Extreme Lateral Supracerebellar Infratentorial Approach for Petroclival Meningioma with an Ophthalmic Artery Originating from the Middle Meningeal Artery: Illustrative Case

Abstract

Petroclival meningiomas are traditionally resected via the combined transpetrosal approach. However, rare anatomical variants, such as the ophthalmic artery originating from the middle meningeal artery, preclude the combined transpetrosal approach due to the risk of permanent blindness from middle meningeal artery sacrifice. We present a 46-year-old woman with a left petroclival meningioma (Upper Clivus type) and trigeminal neuralgia, in whom preoperative angiography revealed an ophthalmic artery arising from the middle meningeal artery (incidence -1.45%) and a non-dominant left transverse sinus. To preserve visual function, the extreme lateral supracerebellar infratentorial approach was employed. By ligating the non-dominant transverse sinus and incising the tentorium laterally under exoscopic visualization, a wide corridor to the superior petroclival region was achieved while preserving the middle meningeal artery. Subtotal resection was performed; firm tumor adherence to the lateral midbrain, proximal superior cerebellar artery perforators, and posterior cerebral artery precluded complete removal. Postoperatively, transient right hemiparesis and oculomotor palsy resolved within 3 months. Histopathology confirmed a world health organization grade 1 meningothelial meningioma (mitotic count: 1/10 high-power fields) with preserved MTAP expression and retained H3K27me3 staining. Despite benign histology, the MIB-1 index of 3%-5% correlated with tumor progression at 13 months, which was managed with stereotactic radiosurgery; the patient remains neurologically stable at 3 years. The extreme lateral supracerebellar infratentorial approach is a viable alternative for petroclival meningiomas when standard corridors are precluded by vascular anomalies, though its limitations, including restricted access to the middle cranial fossa and the required microsurgical expertise, must be recognized. Detailed preoperative vascular screening is essential for optimal approach selection.

Introduction

Petroclival meningiomas (PCMs) represent one of the most surgically demanding intracranial tumors due to their deep location and intimate relationship with critical neurovascular structures.^1,2) Surgical corridors are traditionally selected based on tumor size, extension, and adjacent anatomy, with the combined transpetrosal approach (CTPA) and retrosigmoid approach being the most common.²⁾ At our institution, the CTPA is frequently utilized for its wide exposure and ability to achieve early devascularization. However, this approach routinely necessitates the sacrifice of the middle meningeal artery (MMA), which may result in irreversible visual loss in patients with specific vascular anomalies.

The ophthalmic artery (OphA) originating from the MMA, referred to as the meningo-ophthalmic variant, is a rare but clinically critical anomaly, occurring in approximately 1.45% of the population.^3,4) In such cases, the MMA provides the primary blood supply to the orbit, and its inadvertent injury or planned ligation during a craniotomy can lead to permanent visual impairment.⁴⁾ Although Hayashi et al.⁵⁾ previously reported approach modification for skull base meningiomas with MMA-origin OphA, including 2 petroclival cases managed via a posterior transpetrosal corridor, the adoption of extreme lateral supracerebellar infratentorial approach (EL-SCITA) with transverse sinus (TS) ligation as an MMA-sparing alternative in this setting has not been previously described. When standard skull base approaches like the CTPA are contraindicated due to such anatomical constraints, alternative strategies must be employed. The EL-SCITA has emerged as a versatile route to the clivus and tentorial incisura.^6,7) Giammattei et al.⁶⁾ provided a comprehensive anatomical description and literature review of the EL-SCITA, confirming its applicability to a range of posterolateral mesencephalic and tentorial lesions. In the specific context of PCMs, Watanabe et al.⁸⁾ reported favorable surgical outcomes in a series of 26 patients using a lateral supracerebellar transtentorial trajectory for upper clival tumors, establishing this posterolateral corridor as a viable oncological option. By combining this approach with exoscopic visualization and a lateral tentorial incision, surgeons can achieve a wide surgical corridor while preserving the MMA and its distal branches. In this report, we describe a case of PCM resected via the EL-SCITA and discuss the surgical advantages and limitations of this approach.

Case Report

A 46-year-old woman presented with left trigeminal neuralgia. Neurological examination revealed facial pain in the distribution of the left trigeminal nerve without other significant neurological deficits. Magnetic resonance imaging (MRI) revealed a 4-cm, homogeneously enhancing extra-axial mass in the left petroclival region. The tumor extended to the posterolateral surface of the midbrain; the superior cerebellar artery (SCA) coursed along the medial margin of the tumor, whereas the proximal segment of the PCA was partially embedded within the tumor (Figure 1A, B, and C).

Figure 1

Preoperative imaging and surgical simulation.

