Intraventricular meningioma resection and visual outcomes

J Neurosurg 140:1001–1007, 2024

Intraventricular meningiomas (IVMs) of the lateral ventricle are rare tumors that present surgical challenges because of their deep location. Visual field deficits (VFDs) are one risk associated with these tumors and their treatment. VFDs may be present preoperatively due to the tumor and mass effect (tumor VFDs) or may develop postoperatively due to the surgical approach (surgical VFDs). This institutional series aimed to review surgical outcomes following resection of IVMs, with a focus on VFDs.

METHODS Patients who received IVM resection at one academic institution between the years 1996 and 2021 were retrospectively reviewed. Diffusion tensor imaging (DTI) reconstructions of the optic radiations around the tumor were performed from preoperative IVM imaging. The VFD course and resolution were documented.

RESULTS Thirty-two adult patients underwent IVM resection, with gross-total resection in 30 patients (93.8%). Preoperatively, tumor VFDs were present in 6 patients, resolving after surgery in 5 patients. Five other patients (without preoperative VFD) had new persistent surgical VFDs postoperatively (5/32, 15.6%) that persisted to the most recent follow-up. Of the 5 patients with persistent surgical VFDs, 4 received a transtemporal approach and 1 received a transparietal approach, and all these deficits occurred prior to regular use of DTI in preoperative imaging.

CONCLUSIONS New surgical VFDs are a common neurological deficit after IVM resection. Preoperative DTI may demonstrate distortion of the optic radiations around the tumor, thus revealing safe operative corridors to prevent surgical VFDs.

The learning curve for cavernous sinus surgery illustrated by symptomatic intracavernous aneurysm clipping through a pretemporal transcavernous approach

J Neurosurg 140:183–193, 2024

OBJECTIVE The anatomy of the cavernous sinus (CS) has been well studied in the laboratory for decades; however, performing surgery in and around the CS is still a challenge. To reveal the learning curve for CS surgery via the pretemporal transcavernous approach (PTTC), surgical procedures were examined. The authors proposed 4 levels of surgical difficulty in opening the walls of the CS through this approach. Details of the approach were illustrated by surgical videos of symptomatic intracavernous aneurysm clipping.

METHODS Four levels of surgical difficulty were proposed. The higher the level, the more the CS walls were opened. Pathologies corresponding to each level of difficulty in and around the CS were categorized in each level together with explanations. From 2015 to 2021, 5 patients with symptomatic intracavernous aneurysms (diplopia due to compressive cranial neuropathy) underwent the PTTC at the authors’ institute and served as representative cases in opening the walls of the CS. All CS cases from 2009 to 2021 were reviewed and categorized to demonstrate the learning curve.

RESULTS Four levels of surgical difficulty are as follows: level 1, a basic Dolenc extradural approach, which involves opening the anterior third of the superior and lateral walls of the CS; level 2, mobilizing the internal carotid artery (ICA) and opening the proximal dural ring to enter the roof of the CS and treat lesions around the clinoid and upper cavernous ICA; level 3, opening the entire aspect of the superior and lateral walls of the CS, which involves opening the oculomotor triangle and peeling the lateral wall of the CS to the tentorial incisura; and level 4, mobilizing cranial nerves III, IV, and V1 to gain access to the supra-/infratrochlear triangles to have proximal ICA control and opening the posterior wall as the last step to enter the posterior fossa. Surgical steps were described and illustrated with surgical videos of symptomatic intracavernous aneurysm clipping.

CONCLUSIONS The learning curve for CS surgery is long. The authors use 4 levels of surgical difficulty to describe applications of the PTTC in CS surgery. This approach serves as an effective workhorse in treating CS pathologies with low morbidity and high success rates when performed by experienced neurosurgeons.

A new classification of parasagittal bridging veins based on their configurations and drainage routes pertinent to interhemispheric approaches: a surgical anatomical study

J Neurosurg 140:271–281, 2024

OBJECTIVE Opening the roof of the interhemispheric microsurgical corridor to access various neurooncological or neurovascular lesions can be demanding because of the multiple bridging veins that drain into the sinus with their highly variable, location-specific anatomy. The objective of this study was to propose a new classification system for these parasagittal bridging veins, which are herein described as being arranged in 3 configurations with 4 drainage routes.

METHODS Twenty adult cadaveric heads (40 hemispheres) were examined. From this examination, the authors describe 3 types of configurations of the parasagittal bridging veins relative to specific anatomical landmarks (coronal suture, postcentral sulcus) and their drainage routes into the superior sagittal sinus, convexity dura, lacunae, and falx. They also quantify the relative incidence and extension of these anatomical variations and provide several preoperative, postoperative, and microneurosurgical clinical case study examples.

