The Basal or Sphenopetrosal Superficial Middle Cerebral Vein Type

Background and Objectives: The adult superficial middle cerebral vein (SMCV) commonly drains into the middle cranial fossa. However, different embryonic types persist, in which the SMCV drains into the lateral sinus. The basal type of SMCV coursing on the middle fossa floor is a scarce variant. Materials and Methods: During a retrospective study of archived computed tomography angiography (CTA) and magnetic resonance angiography (MRA) files, three rare adult cases of the basal or sphenopetrosal type of SMCV were found and further documented. Results: In the first case, which was evaluated via CTA, the basal type of SMCV formed a sagittal loop. It continued on the middle fossa floor, over a dehiscent tegmen tympani, to drain into the lateral sinus. In the second case, documented via MRA, the basal type of SMCV's anterior loop was in the coronal plane and closely related to the internal carotid artery and the cavernous sinus. It continued with the basal segment over a dehiscent glenoid fossa of the temporomandibular joint (TMJ). In the third case, documented via CTA, the initial cerebral part of the SMCV had a large fenestration. The middle fossa floor coursed within a well-configured sulcus of the SMCV and received a tributary through the tympanic roof. Its terminal had a tentorial course. Conclusions: Beyond the fact that such rare variants of the SMCV can unexpectedly interfere with specific approaches via the middle fossa, dehiscences of the middle fossa floor beneath such variants can determine otic or TMJ symptoms. Possible loops and fenestrations of the SMCV should be considered and documented preoperatively.

Fetal insular measurements in pregnancy with estimated fetal weight <10th centile and childhood neurodevelopmental outcomes

BACKGROUND

A growing body of evidence suggests that fetal growth restriction is associated with changes in brain structures as a result of chronic hypoxia. However, less is known about the effects of growth restriction on the fetal insula, particularly in less severely affected late-onset growth-restricted fetuses.

OBJECTIVE

This study aimed to (1) compare sonographic insular measurements between fetal-growth restricted, small-for-gestational-age, and appropriate-for-gestational-age control fetuses; and (2) evaluate the association of sonographic insular measurements with perinatal and neurodevelopmental outcomes in fetuses categorized as fetal-growth restricted or small-for-gestational-age.

STUDY DESIGN

This was a cohort study of singleton nonanomalous pregnancies with an estimated fetal weight <10th centile. Using data from the last examination before delivery, fetal insular depth, Sylvian fissure depth, hypoechoic insular zone thickness, circumference, and area were measured. All measurements were adjusted for by head circumference. Neurodevelopmental outcomes were evaluated at 2 to 3 years of age using the Bayley-III scales. Kruskal-Wallis H tests were performed to compare insular measurements between groups. Paired t tests were used to compare insular measurements between appropriate-for-gestational-age fetuses and gestational age-matched growth-restricted fetuses. Insular measurements for patients with and without an adverse perinatal outcome were compared using independent-samples t-tests. Spearman correlations were performed to evaluate the relationship of insular measurements to the percentile scores for each of the 5 Bayley-III subscales and to a summative percentile of these subscales.

RESULTS

A total of 89 pregnancies were included in the study; 68 of these pregnancies had an estimated fetal weight <10th percentile (fetal-growth restricted: n=39; small-for-gestational-age: n=29). The appropriate-for-gestational-age cohort consisted of 21 pregnancies. The gestational age at measurement was similar between fetal-growth restricted and small-for-gestational-age groups, but lower in the appropriate-for-gestational-age group. Differences between groups were noted in normalized insular depth, Sylvian fissure depth, and hypoechoic insular zone (P<.01). Normalized insular depth and hypoechoic insular zone circumference were larger in the growth-restricted cohort (P<.01). Normalized Sylvian fissure depth was smaller in the growth-restricted cohort (P<.01). There were no significant differences in insular measurements between pregnancies with and without an adverse perinatal outcome. Bayley-III results were available in 32 of the growth-restricted cases. Of all insular measurements, hypoechoic insular zone circumference was inversely correlated with the adaptive behavior Bayley-III score.

CONCLUSION

In our cohort, fetuses with estimated fetal weight <10th percentile had smaller Sylvian fissure depths and larger insular depths and hypoechoic insular zone circumferences than normally grown controls. A larger hypoechoic insular zone circumference was substantially correlated with worse neurodevelopmental outcomes in early childhood. We speculate that enlargement of this region may be an indication of accelerated neuronal maturation in growth-restricted fetuses with mild hypoxia.

The Microcisternal Drainage Technique

BACKGROUND

Microsurgical dissection of arachnoid cisterns requires a combination of anatomic knowledge and microsurgical skill. The latter relies on experience and microsurgical dexterity, which depend on visual identification of cisternal microvasculature. We describe a novel standardized operative sequence to allow for bloodless arachnoid dissection when cisternal anatomy is challenging.

METHODS

We used the reported technique in 1928 cases over the past 5 years (2018-2022). The outer arachnoid was incised to enter the cisternal space. A cotton pledget was placed in contact with an inner membrane and gently pushed laterally and superficially with the suction cannula at medium suction power. When the arachnoid membranes dried, arachnoid trabeculae were cut and microvasculature were released at the convexity of their loops and gently transposed off the dissection trajectory. The same principle was used to release parent and perforating arteries from the aneurysm dome.

RESULTS

The microcisternal drainage technique enabled safe and efficient access through adhered arachnoid in all cases. A complex anterior communicating artery aneurysm in a 52-year-old lady demonstrated the use of the microcisternal drainage technique during access through the pericallosal cistern. This technique was used in all cases where cisternal dissection was needed.

CONCLUSIONS

The microcisternal drainage technique uses deliberate and strategic suction, dynamic retraction, and nuanced scissor cuts to enable precise and bloodless microdissection of adherent arachnoid cisterns. This technique combines common neurosurgical maneuvers in a novel standardized sequence to improve efficiency and safety during arachnoid dissection.

Sylvian fissure lipoma associated with fusiform aneurysm in the middle cerebral artery trifurcation: A case report and literature review

BACKGROUND

The intracranial lipomas are rare congenital malformations accounting for approximately 0.1-1.3% of all intracranial tumors, of which Sylvian fissure lipomas account for <5%. These lesions are frequently associated with dysgenesis of neuronal brain tissues and vascular malformations and in the majority are asymptomatic. Intracranial lipomas on magnetic resonance imaging (MRI) may mimic late subacute hemorrhage due to similar radiological features. Due to the tight adhesion of the lipoma to the surrounding nerve structures and vessels, complete removal is difficult and does not guarantee the disappearance of symptoms.

CASE DESCRIPTION

We present the case of a 42-year-old woman with chronic headaches and short-term memory impairment who was admitted to the emergency room after an out-of-hospital brain MRI with suspected ruptured right middle cerebral artery (MCA) aneurysm and late subacute intracranial hemorrhage. In the hospital, after clinical evaluation, emergency computed tomography (CT) angiography was performed, which revealed an unruptured fusiform aneurysm located in the right MCA trifurcation surrounded by an extremely hypodense lesion corresponding to fat in the right Sylvian fissure. No features of intracranial hemorrhage were present. The diagnosis of intracranial lipoma was finally confirmed after the MRI of the brain with a fat suppression sequence. Surgical treatment was not attempted, and the patient was treated conservatively with a satisfactory general outcome.

CONCLUSION

A Sylvian fissure lipoma may be associated with a fusiform aneurysm in the MCA trifurcation. By modifying the standard MRI protocol and performing a CT scan, an intracranial lipoma can be detected and a late subacute intracranial hemorrhage can be excluded.

A novel surgical classification of the Sylvian Fissure and its implications on the clinical and radiological outcomes of patients undergoing clipping for unruptured middle cerebral artery aneurysms

BACKGROUND

The main access route for middle cerebral artery (MCA) aneurysms is the transsylvian approach. Although Sylvian fissure (SF) variations have been assessed, none have examined how this affect MCA aneurysm surgery. The objective of this study is to investigate how SF variants affect clinical and radiological outcomes for surgically-treated unruptured MCA aneurysms.

METHODS

This retrospective study examined consecutive unruptured MCA aneurysms in 101 patients undergoing SF dissection and aneurysm clipping. SF anatomical variants were categorized using a novel functional anatomical classification: Type I: Wide straight, Type II: Wide with frontal and/or temporal opercula herniation, Type III: Narrow straight, Type IV: Narrow with frontal and/or temporal opercula herniation. The relationships between SF variants and postoperative edema, ischemia, hemorrhage, vasospasm, and Glasgow Outcome Scale (GOS) were analyzed.

