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.     

Microsurgical approaches to the perimesencephalic cisterns and related segments of the posterior cerebral artery: comparison using a novel application of image guidance

OBJECTIVE: To describe the exposure obtained through six approaches to the perimesencephalic cisterns with an emphasis on exposure of the posterior cerebral artery and its branches. METHODS: Dissections in 12 hemispheres exposed the crural, ambient, and quadrigeminal cisterns and related segments of the posterior cerebral artery. A Stealth Image Guidance workstation (Medtronic Surgical Navigation Technologies, Louisville, CO) was used to compare the approaches. RESULTS: The transsylvian approach exposed the interpeduncular and crural cisterns. The subtemporal approach exposed the interpeduncular and crural cisterns as well as the lower half of the ambient cistern. Temporal lobe retraction and the position of the vein of Labbé limited exposure of the quadrigeminal cistern. Occipital transtentorial and infratentorial supracerebellar approaches exposed the quadrigeminal and lower two-thirds of the ambient cistern. Transchoroidal approaches exposed the posterior third of the crural cistern, the upper two-thirds of the ambient cistern, and the proximal quadrigeminal cistern. Transchoroidal approaches exposed the posterior portion of the P2 segment (P2p) in 9 of 10 hemispheres and were the only approaches that exposed the lateral posterior choroidal arteries and the plexal segment of the anterior choroidal artery. Occipital transtentorial and infratentorial supracerebellar approaches provided access to the P3 segment in all cases and exposed the P2p segment in 4 of 10 hemispheres. The subtemporal approach provided access to the cisternal and crural segments of the anterior choroidal and medial posterior choroidal arteries and exposed the P2p segment in 3 of 10 hemispheres. CONCLUSION: Surgical approaches to lesions of the perimesencephalic cisterns must be tailored to the site of the pathological findings. The most challenging area to expose is the upper half of the ambient cistern, particularly the P2p segment of the posterior cerebral artery.     

The variations of sylvian veins and cisterns in anterior circulation aneurysms

Summary The anatomical variations of Sylvian vein and cistern were investigated during the pterional approach in 230 patients with 276 aneurysms of anterior circulation arteries, that were operated on at the Neurosurgical Department of Atatürk University Medical School, Erzurum, Turkiye. All patients underwent radical surgery for aneurysm by the right or left pterional approach. The findings were recorded during surgical intervention and observed through the slides and videotapes of the operations.In our study, we surgically classified the variations of the Sylvian vein, according to its branching and draining patterns. Type I: The fronto-orbital (frontosylvian), fronto-parietal (parietosylvian) and anterior temporal (temporosylvian) veins drain into one sylvian vein. Type II: Two superficial Sylvian veins with separated basal vein draining into the sphenoparietal and Rosenthal's basal vein. Type III: Two superficial Sylvian veins draining into the sphenoparietal and the superior petrosal veins. Type IV: Hypoplastic superficial Sylvian vein and the deep one. Four types of Sylvian vein variations were defined as follows. The Type I was seen in 45% (n = 103), the Type II was found in 29% (n = 67), Type III was recorded in 15% (n = 34) and Type IV, or hypoplastic and deep form was discovered in 11% (n = 26) of patients. The course of the Sylvian vein was on the temporal side (Temporal Coursing) in 70 percent of the cases (n= 160), on the frontal side (Frontal Coursing) in 19% of the patients (n = 45) and in 8 percent of the cases (n= 18) in the deep localization (Deep Coursing). Only 3 percent of the cases (n = 7) showed a mixed course. The variations of the Sylvian cisterns were classified into three types, according to the relationships between the lateral fronto-orbital gyrus and the superior temporal gyrus. In Sylvian Type, the frontal and temporal lobes are loosely (Sylvian Type A, Large) or tightly (Sylvian Type B, Close and Narrow) approximated on the surface thereby covering the area of the Sylvian cistern. In frontal type, the proximal part of the lateral fronto-orbital gyrus herniated into the temporal lobe. In temporal type, the proximal part of the superior temporal gyrus herniated into the lateral fronto-orbital gyrus. The variations of the Sylvian cisterns in 230 patients were as follows: in 31% (n = 71) Sylvian Type A, in 21% (n = 48) Sylvian Type B, in 34% (n = 78) Frontal Type, and in 14% (n = 33) Temporal Type.We concluded that venous perfusion disorder of the brain is the most important factor during the pterional approach. Careful intraoperative assessment and protection of the Sylvian vein, which is a surgical pitfall, is an indispensable part of the operation. The recognition of the anatomical variations of the Sylvian vein and cistern, and the detailed knowledge of the microvascular relationships at that level will allow the neurosurgeon to construct a better and safter microdissection plan, to save time and can prevent postoperative neurological deficits.     