(A) Axial gadolinium-enhanced T1-weighted MRI demonstrating the SCA coursing along the medial margin of the tumor (arrowhead) and the proximal segment of the PCA (white arrow). (B) Coronal gadolinium-enhanced T1-weighted MRI demonstrating the overall tumor extent; inset shows the PCA coursing along the tumor margin (white arrow). (C) Sagittal gadolinium-enhanced T1-weighted MRI demonstrating the overall tumor extent; inset demonstrates the proximal segment of the PCA partially embedded within the tumor (white arrow). (D) Lateral view of the left internal carotid angiogram showing the absence of the ophthalmic artery (OphA) from the carotid canal. (E) Lateral view of the left external carotid angiogram demonstrating the OphA arising via the recurrent meningeal artery (white arrowhead), and the retinochoroidal blush confirming orbital blood supply (open arrowhead). (F) Anteroposterior view of the left internal carotid angiogram confirming a hypoplastic, non-dominant left transverse sinus (TS) (arrowhead). (G) Simulated surgical view via the standard retrosigmoid approach, demonstrating limited access to the superior tumor pole. (H) Simulated anterior view via the endoscopic endonasal approach (EEA), highlighting the superior and posterior tumor extension and the difficulty of achieving a direct corridor to the upper pole without significant neurovascular manipulation. (I) Simulated view of the EL-SCITA after TS ligation and lateral tentorial incision, confirming the wide and direct visualization of the superior cerebellar surface and the tumor-SCA interface.

EL-SCITA: extreme lateral supracerebellar infratentorial approach; ICA: internal carotid artery; Lower CNs: lower cranial nerves; MRI: magnetic resonance imaging; PCA: posterior cerebral artery; SCA: superior cerebellar artery

Preoperative planning and simulation

Left internal carotid angiography showed the absence of the OphA from the carotid canal; instead, the OphA originated from the MMA via the recurrent meningeal artery (Figure 1D and E). The left TS was hypoplastic, and the venous drainage was right-dominant (Figure 1F). Based on the Ichimura classification, the tumor was categorized as an Upper Clivus (UC) type.⁷⁾ Because the CTPA requires sacrifice of the MMA, it was deemed contraindicated due to the risk of permanent blindness.⁹⁾ Preoperative simulation¹⁰⁾ demonstrated that the retrosigmoid approach provided inadequate visualization of the superior tumor pole (Figure 1G), and the endoscopic endonasal approach (EEA) was limited in its ability to reach the superior extension of the tumor without significant manipulation of neurovascular structures (Figure 1H). In contrast, the EL-SCITA, combined with TS ligation and tentorial incision, was found to provide the most direct and safe surgical corridor to the superior cerebellar surface and lateral midbrain (Figure 1I).

Operation

The patient was placed in the right lateral position (Figure 2A). Following an extended retrosigmoid craniotomy, the TS was ligated and divided medial to the vein of Labbé, as the sinus was non-dominant (Figure 2B, C, D, E, and F). The tentorium was incised laterally with meticulous preservation of the trochlear nerve (CN IV) (Figure 2G). Under exoscopic guidance, the tumor was resected through this expanded corridor. The tumor was found to be displacing trigeminal nerve (CN V), facial nerve (CN VII), and vestibulocochlear nerve (CN VIII) laterally and posteriorly. Although the majority of the tumor was removed (Figure 2H, I, J, and K), firm adherence of the remaining tumor to the lateral midbrain and proximal SCA perforators necessitated subtotal resection to avoid permanent neurological deficits (Figure 2L).

Figure 2

Intraoperative photographs under exoscopic visualization.

(A) The patient in the right lateral position with a curvilinear retroauricular skin incision. (B) Extended retrosigmoid and occipital craniotomy exposing the TS. (C) Dural incision of the posterior fossa. (D) Opening of the arachnoid over the cerebellopontine angle; the tumor (T) is identified deep to the trigeminal nerve (V) and the superior petrosal vein (SPV). (E) Identification of the trochlear nerve (IV) at the undersurface of the tentorium. (F) Ligation and division of the non-dominant TS medial to the vein of Labbé. (G) Lateral tentorial incision performed with meticulous preservation of the trochlear nerve. (H) Tumor dissection through the expanded tentorial corridor. (I) Dissection of the tumor from the brainstem with visualization of the basilar artery (BA). (J) Dissection of the tumor from the SCA and coagulation of its feeding arteries. (K) Resection of the inferior tumor component between the trigeminal (V) and vestibulocochlear (VIII) nerves. (L) Final view showing residual tumor adherent to the lateral midbrain, which was coagulated to prioritize neurological safety.