RESULTS

Study included 101 patients (53.5% women), 60.9±9.4 (range 24-78) years. SF types were 29.7% Type I, 19.8% Type II, 35.6% Type III, 14.9% Type IV. The SF type with the highest proportion of females was Type IV (n=11, 73.3%), while it was Type III for males (n=23, 63.9%) (p=0.03). There were significant differences between SF types, ischemia and edema (p<0.001, p=0.008, respectively). Although narrow SF types had poorer GOS scores (p=0.055), there were no significant differences between SF types and GOS, postoperative hemorrhage, vasospasm, or hospital stay.

CONCLUSIONS

Sylvian fissure variants may impact intraoperative complications during aneurysm surgery. Thus, pre-surgical determination of SF variants can predict surgical difficulties, thereby potentially reducing morbidity for patients with MCA aneurysms and other pathologies requiring SF dissection.

"Microcisternal Drainage" Technique for Clipping a Middle Cerebral Artery Aneurysm

Arachnoid dissection is often challenging because of tight corridors, microvasculature crossing the membranes, and a narrow operative field.^1-4 It is often said that "splitting" the sylvian fissure measures the talent of a cerebrovascular neurosurgeon, and there are as many styles of sylvian fissure dissection as neurosurgical schools.^4-8 Our principle is to dissect the subarachnoid space sharply and with minimal trauma to neither the microvasculature nor the pia matter.^4,7-10 We have developed a technique that allows efficient and safe sharp dissection through the subarachnoid space: the "microcisternal drainage" technique. This technique (Video 1) consists of applying a pledget to a narrow cistern and suctioning the cerebrospinal fluid while maintaining uplifting retraction with the suction shaft. Clear trabeculae are dissected sharply to release microvessels at the convexity of their turns. This technique is especially advantageous when cisterns are narrow (e.g., pia-to-pia) or highly eloquent structures are at risk. The main advantages over conventional cisternal dissection are avoidance of refractive effect, enhanced identification of the microvasculature from the trabeculae, and preservation of pia matter. Using the microcisternal drainage technique, the microvasculature, arachnoid membranes, and pia reveal themselves, and we avoid the cerebrospinal fluid-related refractive effect, therefore maximizing depth perception. We report an example of the "microcisternal drainage" technique to split the sylvian fissure during treatment of an irregular middle cerebral artery bifurcation aneurysm on a 56-year-old woman. The patient tolerated the procedure well, was discharged without neurologic deficits, and resumed normal life with no aneurysm remnant. The patient consented to the procedure and video and photography publication.

Exploring the emergence of morphological asymmetries around the brain's Sylvian fissure: a longitudinal study of shape variability in preterm infants

Brain folding patterns vary within the human species, but some folding properties are common across individuals, including the Sylvian fissure's inter-hemispheric asymmetry. Contrarily to the other brain folds (sulci), the Sylvian fissure develops through the process of opercularization, with the frontal, parietal, and temporal lobes growing over the insular lobe. Its asymmetry may be related to the leftward functional lateralization for language processing, but the time course of these asymmetries' development is still poorly understood. In this study, we investigated refined shape features of the Sylvian fissure and their longitudinal development in 71 infants born extremely preterm (mean gestational age at birth: 26.5 weeks) and imaged once before and once at term-equivalent age (TEA). We additionally assessed asymmetrical sulcal patterns at TEA in the perisylvian and inferior frontal regions, neighbor to the Sylvian fissure. While reproducing renowned strong asymmetries in the Sylvian fissure, we captured an early encoding of its main asymmetrical shape features, and we observed global asymmetrical shape features representative of a more pronounced opercularization in the left hemisphere, contrasting with the previously reported right hemisphere advance in sulcation around birth. This added novel insights about the processes governing early-life brain folding mechanisms, potentially linked to the development of language-related capacities.

Temporal sylvian fissure arachnoid cyst in children: treatment outcome following microsurgical cyst fenestration with special emphasis on cyst reduction and subdural collection

OBJECTIVES

Controversy remains regarding surgical managements of sylvian fissure arachnoid cyst (SFAC). This review presents our experience in the microsurgical fenestration of pediatric patients with SFAC to define surgical indication, and risks and benefits with special emphasis on postoperative subdural fluid collection (SDFC) and cyst size reduction.

METHODS

Thirty-four children with SFAC who underwent microsurgical cyst fenestration at a single institution over a 10-year period were retrospectively reviewed for their clinical presentation, neuroimaging findings, and postsurgical course. The SFACs were classified by a novel grading system based on the degree of arachnoid cyst extension from the sylvian fissure to the insular cistern shown on MR images: grade 0 - little or no prominence of sylvian fissure, grade I - SFAC confined to the sylvian fissure, grade II - SFAC partially extending to the insular cistern, grade III - SFAC extending to the entire insular cistern.

RESULTS

There were 26 males and 8 females. SFAC was present in the left side in 24. Twelve patients presented with cyst rupturing to the subdural space. Cyst grading did not show significant difference compared with rupture status (p > 0.9). All patients underwent microsurgical cyst fenestration. Postoperative SDFC is common but often resolved overtime in two-thirds of the cases with the mean average of 6 months. However, 3 patients had symptomatic postoperative SDFC and needed reoperation shortly after the first operation. Microsurgical cyst fenestrations for SFAC effectively resolved the presenting symptoms and often showed restorations of intracranial structures on follow-up imaging. Cyst resolution or reduction greater than 75% was noted in 61.8% of the patients postoperatively which was noted in a half of the SFAC of children even with age of 11 years or older. During the follow-up, no cyst recurrence or SDFC was noted. Patients with greater surgical reduction of cyst size tended to occur in younger children, and those with lower MR grade.

CONCLUSION

Our results showed a high reduction rate of SFAC and brain re-expansion after microsurgical fenestration together with symptomatic improvements regardless the patient's age. Considering the developing CNS during childhood, reductions of a large space-occupying lesion followed by restorations of the structural integrity of the developing brain are very desirable. However, a multi-center cooperative prospective longitudinal study on long-term comparative data of those treated and untreated of neuro-psychological outcome and cyst rupture incidence is needed.

Effectiveness of multiple endoscopic fenestrations for the treatment of Sylvian fissure arachnoid cysts: a multicenter study

PURPOSE

Arachnoid cysts are usually asymptomatic lesions. However, they can sometimes cause intracranial hypertension, headache, seizures, focal neurological deficits, and bleeding. The most commonly used surgical techniques are microsurgical cyst fenestration/excision/drainage, cyst shunting, and endoscopic procedures. We aimed to investigate the success of different surgical techniques.

METHODS

Between 2000 and 2021, patients with Sylvan fissure arachnoid cysts who received treatment via an endoscopic approach chosen as the first-line treatment in three centers were enrolled. All case notes and radiological studies were evaluated retrospectively.

RESULTS

The study included 131 (female, n = 28; male, n = 103) patients with a mean age of 87.04 ± 66.76 (range, 0-216) months. Of the patients, 25 had Galassi type II left-sided arachnoid cysts, 33 had Galassi type II right-sided arachnoid cysts, 40 had Galassi type III left-sided arachnoid cysts, and 32 had Galassi type III right-sided arachnoid cysts. No difference was found between patients who underwent single and multiple fenestrations in terms of Galassi type, side, clinical outcome, and cyst size (p > 0.05). On the contrary, the rate of additional surgical intervention was lower in patients with multiple fenestrations than in those with single fenestration (36.10% vs. 5.30%; p < 0.001).

CONCLUSION

Endoscopic fenestration of Sylvian fissure arachnoid cysts is a good alternative to open surgery or cystoperitoneal shunting, and the number of fenestrations made during this surgery decreases the need for a second surgical procedure.

Surgical indications in pediatric arachnoid cysts

INTRODUCTION

Arachnoid cysts are developmental lesions consisting of CSF collections within the subarachnoid space. There are many theories and hypotheses about their pathogenesis and histopathology and this may also explain the diversities seen in clinical behaviors of these cysts, their natural history and consequently their management where there is a great controversy about selecting patients for surgical intervention. The most common location in pediatrics is the Sylvian or middle cranial fossa and this made it gain more concern and greater debate about its management where its diagnosis is often accidently or associated with nonspecific symptoms.