RESULTS The authors describe 3 anatomical configurations for venous drainage, which improves on the 2 types that have been previously described. In type 1, a single vein joins; in type 2, 2 or more contiguous veins join; and in type 3, a venous complex joins at the same point. Anterior to the coronal suture, the most common configuration was type 1 dural drainage, occurring in 57% of hemispheres. Between the coronal suture and the postcentral sulcus, most veins (including 73% of superior anastomotic veins of Trolard) drain first into a venous lacuna, which are larger and more numerous in this region. Posterior to the postcentral sulcus, the most common drainage route was through the falx.

CONCLUSIONS The authors propose a systematic classification for the parasagittal venous network. Using anatomical landmarks, they define 3 venous configurations and 4 drainage routes. Analysis of these configurations with respect to surgical routes indicates 2 highly risky interhemispheric surgical fissure routes. The risks are attributable to the presence of large lacunae that receive multiple veins (type 2) or venous complex (type 3) configurations that negatively impact a surgeon’s working space and degree of movement and thus are predisposed to inadvertent avulsions, bleeding, and venous thrombosis.

 

Distinct Pattern of Membrane Formation With Spinal Cerebrospinal Fluid Leaks in Spontaneous Intracranial Hypotension

Operative Neurosurgery 26:71–77, 2024

To systematically describe pertinent, intraoperative anatomic findings encountered when approaching spinal cerebrospinal fluid (CSF) leaks and CSF-venous fistulas in spontaneous intracranial hypotension (SIH).

METHODS: In a retrospective study, we included surgically treated patients suffering from SIH at our institution from April 2018 to March 2022. Anatomic, intraoperative data were extracted from operative notes and supplemented with data from surgical videos and images. Prominent anatomic features were compared among different types of CSF leaks.

RESULTS: The study cohort consists of 120 patients with a mean age of 45.2 years. We found four distinct patterns of spinal membranes specifically associated with different types of CSF leaks: (i) thick, dorsal membranes, which were hypervascular and may mimic the dura (pseudodura); (ii) thin, lateral membranes encapsulating a ventral epidural CSF compartment (confining the spinal longitudinal extradural CSF collection); (iii) ventral membranes constituting a transdural funnel–like CSF channel; and (iv) lateral membranes forming spinal cysts/meningeal diverticulae associated with lateral CSF leaks. The latter three types resemble a layer of arachnoid herniated through the dural defect.

CONCLUSION: We describe four distinct spinal (neo-)membranes in association with spinal CSF leaks. Formation of these membranes, or emergence by herniation of arachnoid through a dural defect, constitutes a specific pathoanatomic feature of patients with SIH and CSF leaks. Recognition of these membranes is of paramount importance for diagnosis and treatment of patients with spinal CSF leaks.

Variability in the Arterial Supply of Intracranial Meningiomas: An Anatomic Study

Neurosurgery 93:1346–1352, 2023

Intracranial meningiomas are a diverse group of tumors, which vary by grade, genetic composition, location, and vasculature. Expanding the understanding of the supply of skull base (SBMs) and non–skull base meningiomas (NSBMs) will serve to further inform resection strategies. We sought to delineate the vascular supply of a series of intracranial meningiomas by tumor location.

METHODS: A retrospective study of intracranial meningiomas that were studied using preoperative digital subtraction angiograms before surgical resection at a tertiary referral center was performed. Patient, tumor, radiologic, and treatment data were collected, and regression models were developed.

RESULTS: One hundred sixty-five patients met inclusion criteria. The mean age was 57.1 years (SD: 12.6). The mean tumor diameter was 4.9 cm (SD: 1.5). One hundred twenty-six were World Health Organization Grade I, 37 Grade II, and 2 Grade III. Arterial feeders were tabulated by Al-Mefty’s anatomic designations. SBMs were more likely to derive arterial supply from the anterior circulation, whereas NSBMs were supplied by external carotid branches. NSBMs were larger (5.61 cm vs 4.45 cm, P = <.001), were more often presented with seizure (20% vs 8%, P = .03), were higher grade (P = <.001) had more frequent peritumoral brain edema (84.6% vs 66%, P = .04), and had more bilateral feeders (47.7% vs 28%, P = .01) compared with SBMs. More arterial feeders were significantly associated with lower tumor grade (P = .023, OR = 0.59). Higher tumor grade (Grade II/III) was associated with fewer arterial feeders (P = .017, RR = 0.74).

