Refining the Keyhole Approach for Aneurysms

The management of anterior circulation intracranial vascular lesions continues to undergo rapid evolutionary changes. In modern neurovascular centers, selecting an optimal keyhole approach for aneurysms offers remarkable benefits over traditional extensive craniotomies. Surgeons achieve effective vascular occlusion while dramatically reducing brain retraction, soft tissue dissection, and postoperative pain. Historically, the standard pterional craniotomy served as the universal workhorse for anterior circulation pathology. However, minimally invasive keyhole corridors now present viable, less disruptive alternatives for carefully selected surgical candidates. Among these modern alternatives, the minipterional route and the lateral supraorbital corridor have gained substantial global acceptance. Recently, skull base surgeons introduced the transorbital corridor as an innovative ventral pathway to reach the Sylvian fissure and the carotid cistern. Consequently, neurosurgeons require precise quantitative anatomical comparisons to understand the distinctive advantages, boundary limits, and mechanical freedom of each individual technique. By adopting individualized surgical planning, clinicians can safely tailor keyhole procedures to match patient anatomy.

Anatomical Quantification Across Anterior Corridors

To establish objective clinical indications, investigators conducted an anatomical simulation using four adult cadaveric specimens across eight cranial sides. The researchers completed high-resolution basal computed tomography scans to facilitate precision neuronavigation throughout all dissections. Furthermore, the investigators executed realistic surgical simulations comparing the transorbital, lateral supraorbital, and minipterional techniques. The experimental design scrutinized four primary anterior circulation targets: the posterior communicating artery origin, the internal carotid bifurcation, the middle cerebral artery M1 segment, and the middle cerebral artery bifurcation. Through meticulous microdissection, the operative teams successfully accessed the internal carotid C6 and C7 segments, alongside all four primary targets, via all three approaches. Moreover, the surgical teams quantified instrument manoeuvrability, horizontal working angles, ventral trajectories, and total surgical freedom at each predefined vascular landmark. The authors subsequently evaluated quantitative differences across the corridors using Kruskal-Wallis statistical testing. Therefore, this rigorous experimental model yields reproducible measurements that clarify spatial limitations for practicing cerebrovascular specialists.

Carotid and Posterior Communicating Artery Exposure

Vascular targets along the proximal internal carotid axis reveal substantial differences in surgical freedom among the three approaches. Specifically, when targeting the posterior communicating artery, the minipterional approach delivered the greatest surgical freedom area, averaging 101.59 square centimeters. In contrast, the lateral supraorbital corridor provided 71.35 square centimeters, whereas the transorbital route afforded only 36.19 square centimeters. This anatomical difference demonstrated clear statistical significance across the investigated specimens. Conversely, target dynamics shifted markedly when evaluating the internal carotid artery bifurcation. At this distal junction, the lateral supraorbital approach provided the maximum surgical freedom, achieving an area of 85.34 square centimeters. Furthermore, the lateral supraorbital trajectory offered superior ventral and horizontal manipulation angles compared to its surgical alternatives. Although the transorbital approach exposed these proximal internal carotid structures, its working cone remained constrained by orbital bony margins. Therefore, surgeons treating low-lying posterior communicating aneurysms may favor the minipterional route, while internal carotid bifurcation lesions strongly favor a lateral supraorbital trajectory.

Manoeuvrability Along the Middle Cerebral Artery

Dissection along the middle cerebral artery complex demonstrated unique spatial advantages for both lateral and ventral corridors. Along the horizontal M1 segment, quantitative analysis showed no statistically significant differences in surgical freedom among the three corridors. Notably, the transorbital approach demonstrated its highest performance at this specific vascular site, achieving an impressive surgical freedom area of 68.02 square centimeters. Furthermore, the transorbital route provided remarkable instrument angulation along the proximal middle cerebral trunk, facilitating excellent line-of-sight visualization. When researchers shifted focus to the middle cerebral artery bifurcation, the minipterional route yielded the largest operative manoeuvrability, reaching 90.99 square centimeters. The lateral supraorbital approach followed closely with 72.02 square centimeters, while the transorbital approach provided 42.38 square centimeters. Although these bifurcation differences did not achieve formal statistical significance, the minipterional corridor clearly offered superior lateral trajectory and wider dynamic control. Consequently, complex middle cerebral bifurcations benefit significantly from the broader lateral exposure of the minipterional technique.

