Subtemporal Transtentorial Approach Research Articles

Microanatomical Investigation of the Subtemporal Transtentorial Approach

To study the microanatomic structure of the subtemporal transtentorial approach to the lateral side of the brainstem, and to provide anatomical information that will assist clinicians to perform surgeries on the lateral, circumferential, and petroclival regions of the brainstem. Anatomical investigations were conducted on 8 cadaveric head specimens (16 sides) using the infratemporal transtentorial approach. The heads were tilted to one side, with the zygomatic arch at its highest point. Then, a horseshoe incision was made above the auricle. The incision extended from the midpoint of the zygomatic arch to one third of the mesolateral length of the transverse sinus, with the flap turned towards the temporal part. After removing the bone, the arachnoid and the soft meninges were carefully stripped under the microscope. The exposure range of the surgical approach was observed and the positional relationships of relevant nerves and blood vessels in the approach were clarified. Important structures were photographed and the relevant parameters were measured. The upper edge of the zygomatic arch root could be used to accurately locate the base of the middle cranial fossa. The average distances of the star point to the apex of mastoid, the star point to the superior ridge of external auditory canal, the anterior angle of parietomastoid suture to the superior ridge of external auditory canal, and the anterior angle of parietomastoid suture to the star point of the 10 adult skull specimens were 47.23 mm, 45.27 mm, 26.16 mm, and 23.08 mm, respectively. The subtemporal approach could fully expose the area from as high as the posterior clinoid process to as low as the petrous ridge and the arcuate protuberance after cutting through the cerebellar tentorium. The approach makes it possible to handle lesions on the ventral or lateral sides of the middle clivus, the cistern ambiens, the midbrain, midbrain, and pons. In addition, the approach can significantly expand the exposure area of the upper part of the tentorium cerebelli through cheekbone excision and expand the exposure range of the lower part of the tentorium cerebelli through rock bone grinding technology. The total length of the trochlear nerve, distance of the trochlear nerve to the tentorial edge of cerebellum, length of its shape in the tentorial mezzanine, and its lower part of entering into the tentorium cerebelli to the petrosal ridge were (16.95±4.74) mm, (1.27±0.73) mm, (5.72±1.37) mm, and (4.51±0.39) mm, respectively. The cerebellar tentorium could be safely opened through the posterior clinoid process or arcuate protrusion for localization. The oculomotor nerve could serve as an anatomical landmark to locate the posterior cerebral artery and superior cerebellar artery. Through microanatomic investigation, the exposure range and intraoperative difficulties of the infratemporal transtentorial approach can be clarified, which facilitates clinicians to accurately and safely plan surgical methods and reduce surgical complications.

Posterolateral Routes to the Skull Base, Craniocervical Junction, and Jugular Foramen-The Far Lateral Transcondylar Approach and Combined Transpetrosal Transcervical Approaches.

The far lateral approach provides wide surgical access to the lower third of the clivus, pontomedullary junction, and anterolateral foramen magnum and rarely requires craniovertebral fusion. The most common indications for this approach are posterior inferior cerebellar artery and vertebral arteryaneurysms, brainstem cavernous malformations, and tumors anterior to the lower pons and medulla, including meningiomas of the anterior foramen magnum, schwannomas of the lower cranial nerves, and intramedullary tumors at the craniocervical junction. We provide a stepwise description of how we perform the far lateral approach, as well as how to combine the far lateral approach with other skull base approaches, including the subtemporal transtentorial approach, for lesions involving the upper clivus; the posterior transpetrosal approach, for lesions involving the cerebellopontine angle and/or petroclival region; and/or lateral cervical approaches, for lesions involving the jugular foramen or carotid sheath regions.

Microsurgical approaches to the cerebellar interpeduncular region: qualitative and quantitative analysis.

