Paraclinoid Aneurysms


Paraclinoid Aneurysms

Paraclinoid aneurysms are common lesions. Although most are now detected at a small size, these aneurysms have a tendency to reach large and giant proportions, particularly in women. In addition, mirror image lesions are common in this location, at times complicating treatment paradigms.

From a surgical perspective, paraclinoid aneurysms can be difficult because of their intimate relationship to the anterior clinoid process, which can interfere with early establishment of proximal control ( Fig. 3.1 ). These aneurysms are exposed through a standard pterional craniotomy, as described in Chapter 1, with aggressive extradural removal of the sphenoid wing. When treating a small lesion, minimal opening of the proximal Sylvian fissure, to avoid tension on the brain and bridging Sylvian veins, is usually adequate. For larger lesions, a wider opening of the fissure is helpful, and an orbitocranial (OC) approach may be useful when treating large or giant aneurysms in this location.

In our experience, in almost all cases, the anterior clinoid process must be removed at least partially and the falciform ligament opened to mobilize the optic nerve safely prior to clip placement . The amount ofclinoid removal varies depending on the local anatomy. In some cases, only a small amount of bone removal is necessary, and often the bone has been thinned already by local pressure from the aneurysm ( Figs. 3.2, 3.3 ). In other instances, particularly in the setting of a short optic nerve (prefixed chiasm), we have found that a wide opening of the optic canal, at times all the way to the posterior orbit, has been necessary to allow for adequate mobilization of the optic nerve to expose the aneurysm properly without placing undue tension on the nerve itself ( Figs. 3.4, 3.5 ).

As a matter of personal preference, we have favored intradural rather than extradural removal of the clinoid. In the past, we used a high-speed diamond drill for clinoidectomy. Several gently curved, fine drill bits are available that optimize the surgeon’s view of the local anatomy during the drilling. For the past 5 years, we have used an ultrasonic bone-cutting device in all cases to avoid the use of a high-speed drill in close proximity to a thin-walled aneurysm. As the clinoid is removed, there is often a small amount of venous bleeding from the bone, which is readily controlled with bone wax applied using a microinstrument. Occasionally, the clinoid is highly pneumatized, and this may pose a risk for delayed cerebrospinal fluid (CSF) fistula development. In such cases, one should aggressively wax the bony opening, and we have sometimes used a small amount of muscle or fat to fill the opening at the conclusion of the procedure to avoid a delayed CSF fistula.

After removal of the clinoid, the falciform ligament is opened, and the optic nerve is freed. The aneurysm neck is then explored and the ophthalmic artery identified. On occasion, we have found the optic nerve to be densely adherent to the aneurysm dome. In such cases, the nerve can be released from under the falciform ligament and left adherent to the aneurysm dome as long as a clip can be worked across the aneurysm neck below the nerve. When treating an ophthalmic region aneurysm, visual impairment can result from overly aggressive manipulation of the optic apparatus with inadequate opening of the falciform ligament and optic canal, ischemic injury to the nerve or chiasm, occlusion of the ophthalmic artery, or thermal injury from drilling near the nerve. Following clip application, the clip itself may, on occasion, put pressure on the optic nerve or chiasm. In such cases, one can gently interpose a piece of collagen sponge material between the clip and the nerve, or a microsuture can be utilized to reposition the clip away from the optic apparatus ( Fig. 3.6 ).

(A) A left pterional craniotomy has been utilized to expose the proximal supraclinoid internal carotid artery (ICA) as well as the distal aspect of the small ophthalmic artery aneurysm (arrowhead), which can be seen distorting the optic nerve just proximal to the edge of the falciform ligament (arrow). (B) After a small amount of the anterior clinoid process is removed and the falciform ligament is opened, the aneurysm can be clipped without stretching the optic nerve (star). Note exposure of the proximal aneurysm neck and its interface with the ophthalmic artery (arrow). (C) The aneurysm has been clipped.
(A) After removal of a small part of the anterior clinoid process and opening of the falciform ligament, this bilobed aneurysm (arrows) is well visualized below the optic nerve (star). (B) Gentle microdissection is used to free the aneurysms from the undersurface of the optic nerve. (C) A single clip is used to obliterate both lesions.
(A) A tiny aneurysm (arrow) incorporating the origin of the ophthalmic artery (arrowhead) in a very young patient is exposed below the optic nerve (star). (B) The aneurysm has been repaired with a small clip, preserving the ophthalmic artery origin.
(A) A pale white optic nerve (star) is shown stretched over the dome of a carotid ophthalmic aneurysm on initial exposure through a pterional approach. The edge of the distal aneurysm neck (arrow) can be seen below the nerve. (B) The dura has been opened, and the anterior clinoid process has been partially removed. The edge of the falciform ligament (arrow) has been left in place and still tethers the optic nerve. (C) The ligament has been opened and the optic nerve more fully exposed, revealing the true extent of the distortion of the nerve by the underlying aneurysm. (D) The aneurysm has been clipped. Note the relaxation of the nerve following repair of the underlying aneurysm.
(A) The dura has been opened over the anterior clinoid process, which has been partially removed (white arrow), leaving the falciform ligament tethering the optic nerve over the underlying aneurysm. Note how the entire aneurysm is essentially hidden from view by the stretched nerve, with only the interface between the distal neck and the ICA (arrowhead) visible. (B) Once the ligament has been opened, the optic nerve (star) has been freed all the way into the posterior orbit, and the broad-based underlying aneurysm (arrowhead) is visualized. A small amount of dural reflection (arrow) remains adherent to the lateral aspect of the aneurysm. (C) The aneurysm has been repaired with a clip, and the nerve is nicely relaxed.