AIM

Our aim in this article was to review the main surgical indications for pediatric arachnoid cysts in the literature.

CONCLUSION

We concluded that the decision for surgical intervention for pediatric arachnoid cysts is not a simple one and highly debatable and should be taken cautiously especially with sylvian arachnoid cysts that may reach a large size without symptoms. However, there is a consensus that the occurrence of symptoms definitely correlated to the presence of these cysts or their rupture with consequent subdural hematoma or hygroma are indications for surgical intervention. Large cysts in locations compressing CSF pathways causing hydrocephalus are also candidates for surgical fenestration. The surgical gain from prophylactic surgery is questionable particularly when asymptomatic.

The microanatomy of the Sylvian fissure

PURPOSE

Microsurgical anatomy of the Sylvian fissure is still a popular research topic for neurosurgeons. It is important for surgeons who perform skull base and Sylvian fissure surgical procedures to master the anatomy of the region. In our study, we aimed to review the current literature on the subject.

METHODS

We reviewed the literature concerning the Sylvian fissure. In addition, we made a microdissection of four human cadaveric brains in order to take images of relevant anatomic structures.

RESULTS

The Sylvian fissure includes both superficial and deep compartments. From the beginning of the surface structures and variable thickened subarachnoid membrane to the vascular structures located at the operculo-insular compartment, the surgical technique requires meticulous dissection in all stages of the surgery.

CONCLUSIONS

From the view of neurosurgery, novel anatomical knowledge should enhance the success of the surgery. From the view of neuroscience, the Sylvian fissure and the Sylvian cistern have unique anatomical, vascular, and genotypical properties to the other areas of the cerebrum, making them complex and special.

Understanding intracranial arachnoid cysts: a review of etiology, pathogenesis, and epidemiology

Arachnoid cysts (AC) are one of the common pathologies encountered in pediatric neurosurgical settings. It comes to clinical attention more often incidentally but also more often than previously due to the wide availability of diagnostic imaging. However, the accurate incidence and prevalence remain unknown. There is an ongoing debate on symptomatology, indications of treatment, and best treatment modalities. In this review, we aimed to discuss the current general knowledge about the arachnoid cyst, focusing on the etiology, pathogenesis, and epidemiology. Specific findings related to locations, such as the Sylvian fissure, are also emphasized.

The unique features of middle cranial fossa and Sylvian fissure arachnoid cysts in children: MRI evaluation

PURPOSE

The purpose of the study is to evaluate MRI findings of middle fossa arachnoid cysts in children according to Galassi classification and determine the differences between types and to assess the morphological changes in cysts during follow-up imaging.

METHODS

MR images of 266 middle fossa arachnoid cysts of 255 pediatric patients were evaluated by two experienced radiologists retrospectively. MRI features including the sidedness of the cyst, Galassi type, parenchymal compression findings (cortical flattening and white matter compression), bone remodeling, and midline shift were evaluated on axial T2- and T1-weighted images. Follow-up MRI and available CSF flow MR imaging data were evaluated for change in cyst size and cisternal connections, respectively.

RESULTS

The most common type was type 1 according to Galassi classification. The accompanying bone remodeling and white matter compression had a higher incidence in Galassi type 2 and 3 groups than Galassi type 1. Mean age of patients with bone remodeling and white matter compression was significantly higher in patients with Galassi type 1. All patients with cyst enlargement were younger than 2 years of age, and all of them were Galassi type 1. Cisternal connection was demonstrated in 7 patients.

CONCLUSION

While parenchymal compression and bone remodeling are expected findings in Galassi type 2 and 3 cysts, these features can also be seen in smaller Galassi type 1 cysts, regardless of size. Most of the middle fossa arachnoid cysts remain stable on follow-up imaging, and the increase in size is not an expected finding, especially in older children.

Epilepsy surgery without lipoma removal for temporal lobe epilepsy associated with lipoma in the Sylvian fissure

Epileptic seizure is the common symptom associated with lipomas in the Sylvian fissure (Sylvian lipomas). Removal of these lipomas carries risks of hemorrhage and brain damage. We report a surgical strategy of not removing the lipoma in a case of intractable temporal lobe epilepsy associated with Sylvian lipoma. We performed anterior temporal lobectomy with preservation of the pia mater of the Sylvian fissure and achieved seizure freedom. Focal cortical dysplasia type 1 of the epileptic neocortex adjacent to the Sylvian lipoma was pathologically diagnosed. We recommend our surgical procedure in similar cases to avoid complications and achieve adequate seizure control.

Small Sphenoid Ridge as a Factor Associated with Laterally Deviated Proximal Sylvian Fissure in Patients Undergoing Pterional Craniotomy

BACKGROUND

During the pterional-transsylvian approach, we sometimes encounter the proximal Sylvian fissure (SF) deviating laterally beyond the fold of the sphenoidal ridge (SR) and experience difficulty dissecting the SF due to the deep and oblique dissection plane. In the present study, we explored the association between the height of the SR and lateral deviation of the SF during the pterional-transsylvian approach.

METHODS

The association between the height of the SR on axial computed tomography and the presence of a laterally deviated SF was evaluated by reviewing patients who had undergone pterional craniotomy.

RESULTS

Among the 52 patients included, lateral deviation of the SF was observed in 8 patients (13.4%). The median height of the SR was significantly smaller in patients with laterally deviated SF (6.0 mm) than in patients with non-deviating SF (13.4 mm; P < 0.0001). The oculomotor nerves and middle fossa were observed at the edge of the dissection plane of the SF in all patients with a laterally deviating SF, while medial structures such as the internal carotid artery or optic nerve were observed in patients with non-deviating SF.

CONCLUSIONS

Small SR was associated with lateral deviation of the proximal SF.

Surgical Resection of a Sylvian Arteriovenous Malformation

Sylvian arteriovenous malformations (sAVMs) are rare and account for approximately 8%-11% of all intracranial arteriovenous malformations (AVMs).¹ Because of their proximity to eloquent structures such as the motor speech center, insular cortex, and internal capsule, microsurgical resection of sAVMs remains a challenge. Several classifications have already been suggested for sAVMs, such as Sugita and Yasargil.^1,2 It is well established that for low-grade AVMs, results of the microsurgical resection are excellent and tend to favor surgery,^1-3 but in high-grade AVM, a multimodal assessment is necessary for formulating treatment strategies.¹ In Video 1, we demonstrate the surgical resection of a ruptured sylvian temporal AVM. This AVM was localized in the superior surface of the temporal lobe, and its nidus was just beneath the cortical surface of this lobe. Because it was 5.1 cm at its largest diameter, had a deep drainage vein, and was localized adjacent to the Wernicke area, we classified it as a Spetzler-Martin grade IV AVM.⁴ Despite the high-grade AVM, microsurgical treatment was the choice in this ruptured AVM and there was no increase in morbidity.

Anatomy of the Cerebral Cortex, Lobes, and Cerebellum

Strong foundational knowledge of the anatomy of the cerebral cortex, lobes, and cerebellum is key to guide the search for potential lesions based on clinical presentation and known focal neurologic deficits. This article provides an introduction and overview of cerebral cortical anatomy, including the key sulci that divide the 4 lobes of the cerebral cortex, as well as the major gyral and sulcal landmarks within each lobe. The organization of the cerebellum and its major anatomic constituents are also described. Commonly encountered anatomic variants and asymmetries in cerebral cortical anatomy are presented and discussed.

A pilot behavioural and neuroimaging investigation on photothrombotic stroke models in rhesus monkeys

BACKGROUND

Ischemic stroke leads to a long-term disability in humans and no efficient clinical therapy exists to date. The middle cerebral artery occlusion (MCAO) model in non-human primates has shown to be of value for translational stroke research. New method In the current study, a photothrombotic (PT) stroke model was established in rhesus monkeys with either a proximal or distal segment of middle cerebral artery (MCA) thrombosis. This study is the first that compares the two approaches of PT stroke in monkeys using behavioral and physiological measurements and MRI scans.

RESULTS

The experiment found that infarct occurred in the MCA target regions, with all monkeys having impaired behavior reflected by deficits in neurologic function, and motor and cognition in object retrieval detour (ORD) task. The monkeys with distal MCA thrombosis developed with sequential photo-irritations of the Sylvian fissure zone, adjacent central anterior gyrus and central posterior gyrus, had similar impairments with respect to behavior and showed a tendency of a small edema volume with proximal MCA thrombosis at days 4 and 7 post PT stroke.

