize surgical resection of insular tumors.