TS: transverse sinus

Pathological findings and postoperative course

Histopathological examination revealed a meningothelial meningioma, World Health Organization (WHO) grade 1.¹¹⁾ The mitotic count was 1 per 10 high-power fields (HPF), and there was no evidence of brain invasion. Immunohistochemical analysis showed preserved MTAP expression and retained H3K27me3 nuclear staining, confirming the absence of CDKN2A/B homozygous deletion and polycomb repressive complex 2 loss, respectively, both of which are associated with high-grade molecular features. Although telomerase reverse transcriptase promoter mutation status was not evaluated due to institutional resource constraints at the time of surgery, the overall molecular and histological profile was consistent with WHO grade 1. The MIB-1 labeling index was 3%-5%.

Postoperatively, the patient experienced transient right hemiparesis and oculomotor nerve palsy, both of which resolved within 3 months. Immediate postoperative MRI demonstrated residual tumor at the lateral midbrain, in association with the proximal SCA and PCA (Figure 3A and B), and a small asymptomatic infarction was noted in the left cerebral peduncle on diffusion-weighted imaging (Figure 3C). Follow-up MRI at 13 months revealed tumor progression at the residual site. The patient was subsequently treated with CyberKnife stereotactic radiosurgery (SRS; 25 Gy in 5 fractions). At 3 years post-surgery, the patient remains neurologically stable with no further progression.

Figure 3

Postoperative imaging.

(A, B) Axial and coronal gadolinium-enhanced T1-weighted MRI obtained postoperative day 1, showing residual tumor (white arrowhead) on the lateral aspect of the upper midbrain, closely associated with the proximal SCA and PCA. (C) Axial diffusion-weighted MRI obtained postoperative day 1 revealing a small asymptomatic infarction in the left cerebral peduncle.

MRI: magnetic resonance imaging; PCA: posterior cerebral artery; SCA: superior cerebellar artery

Discussion

The surgical management of PCMs is dictated by tumor extension and its relationship to critical neurovascular structures.^1,2) Although the CTPA is often preferred for early devascularization via MMA ligation,⁹⁾ our case highlights a critical anatomical contraindication: the OphA originating from the MMA. This rare variant, occurring in approximately 1.45% of cases,³⁾ presents a high risk of permanent blindness if the MMA is sacrificed.⁴⁾ In such scenarios, a comprehensive approach selection analysis and an alternative surgical planning are essential. Hayashi et al.⁵⁾ previously reported 3 skull base meningiomas in which surgical approach was modified to preserve MMA-derived retinal blood supply; notably, 2 petroclival cases were managed via a posterior transpetrosal approach to avoid MMA sacrifice at the foramen spinosum. In contrast, the concurrent identification of a non-dominant TS in our patient enabled the adoption of EL-SCITA with TS ligation as an MMA-sparing alternative to the conventional transpetrosal corridor, a strategy not previously described for this anatomical variant. This uniquely constraining clinical constellation underscores the importance of systematic preoperative vascular screening in all PCM cases and demands individualized approach planning beyond standard algorithms.

Approach selection and tumor classification

The tumor was categorized as a UC type according to the Ichimura classification, with its base located above the level of the internal auditory canal and involving the middle incisural space.⁷⁾ The CTPA, a gold standard for such lesions,⁹⁾ was rendered prohibitive by the OphA-MMA variant, making preservation of the distal MMA branches a primary surgical constraint.^3,4)

We performed a comparative analysis of alternative routes (Table 1). The EEA was deemed suboptimal for several reasons: the tumor showed significant lateral extension with cranial nerves displaced laterally and posteriorly, extending superiorly into the incisura beyond the reach of standard endonasal instrumentation;¹²⁾ the risk of cavernous sinus hemorrhage and postoperative cerebrospinal fluid leakage following large clival duraplasty was considerable; and vascular control for a tumor of this size and consistency is generally more reliable via a transcranial route. The standard retrosigmoid approach was also found insufficient during preoperative simulation,¹⁰⁾ as visualization of the superior tumor pole and the tumor-SCA/PCA interface is frequently obscured by the tentorium and the superior surface of the cerebellum.

Table 1

Comparison of Surgical Approaches for Petroclival Meningiomas

Approach	Advantages	Disadvantages	Suitability for this case
3D: 3-dimensional; CN: cranial nerves; CSF: cerebrospinal fluid; MMA: middle meningeal artery; OphA: ophthalmic artery; SCA: superior cerebellar artery
Retrosigmoid approach (RS)	Familiar technique, minimal bone work, good for inferior/lateral components.	Limited visualization of the superior pole and the SCA-incisura interface.	Suboptimal as 3D simulation predicts limited superior pole exposure and obscured tumor-vessel interface.
Combined transpetrosal approach (CTPA)	Wide exposure, early devascularization, multi-angle access to the clivus.	Invasive bone work, risk of CSF leak, requires MMA sacrifice.	Contraindicated due to the risk of blindness (MMA-origin OphA).
Endoscopic endonasal approach (EEA)	Direct midline access, early devascularization, no brain retraction.	Risk of CSF leak, limited lateral reach beyond CNs, difficult superior extension.	Suboptimal due to lateral displacement of CNs and superior extension into the incisura.
Extreme lateral supracerebellar infratentorial approach (EL-SCITA)	Preserves the MMA, excellent superior visualization, leveraging gravity for retraction.	Deep and narrow corridor, risk of CN IV injury, requires advanced microsurgical skill.	Optimal alternative allowing for safe resection while protecting visual function.