CONCLUSION: Meningioma location is associated with specific vascular supply patterns, grade, and patient outcomes. This information suggests that grade I tumors, especially larger tumors, are more likely to have diverse vascular supply patterns, including internal carotid branches. This study may inform preoperative embolization and surgical considerations, particularly for large skull base tumors.

International Tuberculum Sellae Meningioma Study: Preoperative Grading Scale to Predict Outcomes and Propensity-Matched Outcomes by Endonasal Versus Transcranial Approach

Neurosurgery 93:1271–1284, 2023

Tuberculum sellae meningiomas are resected via an expanded endonasal (EEA) or transcranial approach (TCA). Which approach provides superior outcomes is debated. The Magill–McDermott (M-M) grading scale evaluating tumor size, optic canal invasion, and arterial involvement remains to be validated for outcome prediction. The objective of this study was to validate the M-M scale for predicting visual outcome, extent of resection (EOR), and recurrence, and to use propensity matching by M-M scale to determine whether visual outcome, EOR, or recurrence differ between EEA and TCA.

METHODS: Forty-site retrospective study of 947 patients undergoing tuberculum sellae meningiomas resection. Standard statistical methods and propensity matching were used.

RESULTS: The M-M scale predicted visual worsening (odds ratio [OR]/point: 1.22, 95% CI: 1.02-1.46, P = .0271) and gross total resection (GTR) (OR/point: 0.71, 95% CI: 0.62-0.81, P < .0001), but not recurrence (P = .4695). The scale was simplified and validated in an independent cohort for predicting visual worsening (OR/point: 2.34, 95% CI: 1.33-4.14, P = .0032) and GTR (OR/point: 0.73, 95% CI: 0.57-0.93, P = .0127), but not recurrence (P = .2572). In propensity-matched samples, there was no difference in visual worsening (P = .8757) or recurrence (P = .5678) between TCA and EEA, but GTR was more likely with TCA (OR: 1.49, 95% CI: 1.02-2.18, P = .0409). Matched patients with preoperative visual deficits who had an EEA were more likely to have visual improvement than those undergoing TCA (72.9% vs 58.4%, P = .0010) with equal rates of visual worsening (EEA 8.0% vs TCA 8.6%, P = .8018).

CONCLUSION: The refined M-M scale predicts visual worsening and EOR preoperatively. Preoperative visual deficits are more likely to improve after EEA; however, individual tumor features must be considered during nuanced approach selection by experienced neurosurgeons.

Anatomic Variants in the Anterior Inferior Cerebellar Artery Encountered During Resection of Vestibular Schwannomas

Operative Neurosurgery 25:512–520, 2023

Vestibular schwannomas (VS) are often phenotypically benign lesions that may be technically challenging to resect because of involvement of neurovascular structures. The anterior inferior cerebellar artery (AICA) is commonly identified near VS, with variable position in relation to the tumor; however, little published literature describes anatomic and pathologic variants of AICA observed during VS resection.

METHODS: A prospectively maintained cohort of surgically managed VS with available operative reports and clinical/ radiographic follow-up was queried and reviewed for noted aberrations.

RESULTS: We identified 66 cases with noted AICA abnormalities among 880 reviewer cases, including 20 loops extending into the internal auditory canal (2.3%), 18 arteries embedded in dura (2.0%), 15 AICA branches directly within VS (1.7%), 8 main trunk arteries coursing between cranial nerves 7 and 8 (0.9%), 3 arteries embedded in temporal bone (0.2%), 1 aneurysm (0.1%), and 1 artery bifurcating cranial nerve 6 (0.1%). The median age of AICA-variant patients was 55 years (range 19-74), and 29 were female (45%). Compared with the other AICA variants, tumors embedded with AICA tended to be larger lesions on maximal axial diameter (2.9 vs 1.6 cm; P = .006), they more commonly underwent less than total resection (73% vs 28%; P = .0001), and they had higher rates postoperative House-Brackmann scores >2 (47% vs 20%; P = .005). Two patients had radiographic and symptomatic postoperative cerebral ischemia or hemorrhage—1 from a bone-encased AICA and 1 from a dural embedded variant.

CONCLUSION: Anatomic variants of AICA occur in approximately 7% of VS operations. Most aberrations do not affect surgical or clinical outcomes, and the rate of major vascular injury was low. However, certain types variably add operative time and in the case of AICA encasement in the tumor, likely indicate a more aggressive tumor phenotype with lower rates of gross total resection and high incidences of facial nerve weakness.