Microsurgical anatomy of the interpeduncular cistern and related arachnoid membranes

OBJECT: The goal of this study was to investigate the microsurgical anatomy of the interpeduncular cistern and related arachnoid membranes. METHODS: The interpeduncular cistern and related arachnoid membranes were studied in eight Han Chinese adult human cadaveric brains with the aid of an operating microscope. The interpeduncular cistern is one area in the cranial cavity in which the arachnoid membranes and trabeculae are extremely luxuriant and complicated. The Liliequist membrane, the medial pontomesencephalic membrane, and the lateral pontomesencephalic membranes form the walls of the interpeduncular cisterns. The basilar artery (BA) bifurcation membrane, posterior perforated membrane, and arachnoid trabeculae fill the cistern. These arachnoid membranes and trabeculae adhere to the hypothalamus, brainstem, and oculomotor nerves, and bind the bifurcation of the BA, posterior cerebral arteries, superior cerebellar arteries, posterior communicating arteries, and their perforating branches. CONCLUSIONS: Arachnoid membranes and trabeculae complicate the exposure and dissection of lesions within the interpeduncular cistern. All arachnoid membranes and trabeculae should be dissected and incised sharply during surgical procedures. The BA bifurcation membrane and the posterior perforated membrane must be incised after opening the Liliequist membrane for sufficient exposure of deep structures within the interpeduncular cistern.     

The transsylvian trans-limen insular approach to the crural,ambient and interpeduncular cisterns

Summary Background. The authors introduce the transsylvian trans-limen insular approach to the crural, ambient and interpeduncular cisterns.Method. The transsylvian trans-limen insular approach was performed in 7 patients; 3 for aneurysm, 2 for isolated temporal horn hydrocephalus, one for tumour and one for an arteriovenous malformation. This approach is summarized in 4 procedures; the exposure of the inferior limiting sulcus of the insular cortex, the exposure of the inferior horn of the lateral ventricle, the dissection of the inferior part of the choroidal fissure and the splitting of the inferior border of the limen insula.Findings. Four among 7 patients underwent surgery for the lesions in the crural or ambient cistern. The other 3 patients underwent surgery for the lesion in the interpeduncular cistern. Two patients of the latter group postoperatively had temporal lobe infarction.Conclusions. The transsylvian trans-limen insular approach may be indicated for lesions in the crural and the anterior ambient cisterns, and the lesions which need wider exposure of the interpeduncular cistern. For the former lesions, this approach can afford good results. For the latter lesions, careful brain retraction and some other techniques to avoid temporal lobe infarction are necessary. Further neuropsychological assessment should be also necessary to prove the validity of this approach.     

