Operative Approach: Subtemporal Craniotomy (± Zygomatic Osteotomy / Anterior Petrosectomy)

Case / Approach Snapshot

• Anatomy at risk: corridor-defining nerves, arteries, veins/sinuses, cisterns, bone landmarks, muscle/fascial planes, and closure structures that determine exposure and morbidity.
• Operative steps: confirm position and trajectory, mark landmarks, protect soft tissue and named neurovascular structures, perform the bone/soft-tissue corridor, open/close dura or target compartment deliberately, and verify hemostasis/reconstruction; use the detailed operative sequence and approach notes below as the step-by-step source.
• Rescue plans: brain relaxation failure, venous or sinus bleeding, cranial nerve/perforator risk, exposure that is too narrow, CSF leak, cosmetic/temporalis/frontalis problems, and conversion to a wider or alternate corridor.
• Figures: review Figures, Imaging & Video and the Curated Image Set; embedded local figures should remain open-access, public-domain, or otherwise reusable with attribution.
• Papers: review High-Yield Literature for seminal sources, modern reviews, and outcome data specific to this page.

Figures, Imaging & Video

🎥 Operative video — search operative video on YouTube ▸ · The Neurosurgical Atlas ▸

Neurosurgical Atlas — Subtemporal · Radiopaedia — petroclival · PubMed Central — subtemporal / Kawase

High-Yield Literature

• Anterior Petrosectomy vs. Retrosigmoid Approach-Surgical Anatomy and Navigation-Augmented Morphometric Analysis: A Comparative Study in Cadaveric Laboratory Setting — Signoretti S. Brain sciences 2025. PubMed
• Cranio-Orbito-Zygomatic Approach: Core Techniques for Tailoring Target Exposure and Surgical Freedom — Luzzi S. Brain sciences 2022. PubMed
• The posterior subtemporal keyhole approach combined with the transchoroidal approach to the ambient cistern: microsurgical anatomy and image-guided quantitative analysis — Wang H. Acta neurochirurgica 2010. PubMed
• Tentorial dural arteriovenous fistulas — Zhou LF. Surgical neurology 2007. PubMed
• Combined transsylvian-subtemporal exposure of cerebral aneurysms involving the basilar apex — Kopitnik TA. Microsurgery 1994. PubMed
• Subtemporal approach to posterior cerebral artery aneurysms — Goehre F. World neurosurgery 2015. PubMed
• Surgical approaches for the lateral mesencephalic sulcus — Cavalcanti DD. Journal of neurosurgery 2020. PubMed
• Microsurgical Management of Blister-Type Basilar Artery Apex Region Aneurysms: Companion Cases Demonstrate Technical Nuances of the Subtemporal Approach: 2-Dimensional Operative Video — Howard BM. Operative neurosurgery (Hagerstown, Md.) 2021. PubMed
• Comparison of lateral microsurgical preauricular and anterior endoscopic approaches to the jugular foramen — Komune N. The Journal of laryngology and otology 2015. PubMed
• The oculomotor-tentorial triangle. Part 1: microsurgical anatomy and techniques to enhance exposure — Tayebi Meybodi A. Journal of neurosurgery 2019. PubMed

Curated Image Set

Open-access figures are embedded from PubMed Central articles and kept unique to this guide.

Fig. 4. Subtemporal approach. A-E. A A retractor is placed under the brain, identifying the collateral sulcus. A cortical incision is made near the uncus (yellow), and care is taken to preserve… Source: Anatomical considerations in selective amygdalohippocampectomy techniques for refractory temporal lobe epilepsy: a cadaveric study with emphasis on white matter tract anatomy — Surgical and Radiologic Anatomy 2024; CC BY.

Fig. 5. Transsylvian approach. A-E. A A pterional craniotomy is performed. The sylvian fissure (red dots) is opened from the internal carotid artery bifurcation to 2 cm beyond the MCA… Source: Anatomical considerations in selective amygdalohippocampectomy techniques for refractory temporal lobe epilepsy: a cadaveric study with emphasis on white matter tract anatomy — Surgical and Radiologic Anatomy 2024; CC BY.