The cerebellar interpeduncular region (CIPR) is a gate for dorsolateral pontine and cerebellar lesions accessed through the supracerebellar infratentorial approach (SCITa), the occipital transtentorial approach (OTa), or the subtemporal transtentorial approach (STa). The authors sought to compare the exposures of the CIPR region that each of these approaches provided. Three approaches were performed bilaterally in eight silicone-injected cadaveric heads. The working area, area of exposure, depth of the surgical corridor, length of the interpeduncular sulcus (IPS) exposed, and bridging veins were statistically studied and compared based on each approach. The OTa provided the largest working area (1421 mm2; p < 0.0001) and the longest surgical corridor (6.75 cm; p = 0.0006). Compared with the SCITa, the STa provided a larger exposure area (249.3 mm2; p = 0.0148) and exposed more of the length of the IPS (1.15 cm; p = 0.0484). The most bridging veins were encountered with the SCITa; however, no significant differences were found between this approach and the other approaches (p > 0.05). To reach the CIPR, the STa provided a more extensive exposure area and more linear exposure than did the SCITa. The OTa offered a larger working area than the SCIT and the STa; however, the OTa had the most extensive surgical corridor. These data may help neurosurgeons select the most appropriate approach for lesions of the CIPR.

Surgical Treatment of Trochlear Nerve Schwannomas: Case Series and Systematic Review

Cranial nerve schwannomas almost always arise from sensory or mixed nerves. Motor cranial nerves, such as the trochlear nerve, are rarely associated with schwannomas. No consensus has yet been made for surgical intervention because of the low number of reported cases of trochlear nerve schwannomas. This study comprises a systematic review of the literature and our experience for surgically treated trochlear nerve schwannomas. Three databases (Web of Science, PubMed, and Cochrane Library) were searched without date restrictions. Studies were included if they were published in the English literature and presented patients of any age who underwent surgical treatment for trochlear schwannoma. Data extracted from the included studies were combined with our experience. Forty-one studies, presenting 43 patients, met the inclusion criteria. The total number of patients was 45 after our experience was added. The most common symptoms were diplopia (62.2%), headache (46.7%), and motor weakness (37.8%). Mean age during the diagnosis was 45.1 years. Although the subtemporal transtentorial approach (n= 14) is the most preferred method, its application has decreased in recent years. In the last decade, the lateral suboccipital approach (n= 11) has gained popularity. Residual postoperative trochlear nerve deficit was detected in 81% of patients. The probability of neurologic deficit was not statistically associated with tumor volume (P= 0.914), location (P= 0.669), or resection rate (P= 0.554). Although trochlear schwannomas are rare and their treatment involves challenges, total resection with the proper approach provides the most desirable results.

Surgical Treatment and Clinical Outcomes of Petroclival Meningiomas: A Single-Center Experience of 107 Patients.

ObjectiveThis study aimed to establish optimal surgical strategies via reviewing the clinical outcomes of various surgical approaches for the pertroclival meningiomas (PCMs).MethodsThis retrospective study enrolled 107 patients with PCMs at the authors’ institution from year 2010 to 2020. Patient demographics, the clinical characteristics, various operative approaches, major morbidity, post-operative cranial nerve deficits and tumor progression or recurrence were analyzed.ResultsThe subtemporal transtentorial approach (STA), the Kawase approach (KA), the retrosigmoid approach (RSA) and the anterior sigmoid approach (ASA), namely the posterior petrosal approach (PPA) were adopted for 17 cases, 22 cases, 31 cases and 34 cases respectively. Total or subtotal resection was achieved in 96 cases (89.7%). The incidence of new-onset and aggravated cranial nerve dysfunction were 13.1% (14/107) and 10.4% (15/144), respectively. Furthermore, 14 cases suffered from intracranial infection, 9 cases had cerebrospinal fluid leakage, and 3 cases sustained intracranial hematoma (1 case underwent second operation). The mean preoperative and postoperative Karnofsky Performance Status (KPS) score was 80 (range 60-100) and 78.6 (range 0-100), but this was not statistically significant (P>0.05). After a mean follow-up of 5.1 years (range 0.3- 10.6 years), tumor progression or recurrence was confirmed in 23 cases. Two cases died from postoperative complications.ConclusionsFor the treatment of PCMs, it is still a challenge to achieve total resection. With elaborate surgical plans and advanced microsurgical skills, most patients with PCMs can be rendered tumor resection with satisfactory extent and functional preservation, despite transient neurological deterioration during early postoperative periods.