A taxonomy for deep cerebral cavernous malformations: subtypes of thalamic lesions

J Neurosurg 139:1681–1696, 2023

Anatomical taxonomy is a practical tool to successfully guide clinical decision-making for patients with brain arteriovenous malformations and brainstem cavernous malformations (CMs). Deep cerebral CMs are complex, difficult to access, and highly variable in size, shape, and position. The authors propose a novel taxonomic system for deep CMs in the thalamus based on clinical presentation (syndromes) and anatomical location (identified on MRI).

METHODS The taxonomic system was developed and applied to an extensive 2-surgeon experience from 2001 through 2019. Deep CMs involving the thalamus were identified. These CMs were subtyped on the basis of the predominant surface presentation identified on preoperative MRI. Six subtypes among 75 thalamic CMs were defined: anterior (7/75, 9%), medial (22/75, 29%), lateral (10/75, 13%), choroidal (9/75, 12%), pulvinar (19/75, 25%), and geniculate (8/75, 11%). Neurological outcomes were assessed using modified Rankin Scale (mRS) scores. A postoperative score ≤ 2 was defined as a favorable outcome and > 2 as a poor outcome. Clinical and surgical characteristics and neurological outcomes were compared among subtypes.

RESULTS Seventy-five patients underwent resection of thalamic CMs and had clinical and radiological data available. Their mean age was 40.9 (SD 15.2) years. Each thalamic CM subtype was associated with a recognizable constellation of neurological symptoms. The common symptoms were severe or worsening headaches (30/75, 40%), hemiparesis (27/75, 36%), hemianesthesia (21/75, 28%), blurred vision (14/75, 19%), and hydrocephalus (9/75, 12%). The thalamic CM subtype determined the selection of surgical approach. A single approach was associated with each subtype for most patients. The main exception to this paradigm was that in the surgeons’ early experience, pulvinar CMs were resected through a superior parietal lobule–transatrial approach (4/19, 21%), which later evolved to the paramedian supracerebellar-infratentorial approach (12/19, 63%). Relative outcomes implied by mRS scores were unchanged or improved in most patients (61/66, 92%) postoperatively.

CONCLUSIONS This study confirms the authors’ hypothesis that this taxonomy for thalamic CMs can meaningfully guide the selection of surgical approach and resection strategy. The proposed taxonomy can increase diagnostic acumen at the patient bedside, help identify optimal surgical approaches, enhance the clarity of clinical communications and publications, and improve patient outcomes.

Comparative Analysis of Surgical Working Corridors for Meckel Cave Trigeminal Schwannomas: A Quantitative Anatomic Study

Operative Neurosurgery 25:E251–E266, 2023

Volumetric analysis of the working corridors of the interdural approach to the Meckel cave may lead to a selection of routes which are anatomically more advantageous for trigeminal schwannoma resection. The herein-reported anatomic study quantitively compares the infratrochlear (IT) transcavernous, anteromedial (AM), and anterolateral (AL) corridors, highlighting their feasibility, indications, advantages, and limitations.

METHODS: Anatomic boundaries and depth of Meckel cave, porus trigeminus, IT transcavernous, AM, and AL corridors were identified in 20 formalin-fixed latex-injected cadaveric heads and were subsequently measured. The corridor areas and volumes were derived accordingly. Each opening angle was also calculated. Angles and volumes were compared using analysis of variance. Statistical significance was set at a P-value <.05.

RESULTS: The IT transcavernous corridor volume was greater than that of the AM and AL. The opening angle of the AM middle fossa triangle was wider than the other 2.

CONCLUSION: The IT corridor can be advantageous for Meckel cave schwannomas invading the cavernous sinus and those with a notable extension into the posterior fossa because the transcavernous approach maximizes the working space into the retrosellar area. The AM middle fossa corridor is strategic in schwannomas confined to the Meckel cave with a minor extension into the posterior fossa. It raises the chance of total resection with a single approach involving the porus trigeminus opening.

The “candy wrapper” of the pituitary gland: a road map to the parasellar ligaments and the medial wall of the cavernous sinus

Acta Neurochirurgica (2023) 165:3431–3444

The anatomy of the medial wall of the cavernous sinus (MWCS) and parasellar ligaments (PLs) has acquired increasing importance in endoscopic endonasal (EE) surgery of the cavernous sinus (CS), including resection of the MWCS in functioning pituitary adenomas (FPAs). Although anatomical studies have been published, it represents a debated topic due to their complex morphology. The aim is to offer a description of the PLs that originate from the MWCS and reach the lateral wall of the cavernous sinus (LWCS), proposing the “candy wrapper” model. The relationships between the neurovascular structures and histomorphological aspects were investigated.