Fig. 1. A-C Subtemporal Transtentorial Approach (A): Schematic of the Subtemporal Transtentorial Approach craniotomy bone flap. (B): Following elevation of the temporal base, the tentorium is… Source: Analysis of Pontine cavernous malformation resection based on 3D microanatomical study — Neurosurgical Review 2025; CC BY-NC-ND.

Fig. 4. Exposure ranges of surgical approaches and safety entry zones (Yellow quadrilateral: Superior trigeminal quadrangular space. Purple quadrilateral: Inferior trigeminal quadrangular space…. Source: Analysis of Pontine cavernous malformation resection based on 3D microanatomical study — Neurosurgical Review 2025; CC BY-NC-ND.

Fig. 5. A-C Preoperative magnetic resonance imaging (MRI) demonstrates hemorrhagic stroke within the right PCMs. D Stereotactic guidance was employed to define the surgical trajectory. E-H A… Source: Analysis of Pontine cavernous malformation resection based on 3D microanatomical study — Neurosurgical Review 2025; CC BY-NC-ND.

Figure 6. (A) Bone flap. (B) The thinned sphenoid ridge is demonstrated following basal drilling with the aid of a dissector. Source: Exploring the Lamina Terminalis: A Stepwise Anatomical Comparison of Pterional and Orbitozygomatic Craniotomy Approaches — Life 2025; CC BY.

Figure 7. After the dural incision was made, the dura was elevated and suspended. (A). Illustration, (B). Cadaver footage. Source: Exploring the Lamina Terminalis: A Stepwise Anatomical Comparison of Pterional and Orbitozygomatic Craniotomy Approaches — Life 2025; CC BY.

Figure 8. (A) Exposure of the lamina terminalis. (B) After Sylvian fissure dissection, retractors provided access to the anterior and middle skull base. (C) The lamina terminalis cistern was… Source: Exploring the Lamina Terminalis: A Stepwise Anatomical Comparison of Pterional and Orbitozygomatic Craniotomy Approaches — Life 2025; CC BY.

Figure 9. Incision plan for the one-piece orbitozygomatic approach [(A) incision sketch, (B) cadaver view: red line indicating midline; blue line indicating incision]. Source: Exploring the Lamina Terminalis: A Stepwise Anatomical Comparison of Pterional and Orbitozygomatic Craniotomy Approaches — Life 2025; CC BY.

Figure 10. The skin flap was retracted anteriorly, and the superficial temporal artery (A) and facial nerve branches (B) were carefully dissected and mobilized with a dissector. Source: Exploring the Lamina Terminalis: A Stepwise Anatomical Comparison of Pterional and Orbitozygomatic Craniotomy Approaches — Life 2025; CC BY.

The subtemporal craniotomy is the inferolateral middle-fossa corridor to the tentorial incisura, lateral midbrain, and upper posterior fossa. By elevating the temporal lobe off the middle-fossa floor, the surgeon looks medially across the incisura to the crural/ambient/interpeduncular cisterns — reaching the basilar trunk and apex, SCA/PCA, P1–P2, CN III and IV, the posterior cavernous sinus, and Meckel’s cave. Adding a zygomatic osteotomy drops the temporalis and reduces temporal-lobe retraction; adding an anterior petrosectomy (Kawase) extends the reach to the petroclival junction, upper clivus, and ventral pons.

General Considerations

• What it accesses: the tentorial incisura and its three cisternal compartments (crural, ambient, interpeduncular) and the lateral midbrain; the upper basilar complex; Meckel’s cave and the posterior cavernous sinus. With petrous apex drilling it crosses into the petroclival region.
• The defining trade-off is temporal-lobe retraction. Everything in this approach is organized around minimizing it: a craniotomy flush to the floor, gravity (lateral position), CSF drainage (lumbar drain), and — when needed — a zygomatic osteotomy. The vein of Labbé is the anatomic limit; its preservation governs how far posteriorly the temporal lobe may be elevated.
• Extensions (know the ladder):
  • + Zygomatic osteotomy → temporalis drops inferiorly; less retraction, wider upward angle (useful for higher basilar apex).
  • + Anterior petrosectomy (Kawase/Glasscock-Kawase rhomboid) → extradural drilling of the petrous apex medial to the IAC opens the petroclival junction and the ventral pons / upper basilar trunk with tentorial division.
  • Combined petrosal / presigmoid when the lesion spans the whole clivus (see presigmoid-petrosal-approach.md).