Abordaje presigmoideo transpetroso (petrosectomía parcial) combinado con abordaje subtemporal transtentorial para meningioma petroclival

Introduction: Petroclival meningiomas constitute 3 to 10% of meningiomas of the posterior fossa, they originate in the petroclival fissure, in the upper part of the clivus, petrosal apex, and medial to the trigeminal nerve. Resection of these tumors is a neurosurgical challenge. The combined partial petrosectomy approach associated with a sub-temporal approach is a technique described by various authors; however, its performance is considered highly complex. We report the case of a petroclival meningioma operated successfully in our hospital using a combined presigmoid and subtemporal transtentorial transpetrosal approach. Clinical case: 33-year-old female patient with a clinical picture of headache, nausea, and gait disturbance. Brain magnetic resonance imaging showed a large right petroclival tumor (4.2x3.9x3.8cm) that displaced the brainstem and secondary hydrocephalus. The hydrocephalus was treated with a ventricular peritoneal shunt. Then, the tumor was resected using a combined presigmoid and subtemporal transpetrosal approach, a technique that allowed adequate exposure of the tumor, achieving complete resection, without intraoperative complications. Postoperative evolution was favorable, with no sequelae. Conclusion: The combined presigmoid and transtentorial subtemporal transpetrous approach for petroclival meningiomas is an effective and feasible technique to perform in our environment. The support of technology such as Neuronavigation, the ultrasonic aspirator, intraoperative monitoring, and adequate experience in skull base surgery are fundamental factors for the success of this surgery. Keywords: Meningioma, Skull Base Neoplasms, Craniotomy, Neurosurgical Procedures. (Source: MeSH NLM)

Surgical anatomy of the vein of Labbé

The objective is to study surgical anatomy of the vein of Labbé (inferior anastomotic vein) and venous drainage of the mediobasal surface of the temporal lobe, as well as to identify the most common variants of drainage of the lateral and basal parts of the temporal lobe which are necessary to take into account during surgical approach. Materials and methods . The study was conducted on 50 non-preserved human brain hemispheres with homolateral surface of the base of the skull. Surgical part of the study was conducted on 25 cadavers. Anterior and posterior petrosal subtemporal transtentorial approaches were modelled. Standard neurosurgical set of microinstruments, surgical microscope and high-speed neurosurgical drills were used. At the intradural stage of the approach, the vein of Labbé was identified, its anastomotic type and the character of outflow into the venous collectors were determined. Results . In total, 115 groups of veins draining the brain were identified. Venous drainage of the transversal group was identified in 100 % of cases, of the tentorial group – in 72 % of cases, of the petrosal group – in 58 % of cases. No significant differences between the locations of vein inflow were identified on the right and left. Three (3) variants of drainage of the lateral and basal parts of the temporal lobe were identified: 1) inflow of venous drainage groups into the sinodural angle, posterior third of the petrosa; sinus and anterior parts of the transverse sinus – 14 (28 %) cases; 2) inflow into the sinodural angle, anterior parts of the transverse sinus and tentorial surface – 21 (42 %) cases; 3) inflow into all of the venous collectors (sinodural angle, petrosal, transverse, tentorial sinuses) – 15 (30 %) cases. Two (2) anastomotic types of the vein of Labbé were identified: with direct (12 %) and indirect (88 %) outflow into the venous collectors of the base of the skull. In the indirect type, “venous star” was observed comprised of several venous trunks which converged near the sinodural angle. The veins of Labbé with indirect type of outflow entered the petrosal sinus (4 % of cases), sinodural angle (14 %), tentorium (10 %) and transverse sinus (60 %) through the posterior inferior superficial temporal vein (8 %), medial inferior superficial temporal vein (26 %) and posterior inferior superficial temporal vein (54 %). The vein of Labbé with direct type of drainage entered only the transverse sinus. In most cases, the vein of Labbé entered the transverse sinus 10 mm behind the sinodural angle. Large diameter veins (dominant veins) were observed in 38 % of cases, all of them entered the transverse sinus. Conclusion . The identified variants of venous drainage of the lateral and basal parts of the temporal lobe and anastomotic variants of the vein of Labbé allow to select the optimal surgical approach and correct its direction, refine the character of temporal lobe traction and predict technical difficulties during supratemporal approach.