COMPARISON WITH EXISTING METHODS

The distal MCA thrombosis developed with sequential photo-irritations might provide a consistent and well-tolerated focal ischemia in rhesus monkeys, compared with other PT stroke models which usually were singly conducted on the animal's motor cortex and had a temporal effect.

CONCLUSIONS

The sequentially photo-irritated PT stroke model is a promising ischemic stroke model in rhesus monkey for studying human stroke pathology and physiology and for new therapies development.

Sylvian fissure arteriovenous malformations: case series and systematic review of the literature

BACKGROUND

Sylvian fissure arteriovenous malformations are rare but important vascular lesions, whose importance lies in both haemorrhage and seizure risk. Although surgery has been recommended as a treatment, the overall estimation of success has not been reported to render outcomes easier to understand in comparison to other treatment modalities.

OBJECTIVES

This systematic review of the literature and two cases aims to illustrate the results of surgery as a contemporary treatment option and present a novel anatomical classification system for Sylvian fissure arteriovenous malformations.

MATERIALS AND METHODS

A systematic review was performed by searching MEDLINE (PubMed), EMBASE and Cochrane electronic bibliographic databases from conception to 2018. The following keywords were used: 'Sylvian fissure' AND 'AVM' OR 'arteriovenous malformation' OR 'intracranial arteriovenous malformation' OR 'cerebral arteriovenous malformation' OR 'brain arteriovenous malformation'. The search strategy was not limited by study design but only included keywords in the English language. In addition, two local institution Sylvian fissure arteriovenous malformations are presented and incorporated.

RESULTS

A total of nine full-text articles were included in the analysis. The results of reported cases and the literature review emphasise the role of surgery in the treatment of Sylvian fissure arteriovenous malformations, with an acceptable result in carefully selected patients. We propose a classification system which may inform the choice of surgical approach for these lesions.

CONCLUSIONS

Surgery remains the cornerstone of Sylvian fissure arteriovenous malformation treatment, which may apply to high-grade lesions in this special anatomical location.

A Systematic Review of Methodology Used in Studies Aimed at Creating Charts of Fetal Brain Structures

Ultrasound-based assessment of the fetal nervous system is routinely recommended at the time of the mid-trimester anatomy scan or at different gestations based on clinical indications. This review evaluates the methodological quality of studies aimed at creating charts for fetal brain structures obtained by ultrasound, as poor methodology could explain substantial variability in percentiles reported. Electronic databases (MEDLINE, EMBASE, Cochrane Library, and Web of Science) were searched from January 1970 to January 2021 to select studies on singleton fetuses, where the main aim was to construct charts on one or more clinically relevant structures obtained in the axial plane: parieto-occipital fissure, Sylvian fissure, anterior ventricle, posterior ventricle, transcerebellar diameter, and cisterna magna. Studies were scored against 29 predefined methodological quality criteria to identify the risk of bias. In total, 42 studies met the inclusion criteria, providing data for 45,626 fetuses. Substantial heterogeneity was identified in the methodological quality of included studies, and this may explain the high variability in centiles reported. In 80% of the studies, a high risk of bias was found in more than 50% of the domains scored. In conclusion, charts to be used in clinical practice and research should have an optimal study design in order to minimise the risk of bias and to allow comparison between different studies. We propose to use charts from studies with the highest methodological quality.

Unilateral Tension Pneumocephalus of the Sylvian Fissure: A Rare Neurosurgical Complication

Tension pneumocephalus is an uncommon complication of neurosurgical procedures. We report a patient who presented with headache, vomiting, left hemiparesis and rhinorrhea 30 days after correction of a recurrent nasal cerebrospinal fluid fistula and shunt placement. A computed tomography scan revealed a massive collection of air with air-fluid level in the right sylvian fissure and midline shift. A right pterional craniotomy was performed and a small corticectomy resulted in evacuation of air from the sylvian fissure. A dural graft from the previous surgery was recognized to be acting as a ball-valve mechanism, trapping air from the nasal cavity. It was removed and the cranial defect was corrected with a split calvarial bone graft. Follow-up brain computed tomography revealed complete resolution of pneumocephalus. After surgery there was progressive improvement of neurological symptoms over 10 days, and the patient was asymptomatic after 1 month of follow-up.

Morphometric Comparison of the Pterional Trans-Sylvian and the Pretemporal Trans-Clinoidal Approaches to the Posterior Communicating Artery

BACKGROUND

Posterior communicating (Pcom) aneurysms in the modern era have tended toward increased complexity and technical difficulties. The pretemporal approach is a valuable extension to the pterional approach for basilar apex aneurysms, but its advantages for Pcom aneurysms have not been previously elucidated.

OBJECTIVE

To quantify characteristics of the pretemporal approach to the Pcom.

METHODS

We dissected 6 cadaveric heads (12 sides) with a pretemporal transclinoidal approach and measured the following variables: (1) exposed length of internal carotid artery (ICA) proximal to the Pcom artery; (2) exposed circumference of ICA at the origin of Pcom; (3) deep working area between the optic nerve and tentorium/oculomotor nerve; (4) superficial working area; (5) exposure depth; and (6) the frontotemporal (superior posterolateral) and (7) orbito-sphenoidal (inferior anterolateral) angles of exposure.

RESULTS

Compared with pterional craniotomy, the pretemporal transclinoidal approach increased the exposed length of the proximal ICA from 3.3 to 11.7 mm (P = .0001) and its circumference from 5.1 to 7.8 mm (P = .0003), allowing a 210° view of the ICA (vs 137.9°). The deep and superficial working areas also significantly widened from 53.7 to 92.4 mm2 (P = .0048) and 252.8 to 418.2 mm2 (P = .0001), respectively; the depth of the exposure was equivalent. The frontotemporal and spheno-Sylvian angles increased by 17° (P = .0006) and 10° (P = .0037), respectively.

CONCLUSION

The pretemporal approach can be useful for complex Pcom aneurysms by providing easier proximal control, wider working space, improved aneurysm visualization, and more versatile clipping angles. Enhanced exposure results in a potentially higher rate of complete aneurysm obliteration and complication avoidance.

Comparison Between Minipterional Craniotomy Associated With Focused Sylvian Fissure Opening and Standard Pterional Approach With Extended Sylvian Fissure Dissection for Treatment of Unruptured Middle Cerebral Artery Aneurysms

BACKGROUND

In our institution, standard pterional craniotomy (PC) with an extended Sylvian fissure opening (ESFO) represented the standard approach for unruptured middle cerebral artery (MCA) aneurysm clipping until 2014, when we progressively started to prefer minipterional craniotomy (MPC) associated with a focused Sylvian fissure opening (FSFO). In the present study, we compared our results in terms of the efficacy of clipping and the rate of complications with these 2 different techniques.

METHODS

We included patients with small- and medium-size unruptured MCA aneurysms from January 2008 to December 2018 with follow-up of >12 months. The clinical and radiologic data were reviewed from the medical records. The outcomes were measured in terms of efficacy (aneurysmal exclusion rate) and safety (intracranial complication rate).

RESULTS

Overall, 134 patients who had presented with unruptured MCA aneurysms <1.5 cm were treated at our institution from January 2007 to December 2018: PC and ESFO were used in 73 patients and MPC and FSFO in 61. The demographics and angioarchitectural features were comparable between the 2 groups, except for age, which was older in the FSFO group. The aneurysm exclusion rate was not different between the 2 groups. The intracranial complication rate was, overall, significantly lower in the FSFO group (P < 0.001), especially for the rate of postoperative seizures. Finally, the FSFO group had had shorter postoperative hospitalization and better short- and long-term clinical outcomes.

CONCLUSIONS

The association between MPC and FSFO should represent the standard of treatment of unruptured MCA aneurysms in all referral cerebrovascular centers, allowing for the achievement of the same efficacy of standard PC with ESFO and minimizing the complications.

Changing Hands: A Rising Role of the Tumor Surgeon in Teaching Sylvian Fissure Dissection

OBJECTIVE

The landscape of microneurosurgery has changed considerably over the past 2 decades, with a decline in indications for open surgery on cerebrovascular pathology and ever-increasing indications for open resection of brain tumors. This study investigated how these trends in case volume affected residents' training experiences in microsurgery and, specifically, Sylvian fissure dissection.