Indications

• Low-lying basilar apex / basilar trunk and SCA aneurysms (an alternative/complement to orbitozygomatic) → see basilar-tip-aneurysm.md
• Petroclival meningioma (anterior petrosectomy variant) → see petroclival-meningioma.md
• Trigeminal schwannoma / Meckel’s cave and posterior cavernous sinus lesions
• Lateral mesencephalic / tentorial-incisural lesions (e.g., midbrain cavernoma via the lateral mesencephalic sulcus), tentorial meningioma
• Selected P2 PCA aneurysms, tentorial dural fistulas

Relevant Surgical Anatomy

• Middle-fossa floor: from lateral to medial — foramen spinosum (MMA), foramen ovale (V3), arcuate eminence (superior semicircular canal), greater superficial petrosal nerve (GSPN) running to the facial hiatus, and the petrous ridge.
• Kawase’s (Glasscock-Kawase) rhomboid / anterior petrosectomy triangle: bounded by the GSPN (anterolateral), the petrous ridge/superior petrosal sinus (posterior), the arcuate eminence (posterolateral), and V3 / the trigeminal porus (anteromedial). Drilling this bone — medial to the IAC and cochlea, above the petrous ICA, anterior to the labyrinth — opens the petroclival window.
• Tentorial incisura: the free edge carries CN IV (enters the tentorium near the incisural apex — protect it during tentorial division), with CN III anteriorly at the interpeduncular cistern.
• Vein of Labbé: the dominant inferior anastomotic vein from the temporal lobe to the transverse sinus — sacrifice risks temporal venous infarction and (dominant side) aphasia.

Comprehensive microsurgical anatomy of the middle cranial fossa, Part I. Front Surg 2023;10:1132774 — CC BY 4.0.

Preoperative Evaluation

• MRI/CISS for the lesion and the incisural cisterns; CTA/MRA for vascular targets and basilar apex height relative to the posterior clinoid.
• Thin-cut CT of the petrous bone before any petrosectomy: position of the cochlea, IAC, petrous ICA, and labyrinth; degree of air-cell pneumatization (CSF-leak risk).
• Vein of Labbé / venous anatomy (MRV) — dominant drainage influences retraction strategy and side.
• Audiometry/facial baseline if petrous drilling is planned. Dominant-hemisphere considerations for retraction.

Logistics, OR Setup & Orders

• OR setup: Mayfield/head holder plan, microscope/endoscope, navigation, vascular instruments/ICG when applicable, skull base reconstruction supplies, and approach-specific retractors/drills ready before opening.
• Special needs: arterial line for major intracranial or vascular cases, Foley for long cases, neuromonitoring by corridor, dexamethasone/antiepileptic/BP plan by pathology, and blood products for vascular or skull base exposure.
• Immediate postop orders: disposition and neuro-check frequency, HOB/activity, postop CT/MRI/CTA timing, BP goals, steroid/antiepileptic plan, DVT prophylaxis timing, drain management, and focused cranial nerve/visual/language/motor exams.

Anesthesia & Neuromonitoring

• GA/TIVA; lumbar drain is commonly placed to relax the temporal lobe (drain after dura is opened to avoid herniation). SSEP/MEP, BAER and facial EMG for petrous work, CN III/IV/VI EMG as indicated; EEG/burst-suppression for temporary clipping. Normotension.