Subtemporal Transtentorial Approach in Mesencephalic and Perimesencephalic Lesions in Children-A Series of 20 Patients.

Midbrain and surrounding areas are among the most difficult regions to surgically approach in neurosurgery. The subtemporal approach is a well-known neurosurgical approach that is rarely described in children. To assess the feasibility, advantages, and disadvantages of subtemporal approach in children. A total of 20 pediatric patients with intra-axial tumors involving the lateral midbrain or superior cerebellar peduncle or with extra-axial tumors in the middle incisural space/Meckel cave underwent subtemporal transtentorial approaches with the aim to remove (16 cases) or biopsy (4 cases) their lesions. These cases were retrospectively reviewed and the surgical approach described. Total resection was achieved in 11 patients. In the 4 patients who underwent biopsies, a diagnosis was obtained. A total of 5 patients presented non-neoplastic lesions (dermoid tumors or cavernomas). A total of 9 patients harbored low-grade tumors and 6 high-grade tumors. Patients with low-grade tumors and non-neoplastic lesions are all alive with no evidence of disease or stable residue. Four patients affected by high grade tumors died. No patient suffered permanent neurological deficits related to the surgical approach. Three patients presented temporary neurological deficits following the procedure: one case of strabismus, one case of aphasia and hemiparesis, secondary to delayed, transient thrombosis of the Labbé vein, and 1 case of trigeminal neuralgia. The subtemporal approach represents a feasible approach for mesencephalic and perimesencephalic lesions in children. It provides an ample and direct access, with excellent outcomes and acceptable postoperative morbidity.

A history of the Jannetta procedure.

Peter Jannetta was a neurosurgery resident when he proposed the neurovascular compression theory. He built upon the astute observations of Dandy, Gardner, and others who, in the era before the operating microscope, had successfully ventured into the posterior fossa. In 1965, Jannetta performed cranial nerve microdissections for dental students and identified the trigeminal portio intermedia. He proposed that preservation of these sensory fibers may avoid complete facial numbness, and together with Robert Rand developed a subtemporal transtentorial approach for selective rhizotomy for trigeminal neuralgia (TN). Such rash surgery, using an operating microscope, was then forbidden at their University of California, Los Angeles center, so they collaborated with John Alksne to perform the first surgery at Harbor General Hospital. Upon visualizing the trigeminal nerve root, Jannetta was surprised to see a pulsating superior cerebellar artery compressing the nerve and said "That's the cause of the tic." He also hypothesized that alleviating the observed vascular cross-compression may be curative.A few months later, while assessing a patient with hemifacial spasm, Jannetta had the epiphany that this was the same disease process as TN, but instead affecting the facial nerve. The patient consented to what would become Jannetta's first microvascular decompression procedure. The senior faculty members who had forbidden such surgery were away, so the supervising neurosurgeon, Paul Crandall, granted the approval to perform the surgery and assisted. Via a retromastoid approach with the patient in the sitting position and using the operating microscope, Jannetta identified and alleviated the culprit neurovascular compression, with a cure resulting.Jannetta presented his neurovascular compression theory and operative findings to the neurosurgical patriarchy of the time. Elders of the field were generally not inclined to accept the bold speculations of an untested neurosurgeon, and were often determined to discredit the new "cure" of the old diseases. Over decades of refining his surgical technique, documenting the outcomes, and enduring the skepticism he often faced, Jannetta's theory and his microvascular decompression procedure withstood critical analysis and have become recognized as one the great discoveries and advances in neurosurgery and medicine.

Anterior Transpetrosal Approach for Petroclival Meningioma: Operative Nuances

Petroclival meningiomas are unique neurosurgical challenges that require planning an approach to the retrosellar and upper and mid retroclival locations. The classical subtemporal-transtentorial approach went into disrepute due to excessive brain retraction. To resolve this challenge Buchenek and Kukwa introduced extradural approach with drilling of the petrous bone and called it the extended middle fossa approach. It was Kawase et al who modified the extended middle fossa approach initially for dealing with basilar trunk aneurysms. This anterior transpetrosal approach has been described below for dealing with the petroclival meningiomas.

Subtemporal transtentorial approach for resection of a pontomesencephalic cavernous malformation.

