Summary
Group | No. | Names | Borders (B)/Apex (A) | Contents | Clinical significance |
Medial group Cavernous sinus triangles | 1 | Superoposterior triangle Oculomotor triangle Hakuba's triangle Medial triangle | (A) Anterior Clinoid (A) Posterior clinoid (A) Apex of petrous part | CN3 ICA horizontal segment) | Access to: Horizontal portion of cavernous ICA |
2 | Superior triangle Anteriomedial triangle Clinoidal triangle Dolenc's triangle | (B) CN2 (B) CN3 before entering the superior orbital fissure (B) Dural fold between dural entries of CN2 and CN3 | Clinoidal internal carotid artery (ICA) Anterior clinoid process. | Access to: Clinoid ICA | |
3 | Middle triangle Paramedial triangle Paramedian triangle Supratrochlear triangle | (B) CN3 (B) CN4 (B) Dural fold between dural entries of CN3 and CN4 | Meningohypophyseal trunk origin inferolateral trunk the medial loop of the ICA (less commonly) | Access to: Medial loop of intracavernous ICA and meningohypophyseal trunk | |
4 | Inferior triangle Superolateral triangle Infratrochlear triangle Parkinson's triangle | (B) CN4 (B) CN V1 (B) Dural fold between dural entries of CN4 and CN V1 | ICA (cavernous) CN 6 | Triangular area is narrow, but can be enlarged during surgical approaches via retraction or dissection of the trochlear nerve medially and the trigeminal nerve laterally. Expanding of this space allows the entire intracavernous segment of the ICA to be explored from lateral ring to proximal ring. Permits the CN6 to be completely exposed from its entry through Dorello’s canal to its exit through the superior orbital fissure | |
Lateral group Middle cranial fossa triangles | 5 | Anteromedial triangle Anterolateral triangle Mullan's triangle | (B) CN V1 (B) CN V2 (B) Between the superior orbital fissure and the foramen rotundum | Superior orbital vein, CN6 Sphenoid sinus Ophthalmic vein. | Further dissection within Mullan’s space allows for access to carotid-cavernous fistulas. |
6 | Anterolateral triangle Lateral triangle | (B) Maxillary nerve (B) Mandibular nerve (B) Between the foramen rotundum and foramen ovale | Lateral sphenoid wing Sphenoidal emissary vein Cavernous-pterygoid venous anastomosis | Through this window, lesions located in the lateral part of the cavernous sinus are uncovered Sphenoidal emissary vein (between cavernous sinus and pterygoid venous plexus), masses extending laterally in the cavernous sinus | |
7 | Posterolateral triangle Glasscock's triangle | (B) CN V2 (B) GSPN (B) Between foramen ovale and hiatus of greater petrosal nerve | Foramen spinosum horizontal petrous ICA Infratemporal fossa | Other possible structures that can be found when drilled: greater and lesser petrosal nerves, tensor tympani muscle, Eustachian tube, middle meningeal artery, foramen spinosum, infratemporal fossa, and most importantly, the horizontal petrous ICA • Identifies the triangular area of bone that must be removed to access horizontal intrapetrosal ICA for proximal control or bypass graft | |
8 | Posteromedial triangle Kawase's triangle | (B) CN5 ganglion (B) GSPN (B) Between hiatus of greater petrosal nerve and apex of petrous part OR CN5 ganglion, GSPN, Petrous ridge, Arcuate eminence (Superior semis circular canal) | IAM | Removing the bone in this triangle permits the petrous apex or petroclival area and internal acoustic meatus to be exposed. This section of petrous bone does not contain vascular or neural structures and can be drilled safely. | |
Posterior group Paraclival region triangle | 9 | Lateral triangle Inferolateral triangle inferolateral paraclival triangle | (A) Dural entry of CN4 (A) Dural entry of CN6 (A) Apex of petrous part | Porous trigeminii (Meckel’s cave). | Access to meckel's cave |
10 | Medial triangle Inferomedial triangle | (A) Dural entry of CN4 (A) Dural entry of CN6 (A) Posterior clinoid process | Porous abducens (Dorello’s canal) Gruber’s ligament | Access to dorello's canal | |
Posterior fossa | Trautmann’s triangle Retromeatal trigone | Jugular sinus Superior petrosal sinus Anteriorly by the posterior semicircular canal | Mastoid air cells Endolymphatic sac | Intracranial access via the retrolabyrinthine approach exposes a portion of the dura mater on the posterior side of the temporal bone that faces the cerebellopontine angle. Much of this area is resected during posterior petrosectomy Bone here is thin so infection can enter cerebellum from mastoiditis infection |
1-6 Mnemonic: Happy, Dolphins, Make, perfect, Moves, Always
Anterior cranial fossa triangles
Triangles around the cavernous sinus
Dolenc's triangle/Clinoidal Triangle/Antero-medial triangle
- Bordered
- Optic nerve
- Oculomotor nerve
- Exposed by removing the anterior clinoid process
- Contains
- Anterior 1/3 of triangle: Optic strut in its anterior part
- Coronal histological sections of the right cavernous orbital region.