METHODS

Resident case logs were reviewed, identifying open cerebrovascular operations and craniotomies for tumor. Operations involving Sylvian fissure dissection were identified through operative reports. Changes in case number by resident were plotted over time, and linear regression was applied.

RESULTS

Among 23 chief residents, 3045 operations were identified, 1071 of which were for cerebrovascular pathology and 1974 for tumor. Open cerebrovascular experience decreased (P < 0.0001) while tumor volume remained unchanged (P = 0.221). The number of Sylvian fissure dissections per resident did not change over time overall (P = 0.583) or within cerebrovascular operations (P = 0.071). The number of Sylvian fissure dissections in tumor operations increased (P = 0.004). This effect was predominated by an increase in intraaxial tumors approached via Sylvian fissure dissection (P = 0.003). The proportion of Sylvian fissure dissections in tumor surgery increased from 15% in 2009 to 34% by 2019 (P = 0.003).

CONCLUSIONS

Residents are seeing an increasing proportion of their Sylvian fissure dissection experience during tumor operations. The distribution of this experience will continue to evolve as surgical indications change but suggests a growing role for tumor surgeons in resident training in microsurgery.

International standards for fetal brain structures based on serial ultrasound measurements from Fetal Growth Longitudinal Study of INTERGROWTH-21st Project

OBJECTIVE

To create prescriptive growth standards for five fetal brain structures, measured using ultrasound, in healthy, well-nourished women at low risk of impaired fetal growth and poor perinatal outcome, taking part in the Fetal Growth Longitudinal Study (FGLS) of the INTERGROWTH-21^st Project.

METHODS

This was a complementary analysis of a large, population-based, multicenter, longitudinal study. The sample analyzed was selected randomly from the overall FGLS population, ensuring an equal distribution among the eight diverse participating sites and of three-dimensional (3D) ultrasound volumes across pregnancy (range: 15-36 weeks' gestation). We measured, in planes reconstructed from 3D ultrasound volumes of the fetal head at different timepoints in pregnancy, the size of the parieto-occipital fissure (POF), Sylvian fissure (SF), anterior horn of the lateral ventricle, atrium of the posterior horn of the lateral ventricle (PV) and cisterna magna (CM). Fractional polynomials were used to construct the standards. Growth and development of the infants were assessed at 1 and 2 years of age to confirm their adequacy for constructing international standards.

RESULTS

From the entire FGLS cohort of 4321 women, 451 (10.4%) were selected at random. After exclusions, 3D ultrasound volumes from 442 fetuses born without a congenital malformation were used to create the charts. The fetal brain structures of interest were identified in 90% of cases. All structures, except the PV, showed increasing size with gestational age, and the size of the POF, SF, PV and CM showed increasing variability. The 3^rd , 5^th , 50^th , 95^th and 97^th smoothed centiles are presented. The 5^th centiles for the POF and SF were 3.1 mm and 4.7 mm at 22 weeks' gestation and 4.6 mm and 9.9 mm at 32 weeks, respectively. The 95^th centiles for the PV and CM were 8.5 mm and 7.5 mm at 22 weeks and 8.6 mm and 9.5 mm at 32 weeks, respectively.

CONCLUSIONS

We have produced prescriptive size standards for fetal brain structures based on prospectively enrolled pregnancies at low risk of abnormal outcome. We recommend these as international standards for the assessment of measurements obtained using ultrasound from fetal brain structures. © 2020 Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Transylvian Clip Occlusion of an Enlarging High-Flow Tentorial Arteriovenous Fistula: 2-Dimensional Operative Video

Endovascular therapy is the primary treatment for the majority of tentorial dural arteriovenous fistulas (dAVF). Surgical occlusion is an effective alternative when embolization is not possible. This video demonstrates microsugical occlusion of a right-sided tentorial dAVF in a symptomatic 45-yr-old male. The dAVF was fed directly by meningohypophyseal trunk. Venous drainage was retrograde through the sphenoparietal sinus, superficial sylvian vein, vein of Labee, and transverse sinus. The patient underwent a right-sided pterional craniotomy; the sylvian fissure was widely opened. Subarachoid dissection was performed until a large arterialized draining vein was identified exiting dura subtemporally. Intraoperative indocyanine green angiography confirmed the fistulous site and the draining vein was occluded and divided. The patient remained neurologically intact after surgery. Immediate angiography demonstrates complete occlusion of the dAVF. This video demonstrates the surgical access obtained through a transylvian approach for this tentorial dAVF. Occlusion of the draining vein, with or without resection of the fistula, is enough to permanently treat these lesions.

Sylvian Fissure Meningiomas: Case Report and Literature Review

Meningiomas are primary intracranial tumors derived from arachnoid cap cells or meningothelial cells and usually display dural attachment. However, a small proportion of meningiomas that arise from the Sylvian fissure do not manifest dural attachment. Sylvian fissure meningiomas are relatively rare and have differential characteristics as compared with typical meningiomas. Herein, we reported a special case of atypical meningioma in the Sylvian fissure, that showed non-enhancement after contract management. The patient was a 30-year-old woman with a 2-year history of seizures. Preoperative computerized tomography and magnetic resonance imaging scans showed a calcific, non-enhancing lesion in the right insula lobe. The lesion was excised surgically for seizure control. Intraoperatively, the tumor was observed to be closely adhered to the middle cerebral artery (MCA), resulting in mild arterial damage. A case of Sylvian fissure meningioma was ultimately diagnosed by histopathological examination of the resected specimens. Sylvian fissure meningiomas are closely associated with the MCA and exhibit unusual imaging characteristics. Preoperative misdiagnosis may have serious adverse consequences and may result in incorrect surgery. To improve awareness of Sylvian fissure meningiomas on the differential diagnosis of Sylvian fissure lesions among clinicians, we present this report and briefly summarize previously reported cases to describe the clinical, pathological, radiological, and surgical features.

Neocortical morphometry in Huntington's disease: Indication of the coexistence of abnormal neurodevelopmental and neurodegenerative processes

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We found shallower central, intraparietal and left intermediate frontal sulci in HD.

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Shallow calcarine fissure is further evidence of primary cortical degeneration in HD.

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Healthy subjects show strong asymmetry in length of posterior Sylvian fissure (pSF).

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Absence of pSF asymmetry in HD indicates genetic interplay with neurodevelopment.

Huntington's disease (HD) is an inherited, autosomal dominant disorder that is characteristically thought of as a degenerative disorder. Despite cellular and molecular grounds suggesting HD could also impact normal development, there has been scarce systems-level data obtained from in vivo human studies supporting this hypothesis. Sulcus-specific morphometry analysis may help disentangle the contribution of coexisting neurodegenerative and neurodevelopmental processes, but such an approach has never been used in HD. Here, we investigated cortical sulcal depth, related to degenerative process, as well as cortical sulcal length, related to developmental process, in early-stage HD and age-matched healthy controls. This morphometric analysis revealed significant differences in the HD participants compared with the healthy controls bilaterally in the central and intra-parietal sulcus, but also in the left intermediate frontal sulcus and calcarine fissure. As the primary visual cortex is not connected to the striatum, the latter result adds to the increasing in vivo evidence for primary cortical degeneration in HD. Those sulcal measures that differed between HD and healthy populations were mainly atrophy-related, showing shallower sulci in HD. Conversely, the sulcal morphometry also revealed a crucial difference in the imprint of the Sylvian fissure that could not be related to loss of grey matter volume: an absence of asymmetry in the length of this fissure in HD. Strong asymmetry in that cortical region is typically observed in healthy development. As the formation of the Sylvian fissure appears early in utero, and marked asymmetry is specifically found in this area of the neocortex in newborns, this novel finding likely indicates the foetal timing of a disease-specific, genetic interplay with neurodevelopment.

Anatomic Analysis of the Internal and External Aspects of the Pterion

OBJECTIVE

The pterion is an H-shaped suture complex. This study's goal was to determine the location of its external and internal surfaces and extension and emphasize and discuss its surgical importance.

METHODS

Fifty dried adult human skulls were obtained from the Department of Anatomy. A 2-mm drill bit was placed externally over the pterion, and the pterion was drilled through the bone perpendicular to the skull's surface.