In this 3D video we review the case of a pontomesencephalic cavernous malformation in a 27-year-old woman who presented with hemiparesis and diplopia. The cavernous malformation was completely resected through a subtemporal transtentorial approach and an epitrigeminal brainstem entry zone, with a significant improvement in the patient’s hemiparesis. The relevant anatomy is reviewed in detail through multiple anatomical brainstem dissection specimens, as well as high-definition fiber tractography images. The rationale for the approach is analyzed relative to other possible options, and a number of technical pearls are provided.The video can be found here: https://youtu.be/8EoIWL7XqAc.

Surgical treatment of pontine cavernous malformations via subtemporal transtentorial and intradural anterior transpetrosal approaches.

The aim of this study was to report our surgical experience on resection of the pontine cavernous malformations (CMs) via subtemporal transtentorial approach (STTA) and intradural anterior transpetrosal approach (ATPA). Clinical data were retrospectively reviewed in 61 patients with pontine CMs that were surgically treated by the STTA and the intradural ATPA. The surgical procedures, complications, and outcomes were analyzed. The study consists of 61 patients with a total of 61 pontine CMs. Other than 4 lesions located medially in the pons, all CMs were in the lateral pons with a left or right lateral epicenter (the left/right ratio was 22/35). Totally, 11 patients (18.0%) with lesions located in the upper pons were treated by the STTA, and 50 patients (82.0%) with lesions involving the lower pons were treated by the intradural ATPA. Postoperatively, the complete resection was achieved in 58 patients (95.1%) and incomplete resection in 3 patients (4.9%). Twenty-seven patients (44.3%) suffered from a new or worsened neurological deficit in the immediate postoperative period, and 8 patients (13.1%) encountered a non-neural complication, including rebleeding, cerebrospinal fluid leak, intracranial infection, and pulmonary infection, and 3 patients had contusion of temporal lobe. With a mean follow-up of 54.2months, the patients' neurological condition had improved in 43 cases (71.6%), not changed in 10 cases (16.7%), and worsened in 7 cases (11.7%), respectively. The Karnofsky Performance Scale (KPS) score evaluated at the last time for per patient was significantly better than their baseline status (t = 6.677, p < 0.001). However, 21 patients (35.0%) suffered from a new or worsened persistent postoperative deficit. The lateral and anterolateral pons can be exposed well by the subtemporal transtentorial and intradural anterior transpetrosal approaches. Lesions of CMs located in the lateral pons, including ventrolateral and dorsolateral pons, could be totally removed by these two lateral approaches with an acceptable surgical morbidity.

Surgical Management of Brainstem Cavernous Malformation: Report of 67 Patients

Brainstem cavernous malformations (CMs) are benign lesions, often show an acute onset, and result in a high rate of morbidity. Surgical resection could inhibit the progressive deterioration of neurologic function caused by repetitive hemorrhage. This study aimed to summarize timing, approaches, and techniques of surgery and to evaluate outcomes of treatment. Between March 2011 and May 2013, 67 patients (32 male, 35 female; average age 40 years; range, 14-68 years) with brainstem CMs received surgical treatment. Clinical presentation, surgical approaches, and results of follow-up were retrospectively analyzed. Seven surgical approaches were used: orbitozygomatic approach (1 case), suboccipital transtentorial approach (Poppen approach; 3 cases), subtemporal transtentorial approach (32 cases), subtemporal transtentorial/anterior petrosectomy approach (9 cases), suboccipital retrosigmoid approach (3 cases), midline suboccipital approach (16 cases), and far lateral approach (3 cases). Total resection of the brainstem CM was achieved in all cases (100%). No operative mortality was encountered. Nine patients had new symptoms after surgery: 3 had diplopia, 3 had facial numbness, 1 had numbness of contralateral limbs, 1 had transient aphasia, and 1 had reduced muscle strength of contralateral limbs. Symptoms significantly improved in 23 patients (34.3%), symptoms were unchanged in 36 patients (53.7%), and new postoperative symptoms occurred in 9 patients (13.4%). Choosing a proper surgical approach and using appropriate techniques are fundamental for favorable outcomes of patients with brainstem CMs.

The Tentorial Bridge to Deep Skull Base Exposure: Anatomic Morphometric Study.

