Dolenc technique

View Details

Status

Done

Parent item

Anterior fossa approaches

Indication

• Access to Lesions in the Cavernous Sinus:
• Tumours
• Skull base tumours
• Intracavernous Vascular Lesions
• Carotid-Ophthalmic Aneurysms
• Allows control of the Petrous ICA for proximal control and using the petrous ICA for anastomsis

Surgical technique

Patient Positioning

• Supine position

• Head:
• Extended 15°
• Rotated 30°

Pterional craniotomy

• Extends anteriorly along the superior orbital rim to the midpoint of the orbit and inferiorly to the zygoma.

Extradural Stage (Bone Removal)

• This phase involves removing bone from the anterior and middle cranial fossae to "unlock" the neurovascular structures in the skull base

• Superior view of the skull base depicting areas o1 bone to be removed at the extradural phase
• la = posterior two-thirds of the orbital floor
• lb = roof of the optic canal;
• 2 = anterior clinoid process;
• 3 = lateral bony wall of the superior orbital fissure;
• 4 = bony rim of the foramen rotundum;
• 5 = bony rim of the foramen ovale;
• 6 = bone of Glasscock's triangle overlying the horizontal portion of the petrous carotid artery

Step 1a: Orbital Roof exposure:

• The dura is separated from the floor of the anterior cranial fossa, and the posterior two-thirds of the orbital roof is removed.

• Do not go too medial into the cribriform plate otherwise might enter the sphenoid and ethmoid sinus

 

Step 1b: Optic Canal exposure:

• The bony roof of the optic canal is removed using a diamond burr, which is essential to permit mobilisation of the optic nerve and avoid injury during the subsequent dissection of the anterior clinoid process.

Step 2: Anterior Clinoid Process (ACP):

• The ACP is cored with a diamond burr, leaving a thin shell of cortical bone that can be fractured inward.

• This step exposes the clinoid segment of the Internal Carotid Artery (ICA) and disconnects the ACP from the skull base.

• This process can also be achieved by peeling the dura off the ACP, literally opening it up for the anticlinoidecotmy.

• This will also expose the bony strut beneath the optic nerve.
• Removal of the medial sphenoid wing and bony strut disconnects the anterior clinoid process from the skull base.

• The anterior clinoid process lies within the Dolenc’s triangle bordered by the optic nerve medially and oculomotor nerve laterally.
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.

Step 3: Superior Orbital Fissure (SOF):

• The lateral bony wall of the SOF is thinned, fractured, and removed.

• This is done by removing the medial sphenoid wing

• This will expose the meningio-orbital band

Step 4: Foramen Rotundum:

• A small island of bone separates the inferior aspect of the superior orbital fissure from the foramen rotundum.

• The anterolateral rim of the foramen is removed, permitting mobilization of the maxillary division (V2) of the trigeminal nerve.

 

Step 5: Foramen Ovale:

• Elevation of the middle fossa dura is continued to the vertical inclination of the petrous pyramid revealing
• Foramen spinosum: The middle meningeal artery is sacrificed.
• Foramen ovale: The anterolateral boundaries of the foramen ovale are expanded enabling mobilization of the mandibular nerve

Step 6: Glasscock's Triangle:

• The greater superficial petrosal nerve is sacrificed to avoid traction injury to the geniculate ganglion and facial nerve.

• The bone of Glasscock's triangle is removed with a diamond burr exposing the lateral loop of the ICA within the petrous bone.
• Unroofing of the petrous bone over the ICA should not proceed posteriorly beyond the point where the ICA turns vertically if injury to the cochlea is to be avoided.
• Exposure of the petrous ICA permits proximal arterial control and offers a potential site for bypass vascular grafting

Glasscock's triangle

• 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.

Intradural Stage (Neurovascular Exploration)

Step 1: Dural Opening:

• Along the line of the sylvian fissure.

