Retrosigmoid Intradural Suprameatal Approach Research Articles

Retrosigmoid Intradural Suprameatal Approach: 2-Dimensional Operative Video

INDICATIONS: CORRIDOR AND LIMITS OF EXPOSURE: The retrosigmoid intradural suprameatal approach is mostly indicated for tumors in the cerebellopontine angle extending toward the Meckel cave and supratentorial regions, most frequently meningiomas and schwannomas. This approach was first established by the senior author in 1982. ANATOMIC ESSENTIALS: NEED FOR PREOPERATIVE PLANNING AND ASSESSMENT: Nervous structures: cranial nerves III to XII, cerebellum, and brainstem. Vascular structures: anterior inferior cerebellar artery, posterior inferior cerebellar artery, superior cerebellar artery, basilar artery, vertebral artery, transverse, sigmoid, and petrous sinus, petrosal vein/veins, basilar plexus, and the mastoid emissary vein. Bony structures: petrous bone with internal auditory canal, jugular foramen and suprameatal tubercle, petrous apex, dorsum sellae, and posterior clinoid process. Structures within the petrous bone: vestibule, semicircular canals, and jugular bulb. ESSENTIALS STEPS OF THE PROCEDURE: After a suboccipital retrosigmoid craniectomy in the semisitting position and debulking of the tumor mass in the cerebellopontine angle, extension is achieved by drilling suprameatal tubercle above cranial nerve VII and VIII toward the petrous apex. The extent of bone drilling is tailored for each patient. PITFALLS/AVOIDANCE OF COMPLICATIONS: Avoid damage to cranial nerves, arteries, and veins during drilling, dissection, and tumor removal or by retraction. VARIANTS AND INDICATIONS FOR THEIR USE: In case of extreme supratentorial extensions laterally and dorsally, the opening of the tentorium may be helpful. For inferior extensions toward the upper spinal canal, opening of the foramen magnum and hemilaminectomy of C1 may be necessary. The patient consented to the procedure and to the publication of his/her image. Institutional logo in title slide, © 2023, INI Hannover. Used with permission.

Comparative Anatomic Study Between Intradural Suboccipital Retrosigmoid and Extradural Transzygomatic Middle Fossa Approaches to Expose the Trigeminal Nerve

Meckel cave tumors are relatively rare, especially trigeminal nerve (TN) schwannomas. These tumors frequently project through the trigeminal pore, occupying the middle and posterior fossae. The most used routes to this region are the suboccipital retrosigmoid intradural approach (SORSA) and the transzygomatic middle fossa approach (TZMFA). Both approaches allow further exposure by adding intraoperative techniques, such as removing the suprameatal tubercle (retrosigmoid intradural suprameatal approach [RISA]) and the petrous apex (TZMFA-PA), respectively. This study aims to understand how TN exposure differs between both surgical approaches and how it increases by adding specific surgical maneuvers to these techniques. Five formalin-fixed adult cadaver heads were submitted to high-resolution computed tomography and their images were loaded into the neuronavigation device. Anatomic key points were defined along the outline of the TN, and their three-dimensional spatial locations were collected following each surgical approach. This process allowed the calculation of the TN exposed area obtained through each technique. The mean areas of exposure of the TN were 125.9 mm2 with SORSA and 208.9 mm2 with RISA, which represents an additional mean gain of 61.92% (P= 0.047). Using TZMFA, a mean exposure of 419.24 mm2 was obtained. When TZMFA-PA was used, the mean exposed area was 486.03 mm2, representing a mean gain in the exposure area of 16.81% (P= 0.072). Our study suggests that TZMFA allows better exposure of TN ganglionic and postganglionic segments, and the removal of the PA adds the preganglionic segment visualization, although with less TN exposed area compared with RISA. With SORSA, the additional suprameatal tubercle removal shows the trigeminal pore and the medial margin of the central portion of the TN ganglionic segment, making it possible to expose the mouth of the Meckel cave and part of its contents.