Skull base surgeons split the tentorium to expand exposure, minimize brain retraction, and combine the supratentorial and infratentorial compartments for resection of large skull base lesions. The aim of this study was to describe stepwise techniques for splitting the tentorium to access deeply located skull base lesions and morphometrically assess gained exposure. Surgical exposures were performed through transsylvian, subtemporal, posterior transpetrosal, and combined posterior supratentorial/infratentorial-transsinus approaches. A custom software program was used to trace the surgical exposure region of interest for area analysis with the ability to accurately assess most irregular areas. Qualitative morphometric assessment was done of the gain in anatomic exposure achieved by splitting the tentorium. In the transsylvian transtentorial approach, mean surface area increased 154.17%, from 0.14 cm2 before expansion to 0.32 cm2 after expansion. In the subtemporal transtentorial approach, mean surface area increased 137.61%, from 0.66 cm2 before expansion to 1.52 cm2 after expansion. In the posterior transpetrosal transtentorial approach, mean surface area increased 171.06%, from 1.08cm2 before expansion to 2.81 cm2 after expansion. Inthe combined supratentorial/infratentorial-transsinus approach, mean surface area increased 222.03%, from 0.78cm2 before expansion to 2.38 cm2 after expansion. With splitting of the tentorium, a substantial area of expansion is obtained, minimizing the need for brain retraction and improving visualization of deep neurovascular structures in the skull base.

Fourth cranial nerve: surgical anatomy in the subtemporal transtentorial approach and in the pretemporal combined inter-intradural approach through the fronto-temporo-orbito-zygomatic craniotomy. A cadaveric study.

Despite the recent progress in surgical technology in the last decades, the surgical treatment of skull base lesions still remains a challenge. The purpose of this study was to assess the anatomy of the tentorial and cavernous segment of the fourth cranial nerve as it appears in two different surgical approaches to the skull base: subtemporal transtentorial approach and pretemporal fronto-orbito-zygomatic approach. Four human cadaveric fixed heads were used for the dissection. Using both sides of each cadaveric head, we made 16 dissections: 8 with subtemporal transtentorial technique and 8 with pretemporal fronto-orbito-zygomatic approach. The first segment that extends from the initial point of contact of the fourth cranial nerve with the tentorium (point Q) to its point of entry into its dural channel (point D) presents an average length of 13.5mm with an extremely wide range and varying between 3.20 and 9.3mm. The segment 2, which extends from point D to the point of entry into the lateral wall of the cavernous sinus, presents a lesser interindividual variability (mean 10.4mm, range 15.1-5.9mm). A precise knowledge of the surgical anatomy of the fourth cranial nerve and its neurovascular relationships is essential to safely approach. The recognition of some anatomical landmarks allows to treat pathologies located in regions of difficult surgical access even when there is an important subversion of the anatomy.

Giant Petrous Bone Osteoma Associated With Ipsilateral Clivus Meningioma in an Adult

Background and Importance: An association with multiple primary intracranial tumors of different histologic types not relating to radiotherapy or phacomatosis is a rare event. To the best of the authors’ knowledge, a giant osteoma originating from the inner surface of the petrous bone associated with an ipsilateral clivus meningioma has never been reported. Clinical Presentation: A 43-year-old patient with trigeminal neuralgia was found to have a posterior fossa bony lesion measuring 4 cm, with a solid enhancing lesion in juxtaposition and a separate bony lesion on the occipital bone on magnetic resonance and computed tomography imaging. A satisfactory resection of the coexisting tumors in the petroclival region was performed through a subtemporal transtentorial approach. The tumors were finally confirmed as an osteoma and a meningioma by pathologic evaluation. The patient demonstrated an improvement in her trigeminal neuralgia over a 3-month postoperative period of time. Conclusions: This case presents new clinical and radiographic findings associated with a rare lesion. Dependent tumors that one tumor may act as an irritating agent for the local proliferation of the other most likely accounted for this pattern of tumoral linkage. A satisfactory surgical result was achieved through a relatively minimal approach and different strategies. Trigeminal neuralgia, the initial presenting symptom, improved during the follow-up period.

