The arteriographic pattern of the insula: its normal appearance and variations in cases of tumour of the cerebral hemispheres

Identifying the Sylvian Triangle on CT angiography: A technique for detecting distal middle cerebral artery occlusions

Medium vessel occlusions (MeVOs), defined as occlusion of the M2/M3 and A2/A3 segments of the middle cerebral artery (MCA) and anterior cerebral artery, can be challenging to visualize on CT angiography (CTA) and MR angiography (MRA), given the anatomic complexity of the mid- and distal intracranial vasculature and smaller vessel caliber (Leary MC, Kidwell CS, Villablanca JP, et al. Validation of computed tomographic MCA "dot" sign: an angiographic correlation study. Stroke 2003; 34: 2636-2640; Luijten SPR, Wolff L, Duvekot MHC, et al. Diagnostic performance of an algorithm for automated large vessel occlusion (LVO) detection on CTA. J Neurointerv Surg 2022; 14: 794-798). In turn, the appearance of a sudden vessel cutoff in these vascular distributions on CTA or MRA is not always straightforward and may represent true occlusion, variant anatomy, and/or artifact (Leary MC, Kidwell CS, Villablanca JP, et al. Validation of computed tomographic MCA "dot" sign: an angiographic correlation study. Stroke 2003; 34: 2636-2640; Luijten SPR, Wolff L, Duvekot MHC, et al. Diagnostic performance of an algorithm for automated LVO detection on CTA. J Neurointerv Surg 2022; 14: 794-798). Given the importance of rapidly establishing an accurate diagnosis in the setting of stroke, combined with recent clinical trials and movements promoting the efficacy of endovascular therapeutic approaches to treat MeVOs, it remains imperative to detect such occlusions accurately and quickly on imaging. In turn, we present five imaging patterns of the Sylvian Triangle on sagittal reformatted images from CTA Head examinations, which our practice has utilized to assess patency of the M2 and M3 divisions. This approach is rapidly deployable and can be utilized by radiology and non-radiology healthcare providers alike, thus facilitating rapid and accurate diagnosis of MeVO, timely evaluation of candidacy for endovascular therapy, and ultimately supporting favorable door-to-intervention time and successful patient outcomes.

Feasibility and safety of partial resection of the anterior insular cortex for microsurgical treatment of middle cerebral artery aneurysms located in the limen recess: patient series

BACKGROUND

When performing clip ligation of superior projecting aneurysms of the proximal (M1) segment of the middle cerebral artery (MCA), meticulous sylvian fissure dissection alone may be inadequate for safe clip application, especially in cases in which the aneurysm is buried in the limen recess, since the limen insulae may be positioned lateral to the aneurysm. In the present patient series, the authors present their surgical technique for clip ligation of aneurysms located in the limen recess, with partial resection of the limen insulae.

OBSERVATIONS

A retrospective analysis of patients who had undergone clip ligation of MCA aneurysms located at the limen recess at a single institute was performed. Patients with angiographic and clinical follow-up data were considered eligible. A total of 11 aneurysms (4 ruptured and 7 unruptured aneurysms) in 11 patients were evaluated. Postoperative ischemic lesions were observed on images obtained within 1 week after surgery in 5 (45.5%) patients who had undergone partial resection of the limen insulae, although none of them presented with neurological deterioration.

LESSONS

Partial resection of limen insulae may be feasible to avoid severe ischemic complications following clip ligation of M1 aneurysms embedded in the limen recess.

Microsurgical anatomy of the insula and the sylvian fissure

Object. The purpose of this study was to define the topographic anatomy, arterial supply, and venous drainage of the insula and sylvian fissure.

Methods. The neural, arterial, and venous anatomy of the insula and sylvian fissure were examined in 43 cerebral hemispheres.