Positioning

• Lateral or supine with a large ipsilateral shoulder roll, head in Mayfield, turned ~90° so the middle-fossa floor is roughly horizontal (vertex slightly down) — the temporal lobe then falls away from the floor by gravity, the single most effective way to limit retraction.
• The lateral position is favored for extensive work (gravity does more of the retraction); ensure the dependent shoulder/brachial plexus is protected and venous outflow is unobstructed.
• Slight neck extension brings the floor into view; confirm the zygoma is accessible if an osteotomy is planned.

Incision & Soft Tissue

• A question-mark or vertical/linear temporal incision centered over the ear root and zygoma (a “T”-bar or reverse-question-mark for larger exposures). Stay above the arch anteriorly to protect the facial nerve frontal branch (interfascial dissection if the flap extends anteriorly — see pterional).
• Reflect temporalis inferiorly; for a zygomatic osteotomy, expose the arch subperiosteally and cut it (anterior and posterior) so the temporalis drops, opening a flat trajectory to the floor.

Craniotomy

1. A temporal craniotomy centered low over the middle fossa; rongeur/drill the inferior bone edge flush with the middle-fossa floor — any residual bony lip forces additional temporal-lobe retraction and must be removed.
2. Wax exposed air cells. If a zygomatic osteotomy was done, the inferior trajectory is now flat.
3. For the anterior petrosectomy variant, elevate the middle-fossa dura extradurally from posterior to anterior (to avoid avulsing the GSPN and a dehiscent geniculate facial nerve), identify the landmarks, and drill Kawase’s rhomboid.

Comprehensive microsurgical anatomy of the middle cranial fossa, Part I. Front Surg 2023;10:1132774 — CC BY 4.0. The anterior petrosectomy is drilled within this rhomboid, medial to the IAC/cochlea and above the petrous ICA.

Dural Opening & Intradural Work

1. Open the temporal dura based inferiorly; elevate the temporal lobe gently (after CSF egress via the lumbar drain) to reach the tentorial edge. Identify and protect the vein of Labbé — do not tether or sacrifice it.
2. Follow the free edge medially; identify CN IV entering the tentorium and CN III anteriorly. To open the posterior fossa, place a tentorial-edge stitch and divide the tentorium behind the entry point of CN IV, reflecting it to expose the petroclival/upper-basilar region.
3. Open the incisural cisterns sharply: the crural and ambient cisterns (P2/PCA, SCA, basal vein), and the interpeduncular cistern (basilar apex, P1, perforators, CN III). Proceed to lesion-specific steps (basilar apex clipping, petroclival tumor via the petrosectomy window, Meckel’s cave/trigeminal schwannoma).
4. Anterior petrosectomy completed: with the rhomboid drilled and the superior petrosal sinus/tentorium divided, the ventral pons and mid-upper clivus come into view for petroclival lesions.

Closure

• Watertight dura with graft as needed (the temporal floor and any petrous defect are leak-prone); obliterate drilled petrous air cells with fat/wax and reinforce with a vascularized flap (temporalis/pericranium) for petrosectomy defects.
• Replace the bone flap and re-plate the zygomatic arch anatomically if osteotomized. Reattach temporalis to limit hollowing/trismus. Lumbar drain managed per leak risk.

Further operative anatomy & technique

Comprehensive microsurgical anatomy of the middle cranial fossa, Part I. Front Surg 2023;10:1132774 — CC BY 4.0.

Comprehensive microsurgical anatomy of the middle cranial fossa, Part I. Front Surg 2023;10:1132774 — CC BY 4.0.

Nuances & Pitfalls (surgeon-level)

• The vein of Labbé is sacrosanct. Plan the corridor anterior to it; if posterior reach is needed, mobilize rather than divide. Venous infarction is the signature catastrophic complication.
• Take the bone to the floor. The commonest technical error is leaving an inferior bony lip that converts a gravity approach into a retraction approach.
• Lumbar drain then elevate. Relax the temporal lobe with CSF before any retraction; intermittent (not fixed, prolonged) retraction limits contusion/aphasia.
• Protect CN IV during tentorial division — divide behind its tentorial entry and tag the edge.
• Petrosectomy hazards: the petrous ICA (below the GSPN — avulsing the GSPN can tear a dehiscent geniculate facial nerve or injure the ICA), the cochlea (at the GSPN–arcuate-eminence angle), and the IAC/labyrinth. Drill within the rhomboid under navigation and with facial/BAER monitoring.
• Air cells = CSF leak. Wax/fat-graft meticulously, especially after petrous drilling.
• Decide on the zygomatic osteotomy up front when the target is high (basilar apex above the posterior clinoid) — it buys upward angle without more brain retraction.