Direct Comparison Between the Kawase Approach and Retrosigmoid Intradural Suprameatal Corridor to Access the Petroclival Region Using Computed Tomography Quantitative Volumetric Analysis: A Cadaveric Study

The anterior petrosectomy, also known as the Kawase approach, and the retrosigmoid intradural suprameatal approach (RISA) have both been used to reduce the petrous apex and access the petroclival region. Our goal was to compare the volumes and 3-dimensional shapes of bony resection obtained through each approach while trying to resemble realistic surgical settings. Five cadaveric specimens totaling 10 sides were dissected and analyzed. In every specimen, 1 side was used for the Kawase approach while the opposite side was used for the RISA. Petrosectomy volumes were assessed by comparing preoperative and postoperative thin-sliced computed tomography scans. Petrosectomy volumes were significantly larger through the Kawase approach than through the RISA (0.82 ± 0.11 vs. 0.49 ± 0.07 cm3, P < 0.001). In addition, surgical maneuverability and freedom were greater in the Kawase operative variant. Lastly, the morphology of the bony window achieved through each approach was clearly different: trapezoid for the anterior petrosectomy versus elongated ellipsoid for the RISA. The Kawase approach invariably results in larger volumes of bony removal than the RISA operative variant, and the volume of petrosectomy that is spatially congruent is only partially identical. The Kawase corridor is best suited for middle fossa lesions that extend into the posterior fossa, while the RISA is suitable for pathologies mainly residing in the posterior fossa and extending into the Meckel cave.

Microsurgical Anatomy of the Endoscopy-Assisted Retrosigmoid Intradural Suprameatal Approach to the Meckel's Cave.

Understanding the microsurgical anatomical features of the endoscopy-assisted retrosigmoid intradural suprameatal approach (RISA) is critical for surgeons treating petroclival tumors or lesions in the cerebellopontine region that extend into Meckel's cave. To evaluate increased exposure for Meckel's cave in the RISA and assess the surgical landmarks for this approach. A standard retrosigmoid craniotomy to the cerebellopontine region was performed in 4 cadaveric specimens (8 hemispheres) with microscope-assisted endoscopy. The length and depth of the drilling region from the suprameatal tubercle to the petrous apex were analyzed. After opening Meckel's cave and mobilizing the trigeminal root completely, the landmarks for this approach were investigated. The endoscopy-assisted RISA facilitates mobilization of the trigeminal root and enhances surgical exposure in the region of Meckel's cave and the petrous apex with increases of 10.1±1.3 mm in depth, 21.4±3.2 mm in length, and 6.4±0.6 mm in height. The posterior and superior semicircular canals, internal auditory canal, superior petrous sinus, and internal carotid artery (petrous segment) served as important landmarks for this approach. One case illustration is presented to describe the application of this approach. The RISA is suitable mainly for lesions in the posterior fossa that extend into Meckel's cave. The endoscopy-assisted reach optimizes accessibility to the petrous apex region, obviates the need for extensive drilling, and decreases the risk of internal carotid artery injury. Better realization and recognition of microsurgical landmarks and parameters of this approach are crucial for successful outcomes.

Petrous Apex Meningioma with Extension into Meckel's Cave: Resection using a Retrosigmoid Intradural Suprameatal Approach

The retrosigmoid intradural suprameatal approach was first introduced in 1983 by Samii et al, as a modification of the classic retrosigmoid approach intended to open Meckel's cave, exposing the trigeminal nerve and access the middle fossa. 1 The area of bone resected in this approach is similar to that removed in a Kawase's approach. 2 Whereas the direction of drilling in a Kawase's approach is from anterior and superior, it is from posterior and inferior in the retrosigmoid intradural suprameatal approach. Seoane and Rhoton quantified the exposure of Meckel's cave, finding that this approach allowed access, on average, to the posterior 10.3 mm of Meckel's cave. 3 This was confirmed by Chanda and Nanda who found that suprameatal drilling resulted in a mean gain of exposure of the trigeminal nerve of 10.7 mm. 4 In this video, we present the case of a patient when an enlarging petrous apex meningioma with extension into Meckel's cave ( Fig. 1 ). The patient underwent a retrosigmoid intradural suprameatal approach to achieve a Simpson's grade II resection. This approach was ideally suited for this case to obtain access to tumor located at the petrous apex and within Meckel's cave ( Fig. 2 ). Without access to Meckel's cave provided in this approach a significant portion of tumor would have remained in situ. The link to the video can be found at: https://youtu.be/eNldkF4a_OI .

