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
- Clinoidal Triangle
- Location: Situated in the interval between the optic and oculomotor nerves.
- Internal Structure: Contains the optic strut in its anterior part, the clinoid segment in its midportion, and the thin roof of the cavernous sinus in its posterior part.
- Exposure: Exposed by removing the anterior clinoid process.
- 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
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 approach) 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
Glasscock's triangle
- Borders
- Posterior edge of foramen ovale
- Cochlea
- J(x) of GSPN and V3
- Content
- Foramen spinosum
- Horizontal petrous ICA
- Infratemporal fossa
- Opening the floor of the middle fossa in this triangle exposes the infratemporal fossa.
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.
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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