- Froelich et al 2007
- FN, Frontal nerve; GSW, Greater sphenoid wing; IRM, Inferior rectus muscle; LN, Lacrimal nerve; LRM, Lateral rectus muscle; LSW, Lesser sphenoid wing; MRM, Medial rectus muscle; NeN, Nasociliary nerve; OA, Ophthalmic artery; SRM, Superior rectus muscle; SS, Sphenoid sinus.
- Middle portion: Clinoid segment in its midportion
- The anterior loop of the carotid artery lies within the floor of this triangle.
- This is the clinoid segment of the internal carotid artery (ICA) which is neither intracavernous nor intradural.
- The majority of carotid-ophthalmic aneurysms which appear to have an intracavernous component actually arise from the clinoid segment of the ICA and violate the distal dural ring.
- Posterior 1/3: Thin roof of the cavernous sinus in its posterior part.
Oculomotor Triangle
- Description: A triangular patch of dura where the oculomotor nerve enters the roof of the cavernous sinus.
- Margins: The posterior margin is formed by the posterior petroclinoid dural fold (extending from the petrous apex to the posterior clinoid process). The lateral margin is formed by the anterior petroclinoid dural fold (extending from the petrous apex to the anterior clinoid process). The medial margin is formed by the intraclinoid dural fold (extending from the anterior to the posterior clinoid).
- The temporal lobe has been elevated to expose the oculomotor and trochlear nerves as they enter the roof of the cavernous sinus.
- The oculomotor triangle is the triangular patch of dura through which the oculomotor nerve enters the roof of the cavernous sinus.
- The optic tract passes backward on the medial side of the uncus.
Supratrochlear Triangle
- Location: Situated between the lower surface of the oculomotor nerve and the upper surface of the trochlear nerve.
- Third Margin: Formed by a line joining the points where the oculomotor and trochlear nerves enter the dura.
- Note: This triangle is characterized as being very narrow.
Infratrochlear Triangle (Parkinson’s triangle)
- Location: Located between the lower margin of the trochlear nerve and the upper margin of the ophthalmic nerve.
- Third Margin: A line connecting the point of entry of the trochlear nerve into the dura to the site where the trigeminal nerve enters Meckel’s cave.
- Contents: Contains the posterior bend of the carotid artery and the origin of the meningohypophyseal trunk.
- Superior view of right side
1 = superoposterior triangle
2 = superior triangle
3 = middle triangle
4 = inferior triangle
5 = anteromedial triangle
6 = anterolateral triangle
7 = posterolateral triangle
8 = posteromedial triangle
9 = lateral triangle
10 = medial triangle
II = optic nerve
III = oculomotor nerve
IV = abducens nerve
V1 = ophthalmic nerve
V2 = maxillary nerve
V3 = mandibular nerve
VI = abducens nerve
TG = trigeminal ganglion.
- Coronal section through the cavernous sinus (shown in blue).
- The paramedian triangle allows access between the oculomotor and trochlear nerves and the infratrochlear triangle allows access between the trochlear and V1 nerves.
- The abducens nerve is seen medal to V1 and the cavernous internal carotid artery is seen in cross-section
- Legend III - oculomotor nerve
- IV - trochlear nerve
- VI - abducens nerve
- V1 - the ophthalmic branch of the trigeminal nerve
- V2 - the maxillary branch of the trigeminal Nerve
- V3 - the mandibular branch of the trigeminal nerve
- Anatomical Exposure and Regions
- The optic strut is exposed in the anterior part of the clinoidal triangle.
- The clinoid segment is exposed in the midportion.
- The roof of the cavernous sinus is exposed in the posterior part.
- The posterior bend of the internal carotid artery (ICA) and the origin of the meningohypophyseal trunk are exposed in the infratrochlear triangle.
- Dural Rings and Membranes
- The upper margin of the clinoid segment is surrounded by the upper dural ring.
- The upper dural ring is formed by the dura extending medially from the upper surface of the anterior clinoid.
- The lower dural ring defines the lower margin of the clinoid segment.