Conclusions. The majority of gyri and sulci of the frontoparietal and temporal opercula had a constant relationship to the insular gyri and sulci and provided landmarks for approaching different parts of the insula. The most lateral lenticulostriate artery, an important landmark in insular surgery, arose 14.6 mm from the apex of the insula and penetrated the anterior perforated substance 15.3 mm medial to the limen insulae. The superior trunk of the middle cerebral artery (MCA) and its branches supplied the anterior, middle, and posterior short gyri; the anterior limiting sulcus; the short sulci; and the insular apex. The inferior trunk supplied the posterior long gyrus, inferior limiting sulcus, and limen area in most hemispheres. Both of these trunks frequently contributed to the supply of the central insular sulcus and the anterior long gyrus. The areas of insular supply of the superior and inferior trunks did not overlap. The most constant insular area of supply by the cortical MCA branches was from the prefrontal and precentral arteries that supplied the anterior and middle short gyri, respectively. The largest insular perforating arteries usually arose from the central and angular arteries and most commonly entered the posterior half of the central insular sulcus and posterior long gyrus. Insular veins drained predominantly to the deep middle cerebral vein, although frequent connections to the superficial venous system were found. Of all the insular veins, the precentral insular vein was the one that most commonly connected to the superficial sylvian vein.

Arteries of the insula

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.

The insular cortex: morphological and vascular anatomic characteristics

OBJECTIVE

We undertook this anatomic study of the insula to investigate its vasculature, morphological features, and surrounding cortical relationships.

METHODS

Under magnification of x2 to x32, 53 formalin-fixed, adult cadaver hemispheres were dissected. Overlying opercular landmarks were identified and used as guides to portions of the deeper insula.

RESULTS

The insula has a complex venous system; 50 (94.3%) hemispheres exhibited a combination of superficial and deep venous connections. The venous connections divide the insular cortex into the following three anatomic zones, with some overlap: subapical region (insular pole), anterior lobe, and posterior lobe. Arterial contributions to the insula originated entirely from the middle cerebral artery, predominantly via the superior division. Thirty-six (67.9%) specimens exhibited a dedicated terminal vessel to the insula; in 34 of these (94.4%), this terminal vessel arose from the middle cerebral artery branch to the central sulcus. There was never more than one terminal vessel in each insular cortex.

CONCLUSION

Historically, it has been reported that the insula drains primarily via the deep middle cerebral vein (DMCV). We found more complex (typically both superficial and deep) venous connections. In most specimens, the DMCV exhibited a direct venous connection to only a portion of the insular cortex. The deep drainage connections of the insula and the vessels that form the DMCV suggest that the DMCV drains primarily the lateral lenticular veins and secondarily the insula. Arterial contributions to the insula tended to be centered around the central insular sulcus, independent of the location of the middle cerebral artery bifurcation. Although the insular vascular anatomic features showed great variability, the anatomic and structural relationships described in this dissection series should facilitate safe surgical and endovascular interventions.

The normal angiographic sylvian point on the lateral cerebral angiogram

The angiographic sylvian point (ASP) is one of the most useful landmarks on cerebral angiograms for detecting retrosylvian masses. Although it is suggested to be the halfway point on the clinoparietal line (CPL), its exact normal position has not been defined. The lateral carotid angiograms of 100 consecutive patients from 22 to 65 years of age were used to study the normal ASP in relation to the CPL. Patients with severe neurological deficits or angiographic evidence of hydrocephalus, severe vascular disease or mass lesions were eliminated from this study. In our 100 normals, the normal ASP was within 8 mm above and below the CPL, and in the majority (82%) it was located behind the midpoint of the CPL. It was not situated more than 14.4 mm posterior and never more than 3.1 mm anterior to the midpoint. Application of these normal relationships facilitates detection of small, deep retrosylvian masses occupying the medial portions of the parietal, occipital and temporal lobes.

Microsurgery of tumours of the frontal white matter

Seventy eight microsurgical extirpations of tumours located in the frontal white matter led to adjustment of the normal anatomy of the frontal brain according to microsurgical requirements, and also to relation with modern diagnostic procedures, especially computerized tomography (CT-scanning). The advantages of microsurgical treatment have been demonstrated. Thus, only exact comprehension of topographical anatomy allows a methodical, careful, and radical procedure. As vessels were commonly saved, postoperative courses were relatively benign because of less tendency to oedema. Out of 78 patients, 3 died while in hospital, and two recurrences were observed in the following 23 months. Postoperatively 51 patients improved, 18 stayed unchanged neurologically, and 9 patients deteriorated permanently. The usual microsurgical instruments were employed. Vascular problems were dealt with by the routine techniques used at our hospital.