Retrosigmoid Intradural Suprameatal Approach for Petroclival Meningioma

Background  Anterior transpetrosal approach and the combined transpetrosal approach are the major surgical approaches for petroclival meningiomas. However, anterior petrosectomy is not preferable in cases with postoperative venous drainage disorder of the sylvian vein due to anatomical variations. Here we present a case of the successful removal of petroclival meningioma by the retrosigmoid intradural suprameatal approach (RISA). Case Presentation  The patient was a 59-year-old woman with incidentally detected right petroclival meningioma. Although she had no neurological deficit, the tumor manifested with gradual growth on annual magnetic resonance imaging (MRI) during an 8-year follow-up. Three-dimensional computed tomography venography (3D–CTV) revealed sphenobasal type of the sylvian vein throughout the lateral side of the foramen ovale. Because the suprameatal tubercle was an obstacle to observe the Meckel's cave, RISA was selected for complete tumor excision. RISA could provide an excellent operative field around the Meckel's cave to confirm the remnant tumor. Postoperative MRI showed no evidence of the tumor, and the patient was discharged without any neurological deficit. Conclusion  RISA can provide a favorable operative field for petroclival meningioma, particularly for cases with high risk of postoperative complications related to the sylvian vein. The link to the video can be found at: https://youtu.be/cfci_zk0StU .

The Suprameatal Dural Flap for Superior Petrosal Vein Protection during the Retrosigmoid Intradural Suprameatal Approach

The drilling of the suprameatal bone during the retrosigmoid intradural suprameatal approach (RISA) puts the superior petrosal vein complex at risk of heating and mechanical injury, which may lead to cerebellar swelling and infarction. We present a new technique to protect the superior petrosal venous complex during suprameatal bone drilling. A microanatomical laboratory investigation on cadaver was conducted. The surgical technique is described and intraoperative schematic pictures are provided. The surgical steps of this technique and the related intraoperative images are reported. One case illustration regarding the removal of a large petrous apex meningioma with Meckel cave extension is described to demonstrate the application of the technique in a clinical setting. Reflecting a dural flap onto the posterior trigeminal nerve root and the superior petrosal vein complex can be a simple way to protect the nerve and the vein during the suprameatal bone drilling during the RISA.

The Suboccipital Transtentorial Approach: Indications, Technique, and Outcomes in Five Illustrative Cases

Introduction: The suboccipital retrosigmoid approach is an effective alternative to transpetrosal approaches to petroclival meningiomas. Samii modified this with a retrosigmoid intradural suprameatal approach to increase access to the middle fossa and Meckel's cave. More recently, Watanabe et al modified this by preferentially dividing the tentorium with limited drilling of the suprameatal bone, which they termed the “lateral supracerebellar transtentorial approach.” Poppen introduced sectioning of the tentorium via an occipital approach for pineal region pathology. We present our experience with a suboccipital transtentorial approach.

Lateral supracerebellar transtentorial approach for petroclival meningiomas: operative technique and outcome

The retrosigmoid intradural suprameatal approach with the patient in a semisitting position is an effective alternative to transpetrosal approaches for the treatment of petroclival meningiomas. The authors have made a simple modification to the retrosigmoid intradural suprameatal approach by using the lateral oblique position and preferentially dividing the tentorium with limited drilling of the suprameatal bone, which is termed the "lateral supracerebellar transtentorial approach." Twenty-six patients with petroclival meningiomas surgically treated via the lateral supracerebellar transtentorial approach were analyzed. All tumors had most of their bulk in the posterior fossa with some degree of extension into the middle fossa and/or Meckel cave. The patient is placed in the lateral oblique position, and a standard retrosigmoid craniotomy is performed. The tentorium medial to the trigeminal nerve is incised toward the free edge, which improves exposure to the petroclival region without extensive resection of the suprameatal petrous bone. Gross-total resection was achieved in 11 patients (42%). Ten patients (38%) underwent subtotal resection, and 5 patients (19%) underwent partial resection. There was no incidence of operative death, and the postoperative permanent morbidity rate was 15%. All patients except one did well postoperatively and were independent at the time of their last follow-up examinations. The lateral supracerebellar transtentorial approach provides the simplest and safest access to the petroclival region. It offers an advantageous approach to petroclival meningiomas exclusively located in the posterior fossa with minimal extension into the Meckel cave and middle fossa.