- The dura on the lower margin of the anterior clinoid is referred to as the carotidoculomotor membrane.
- The carotidoculomotor membrane separates the lower surface of the anterior clinoid from the upper surface of the oculomotor nerve.
- This membrane extends medially to form the lower dural ring.
- Internal Carotid Artery (ICA) and Branches
- The meningohypophyseal trunk arises near the posterior bend of the ICA.
- The meningohypophyseal trunk gives rise to the tentorial and dorsal meningeal arteries.
- The inferolateral trunk arises from the horizontal segment of the intracavernous carotid.
- Cranial Nerve Pathways
- The abducens nerve passes through Dorello’s canal.
- The abducens nerve passes between the lateral surface of the intracavernous carotid and the medial side of the ophthalmic nerve.
- The inferolateral trunk passes above the abducens nerve.
Triangle vs ICA relationship
- At lateral view of the right side for clinical approaches
1 = superoposterior triangle
2 = superior triangle
3 = middle triangle
4 = inferior triangle
5 = anteromedial triangle
6 = anterolateral triangle
7 = posterolateral triangle
8 = posteromedial triangle
9 = lateral triangle
10 = medial triangle
II = optic nerve
III = oculomotor nerve
IV = abducens nerve
V1 = ophthalmic nerve
V2 = maxillary nerve
V3 = mandibular nerve
VI = abducens nerve
VII = facial nerve
TG = trigeminal ganglion.
- Legend: ICA - internal carotid artery
- V1 - the ophthalmic branch of trigeminal Nerve
- V2 - the maxillary branch of trigeminal nerve
- V3 - the mandibular nerve of the trigeminal nerve (original image).
- Left posterolateral dissection of the anatomy of the inferomedial and inferolateral triangles.
- Legend: ICA - internal carotid artery
- V1 - the ophthalmic branch of trigeminal nerve
- V2 - the maxillary branch of trigeminal nerve
- V3 - the mandibular nerve of the trigeminal nerve
- III - oculomotor nerve
- IV - trochlear nerve
- VI - abducens nerve
Triangles of the middle cranial fossa
Important landmarks
- Arcuate eminence
- Superior semicircular canal
MDK (modified Dolenc-kawase) rhomboid
- Aka
- Fukushima rhomboid
- Temporal rhomboid
- Borders
- Gaserrian ganglia of V3: 13.2mm
- GSPN: 16.6mm
- Arcuate eminence: 16.4mm
- Petrous ridge: 22.2mm
- Area is around 2.9cm2
- An important anatomy to perform safe drilling in the anterior petrosal approach.
- The anteromedial corner of the temporal rhomboid is a safe point to begin drilling in the temporal rhomboid (*)
- Temporal rhomboidectomy provides the skeletonisation of the C6 internal carotid artery, the cochlea at the posterior genu of the C6 carotid, the internal auditory canal (IAC), and the inner petrosal dura.
- The vestibular nerve and facial nerve can be skeletonized at the distal end of IAC between Bill’s bar which indicates the beginning of the tympanic segment of the facial nerve.
- Contains the
- Location: between the greater petrosal nerve and the lateral edge of the trigeminal nerve (behind the point where the greater petrosal nerve passes below the lateral edge of the trigeminal nerve).
- Borders
- Anterior: Mandibular nerve (V3)
- Lateral: The major petrosal groove
- Is one of the anatomical landmarks of Kawase triangle.
- Lateral border of the Kawase triangle
- GSPN courses in this groove
- The GSPN (Greater Superficial Petrosal Nerve) is the most reliable superficial landmark on the middle cranial fossa for drilling of the petrous apex (Kawase’s triangle) in the extradural anterior transpetrosal approach (ATPA)
- The GSPN should be clearly recognized before drilling at Kawase’s triangle to avoid the risk of injury to the facial nerve and ICA.
- Especially, the GSPN can be considered as the superficial lateral border of anterior petrosectomy on the middle fossa to avoid risk of the ICA injury, because of the GSPN path running parallel in the sagittal plane to the ICA.
- GSPN confirmation for a safe extradural anterior petrosectomy and GSPN preservation to prevent symptomatic dry eye are not always easy to achieve.
- Both facial nerve-evoked EMG by antidromic GSPN stimulation and free-running facial muscle EMG monitoring are useful for the confirmation of the GSPN as a landmark for safe extradural anterior petrosectomy and for the preservation of the GSPN itself
- Formed between the
- Sphenopetrosal fissure
- Hiatus facialis
- Posterior: Internal auditory canal (IAC)
- The arcuate eminence (a marker of the Superior semicircular canal) and lies just posterior and lateral to the IAC.