RESULTS

The midpoint of the H shape in the pterion area was not at the same level on the skull's external and internal pterion surfaces. According to these measurements, the external pterion lay above the internal pterion when the skull was viewed externally. Furthermore, the internal pterion was on average longer than the external pterion. The internal and external pterions were schematized such that the skull was viewed from the outside. These areas were divided into 4 quadrants (anterior-superior, anterior-inferior, posterior-superior, and posterior-inferior) by a vertical and horizontal line. In 30 cases (60%), sulci of the middle meningeal artery's parietal branches entered the posterior-superior quadrant on the bone, whereas the artery's frontal branches were located in the anterior-superior and anterior-inferior quadrants, and the Sylvian fissure's origin was in the posterior-inferior quadrant.

CONCLUSIONS

By using a subdivision into 4 quadrants, and considering our anatomic findings, we determined the way surgical procedures can be performed more easily and reliably. Even with modern localization technologies, anatomic landmarks can be useful to the neurosurgeon.

The role of the Sylvian fissure configuration and the vascular anatomy on different bleeding patterns in ruptured middle cerebral artery aneurysms

OBJECTIVE

Ruptured middle cerebral artery (MCA) aneurysms are one of the causes of subarachnoid (SAH) or intracerebral hemorrhage (ICH) but the factors associated with the bleeding type are unknown. The aim of the study was to analyze the association of the morphological variations of the Sylvian fissure (SF) and vascular parameters on occurrence of different bleeding patterns in patients with ruptured MCA aneurysms.

PATIENTS AND METHODS

The data of consecutive 202 patients with ruptured MCA aneurysm of two centers were included for analysis. Patients were divided into three groups: Group 1 with SAH, Group 2 with accompanying ICH and Group 3 with intrasylvian hemorrhage (ISH). The SF was divided into five types according to the previously described classification. Analyzed vascular parameters were aneurysm size, localization, presence of a daughter aneurysm, shape, and angulation of the aneurysm sac.

RESULTS

A total of 202 patients (141 female, 61 male, mean age 52.4 yr) were included in this study. 67 patients (33.2%) had a SAH, 122 (60.4%) an ICH and 13 (6.4%) presented with ISH. Statistical analysis showed a significant association of narrow and twisted SF types 4 and 5 (p < 0.001) and temporal angulation of the aneurysm (p = 0.030) for occurrence of ICH. All other vascular parameters showed no significant association for any kind of hemorrhage.

CONCLUSION

Our results allow the conclusion that the complex SF types 4 and 5, as well as the temporal angulation of the aneurysm sac are associated with the occurrence of ICH in ruptured MCA aneurysms.

Neurosurgical anatomy of the insular cortex

OBJECTIVE

The purpose of this study was to clarify the morphology of the insular cortex focusing not only on the shape of the insula, but also on sulcal and gyral organization.

PATIENTS AND METHODS

Sixty formalin-fixed adult brain hemispheres had their insula exposed and photographed. The dimensions of each gyrus and sulcus were measured using an image analysis software. The morphometric data obtained was statistically analysed.

RESULTS

The insular cortex shape alternates between triangular and trapezoid, being the triangular shape the most common (75%). The angle between the posterior and inferior peri-insular sulcus in the trapezoid insulae had a mean range of 131.17° (SD = 12.277). A minimum of 3 and a maximum of 6 insular gyri were observed, being 5 the most common total number of gyri observed. The accessory gyrus was present in 66% of the insulae and well-developed in 38% of the cases. A statistical association between the number of gyri in the posterior lobe and the presence of a novel gyrus or a more developed accessory gyrus in the anterior lobe was found (P = 0.006). The posterior short gyrus was the longest of the short gyri (P <  0.001), followed by the anterior short gyrus (P < 0.001). The anterior long gyrus was the largest of the long gyri (P = 0.003). The contribution of each of the short gyri to the formation of the insular apex was inconstant. The most common observed apex arrangement was the combination of the anterior and of the middle short gyri.

CONCLUSIONS

This study makes a strong contribution to the understanding of the insular cortex anatomy, allowing neurosurgeons to be more capable to decide the best approach to this cortical area.

Microsurgical dissection of Sylvian fissure-short technical videos of third generation cerebrovascular neurosurgeons

Background

Multiple intracranial pathologies, including aneurysms of the middle cerebral artery, distal basilar artery, and suprasellar pathologies require the microsurgical opening of the Sylvian fissure. Delicate splitting of the arachnoid and safe microdissection of the veins, arteries, and brain parenchyma is the key to successful surgery through the Sylvian fissure corridor. We hypothesize that the geographical and historical environment in which neurosurgeons learn their operative skills is subject to a number of extrinsic influences, including cultural nuances of surgical techniques. Here we try to illustrate some cultural differences and technical aspects of the opening of the Sylvian fissure by four “third generation” cerebrovascular neurosurgeons from three different continents.

Methods

In the video analysis, various microsurgical aspects, including the opening style of the Sylvian fissure, handedness, use of sharp or blunt microinstruments, use of retractors, use of high magnification, and handling of bridging veins are presented.

Results

The video illustrates the two distinct Sylvian fissure opening styles, namely sharp and blunt microdissection, as well as the extent of the opening namely a wide and focal splitting.

Conclusion

The edited video underlines nuances and differences of a few major technical aspects that are perhaps typical to certain surgical environments and cultures. These microsurgical nuances and styles are useful pearls that can be mastered with training by any novice neurosurgeon.

Electronic supplementary material

The online version of this article (10.1007/s00701-019-03999-x) contains supplementary material, which is available to authorized users.

Microsurgical Anatomy of the Insular Region and Operculoinsular Association Fibers and its Neurosurgical Application

OBJECTIVE

To analyze the three-dimensional relationships of the operculoinsular compartments, using standard hemispheric and white matter fiber dissection and review the anatomy of association fibers related to the operculoinsular compartments of the Sylvian fissure and the main white matter tracts located deep into the insula. The secondary aim of this study was to improve the knowledge on this complex region to safely address tumor, vascular, and epilepsy lesions with an integrated perspective of the topographic and white matter fiber anatomy using 2D and 3D photographs.

METHODS

Six cadaveric hemispheres were dissected. Two were fixed with formalin and the arteries were injected with red latex dye; the remaining four were prepared using the Kingler method and white fiber dissections were performed.

RESULTS

The insula is located entirely inside the Sylvian fissure. The topographic hemispheric anatomy, Sylvian fissure, opercula, surrounding sulci and gyri, as well as the M2, M3, and M4 segments were identified. The anatomy of the insula, with the sulci and gyri and the limiting sulci, were also identified and described. The main white matter fiber tracts of the operculoinsular compartments of the Sylvian fissure as well as the main association and commissural fibers located deep in the insula were dissected and demonstrated.

CONCLUSIONS

Complementing topographic anatomy with detailed study of white matter fibers and their integration can help the neurosurgeon to safely approach lesions in the insular region, improving postoperative results in the microsurgical treatment of aneurysmal lesions, insular tumors, or epilepsy surgery.

Deep Sylvian Meningioma without Dural Attachment - A Case Report

Deep Sylvian meningiomas are rare, accounting for 0.3–0.4% of all meningiomas, and mostly present in young adults and children. We report on a 32-year-old man who presented with headache but had no neurological deficits. Computed tomography of brain revealed a 24 × 19 × 21 mm³ mass lesion in the right Sylvian fissure with calcification. Magnetic resonance imaging showed that the lesion was isointense on T₁- and T₂-weighted images (WI), with homogenous enhancement on post-gadolinium T₁WI. The lesion was surgically removed via right fronto-temporal craniotomy. The tumor was located in deep Sylvian fissure and had no dural attachment. Histopathological examination of the lesion revealed both meningothelial and fibroblastic features, thereby suggesting the diagnosis of transitional meningioma (WHO grade I), with Ki-67 labeling index of 6.9%. Thus, meningioma should be considered as a differential diagnosis of enhancing mass lesions in the Sylvian fissure even in the absence of dural tail sign, especially in young adults and children.