Microsurgical Resection of Petroclival Tumors via the Subtemporal Transtentorial Approach.

To study and summarize our experience with the subtemporal transtentorial approach for resection of petroclival tumors. Twenty-eight patients who suffered from petroclival tumors and underwent tumor resection via a subtemporal transtentorial approach between October 2010 and July 2013 were retrospectively reviewed. Total resection was performed in 22 cases, at a rate of 78.57%, subtotal resection in 5 cases, and large portion resection in 1 case. 13 patients who suffered from varying degrees of postoperative nerve dysfunction all improved or recovered, during the 6 to 24 month post-operative follow up. The subtemporal transtentorial approach is one of the best approaches for resection of petroclival tumors, especially for a tumor at the petrosal apex and upper-middle clival region, and has the advantages of less trauma, easy procedure of craniotomy, and also a good surgical exposure.

Successful excision of a pontomesencephalic cavernoma through anterior subtemporal route without mapping: Anatomical landmarks as a road map

Successful excision of a pontomesencephalic cavernoma through anterior subtemporal route without mapping: Anatomical landmarks as a road map

Extended Subtemporal Transtentorial Approach to the Anterior Incisural Space and Upper Clival Region

Although most posterior circulation aneurysms are currently treated by endovascular means, some are not amenable to this treatment modality. The narrow working window afforded by the anterolateral and lateral surgical approaches often translates into suboptimal visualization and limited maneuverability. We present a modified technique of tentorial incision and reflection that optimizes the exposure achieved with the traditional subtemporal approach and report our clinical experience in a series of posterior circulation aneurysms. Retrospective review of patients operated via an extended subtemporal transtentorial approach for posterior circulation aneurysms. The modified tentorial incision implies dissection of the trochlear nerve along its dural canal up to its entrance into the cavernous sinus and incision of a tentorial flap that extends up to Meckel cave, which is then reflected far anterolaterally. Clinical and radiological data were reviewed. This series comprises 18 patients (21 procedures). Ten patients presented (56%) with a subarachnoid hemorrhage. Aneurysms most frequently arose from the basilar tip (61%) and were of small size (50%) and saccular morphology (72%). Two patients underwent surgery following unsuccessful endovascular treatment. Aneurysm treatment was successful on the first attempt in 90% (19/21) and after a second attempt in 10% (2/21). Documented postoperative palsies of the oculomotor (n = 3) and trochlear (n = 1) nerves were all transient. No procedure-related mortality occurred. This modified technique of tentorial incision and reflection optimizes visibility, anatomic orientation, and maneuverability by increasing the rostrocaudal and anterolateral exposure obtained via the extended subtemporal transtentorial route without permanent postoperative trochlear nerve deficit.

The extended subtemporal transtentorial approach: The impact of trochlear nerve dissection and tentorial incision

The subtemporal transtentorial approach provides excellent exposure of the incisural space. Incision of the tentorium improves access to the interpeduncular cistern, basilar artery, and rostral ventral pons. Description of the starting and termination points of the tentorial incision has varied greatly. We assessed the impact on surgical exposure of freeing the trochlear nerve (TN) from its dural canal (DC) in addition to dividing and retracting the tentorium. A subtemporal approach was performed on 10 hemispheres of cadaveric specimens. Following exposure of the middle tentorial incisura, the TN is dissected from its DC over a few millimeters. Two retraction sutures are placed along the tentorial edge, posterior to the TN entrance in its DC. The tentorial incision is started between the sutures. Dissection of TN from its DC continues for a short distance. The tentorial incision is extended straight up towards the superior petrosal sinus. Dissection of the TN DC continues anteriorly, up to its entry into the cavernous sinus. The tentorial incision can then be extended, just over the entrance to Meckel’s cave, and the flap reflected far anterolateraly. Using this technique, the exposure of the interpeduncular cistern and its content increased by a mean of 8.2mm (standard deviation [SD] 3.9mm) in the anteroposterior axis and by 5.5mm (SD 1.9mm) in the rostrocaudal axis. Tentorial incision following dissection of the TN from its DC optimizes reflection of the tentorium flap anterolateraly, maximizes the exposure, and improves lighting and visibility as well as maneuverability within the interpeduncular and rostral pre-pontine cisterns.