Methods Forty-two CSs from twenty-one human heads were studied. Eleven specimens were used for EE dissection; five underwent a microscopic dissection. Five specimens were used for histomorphological analysis.

Results Two groups of PLs with a fan-shaped appearance were encountered. The anterior group included the periosteal ligament (55% sides) and the carotico-clinoid complex (100% sides), formed by the anterior horizontal and the carotico-clinoid ligaments. The posterior group was formed by the posterior horizontal (78% sides), and the inferior hypophyseal ligament (34% sides). The periosteal ligament originated inferiorly from the MWCS, reaching the periosteal dura. The anterior horizontal ligament was divided in a superior and inferior branch. The superior one continued as the carotid-oculomotor membrane, and the inferior branch reached the CN VI. The carotico-clinoid ligament between the middle and anterior clinoid was ossified in 3 sides. The posterior horizontal ligament was related to the posterior genu and ended at the LWCS. The inferior hypophyseal ligament followed the homonym artery. The ligaments related to the ICA form part of the adventitia. Conclusion The “candy wrapper” model adds further details to the previous descriptions of the PLs. Understanding this complex anatomy is essential for safe CS surgery, including MWCS resection for FPAs.

The sub‑occipital transtentorial approach for pineal region tumors

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Acta Neurochirurgica (2023) 165:3461–3465

Two major approaches exist for the surgical removal of pineal region tumors: the supracebellar infratentorial and the sub-occipital transtentorial.

Methods We present the Lyon’s technique of the sub-occipital transtentorial approach for pineal region tumors and our tricks to avoid complications. The principle is to expose the pineal region under the occipital lobe and not through the interhemispheric fissure.

Conclusions The sub-occipital transtentorial approach is a direct, extra cerebral, safe, and effective way to access tumors of the pineal region.

Anatomical step‑by‑step dissection of common approaches to the third ventricle for trainees

Acta Neurochirurgica (2023) 165:2421–2434

Purpose To create a high-quality, cadaver-based, operatively oriented resource documenting the anterior transcortical and interhemispheric transcallosal approaches as corridors to the third ventricle targeted towards neurosurgical trainees at all levels.

Methods Two formalin-fixed, latex-injected specimens were dissected under microscopic magnification and endoscopicassisted visualization. Dissections of the transcortical and transcallosal craniotomies with transforaminal, transchoroidal, and interforniceal transventricular approaches were performed. The dissections were documented in a stepwise fashion using three-dimensional photographic image acquisition techniques and supplemented with representative cases to highlight pertinent surgical principles.

Results The anterior transcortical and interhemispheric corridors afford excellent access to the anterior two-thirds of the third ventricle with varying risks associated with frontal lobe versus corpus callosum disruption, respectively. The transcortical approach offers a more direct, oblique view of the ipsilateral lateral ventricle, whereas the transcallosal approach readily establishes biventricular access through a paramedian corridor. Once inside the lateral ventricle, intraventricular angled endoscopy further enhances access to the extreme poles of the third ventricle from either open transcranial approach. Subsequent selection of either the transforaminal, transchoroidal, or interforniceal routes can be performed through either craniotomy and is ultimately dependent on individual deep venous anatomy, the epicenter of ventricular pathology, and the concomitant presence of hydrocephalus or embryologic cava. Key steps described include positioning and skin incision; scalp dissection; craniotomy flap elevation; durotomy; transcortical versus interhemispheric dissection with callosotomy; the aforementioned transventricular routes; and their relevant intraventricular landmarks.

Conclusions Approaches to the ventricular system for maximal safe resection of pediatric brain tumors are challenging to master yet represent foundational cranial surgical techniques. We present a comprehensive operatively oriented guide for neurosurgery residents that combines stepwise open and endoscopic cadaveric dissections with representative case studies to optimize familiarity with third ventricle approaches, mastery of relevant microsurgical anatomy, and preparation for operating room participation.

Microsurgical anatomy and pathoanatomy of the outer arachnoid membranes in the cerebellopontine angle

Acta Neurochirurgica (2023) 165:1791–1805

The cerebellopontine angle (CPA) is a frequent region of skull base pathologies and therefore a target for neurosurgical operations. The outer arachnoid is the key structure to approach the here located lesions. The goal of our study was to describe the microsurgical anatomy of the outer arachnoid of the CPA and its pathoanatomy in case of space-occupying lesions.

Methods Our examinations were performed on 35 fresh human cadaveric specimens. Macroscopic dissections and microsurgical and endoscopic examinations were performed. Retrospective analysis of the video documentations of 35 CPA operations was performed to describe the pathoanatomical behavior of the outer arachnoid.