- Medial: Petrous ridge/insertion of the tentorium
- Defines the location of the superior petrosal sinus.
- Contents
- Petrous apex
- IAC
- Cochlear
- Located in the angle formed by the GSPN and the facial nerve (CN VII, labyrinthine portion).
- Surgical Exposure:
- Drilling the bony floor of the triangle, specifically in the area behind the internal carotid artery and medial to the cochlea, exposes the lateral edge of the clivus.
- The posterolateral triangle (Glasscock’s triangle) is limited by V3 anteriorly, the GSPN medially, and an imaginary line from the origin of the MMA (foramen spinosum) to the origin of the GSPN from the geniculate ganglion.
- This triangle is an important landmark for exposing the petrous portion of the internal carotid artery. V1, V2=branches of CN V
- Aka:
- Posterolateral triangle
- Borders
- Lateral: line between the foramen spinosum and the arcuate eminence
- Medially: by the groove of the greater superficial petrosal nerve
- Anteriorly/Base: V3
- Content
- Foramen spinosum
- Horizontal petrous ICA
- Infratemporal fossa
- Opening the floor of the middle fossa in this triangle exposes the infratemporal fossa.
Kawase triangle
Glasscock's triangle
Anteromedial Triangle
- Location: Situated between the lower margin of the ophthalmic nerve and the upper margin of the maxillary nerves.
- Third Edge: Formed by a line connecting the point where the ophthalmic nerve passes through the superior orbital fissure and the point where the maxillary nerve passes through the foramen rotundum.
- Surgical Exposure: Removing bone in the medial wall creates an opening into the sphenoid sinus.
Anterolateral Triangle
- Location: Located between the lower surface of the maxillary nerve and the upper surface of the mandibular nerve.
- Third Edge: A line connecting the foramen ovale and foramen rotundum.
- Surgical Exposure: Opening the bone in the medial wall exposes the sphenoid sinus.
Paraclival Triangles
Inferolateral Paraclival Triangle
- Location: Situated on the posterior surface of the clivus and temporal bone.
- Borders
- Medial Margin: Formed by a line connecting the dural entry sites of the trochlear and abducens nerves.
- Upper Margin: Extends from the dural entrance of the trochlear nerve to the point where the first petrosal vein lateral to Meckel’s cave joins the superior petrosal sinus.
- Lower Margin: Formed by a line connecting the point where the abducens nerve enters the dura to the site where the first petrosal vein, lateral to the trigeminal nerve, joins the superior petrosal sinus.
- Contents:
- The medial edge of the inferolateral triangle extends between the dural entrances of the IVth and VIth nerves.
- The inferior limb extends from the VIth nerve to where the first vein lateral to Meckel’s cave joins the superior petrosal sinus and the superior limb extends from that vein to the dural entrance of the IVth nerve.
- The ostium of Meckel’s cave is located within the inferolateral triangle.
The porus, where the posterior trigeminal root enters Meckel’s cave, is situated in the center.
Inferomedial Paraclival Triangle
- Borders
- Upper Margin: Formed by a line extending from the posterior clinoid process to the dural entrance of the trochlear nerve.
- Lateral Margin: Formed by a line connecting the dural entrances of the trochlear and abducens nerves.
- Medial Margin: Formed by a line extending from the dural entrance of the abducens nerve to the posterior clinoid process.
The dura in this triangle constitutes the posterior wall of the cavernous sinus.
- The medial limb of the inferomedial triangle extends from the posterior clinoid to the dural entrance to the abducens nerve.
- The lateral limb extends between the dural entrances of the IVth and VIth nerves and the superior limb extends from the IVth nerve to the posterior clinoid.
- On the right side, there is an abnormal projection of the posterior clinoid process, which extends below the oculomotor nerve toward the petrous apex.
Posterior fossa triangles
Trautmann’s triangle
- Located in posterior fossa at the petrous part of the temporal bone.
- Bordered by:
- The bony labyrinth (anterior boundary)
- The sigmoid sinus (posterior boundary)
- The superior petrosal sinus (superior boundary)
- Surgical importance
- Crucial corridor for neurosurgeons during approaches to lesions around the cerebellopontine angle, petrous apex, and adjacent structures
- provides a window to reach the posterior part of the internal auditory canal and the posterior cranial fossa without crossing the labyrinthine structures, which helps preserve hearing
- Conditions which are often approached via Trautmann’s triangle
- Tumors (e.g., vestibular schwannomas, meningiomas)
- Vascular lesions
- Inflammatory conditions affecting the petrous apex or the cerebellopontine angle
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