Translating Quantitative Data into Clinical Practice

Translating anatomical data into operative success demands careful consideration of patient-specific angioarchitecture and clinical presentation. To validate these laboratory findings, the study authors presented three illustrative clinical cases involving unruptured middle cerebral and internal carotid aneurysms. These successful surgical clippings confirm that each corridor serves distinct anatomical niches rather than competing directly as exclusive methods. For instance, the transorbital route represents a powerful ventral corridor that eliminates brain retraction during access to low-riding M1 segment lesions. However, deep Sylvian splitting through transorbital pathways requires advanced endoscopic and microscopic skill sets. In comparison, the lateral supraorbital approach remains exceptionally versatile, offering rapid access and outstanding working angles for internal carotid bifurcation lesions. Meanwhile, surgeons facing complex, laterally projecting middle cerebral artery bifurcation aneurysms should typically rely on the minipterional craniotomy. Thus, neurovascular teams must tailor the operative corridor to the precise neck orientation, depth, and parental vessel geometry of each aneurysm.

Strategic Adoption Across Indian Cerebrovascular Units

In Indian neurosurgical centers, the implementation of keyhole cerebrovascular techniques requires structured training and deliberate case selection. High-volume tertiary hospitals across India encounter diverse aneurysm presentations, including unruptured incidental lesions that require durable, minimally invasive clipping. Adopting minimally invasive craniotomies reduces hospital stay, accelerates postoperative recovery, and minimizes cosmetic temporal hollowing. However, young neurosurgeons must resist adopting ultranarrow corridors without adequate cadaveric training and microsurgical mentorship. Initially, neurosurgical teams should master the lateral supraorbital and minipterional techniques before incorporating transorbital routes. Additionally, centers must integrate high-definition neuroendoscopy, neuronavigation, and micro-Doppler ultrasonography into the operating room to enhance keyhole safety. When anatomical boundaries restrict working angles, surgeons must maintain low thresholds for converting to standard pterional craniotomies. Ultimately, rigorous quantitative cadaveric data empower Indian surgical teams to select the safest, most effective pathway for intracranial aneurysm repair.

Frequently Asked Questions

Which keyhole approach provides the greatest surgical freedom for ICA bifurcation aneurysms?

The lateral supraorbital keyhole approach provides the greatest surgical freedom for internal carotid artery bifurcation aneurysms, achieving a mean working area of 85.34 square centimeters. Furthermore, this corridor delivers superior ventral and horizontal manipulation angles, allowing surgeons to visualize and clip distal carotid bifurcation lesions with exceptional precision and control.

When is the minipterional route preferred over ventral keyhole techniques?

Surgeons prefer the minipterional route for aneurysms situated at the posterior communicating artery origin and the middle cerebral artery bifurcation. Specifically, the minipterional approach provides superior lateral working angles and maximum surgical freedom at these sites, enabling safer proximal vascular control and easier manipulation around complex, branching vascular architecture.

What role does the transorbital approach play in anterior circulation aneurysm clipping?

The transorbital approach serves as an innovative ventral corridor particularly suited for proximal middle cerebral artery M1 segment pathology. It provides substantial surgical freedom and favorable instrument angulation without substantial frontal lobe retraction. However, restricted working angles at bifurcations currently limit its utility to select, uncomplicated anterior circulation aneurysms.

Disclaimer: This content is for informational and educational purposes only and should not be considered medical advice. Always consult a qualified healthcare professional regarding any medical condition or treatment. Refer to the latest local and national guidelines for clinical practice.

References

1. Mosteiro A et al. Selecting the optimal keyhole approach for internal carotid and middle cerebral artery aneurysms. Anatomical comparison of transorbital, lateral supraorbital and minipterional routes with clinical implications. Acta Neurochir (Wien). 2026 Apr 13. doi: 10.1007/s00701-026-06871-x. PMID: 41975109.


2. Esposito G, Burkhardt JK, Fierstra J, et al. Selection Strategy for Optimal Keyhole Approaches for Middle Cerebral Artery Aneurysms: Lateral Supraorbital Versus Minipterional Craniotomy. World Neurosurg. 2019;122:e349-e357.


3. Salma A, Alkandari A, Sammet S, Ammirati M. Lateral supraorbital approach vs pterional approach: An anatomic qualitative and quantitative evaluation. Neurosurgery. 2011;68(1 Suppl Operative):364-372.