Extended Lateral Orbital Craniotomy: Anatomic Study and Initial Clinical Series of a Novel Minimally Invasive Pterional Approach

Background  Of the minimally invasive "keyhole" alternatives to the pterional region, the supraorbital eyebrow approach is the most widely adopted. Yet it can prove disadvantageous when a more direct lateral microsurgical trajectory of attack to the Sylvian fissure and anterior middle fossa are needed. Objective  The extended lateral orbital (XLO) approach was designed to be direct and minimally invasive, with the sphenoid ridge at the center of exposure. Methods  Five injected cadaver heads were used for anatomic study of the XLO approach. The anatomic course of the frontalis branch of facial nerve was studied in relation to the XLO incision. Following XLO incision, the bone exposure was measured. The intracranial microsurgical exposure was assessed subjectively. Application of the technique in representative clinical operative cases is provided. Results  The frontalis nerve was protected in the subgaleal fat pad, with an average minimum distance of 2.3 cm from the XLO incision. The mean calvarial area exposure was 4.95 cm ² and consistently centered on the sphenoid ridge. Excellent access to ipsilateral Sylvian's fissure, perisylvian regions, and supra-/parasellar structures was possible. The main limitations related to exposure of the posterior Sylvian fissure and the expected limitations of microsurgical instrument manipulation from a smaller craniotomy. Conclusions  The XLO approach is a minimally invasive keyhole approach to the pterional region that affords a unique lateral trajectory via a craniotomy centered on the sphenoid ridge. Excellent exposure to properly selected lesions is possible. The incision is at a safe distance from the frontalis branch and shows excellent cosmetic healing.

Is arachnoid cyst a static disease? A case report and literature review

INTRODUCTION

The increasing use of intracranial imaging has led to more frequent diagnoses of arachnoid cysts (ACs). Although ACs are a frequent finding on neuroimaging in children, the prevalence and natural history of these cysts are not well defined. Most ACs may persist and remain asymptomatic throughout life and not require treatment. However, there have been some case reports of ACs that have become larger or smaller over time and, in rare cases, have even spontaneously resolved. It is the authors' practice to recommend serial neuroimaging in patients with asymptomatic sylvian ACs and not offer surgery to patients without symptoms, even in those with a relatively large cyst.

CASE REPORT

The present article describes a case involving a 6-year-old boy with a large, asymptomatic AC in the left Sylvian fissure involving the temporo-frontal region, which resolved spontaneously during the 2-year follow-up period after initial diagnosis without any surgical intervention. Currently, at the 7-year follow-up, the patient has remained neurologically intact, attends school, and is symptom-free.

CONCLUSION

Clinicians should be mindful of the possibility of spontaneous regression when encountering patients with asymptomatic and/or incidentally diagnosed sylvian ACs.

Sylvian Fissure Meningioma in Childhood: Report of 3 Cases and Review of the Literature

OBJECTIVE

Sylvian fissure-based meningioma is a rare occurrence during childhood. We report a small series including 3 such cases, all attached to the arachnoid leaflets of the Sylvian fissure. We present a review of the literature and discuss the impact of possibly effective clinical, imaging, and surgical variables on the outcome.

METHODS

In a retrospective chart review of children with intracranial meningioma, we encountered 3 cases with Sylvian fissure meningioma operated within the past 32 years.

RESULTS

Two girls, 5 and 7 years old, and 1 boy, 7 years of age, presented with epilepsy, headache, diplopia, and hemiparesis. The duration of illness was 3, 4, and 2 months, respectively. All three tumors were attached to the arachnoid layer of the adjacent Sylvian fissure, and they were not dural based. Gross total resection could be achieved, and no recurrences were encountered after 13, 7, and 2 years.

CONCLUSION

We report 3 very rare cases of Sylvian arachnoid-based meningiomas. To our knowledge, this is the study with the longest follow-up period (mean 7.3 years, median 7 years). Even though the overall prognosis of pediatric meningiomas may be worse than that of adult illness, we would like to emphasize that the "rare location" of the Sylvian fissure was not an important factor contributing to the outcome in our children.

White Epidermoid of the Sylvian Fissure Masquerading as a Dermoid Cyst: An Extremely Rare Occurrence

We report the case of a 30-year-old female with a Sylvian fissure, white epidermoid which was radiologically looking like a dermoid cyst. The female presented with a headache with no neurological deficits. On radiology, the lesion was in Sylvian fissure, T1 hyperintense, T2 hypointense, and with minimal diffusion restriction medially. Hence a preoperative impression of dermoid cyst was made, a quite uncommon location. Intraoperatively, the classical pearly-white flaky appearance of epidermoid was seen which was confirmed histopathologically. White epidermoids appearing so because of high protein content are a rarity and are more likely to cause aseptic meningitis in the event of intraoperative spillage. Differentiating between a dermoid cyst and white epidermoid preoperatively and radiologically is difficult. Dermoids show diffusion restriction and are usually midline, whereas white epidermoids do not show diffusion restriction and are usually lateral. This is the first report of a white epidermoid in Sylvian fissure to the best of our knowledge.

Grade II Sylvian fissure meningiomas without dural attachment: case report and review of the literature

Sylvian fissure meningiomas (SFMs) represent a rare subgroup of nondural-based tumors arising from the meningothelial cells within the arachnoid of the Sylvian fissure. SFMs are more frequent in young males, usually manifest with seizures and display the same radiological features of meningiomas in other locations. Although the absence of dural attachment makes these tumors suitable for a complete resection, their anatomical relationships with the middle cerebral artery branches have impaired its achievement in half of them. To the best of our knowledge, only five atypical WHO grade II SFMs have been previously described. We provide a literature review of SFMs WHO grades I-II and discuss common characteristics and surgical challenges we found in a similar case.

Utility of Indocyanine Green Video Angiography for Sylvian Fissure Dissection in Subarachnoid Hemorrhage Patients - Sylvian ICG Technique

Indocyanine green (ICG) emits fluorescence in the far-red domain under light excitation. ICG video angiography (ICG-VA) has been established as a useful method to evaluate blood flow in the operative field. We report the usefulness of ICG-VA for Sylvian fissure dissection in patients with subarachnoid hemorrhage (SAH). Subjects comprised 7 patients who underwent ICG-VA before opening the Sylvian fissure during neck clipping for ruptured cerebral aneurysm. We observed contrasted Sylvian veins before opening the Sylvian fissure using surgical microscopes. This procedure was termed “Sylvian ICG”. We observed ICG fluorescence quickly in all cases. Sylvian veins that appeared unclear in the standard microscopic operative field covered with subarachnoid hemorrhage were extremely clearly depicted. These Sylvian ICG findings were helpful in identifying entry points and the dissecting course of the Sylvian fissure. At the time of clipping, no residual fluorescence from Sylvian ICG was present, and aneurysm clipping was not impeded. Sylvian ICG for SAH patients is a novel technique to facilitate dissection of the Sylvian fissure. We believe that this technique will contribute to improved safety of clipping surgery for ruptured aneurysms.

Mild prominence of the Sylvian fissure in a Bainbridge-Ropers syndrome patient with a novel frameshift variant in ASXL3

A Japanese boy aged 7 years with Bainbridge‐Ropers syndrome (BRPS) had a prominent domed forehead without metric ridge, mild prominence of the Sylvian fissure with bitemporal hollowing, and a heterozygous de novo novel variant “p.P1010Lfs*14” in ASXL3 gene in addition to typical findings of BRPS.

Contralateral Approach to Middle Cerebral Artery Aneurysms: An Anatomical-Clinical Analysis to Improve Patient Selection

BACKGROUND

A contralateral approach to aneurysm clipping in cases of bilateral middle cerebral artery (MCA) aneurysms reduces surgical time and cost. However, there is a lack of evidence for objective patient selection. In this study, we assessed the change in surgical freedom along the contralateral MCA to provide objective evidence for patient selection.

METHODS

Sixteen cadaveric specimens were studied. Through a pterional approach, the surgical freedom was calculated moving distally along the contralateral MCA in 5-mm increments. In addition, in a series of 19 MCA aneurysms clipped contralaterally by the senior author, the average length of the MCA from its origin to the aneurysm neck was measured on angiography.

RESULTS

In these patients treated via a contralateral approach, the average length of the MCA segment from its origin to the aneurysm neck was 12.4 mm. Starting at the MCA origin, surgical freedom decreased significantly between all adjacent target points except at 5-10 mm from the MCA origin.

CONCLUSIONS

After the proximal 5 mm, there is no significant decrease in surgical maneuverability within the proximal 10 mm of MCA when approached contralaterally. When compared to the average length of the MCA from its origin to the aneurysm neck in the clinical series, it can be concluded that the first 10 mm (average, 12.4 mm) of the contralateral MCA may be considered a surgical comfort zone for a contralateral approach. This criterion may be useful for patient selection for a contralateral approach in cases of multiple bilateral intracranial aneurysms.