Results The outer arachnoid cover is loosely attached to the inner surface of the dura of the CPA. At the petrosal surface of the cerebellum the pia mater is strongly adhered to the outer arachnoid. At the level of the dural penetration of the cranial nerves, the outer arachnoid forms sheath-like structures around the nerves. In the midline, the outer arachnoid became detached from the pial surface and forms the base of the posterior fossa cisterns. In pathological cases, the outer arachnoid became displaced. The way of displacement depends on the origin of the lesion. The most characteristic patterns of changes of the outer arachnoid were described in case of meningiomas, vestibular schwannomas, and epidermoid cysts of the CPA.

Conclusion The knowledge of the anatomy of the outer arachnoid of the cerebellopontine region is essential to safely perform microsurgical approaches as well as of dissections during resection of pathological lesions.

Comparison Between the Supracerebellar Infratentorial and Precuneal Interhemispheric, Transtentorial Approaches to the Cerebellomesencephalic Fissure

Operative Neurosurgery 25:E6–E14, 2023

The dorsal brainstem and cerebellomesencephalic fissure are challenging surgical targets. To afford a preferentially craniocaudal trajectory to this region, the precuneal interhemispheric transtentorial approach (PCIT) has been proposed.

OBJECTIVE: To didactically describe and compare exposures and anatomic indications of the supracerebellar infratentorial approach (SCIT) and PCIT to the cerebellomesencephalic fissure.

METHODS: Nine formalin-fixed, latex-injected cadaveric head specimens were used to perform a midline SCIT and bilateral PCITs and measure the distance of each approach. Twenty-four formalin-fixed specimens were used to measure the distance from the most posterior cortical bridging vein entering the superior sagittal sinus to the calcarine sulcus and the torcula. Fifty-one magnetic resonance images were reviewed to calculate the angle of each approach. Three illustrative surgical cases were described.

RESULTS: Mean distances from the brain or cerebellar surface to the operative target of the PCIT and SCIT were 7.1 cm (range: 5-7.7 cm) and 5.5 cm (range: 3.8-6.2 cm), respectively. The SCIT provided direct access to structures of the quadrigeminal cistern bilaterally. The PCIT provided access from the ipsilateral inferior colliculus to the ipsilateral infratrochlear zone. The PCIT’s benefit was the direct access it provided to the cerebellomesencephalic fissure because of its superior to inferior trajectory.

CONCLUSION: The PCIT is indicated for unilateral lesions of the cerebellomesencephalic fissure and dorsal brainstem that harbor a craniocaudal long axis and do not have a superior extension beyond the superior colliculi. The SCIT is beneficial for lesions that extend bilaterally, have an anteroposterior long axis, or involve the Galenic complex.

 

The transfrontal isthmus approach for insular glioma surgery

J Neurosurg 139:20–28, 2023

The classic transopercular or transsylvian approach to insular gliomas removes the tumor laterally through the insular cortex. This study describes a new anteroposterior approach through the frontal isthmus for insular glioma surgery.

METHODS The authors detailed the surgical techniques for resection of insular gliomas through the transfrontal isthmus approach. Fifty-nine insular gliomas with at least Berger-Sanai zone I involvement were removed with the new approach, and extent of resection and postoperative neurological outcomes were assessed.

RESULTS Fifty-nine patients were enrolled in the study, including 35 men and 24 women, with a mean (range) age 44.3 (19–75) years. According to the Berger-Sanai classification system, the most common tumor was a giant glioma (67.8%), followed by involvement of zones I and IV (18.6%). Twenty-two cases were Yaşargil type 3A/B, and 37 cases were Yaşargil type 5A/B. The average angle between the lateral plane of the putamen and sagittal line was 33.53°, and the average width of the isthmus near the anterior insular point was 33.33 mm. The average angle between the lateral plane of the putamen and the sagittal line was positively correlated with the width of the isthmus near the anterior insular point (r = 0.935, p < 0.0001). The median (interquartile range [IQR]) preoperative tumor volume was 67.82 (57.64–92.19) cm 3 . Of 39 low-grade gliomas, 26 (66.67%) were totally resected; of 20 high-grade gliomas, 19 (95%) were totally resected. The median (IQR) extent of resection of the whole group was 100% (73.7%–100%). Intraoperative diffusion-weighted imaging showed no cases of middle cerebral artery– or lenticulostriate artery–related stroke. Extent of insular tumor resection was positively correlated with the angle of the lateral plane of the putamen and sagittal line (r = −0.329, p = 0.011) and the width of the isthmus near the anterior insular point (r = −0.267, p = 0.041). At 3 months postoperatively, muscle strength grade exceeded 4 in all cases, and all patients exhibited essentially normal speech. The median (IQR) Karnofsky performance score at 3 months after surgery was 90 (80–90).