• Extended medially, perpendicular to the optic nerve

• Laterally across the temporal lobe.
• Parallel to the middle fossa dura

Step 2: Carotid Rings:

• The ICA is fixed by two dural rings:
• Proximal ring is the exit point of the ICA from the cavernous sinus
• Distal ring is the point where the ICA becomes intradural.

• The clinoid segment of the ICA lies between these two rings.

• These tings are sectioned allowing
• Mobilisation of the clinoid segment of the ICA AND
• Entry into the anterior cavernous sinus

• Step 3: Oculomotor Nerve (III):
• The dura overlying the third nerve is incised, avoiding the trochlear nerve.
• The oculomotor nerve is identified as it enters the edge of the tentorial dura lateral to the posterior clinoid process.
• The dura overlying the third nerve is incised using an arachnoid knife.
• This incision is carried rostrally to the point at which the third nerve crosses the ICA (anterior loop)
• This avoids injury to the trochlear nerve which crosses over the oculomotor nerve in the superior orbital fissure.
• The deep membranous layer of the lateral wall of the cavernous sinus separates these nerves from the venous channels of the cavernous sinus.

• Step 4: Trochlear Nerve (IV):
• The trochlear nerve is identified as it enters the edge of the tentorial dura posterolateral to the oculomotor nerve.
• Dissection of dura overlying the fourth nerve is continued anteriorly into the superior orbital fissure
 

• Step 5: Trigeminal Nerve (V):
• The ophthalmic division (V1) is identified rostrally near Superior orbital fissure and its dural covering is dissected
• Dissection is carried posteriorly toward Meckel's cave, exposing the lateral wall of the cavernous sinus.
• Meckel's cave may be exposed by further dissection of dura from the trigeminal ganglion and its second and third divisions.
• The trigeminal ganglion is separated from the ICA by the bony floor of Meckel's cave which may be incompetent

 

• Step 6: Abducens Nerve (VI):
• The abducens nerve enters the cavernous sinus via Dorello's canal.
• The abducens nerve is identified by retraction of the ophthalmic division of the trigeminal nerve.
• This nerve, which may be duplicate or triplicate, is the only cranial nerve truly within the cavernous sinus.
• Lies lateral to the ICA.
• The meningohypophyseal artery can be identified at the junction of the abducens nerve and the ICA

Pros and cons

Pros

• Anatomical Unlocking:
• The removal of specific bony structures in the extradural stage is the key to "unlocking" the neurovascular structures for intradural exploration, making the complex contents accessible.

• Vascular Control:
• The systematic application of this approach facilitates control of the arterial and venous circulation.
• It obviates the need for circulatory arrest, a high-risk method previously used.
• Removal of the bone in Glasscock's triangle exposes the petrous ICA, permitting proximal arterial control.

• Reduced Bleeding during Trans-Cavernous Dissection:
• When utilizing the crucial technique of cutting the lateral margin of the orbital meningeal band and peeling the dura off the true cavernous membrane, the surgeon won't see much bleeding.

• Facilitates Anterior Clinoidectomy (ACP):
• The dissection involved in the approach literally opens up the ACP for the anticlinoidecotmy, making the removal of the ACP easier than "drilling... like you're drilling a molar tooth in a small cavity".

• Extensibility:
• The approach can be extended by combining it with an angular petrous ectomy and tentorial cutting to reach deeper structures, such as the p1 segment, superior cerebellar artery, and the lateral brainstem.

Cons

• High Risk to Neural Function:
• Cranial Nerve Injury:
• Cutting the orbital meningeal band will not harm the cranial nerves (III, IV, V1) as long as the surgeon stays laterally. This implies that performing the dissection incorrectly (i.e., too medially) carries a risk of nerve injury.

• Carotid Artery Risk:
• If the surgeon drills the posterior clinoid process (PCP) and goes through it, there is a risk of injuring the top of the carotid.

• Cochlear Injury Risk:
• During the extradural removal of bone in Glasscock's triangle, unroofing the petrous bone over the ICA should not proceed posteriorly beyond the point where the ICA turns vertically, as this could injure the cochlea.