Transorbital endoscopic approach for exposure of the sylvian fissure, middle cerebral artery and crural cistern: an anatomical study

BACKGROUND

The availability of minimal access instrumentation and endoscopic visualization has revolutionized the field of minimally invasive skull base surgery. The transorbital endoscopic approach using an eyelid incision has been proposed as a new minimally invasive technique for the treatment of skull base pathology, mostly extradural tumors. Our study aims to evaluate the anatomical aspects and potential role of the transorbital endoscopic approach for exposure of the sylvian fissure, middle cerebral artery and crural cistern.

METHODS

An anatomical dissection was performed in four freshly injected cadaver heads (8 orbits) using 0- and 30-degree endoscopes. First, an endoscopic endonasal medial orbital decompression was done to facilitate medial retraction of the orbit. An endoscopic transorbital approach through an eyelid incision, with drilling of the posterior wall of the orbit and lesser sphenoidal wing, was then performed to expose the sylvian fissure and crural cisterns. A stepwise anatomical description of the approach and visualized anatomy is detailed.

RESULTS

A superior eyelid incision followed by orbital retraction provided a surgical window of approximately 1.2 cm (range 1.0-1.5 cm) for endoscopic transorbital dissection. The superior (SOF) and inferior (IOF) orbital fissures represent the medial limits of the approach and are identified in the initial part of the procedure. Drilling of the orbital roof (lateral and superior to the SOF), greater sphenoidal wing (lateral to the SOF and IOF) and lesser sphenoidal wing exposed the anterior and middle fossa dura. A square-shaped dural opening provided visualization of the posterior orbital gyri, sylvian fissure and temporal pole. Intradural dissection allowed exposure of the sphenoidal portion of the sylvian fissure, M1, MCA bifurcation and M2 branches and lenticulostriate perforators. Dissection of the medial aspect of the sylvian and carotid cisterns with a 30-degree endoscope allowed exposure of the mesial temporal lobe and crural cistern.

CONCLUSIONS

The transorbital endoscopic approach allows successful exposure of the sphenoidal portion of the sylvian fissure and M1 and M2 segments of the middle cerebral artery. Angled endoscopes may provide visualization of the mesial temporal lobe and crural cistern. Although our anatomical study demonstrates the feasibility of intradural dissection and closure via an endoscopic transorbital approach, further studies are necessary to evaluate its role in the clinical scenario.

The Lateral Temporal Lobe in Early Human Life

Abnormalities of lateral temporal lobe development are associated with a spectrum of genetic and environmental pathologic processes, but more normative data are needed for a better understanding of gyrification in this brain region. Here, we begin to establish guidelines for the analysis of the lateral temporal lobe in humans in early life. We present quantitative methods for measuring gyrification at autopsy using photographs of the gross brain and simple computer-based quantitative tools in a cohort of 28 brains ranging in age from 27 to 70 postconceptional weeks (end of infancy). We provide normative ranges for different indices of gyrification and identify a constellation of qualitative features that should also be considered in these analyses. The ratio of the temporal area to the whole brain area increased dramatically in the second half of gestation, but then decelerated after birth before increasing linearly around 50 postconceptional weeks. Tertiary gyrification continued beyond birth in a linear process through infancy with considerable variation in patterns. Analysis of 2 brains with gyral disorders of the lateral temporal lobe demonstrated proof-of-principle that the proposed methods are of diagnostic value. These guidelines are proposed for assessments of temporal lobe pathology in pediatric brains in early life.

Computed Tomography- and Magnetic Resonance Image-based Analysis of the Anatomical Variations of the Sylvian Fissure and Characteristics of the Middle Cerebral Artery

The aim of this cross sectional anatomical study is to determine the distribution of the defined anatomical variations of the Sylvian fissure (SF) in a normal population and to analyze its bilateral superposable presentation. Furthermore, we examined the course of the middle cerebral artery (MCA) and the division of the MCA branches in relation to the SF types. A total of 300 cranial CT scans - 100 CT angiography datasets and 86 MRIs of patients without intracranial pathologies - were reviewed. The SF was categorized in five types based on Yasargils description and our previous publication. The length, diameter and branches of the MCA were measured and compared to the SF types. SPSS 23.0 for Windows® was used for statistical analysis. We analyzed data of 300 patients (171 male, 129 female; mean age 51.6years). Symmetric and mirror-imaged coherence of the SF was found in 266 patients (88.7%, χ²(8)=3.04, p=0.932). The distribution of the SF types showed significant differences in patients younger than 60 years compared to older patients. A bifurcation was observed in 72.0%. A trifurcation was observed in 12.0% and a false bifurcation in 16.0% of patients. There was no significant difference of the measured diameters or length of the M1 segments according to the SF types. In this CT and MRI based anatomical study we could show that a twisted and narrow SF occurred more frequently in patients younger than 60 years of age. The SF has a high congruence intra-individually. The anatomical condition might influence the size and configuration of the proximal MCA, which in turn might influence the surgeon's choice of the approach to the SF. Preoperative evaluation on the basis of the presented data, may help to decide for an appropriate approach to the SF.

Telencephalic Flexure and Malformations of the Lateral Cerebral (Sylvian) Fissure

After sagittal division of the prosencephalon at 4.5 weeks of gestation, the early fetal cerebral hemisphere bends or rotates posteroventrally from seven weeks of gestation. The posterior pole of the telencephalon thus becomes not the occipital but the temporal lobe as the telencephalic flexure forms the operculum and finally the lateral cerebral or Sylvian fissure. The ventral part is infolded to become the insula. The frontal and temporal lips of the Sylvian fissure, as well as the insula, all derive from the ventral margin of the primitive telencephalon, hence may be influenced by genetic mutations with a ventrodorsal gradient of expression. The telencephalic flexure also contributes to a shift of the hippocampus from a dorsal to a ventral position, the early rostral pole of the hippocampus becoming caudal and dorsal becoming ventral. The occipital horn is the most recent recess of the lateral ventricle, hence most vulnerable to anatomic variations that affect the calcarine fissure. Many major malformations include lack of telencephalic flexure (holoprosencephaly, extreme micrencephaly) or dysplastic Sylvian fissure (lissencephalies, hemimegalencephaly, schizencephaly). Although fissures and sulci are genetically programmed, mechanical forces of growth and volume expansion are proposed to be mainly extrinsic (including ventricles) for fissures and intrinsic for sulci. In fetal hydrocephalus, the telencephalic flexure is less affected because ventricular dilatation occurs later in gestation. Flexures can be detected prenatally by ultrasound and fetal magnetic resonance imaging and should be described neuropathologically in cerebral malformations.

Arachnoid cyst: a further anomaly associated with Kallmann syndrome?

BACKGROUND

Kallmann syndrome (KS) is defined by the association of hypogonadotropic hypogonadism and anosmia. It is characterized by a significant clinical and genetic heterogeneity; actually, it may present several non-reproductive non-olfactory anomalies, and all the ways of genetic transmission can be involved in the inheritance of the disease. Although six pathogenesis-related genes have been identified so far, KS remains sporadic in 70 % of the cases, and the genetic diagnosis is not available for all of them. The purpose of this paper is to present a further disease that can enrich the wide spectrum of KS variability, that is cerebral arachnoid cyst.

CASE DESCRIPTION

This 11-year-old boy presented with the typical characteristics of KS together with those related to a sylvian arachnoid cyst. He was admitted because of worsening headache. At the admission, the physical examination revealed eunuchoid aspect, micropenis, previous cryptorchidism, and anosmia. MRI pointed out a large, left sylvian arachnoid cyst, agenesia of the olfactory bulbs/tracts complex, and hypoplasia of the left olfactory sulcus. The child was operated on by endoscopic fenestration of the cyst, followed by transient external drainage for subdural hygroma and microscopic fenestration for recurrence of the cyst. His statural growth is normal but the sexual development still delayed in spite of hormone replacement therapy.

CONCLUSION

According to the present and the other four cases in the literature, arachnoid cyst should be included among the anomalies possibly accompanying KS date although this association seems to be occasional as far as embryogenesis and physiopathology are concerned.

The transsylvian approach for resection of insular gliomas: technical nuances of splitting the Sylvian fissure

Insular gliomas represent a unique surgical challenge due to the complex anatomy and nearby vascular elements associated within the Sylvian fissure. For certain tumors, the transsylvian approach provides an effective technique for achieving maximal safe resection. The goal of this manuscript and video are to present and discuss the surgical nuances and appropriate application of splitting the Sylvian fissure. Our hope is that this video highlights the safety and efficacy of the transsylvian approach for appropriately selected insular gliomas.