366 microsurgery of paraclinoid aneurysm

Microsurgery of Paraclinoid Aneurysm

Youmans chapter 366Rose Du, Arthur L. Day

5/01/2016

Definition• aneurysms arising from the internal carotid

artery (ICA) in close proximity to the anterior clinoid process

• beyond the venous lumen of the cavernous sinus and proximal to the origin of the posterior communicating artery—the clinoidal and ophthalmic segments

Osseous Anatomy

Dural anatomy

Neural structure

Vascular structure

Vascular structure

• Ophthalmic segment– ophthalmic artery : supplies the optic nerve

through perforating branches and the retina through the central retinal artery

– superior hypophyseal artery : supply the superior aspect of the pituitary stalk and gland, a portion of the cavernous sinus dura, and the posterior optic nerve and chiasm.

• Clinoidal segment

Aneurysm classification

• Clinoidal Segment Aneurysms– Anterolateral Variant– Medial Variant

• Ophthalmic Segment Aneurysms– Ophthalmic Artery Aneurysms– Superior Hypophyseal Artery Aneurysms– Dorsal Variant Aneurysms

Clinoidal Segment Aneurysms


• Anterolateral Variant• dorsalateral projection• toward the dural ring underneath the ACP• small : erode the optic strut and undersurface of the

ACP to cause monocular visual loss from ipsilateral optic nerve compression within the optic canal

• large : secondarily compress the visual system (nerve or chiasm) within the subarachnoid space


• Medial Variant• enlarges toward the sphenoid sinus and sella• hypopituitarism, pituitary apoplexy• rupture into the sphenoid sinus may cause life-

threatening epistaxis

Ophthalmic Segment Aneurysms


• Ophthalmic Artery Aneurysms– distal to and in relation to the origin of the

ophthalmic artery– project dorsally or dorsomedially– elevate the lateral edge of the nerve against the

falciform ligament pressure to superior surface of the nerve inferior nasal field defect nasal field defect + superior temporal field loss in the contralateral eye

– ipsilateral blindness with marked contralateral deficits


• Superior Hypophyseal Artery Aneurysms– association with the superior hypophyseal artery– parasellar variant (carotid cave aneurysm)

• inferiorly toward the sella into the carotid cave• usually asymptomatic,unlikely to rupture• medial projection and proximity to ICA perforators

also makes them more difficult to treat– suprasellar variant

• projects superiorly into the suprasellar space• can result in bilateral visual field defects


• Dorsal Variant Aneurysms– rare– arise along the dorsal surface of the ICA distinctly

distal to the ophthalmic artery origin– unrelated to any arterial branch point– “blisters” on the dorsal carotid surface– Visual loss or a reliable relationship with the optic

nerve or chiasm is not consistently seen with the dorsal variant

Indications for treatment

• Clinoidal segment– Small symptomatic lesions

• visual deficits or focal, unrelenting headaches• remove

– Small asymptomatic aneurysms(<1 cm)• conservatively and radiographic follow-up

– Most large (≥1 cm)• extended through the overlying dural coverings into the

subarachnoid space• risk for ICH• remove

Indications for treatment

• Opthalmic segment– located within the subarachnoid space– have at least some risk for rupture and intracranial

hemorrhage– patients presenting with visual loss should be

treated urgently

Preoperative evaluation

• CT brain– SAH– Focal erosion of ACP,optic strut

• MRI,MRA– aneurysm’s relationship to soft tissue structures

• 4-vessel angiography : gold standard

anterolateral variant aneurysm Vs. low-lying ophthalmic artery aneurysm

• focal bony erosion evident on CT or MRI• origination proximal to the typical take-off of the

ophthalmic artery• a subtle “double density” along the anterolateral

ICA wall indicating the lesion’s proximal nature• aneurysm projection dorsal and lateral to the ICA • an angiographic “waist” marking the

penetration of the lesion through the overlying dural coverings into the subarachnoid space

medial variant Vs. superior hypophyseal artery aneurysm

medial variant superior hypophyseal artery

Relation to diaphragma sella

beneathAneurysm down to sellar

SuperiorAneurysm parasellar or

suprasellar spaceNeck narrow wideLateral view proximal to Opthalmic a.

Double density below ACParise on the posterior or posteromedial ICA wall

Bony erosion none none

Preoperative evaluation

• visual field testing• cervical carotid bifurcation• prophylactic ATB• control BP• mannitol

Positioning and Exposure• supine on the table with a shoulder roll• head is elevated above the heart, turned 45 to 60

degrees • maxilla is at the highest point• cervical carotid region preparation• skin incision : midline to the zygoma• pterional craniotomy• orbital osteotomy• lateral sphenoid ridge and the posterior portion of the

orbital roof and the lateral orbital wall

Anterior Clinoidectomy• Extradural removal

– high-speed diamond drill– cavernous sinus bleeding

• Intradural removal– dural incision : tip of ACP to edge of ridge resection– second incision : perpendicular to the first near the clinoid tip

extends to and includes sectioning of the falciform ligament– ACP removal– Unroof optic canal– Drilled optic struct

Clinoidal Segment Aneurysms• anterior clinoidectomy and optic strut removal• proximal control in the cervical region• circumferential sectioning of the dural ring • Anterolateral variant

– To eliminate the proximal neck, the clip blades must pass up to or proximal to the COM

– avoid injuring the oculomotor nerve,lateral to COM

• Medial variant– dome of the aneurysm may be adherent to the pituitary stalk and

surrounding dura : dissecting– spare the ophthalmic and any superior hypophyseal or other

perforating vessels


• Opthalmic a. aneurysm– safe than other– anterior clinoidectomy– falciform ligament section

• Superior hypophyseal a. aneurysms– more complex– the most difficult part of the dissection is usually in the

inferior and medial aspect of the aneurysm– perforator injury can lead to visual loss– Preserve : P-com a.,thalamus perforator branchs


• Dorsal carotid wall aneurysms– easier identification of the proximal neck– more fragile can rupture easily during clip

placement– trapping of the affected segment between temporary

clips to reduce pulsations and pressure before clipping

Giant and Complex Aneurysms

• paraclinoid aneurysms are frequently gigantic in size

• temporary proximal cervical carotid ligation• for aneurysm relaxation or collapse

– Trapping– retrograde cervical or intra-aneurysmal suction

decompression • lesion is then open, removal of intraluminal

thrombus before final clip placement

Closure

• A pneumatized optic strut is found in about 10% of patients

• The dural leaves covering the medial sphenoid wing are then closed primarily, followed by watertight closure of the more superficial dural opening

• Bone flap return• Temporalis muscle and fascia are sutured

Surgical complications and outcome

• excellent outcomes• complications

– the ICA,arterial perforators, – cranial nerves

• Visual field defect : improve,stable,worsen• Mechanical injury : manipulation of the optic nerve against

the falciform ligament• Thermal injury : occur during drilling of the anterior clinoid

process• Perforator injury : avoided by wide exposure and dural ring

sectioning

366 microsurgery of paraclinoid aneurysm

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