Complications

Temporal-lobe contusion / venous infarction (vein of Labbé) and aphasia; CN III/IV palsy (diplopia); hearing loss/facial palsy and petrous ICA injury (petrosectomy); CSF leak; seizures; vascular/perforator injury at the basilar apex; trismus/temporal hollowing; infection.

Cross-links

• Related corridors: orbitozygomatic-craniotomy.md · presigmoid-petrosal-approach.md · pterional-craniotomy.md
• Pathology: basilar-tip-aneurysm.md · petroclival-meningioma.md

Figure Use & Attribution

About the figures. Copyrighted operative figures/videos are linked (Neurosurgical Atlas); embedded images are public-domain (Gray’s Anatomy) or CC‑BY (open-access cadaveric anatomy), credited beneath each image. See media-sources.md and figures/CREDITS.md.

Atlas chapter: Temporal / Subtemporal Craniotomy — Neurosurgical Atlas

Chief-Level Corridor Review

Use these as the senior-level mental model for Subtemporal Craniotomy (± Zygomatic Osteotomy / Anterior Petrosectomy):

• Decision point: Define the exposure goal before incision: target, working angles, proximal/distal control, and the structure that cannot tolerate retraction.
• Technical lever: Know the first irreversible step: bone removal, dural opening, vascular control, or muscle/fascial division that commits the corridor.
• Bailout: Verbalize the bailout: extend exposure, change trajectory, add CSF drainage, obtain proximal control, convert to a larger corridor, or stop for imaging.
• Postop watch: Protect closure from the start: vascularized tissue, watertight dural/reconstruction plan, dead-space control, and drain strategy should be chosen before the final intradural step.

Common Pimp Questions

Use these to pressure-test preparation for Subtemporal Craniotomy (± Zygomatic Osteotomy / Anterior Petrosectomy):

1. What patient position and head rotation make gravity work for this corridor?
2. What named nerve, vessel, sinus, or muscle/fascial plane is most commonly injured?
3. What bone work or soft-tissue step creates the exposure rather than simply using more retraction?
4. What is the bailout if exposure is inadequate, bleeding occurs, or the brain is tight?
5. What closure maneuver prevents the signature complication of this approach?

Attending Preference Variables

Items that commonly vary by surgeon or institution:

• Exact head rotation/flexion/extension and pin placement: [attending-specific]
• Skin incision length, flap type, and muscle/fascial preservation technique: [attending-specific]
• Drill, rongeur, endoscope, microscope, retractor, and navigation preferences: [attending-specific]
• Drain use, closure materials, watertightness threshold, and postop imaging routine: [attending-specific]

Case Guides Using This Approach

• No case guide currently links directly to this approach.

References

1. Kawase T, Toya S, Shiobara R, Mine T. Transpetrosal approach for aneurysms of the lower basilar artery. J Neurosurg. 1985;63(6):857–861.
2. Kawase T, Shiobara R, Toya S. Anterior transpetrosal-transtentorial approach for sphenopetroclival meningiomas. Neurosurgery. 1991;28(6):869–876.
3. Day JD, Fukushima T, Giannotta SL. Cranial base approaches to posterior circulation aneurysms. J Neurosurg. 1997.
4. Comprehensive microsurgical anatomy of the middle cranial fossa: Part I — Osseous and meningeal anatomy. Front Surg. 2023;10:1132774. CC BY 4.0. (figures embedded above)
5. Rhoton AL Jr. The tentorial incisura and The middle cranial fossa. Neurosurgery (Rhoton anatomy series).
6. Cohen-Gadol AA. Temporal/Subtemporal Craniotomy. The Neurosurgical Atlas. link