Microsurgical and Endoscopic Anatomy of the Retrosigmoid Intradural Suprameatal Approach to Lesions Extending from the Posterior Fossa to the Central Skull Base

This article evaluates the accessibility of the posterior part of the central skull base via the extended retrosigmoid intradural suprameatal approach. In formaldehyde-fixed specimens, the retrosigmoid intradural suprameatal approach was performed, and the feasibility of reaching central skull base structures was analyzed. Microscopic and endoscopic techniques were used. The main outcome measures were digital films and screenshots, which were analyzed regarding quantitative and qualitative aspects of visual structures. By drilling off the suprameatal tubercle and part of the petrous apex, Meckel's cave may be opened, the trigeminal nerve mobilized, and the tentorium divided. Thus the parasellar area may be exposed and the posterosuperior space of the cavernous sinus approached. Using an endoscope-assisted technique and following cisternal anatomy, the sellar and parasellar region may be explored even if the working space is narrow. The retrosigmoid intradural suprameatal approach provides optimal accessibility to medially located central skull base structures, in particular to the posterior part of the cavernous sinus. Use of the endoscope may remarkably optimize the accessibility.

The retrosigmoid intradural suprameatal approach to posterior cavernous sinus – Microsurgical anatomy

Objective The retrosigmoid intradural suprameatal approach includes the standard retrosigmoid suboccipital route with drilling of the petrous bone above and anterior of the internal auditory meatus, allowing for exposure of the trigeminal nerve within the Meckel's cave and of the middle fossa. In this study, the authors analyzed the potential use of an extended variation of the suprameatal route to approach the posterior cavernous sinus for microsurgery of, e.g., petroclival meningiomas and trigeminal schwannomas. Methods The microsurgical anatomy of the retrosigmoid suprameatal approach was examined by using 10 adult cadaveric specimens (20 sides), using 3–40× magnification. The exposure to the posterior cavernous sinus provided by this approach was focused. Results After drilling the suprameatal tubercle toward the petrous apex, the Meckel's cave was exposed. The trochlear nerve was the landmark for opening the cavernous sinus by this approach. The dura located medially to the entry point of the trochlear nerve into the tentorium was resected, allowing exposure of the intracavernous carotid artery with its meningohypophyseal trunk. Conclusion The extended retrosigmoid intradural suprameatal approach allows exposure of the posterior cavernous sinus and may be used to remove lesions of the posterior fossa extending into the Meckel's cave and into the cavernous sinus.

Endoscope-assisted retrosigmoid intradural suprameatal approach to the middle fossa: Anatomical and surgical considerations

Introduction Lesions involving the posterior and middle fossa may be reached by several surgical approaches depending mostly on tumors' location and characteristics. The retrosigmoid intradural suprameatal approach has been used to remove tumors of the posterior fossa extending into Meckel's cave and the middle fossa. With large tumors, this approach may allow exposure of the oculomotor and optic nerves, the supraclinoid internal carotid and communicating posterior arteries. Methods Three formaldehyde-fixed specimens have been prepared on both sides using the conventional retrosigmoidal-suprameatal approach. The entire endoscopic preparations have been documented via a digital recording system, using a 5 mm endoscope with a 25° perspective. The authors describe the anatomical corridor and technique of the endoscope-assisted retrosigmoid intradural suprameatal approach to lesions that are located predominantly within the posterior fossa and supratentorial extension into Meckel's cave, sellar and parasellar region. Conclusions The endoscope-assisted suprameatal approach provides exposure of the antero-medial middle fossa even in cases of skull base lesions that have not caused significant displacement of neurovascular structures.