CONCLUSIONS The transfrontal isthmus approach changes the working angle from lateral-medial to anterior-posterior, allowing for maximal safe removal of insular gliomas.

A system of anatomical triangles defining dissection routes to brainstem cavernous malformations

J Neurosurg 138:768–784, 2023

Anatomical triangles defined by intersecting neurovascular structures delineate surgical routes to pathological targets and guide neurosurgeons during dissection steps. Collections or systems of anatomical triangles have been integrated into skull base surgery to help surgeons navigate complex regions such as the cavernous sinus. The authors present a system of triangles specifically intended for resection of brainstem cavernous malformations (BSCMs). This system of triangles is complementary to the authors’ BSCM taxonomy that defines dissection routes to these lesions.

METHODS The anatomical triangle through which a BSCM was resected microsurgically was determined for the patients treated during a 23-year period who had both brain MRI and intraoperative photographs or videos available for review.

RESULTS Of 183 patients who met the inclusion criteria, 50 had midbrain lesions (27%), 102 had pontine lesions (56%), and 31 had medullary lesions (17%). The craniotomies used to resect these BSCMs included the extended retrosigmoid (66 [36.1%]), midline suboccipital (46 [25.1%]), far lateral (30 [16.4%]), pterional/orbitozygomatic (17 [9.3%]), torcular (8 [4.4%]), and lateral suboccipital (8 [4.4%]) approaches. The anatomical triangles through which the BSCMs were most frequently resected were the interlobular (37 [20.2%]), vallecular (32 [17.5%]), vagoaccessory (30 [16.4%]), supracerebellar-infratrochlear (16 [8.7%]), subtonsillar (14 [7.7%]), oculomotor-tentorial (11 [6.0%]), infragalenic (8 [4.4%]), and supracerebellar-supratrochlear (8 [4.4%]) triangles. New but infrequently used triangles included the vertebrobasilar junctional (1 [0.5%]), supratrigeminal (3 [1.6%]), and infratrigeminal (5 [2.7%]) triangles. Overall, 15 BSCM subtypes were exposed through 6 craniotomies, and the approach was redirected to the BSCM by one of the 14 triangles paired with the BSCM subtype.

CONCLUSIONS A system of BSCM triangles, including 9 newly defined triangles, was introduced to guide dissection to these lesions. The use of an anatomical triangle better defines the pathway taken through the craniotomy to the lesion and refines the conceptualization of surgical approaches. The triangle concept and the BSCM triangle system increase the precision of dissection through subarachnoid corridors, enhance microsurgical execution, and potentially improve patient outcomes.

Sacrifice or preserve the superior petrosal vein in microvascular decompression surgery

J Neurosurg 138:390–398, 2023

In microvascular decompression (MVD) surgery through the retrosigmoid approach, the surgeon may have to sacrifice the superior petrosal vein (SPV). However, this is a controversial maneuver. To date, high-level evidence comparing the operative outcomes of patients who underwent MVD with and without SPV sacrifice is lacking. Therefore, this study sought to bridge this gap.

METHODS The authors searched the Medline and PubMed databases with appropriate Medical Subject Heading (MeSH) terms and keywords. The primary outcome was vascular-related complications; secondary outcomes were new neurological deficit, cerebrospinal fluid (CSF) leak, and neuralgia relief. The pooled proportions of outcomes and OR (95% CI) for categorical data were calculated by using the logit transformation and Mantel-Haenszel methods, respectively.

RESULTS Six studies yielding 1143 patients were included, of which 618 patients had their SPV sacrificed. The pooled proportion (95% CI) values were 3.82 (0.87–15.17) for vascular-related complications, 3.64 (1.0–12.42) for new neurological deficits, 2.85 (1.21–6.58) for CSF leaks, and 88.90 (84.90–91.94) for neuralgia relief. The meta-analysis concluded that, whether the surgeon sacrificed or preserved the SPV, the odds were similar for vascular-related complications (2.5% vs 1.5%, OR [95% CI] 1.01 [0.33–3.09], p = 0.99), new neurological deficits (1.2% vs 2.8%, OR [95% CI] 0.55 [0.18–1.66], p = 0.29), CSF leak (3.1% vs 2.1%, OR [95% CI] 1.16 [0.46–2.94], p = 0.75), and neuralgia relief (86.6% vs 87%, OR [95% CI] 0.96 [0.62–1.49], p = 0.84).