In contrast, the EL-SCITA offers a unique up-angle trajectory that follows the natural corridor of the supracerebellar infratentorial space.^6,13) This corridor was first systematically explored for PCMs by Watanabe et al.,⁸⁾ who demonstrated its efficacy for upper clival PCMs using a lateral microscopic trajectory. By utilizing non-dominant TS ligation and a lateral tentorial incision, we effectively converted this narrow corridor into a wide, panoramic window providing direct access to the superior cerebellar surface and the tumor-vessel interface in the incisural space. This posterolateral trajectory avoided the anteriorly located vascular variant while enabling safe neurovascular dissection. Compared with the CTPA, the EL-SCITA requires simpler bone work without mastoidectomy or petrosectomy, is associated with shorter operative times, and carries a lower risk of temporal lobe retraction injury and venous compromise.^5,12) However, the approach has recognized limitations: visualization is restricted for tumors extending into the middle cranial fossa or Meckel's cave, and the deep, narrow working angles demand advanced microsurgical skill and thorough familiarity with the posterolateral corridor anatomy.⁵⁾

Technical advantages and risks

The integration of exoscopic visualization was pivotal in managing this deep corridor. The exoscope offers flexible, high-definition viewing angles that are less constrained by craniotomy dimensions than the traditional microscope,¹⁴⁾ providing an advantage for the "up-angle" views required to visualize the superior tumor pole and SCA. Although an endoscope was prepared as an alternative visualization modality, the exoscope ultimately provided sufficient illumination throughout all operative stages. The feasibility of fully endoscopic EL-SCITA for PCMs has been established by Xie et al.,¹⁵⁾ confirming that this corridor is compatible with both exoscopic and endoscopic platforms. As endoscope-assisted skull base surgery continues to evolve, the EL-SCITA is increasingly recognized as a versatile approach well-suited to optical augmentation, and its role in the management of petroclival lesions is likely to expand with further experience. Surgeons must remain cognizant of the trochlear nerve (CN IV), which is at risk during tentorial incision;⁶⁾ meticulous dissection under high-definition visualization is paramount given the small diameter and long cisternal course of this nerve. Regarding TS ligation, the pivotal maneuver that opens the EL-SCITA corridor, safety depends on 3 preoperative criteria: (1) the ipsilateral TS must be non-dominant, with the contralateral sinus or the straight sinus serving as the primary venous outflow; (2) the ligation point must be medial to the vein of Labbé, which should drain independently into the sigmoid sinus rather than the TS itself; and (3) adequate collateral cortical venous drainage must be confirmed on preoperative magnetic resonance or computed tomographic venography.^6,13,16) In this case, the left TS was hypoplastic with right-dominant drainage confirmed preoperatively, satisfying all criteria. Systematic venous phase evaluation is therefore mandatory before planning this approach.

Pathological considerations and clinical course

Under the WHO 2021 Classification, the diagnosis of a grade 1 meningioma is based on mitotic count and the absence of molecular risk factors.¹¹⁾ In this case, the low mitotic count (1/10 HPF), preserved MTAP expression, and retained H3K27me3 staining collectively support a grade 1 designation. Despite this, the tumor showed progression at 13 months, which correlates with the elevated MIB-1 index (3%-5%). Although Ki-67 is not a formal criterion for WHO grading, values exceeding 3% are associated with a significantly increased recurrence risk in grade 1 meningiomas. Our experience underscores that for PCMs with a high MIB-1 index, early adjuvant SRS should be strongly considered rather than a conservative "wait-and-scan" strategy.

Conclusions

When standard transpetrosal routes are precluded by rare vascular variants such as the MMA-origin OphA, the EL-SCITA offers a viable and safe alternative. This approach, enhanced by exoscopic visualization and tailored tentorial incision, allows for effective decompression of the petroclival region while preserving visual function. Detailed preoperative vascular screening is essential in all PCM cases to identify such anatomical contraindications and to guide optimal approach selection. Nevertheless, it should be acknowledged that compared to the CTPA, the EL-SCITA may be less effective for early tumor devascularization and for managing tumors with extensive adherence to the anterior brainstem or involvement of the middle cranial fossa. Further accumulation of clinical experience will be required to refine patient selection criteria and to clarify the long-term outcomes of this approach.

Conflicts of Interest

All authors declare no conflicts of interest.

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