Retrosigmoid Intradural Suprameatal Approach: Advantages and Disadvantages from an Anatomical Perspective

To assess the advantages and disadvantages of the retrosigmoid intradural suprameatal approach by studying the microsurgical anatomy. This study was performed primarily to assess the advantages of the retrosigmoid intradural suprameatal approach by measuring the amount of increased exposure it provides for lesions of the cerebellopontine and petroclival region as well as to identify the disadvantages of the approach. Twenty sides of 10 cadaver heads (embalmed and injected) were dissected under x3 to x40 magnification. A standard retrosigmoid craniotomy was made. The cerebellopontine cistern was entered to expose the neurovascular structures, and the internal auditory canal was opened by drilling the margin of the internal auditory meatus. After this, the suprameatal tubercle was drilled, followed by additional drilling to resect the petrous apex. The trigeminal root was mobilized completely after opening Meckel's cave. During drilling, care was taken to preserve the posterior and superior semicircular canals, petrosal sinus, and the internal carotid artery. The approach enhanced the exposure of the cerebellopontine cistern and Meckel's cave. There was an additional exposure of 10.7 +/- 1.16 mm length of trigeminal nerve on the right side and an additional 10.7 +/- 1.25 mm on the left. This helped to mobilize and further retract the trigeminal root. Although it facilitated the view of the neurovascular structures medial to the internal acoustic meatus, the depth of exposure did not vary much from a traditional retrosigmoid approach nor did it increase the angle of exposure or the visualization of the clivus and more medially located structures. This approach is suitable for lesions mainly in the posterior fossa with some extension into the middle fossa in the anterolateral direction. The key benefits of this approach are the length of trigeminal nerve exposure and the subsequent mobilization that improves visualization of the structures medial to the internal auditory canal, to the petrous apex, Meckel's cave, and the posterior end of the cavernous sinus.

Microsurgical Removal of a Petrous Apex Meningioma after Stereotactic Radiation: Technical Case Report

OBJECTIVE AND IMPORTANCE Stereotactic radiation is increasingly advocated as a primary treatment option for benign cranial base lesions. The clinical course of the patient reported herein raises questions regarding the rationale for initiation of radiotherapy to a petrous apex meningioma before microsurgery. CLINICAL PRESENTATION We report a 50-year-old woman who experienced medically refractory trigeminal pain. She was diagnosed with a meningioma around the petrous apex and treated by fractionated stereotactic radiation. After a short period of alleviation accompanied by hypesthesia, the pain returned in a previously unknown and violent fashion. INTERVENTION Complete tumor removal through a retrosigmoid intradural suprameatal approach resulted in immediate and permanent pain cessation. CONCLUSION Radiotherapy should be withheld for benign and accessible tumors of the cranial base until the option of radical microsurgical treatment has been explored.

Retrosigmoid intradural suprameatal approach to Meckel's cave and the middle fossa: surgical technique and outcome

Object The goal of this study was to determine whether some petroclival tumors can be safely and efficiently treated using a modified retrosigmoid petrosal approach that is called the retrosigmoid intradural suprameatal approach (RISA). Methods The RISA was introduced in 1983, and since that time 12 patients harboring petroclival meningiomas have been treated using this technique. The RISA includes a retrosigmoid craniotomy and drilling of the suprameatus petrous bone, which is located above and anterior to the internal auditory meatus, thus providing access to Meckel's cave and the middle fossa. Radical tumor resection (Simpson Grade I or II) was achieved in nine (75%) of the 12 patients. Two patients underwent subtotal resection (Simpson Grade III), and one patient underwent complete resection of tumor at the posterior fossa with subtotal resection at the middle fossa. There were no deaths or severe complications in this series; all patients did well postoperatively, being independent at the time of their last follow-up examinations (mean 5.6 years). Neurological deficits included facial paresis in one patient and worsening of hearing in two patients. Conclusions The approach described here is a useful modification of the retrosigmoid approach, which allows resection of large petroclival tumors without the need for supratentorial craniotomies. Although technically meticulous, this approach is not time consuming; it is safe and can produce good results. This is the first report on the use of this approach for petroclival meningiomas.