CONCLUSIONS SPV sacrifice is as safe as SPV preservation. The authors recommend intentional SPV sacrifice when gentle retraction fails to enhance surgical field visualization and if the surgeon encounters SPV-related neurovascular conflict and/or anticipates impeding SPV-related bleeding.

 

Hakuba’s triangle: a cadaveric study detailing its anatomy and neurovascular contents with vascular and skull base implications

Neurosurgical Review (2022) 45:2087–2093

Hakuba’s triangle is a superior cavernous sinus triangle that allows for wide and relatively safe exposure of vascular and neoplastic lesions.

This study provides cadaveric measurements of the borders of Hakuba’s triangle and describes its neurovascular contents in order to enrich the available literature.

The anatomical borders of the Hakuba’s triangle (lateral, medial, and posterior borders) were defined based on Hakuba’s description and identified. Then the triangle was dissected to reveal its morphology and relationship with adjacent neurovascular structures in Embalmed Caucasian cadaveric specimens.

The oculomotor nerve occupied roughly one-third of the area of the triangle and the nerve was more or less parallel to its medial border. The mean lengths of the lateral border, posterior border, and medial border were 17 mm ± 0.5 mm, 12.2 mm ± 0.4 mm, and 10.6 mm ± 0.4 mm, respectively. The mean area of Hakuba’s triangle was 63.9 mm 2 ± 4.4 mm 2 .

In this study, we provided cadaveric measurements of the borders of Hakuba’s triangle along with descriptions of its neurovascular contents.

Anatomical relationship between the foramen ovale and the lateral plate of the pterygoid process: application to percutaneous treatments of trigeminal neuralgia

Neurosurgical Review (2022) 45:2193–2199

Our aim was to clarify the variations in the positional relationship between the base of the lateral plate of the pterygoid process and the foramen ovale (FO), which block inserted needles during percutaneous procedures to the FO usually used for the treatment of trigeminal neuralgia.

Ninety skulls were examined. The horizontal relationship between the FO and the posterior border of the base of the lateral plate of the pterygoid process was observed in an inferior view of the skull base. Skulls that showed injury to either the FO or the lateral plate of the pterygoid process on either side were excluded.

One hundred and sixty sides of eighty skulls were eligible. The relationship between the FO and the posterior border of the base of the lateral plate was classified into four types. Among the 160 sides, type III (direct type) was the most common (35%), followed by type I (lateral type, 29%) and type IV (removed type, 21%); type II (medial type) was the least common (15%). Of the 80 specimens, 53 showed the same type bilaterally.

In type IV, the posterior border of the base of the lateral plate is disconnected from the FO, so percutaneous procedures for treating trigeminal neuralgia could fail in patients with this type.

Surgical anatomy of minimally invasive lateral approaches to the thoracolumbar junction

J Neurosurg Spine 36:937–944, 2022

The thoracolumbar (TL) junction spanning T11 to L2 is difficult to access because of the convergence of multiple anatomical structures and tissue planes. Earlier studies have described different approaches and anatomical
structures relevant to the TL junction. This anatomical study aims to build a conceptual framework for selecting and executing a minimally invasive lateral approach to the spine for interbody fusion at any level of the TL junction with appropriate adjustments for local anatomical variations.

METHODS The authors reviewed anatomical dissections from 9 fresh-frozen cadaveric specimens as well as clinical case examples to denote key anatomical relationships and considerations for approach selection.

RESULTS The retroperitoneal and retropleural spaces reside within the same extracoelomic cavity and are separated from each other by the lateral attachments of the diaphragm to the rib and the L1 transverse process. If the lateral diaphragmatic attachments are dissected and the diaphragm is retracted anteriorly, the retroperitoneal and retropleural spaces will be in direct continuity, allowing full access to the TL junction. The T12–L2 disc spaces can be reached by a conventional lateral retroperitoneal exposure with the rostral displacement of the 11th and 12th ribs. With caudally
displaced ribs, or to expose T12–L1 disc spaces, the diaphragm can be freed from its lateral attachments to perform a retrodiaphragmatic approach. The T11–12 disc space can be accessed purely through a retropleural approach without significant mobilization of the diaphragm.

CONCLUSIONS The entirety of the TL junction can be accessed through a minimally invasive extracoelomic approach, with or without manipulation of the diaphragm. Approach selection is determined by the region of interest, degree of diaphragmatic mobilization required, and rib anatomy.