The vascular supply to the spinal cord and its relationship to anterior spine surgical approaches

Background contextThe understanding of vascular supply to the spinal cord is important given that the evolution of surgical approaches to the spine may bring along the potential for more frequent complications, especially a rare but devastating complication: that of spinal cord ischemia or infarction. To maximally avoid this complication, the relationship between the spinal cord vascularity and the anterior spine surgical approach needs further study.PurposeTo provide a theoretical basis that will allow the spinal surgeon to take appropriate steps to avoid spinal cord ischemia during anterior spinal surgery through anatomic means.Study designSpinal cord vascular casting assessment with cadaveric specimen.MethodsTwenty adult cadaveric specimens (11 men and 9 women) were obtained for the latex perfusion and vessel dissection. In addition, nine patients (seven men and two women) underwent superselective angiography of the spinal cord. The segmental arterial anastomosis and radiculomedullary vessels in the thoracolumbar region were shown and reviewed.ResultsThere were approximately 21 pairs of segmental arteries in the thoracolumbar region. Adjacent segmental arteries were networked with each other. The latex infusion specimens demonstrated 72 anterior radiculomedullary arteries and 177 posterior radiculomedullary arteries in all 20 samples. The anterior and posterior spinal arteries were also networked with each other at several levels. Superselective spinal angiography was consistent with the latex infusion specimens showing.ConclusionsThe variety of anatomy of spinal cord arterial networks is shown, and the relation between the blood supply of certain spinal levels and the potential ischemic complications during the anterior surgical approach is discussed. It is hopefully of benefit to surgeons, after fully understanding the anatomy of these spinal vascular supply structures, that there may be even greater avoidance of vascular compromise in these challenging operations.     

Selection of surgical approach for quadrigeminal cistern arachnoid cyst

Preoperative magnetic resonance imaging of 4 cases of quadrigeminal cistern arachnoid cyst were retrospectively reviewed and patterns of extension to surrounding cisterns from the quadrigeminal cistern were examined. Relationship between patterns of extension to surrounding cisterns and selected surgical approach were evaluated. In 2 cases, the cyst extended anteriorly and compressed the quadrigeminal plate. These two cases had hydrocephalus due to aqueductal stenosis. The anteroirly extending cyst was treated with endoscopic ventriculocystocisternostomy via the lateral and third ventricles. In one case, the cyst extended superiorly to the velum interpositum cistern, and was treated with endoscopic ventriculocystocisternostomy via the lateral ventricle. In one case, the cyst extended laterally to the ambient cistern and compressed the posterior horn of the lateral ventricle. This case had loculated hydrocephalus of the inferior horn. The laterally extending cyst was treated with resection of the wall of the arachnoid cyst via an infratentorial supracerebellar approach assisted by endoscope. All cysts were successfully treated. Injury of the foramen of Monro occurred during a procedure using a flexible endoscope in a case with an anterior extending cyst. Exact analysis of the preoperative imaging and selection of appropriate surgical approach are key factors for successful treatment of a quadrigeminal cistern arachnoid cyst.     

带伴行血管尺神经前置术的解剖学研究

目的观察肘部尺神经的血液供应,设计带伴行血管尺神经前置的手术方法。方法取20侧防腐成人上肢标本,观测肘部尺神经血供来源和血管起始处外径、血管起始处至肱骨内上髁距离、血管起始处至尺神经垂直距离及尺神经伴行长度。另采用3侧防腐成人上肢标本模拟临床手术,设计带伴行血管尺神经前置术。结果肘部尺神经血供有3个来源,分别是尺侧上副动脉、尺侧下副动脉和尺侧返动脉后支。3条动脉从起始处至肱骨内上髁的距离分别是14.2±0.9、4.2±0.6和4.8±1.1cm;尺神经伴行长度分别是15.0±1.3、5.1±0.3和5.6±0.9cm;血管起始处外径分别是1.5±0.5、1.2±0.3和1.4±0.5mm;血管起始处至尺神经垂直距离分别是1.2±0.5、2.7±0.9和1.3±0.5cm。结论带伴行血管尺神经前置术治疗肘管综合征是可行的,且最大程度保留了肘部尺神经血供。     

Liliequist's membrane is a fold of the arachnoid mater: study using sheet plastination and scanning electron microscopy

OBJECTIVE: The subarachnoid space consists of a number of distinct subarachnoid cisterns. They are separated from each other by trabecular walls, one of which is Liliequist's membrane. The aim of this study was to investigate the anatomic characteristics of Liliequist's membrane. METHODS: The study used a combined approach, consisting of the modified E12 sheet plastination method for 3 adult cadavers and gross anatomic dissection for 35 cadavers, 2 of which were further examined using scanning electron microscopy. RESULTS: The results from this study indicate that 1) Liliequist's membrane is an avascular fold of the arachnoid mater that lacks openings and spreads out laterally, being in direct continuity with the arachnoid mater covering the tentorium; 2) the carotid-chiasmatic walls, which separate the chiasmatic cistern and carotid cisterns and had been considered to be parts of Liliequist's membrane, are vascular and incomplete trabecular walls and should not be considered parts of Liliequist's membrane; and, 3) as a fold of the arachnoid mater, Liliequist's membrane is not directly attached to the temporal lobes and oculomotor nerves. CONCLUSION: Liliequist's membrane is a double-layer fold of the arachnoid mater and has anatomic characteristics different from those of arachnoid trabecular walls.     

前臂外侧皮神经营养血管远端蒂筋膜皮瓣的解剖和临床应用

目的 观察前臂外侧皮神经营养血管皮瓣的血供和临床应用的可行性。 方法 用３７侧成人上肢标本,对前臂外侧皮神经营养血管的来源,行径,分支分布及其与头静脉的关系等进行解剖观察,并设计了前臂外侧皮神经营养血管远端蒂筋膜皮瓣,应用于临床修复手背疱痕切除后遗留创面。结果 前臂外侧皮神经前支与头静脉紧密伴行,其全程由４支节段性皮动脉发支营养。     

Magnetic resonance cisternography used to determine precise topography of the facial nerve and three components of the eighth cranial nerve in the internal auditory canal and cerebellopontine cistern

OBJECT: The detailed anatomy of intracranial structures has been studied mainly in cadavers, but the absence of cerebrospinal fluid and blood pressure in these models distorts normal spatial relationships. The authors investigated the rotation of the facial nerve (FN), superior vestibular nerve (SVN), inferior vestibular nerve (IVN), and cochlear nerve (CN) in the internal auditory canal (IAC) and cerebellopontine cistern in human volunteers and compared their results with those reported in cadaver studies. METHODS: The IACs and cerebellopontine cisterns of 30 normal adults (34 sides) were examined using magnetic resonance (MR) cisternography with a heavily T2-weighted two-dimensional fast spin-echo technique. The positions of the four components were unaffected by the presence of the meatal loop of the anterior inferior cerebellar artery in the IAC. The spatial relationship between the FN and SVN was quite constant, but the spatial relationship between the CN and SVN was quite variable: the former changed position, mainly in the IAC, on nine (26.5%) of 34 sides, and in the cerebellopontine cistern on the other sides (73.5%), conflicting with findings in cadaver studies. CONCLUSIONS: It is more accurate to describe the CN and IVN as coursing beneath the SVN in either the IAC or cerebellopontine cistern, rather than stating that the three components rotate, as reported in cadaver studies. The MR cisternography studies provided quite detailed information about the topography of the four components and the relationship between the blood vessels and cranial nerves in the IAC and the cerebellopontine cistern.     

Morphometry of the anterior third ventricle region as a guide for the transcallosal-interforniceal approach

The transcallosal-interforniceal approach is the most appropriate approach to localize and totally remove space-occupying lesions around the anterior third ventricle region such as craniopharyngiomas and gliomas. This study examined the microsurgical anatomy of the normal anterior third ventricle region in 81 adult cadaver hemispheres. The central sulcus was identified and surface landmarks determined as the points 5 cm (P5) and 7 cm anterior to the central sulcus (P7). The distances between P5 and P7 and the upper margin of the interventricular foramen, which delineate the surgical corridor chosen to avoid disturbance of important neural structures, were 46.26-60.96 (54.09 +/- 3.35) mm and 48.00-62.00 (54.94 +/- 3.09) mm, respectively. The distances between the upper margin of the hemisphere and the cingulate sulcus, especially important for avoiding damage to the cingulate gyrus and other mesiolimbic structures, were 13.54-30.00 (21.28 +/- 3.89) mm and 12.22-29.52 (21.12 +/- 3.90) mm at the level of P5 and P7. The distances between the upper margin of the hemisphere and the callosal cistern containing the pericallosal artery were 28.34-40.50 (33.94 +/- 2.84) mm and 28.16-40.26 (33.50 +/- 2.61) mm, respectively. Normative morphometric data of the structures involved in the surgical procedure are necessary for planning and performance of the transcallosal-interforniceal approaches. This study of a large series of specimens shows that these measurements have large individual variations.     

Gross and microscopical blood supply of the trachea.

Twenty-one human tracheal specimens were perfused and dissected, 10 with conventional techniques and 11 with clearing and microdissection techniques. The lateral pedicles of the trachea and esophagus induct vessels from the inferior thyroid, subclavian, supreme intercostal, internal thoracic, innominate, and superior and middle bronchial arteries. These vessels are interconnected along the lateral surface of the trachea by an important longitudinal vascular anstomosis. From the 2 lateral longitudinal anastomoses the lateral and anterior tracheal walls receive their blood supply through transverse segmental vessels that run in the soft tissues between the cartilages. These transverse vessels interconnect the longitudinal anastomoses across the midline and feed the submucosal capillary network that arborizes richly beneath the endotracheal mucosa. The tracheal cartilages receive nourishment from the capillary bed applied to their internal surface. The esophageal arteries and their subdivisions that supply the posterior membranous wall of the trachea contribute almost nothing to the circulation of the cartilaginous walls.     

The long thoracic nerve: Possible mechanisms of injury based on autopsy study

Forty dissections in 21 adult cadavers were analyzed to determine whether the long thoracic nerve could be mechanically damaged or its blood supply threatened along its peripheral course. The mean length of the nerve was 21.9 cm measured from the upper border of the serratus anterior; it ended an average of 8.4 cm distal to the inferior angle of the scapula. Three postmortem arteriographs were done, and the blood supply to the lower part of the nerve was observed radiographically and in the dissections. The nerve and its blood supply were found to be vulnerable for both compression and stretching anterior to the lower part of the scapula. The findings differ from previous theory about nerve injury at the level of the second rib. Marked interindividual differences in the course of the nerve were noted; this may explain why some people experience paralysis while others do not.     

Microanatomy of the anterior cerebral artery

The microanatomic features of the anterior cerebral artery were studied in 30 unfixed human brains which were injected with tinted polyester resin via cannulation of the internal carotid arteries under microscopic dissection. The outer diameter, length, and number of perforating branches were measured for each of the following vessels: anterior cerebral artery (proximal A1 segment, distal A2 segment), anterior communicating artery, and recurrent artery of Heubner. The perforating branches of the proximal segment of the anterior cerebral artery penetrated the brain at the anterior perforated substance, lateral chiasm, and optic tracts. The perforating branches of the anterior communicating artery penetrated the brain at the lamina terminalis, anterior perforated substance, and medial chiasm. The first 5 mm of the distal anterior cerebral artery (A2) had perforating branches penetrating the brain at the gyrus rectus and olfactory sulcus. The recurrent artery of Heubner originated from the A2 segment of the anterior cerebral artery in 57% of the cases, from the anterior cerebral artery-anterior communicating artery junction in 35%, and from the A1 segment in 8%. The depth of the interhemispheric fissure at the genu was 36.0 +/- 0.5 mm and at the midbody of the corpus callosum, 35.0 +/- 0.5 mm. Extension of the dissection to approach the anterior communicating artery from the genu of the corpus callosum using the anterior interhemispheric route was an additional 31.7 +/- 0.7 mm. The callosal arterial supply from the anterior cerebral artery showed short callosal branches in all brain specimens and long callosal vessels in 10% of the specimens.     

Surgical anatomy of the human spleen

Post-splenectomy sequelae are now well recognized, and conservative splenic surgery is widely advocated. However, controversies exist regarding splenic surgical anatomy. We studied 127 human spleens using anatomical dissection and a sequential injection method involving both radiology and corrosion casting, with the primary aim of examining segmental splenic anatomy and blood supply. The existence of well-defined splenic segments was confirmed and these ranged in number from 3 to 7 with a mean of 4.3. Each segment had its own arterial supply and venous drainage. The segments were separated from each other by avascular planes. Subsegments with independent blood supply were also identified. The splenic artery was found to divide into two branches; in all cases these further divided into segmental arteries supplying the central segments of the spleen. The polar segments were supplied by segmental vessels of highly variable origin and size. This study aims to highlight the importance of identifying these segmental vessels at operation when splenic conservation is considered.     

Surgical implications of the posterior gastric artery

The posterior gastric artery was identified during gastrectomy in 43 of 51 patients with distal gastric cancer. Two female patients had two posterior gastric arteries that originated separately from the splenic artery. Of these 45 arteries, 6 originated from the proximal third of the splenic artery, 35 from the mid third, and 4 from the distal third. These vessels coursed upward behind the posterior parietal peritoneum. The anterior and posterior walls of the remnant stomach were stained blue after injection of methylene blue solution into the splenic artery. The surgical importance of the posterior gastric artery is obvious because of its high frequency and deep origin and course. In addition, it is another source of blood supply to the stomach, and the lymphatics around this vessel form one of the primary routes draining the gastric fundus.     

Supraorbital Minicraniotomy

The recent use of neuroendoscopy combined to microsurgery allows new surgical approaches. We report our early experience with a supraorbital microcraniotomy. This technique is suitable for small lesions situated in the region of the anterior fossa, suprasellar cisterns, and Sylvian cistern. A 50-mm incision in the eyebrow and a supraorbital minicraniotomy are performed. We report on six patients with different lesions and good cosmetic results. We conclude that this approach is safe and useful in selected cases.     

Assessment of spinal cord ischemia by means of evoked potential monitoring during thoracoabdominal aortic surgery

Besides renal failure and mesenteric infarction, spinal cord ischemia is the most dreaded complication after thoracoabdominal aortic surgery. Several techniques have been developed to improve neurologic outcome of these massive surgical procedures, including pharmacologic adjuncts, epidural cooling, distal aortic perfusion, cerebrospinal fluid drainage, and reattachment of segmental arteries. The authors developed a technique to assess spinal cord integrity as part of the surgical protocol, dictating operative strategies to restore blood supply to the endangered grey matter. Monitoring motor evoked potentials (MEPs) was performed in experimental studies and in 170 patients with a thoracoabdominal aortic aneurysm. The surgical protocol included left heart bypass and cerebrospinal fluid drainage, and MEP monitoring was applied to identify critical intercostal and lumbar arteries. Based on MEPs, the aggressive surgical approach resulted in a significant reduction of neurologic complications (2.3%).     

Supraorbital minicraniotomy

The recent use of neuroendoscopy combined to microsurgery allows new surgical approaches. We report our early experience with a supraorbital microcraniotomy. This technique is suitable for small lesions situated in the region of the anterior fossa, suprasellar cisterns, and Sylvian cistern. A 50-mm incision in the eyebrow and a supraorbital minicraniotomy are performed. We report on six patients with different lesions and good cosmetic results. We conclude that this approach is safe and useful in selected cases.