Paraclinoid aneurysms include a variety of anatomically distinct aneurysm subtypes. True ophthalmic aneurysms are the simplest to treat, although they require the most manipulation of the optic apparatus. Carotid cave and superior hypophyseal aneurysms require facility with skull base dissection to enable adequate exposure and clipping. It may be difficult to visualize the proximal neck of a posteriorly directed paraclinoid aneurysm, and the surgeon requires a good intuitive sense of the three-dimensional anatomy in such cases ( Fig. 3.7 ) . In all these lesions, the aneurysm dome can become intimately adherent to the basal dural reflections, which can significantly complicate the final dissection of the aneurysm. In addition, it may be difficult to predict which aneurysms are partially extradural, and complete clipping may require opening of the proximal and distal dural rings of the cavernous sinus. Bleeding from the cavernous sinus can be bothersome, and surgeons treating these lesions should be comfortable with this possibility.

Large and giant aneurysms in this location are more difficult because of their distortion and compression of the optic apparatus ( Fig. 3.8 ). Options for proximal control include exposure of the cervical internal carotid artery (ICA) through a neck incision, the use of a balloon microcatheter positioned endovascularly in the cervical ICA, or exposure of the petrocavernous carotid through a complex skull base dissection. When treating giant paraclinoid aneurysms, we generally expose the cervical ICA for possible suction decompression of the aneurysm. The endovascular placement of a balloon in the cervical internal carotid artery represents a reasonable alternative, although we have found it faster and more reliable to primarily expose the cervical carotid artery. The use of an endovascular balloon for any period of time carries a thromboembolic risk, and repeated inflation and deflation of the balloon can result in a carotid dissection. In addition, we have occasionally had trouble achieving adequate decompression with a balloon. When using suction decompression, it is important to apply a clip distal to the aneurysm across the supraclinoid internal carotid artery prior to beginning the suction to avoid stealing important collateral flow from the ipsilateral hemisphere. Despite temporary occlusion and suction decompression, giant paraclinoid lesions can be very challenging to clip when densely adherent to the basal dura or the optic apparatus. Examples of giant paraclinoid aneurysms treated with direct clip reconstruction and with bypass and occlusion are included in Chapter 9.

(A) A large ophthalmic-region aneurysm has been exposed by opening the falciform ligament after partial removal of the anterior clinoid process (black star). The optic nerve (white star) is displaced medially by a heavily atheromatous, nonfilling portion of the aneurysm (black arrowhead). The ICA (white arrow) and the ophthalmic artery (white arrowhead) are seen. (B) A fenestrated clip has been used to repair the aneurysm, leaving the atheromatous, nonfilling potion of the aneurysm open in the fenestration, as a simple clip would not close because of the calcification in the wall. Note how the medial aspect of the fenestration indents the optic nerve. (C) A 10-0 microsuture (white arrow) has been used to pull the clip away from the optic apparatus by suturing the clip down to the basal dura.
A proximal paraclinoid aneurysm (black arrowhead) has been clipped using an angled fenestrated clip around the ICA (white arrow). The optic nerve is seen as well (black star).
(A) A lateral internal carotid arteriogram reveals a large paraclinoid aneurysm in a young woman with visual disturbance. (B) The aneurysm has been exposed through a pterional approach, revealing the optic nerve (star), supraclinoid ICA (arrowhead), and third cranial nerve (arrow). (C) The aneurysm has been clipped and deflated (arrowhead) to decompress the optic nerve. (D) Postoperative angiography reveals occlusion of the aneurysm. This lesion is treated in .

When treating a ruptured paraclinoid aneurysm, the issue of proximal control becomes even more critical. In the setting of a severe, unexpected intraoperative rupture of a carotid ophthalmic aneurysm, we have used an intravenous infusion of adenosine to induce transient cardiac standstill, providing temporary flow arrest when proximal control could not be achieved easily. Note that bilateral ophthalmic aneurysms, when small, can often be clipped via a unilateral approach, dissecting and clipping the contralateral aneurysm by working underneath the opposite optic nerve ( Fig. 3.9 ) ( Table 3.1 ).

A left pterional craniotomy has been performed, and bilateral small ophthalmic region aneurysms have been exposed and clipped by opening the falciform ligaments to mobilize the optic nerves (stars) bilaterally.

Paraclinoid Aneurysm Pearls and Pitfalls

Use standard pterional craniotomy with limited opening of proximal Sylvian fissure.

Use aggressive drilling of the sphenoid wing and orbital roof to create a low, flat plane of approach.

Use a wider Sylvian opening and possible orbitocranial approach for larger and giant aneurysms.

Proximal control may be hindered by the anterior clinoid process hiding the proximal aneurysm neck and proximal ICA.

Remove the clinoid and open the falciform ligament to enable optic nerve mobilization.

Consider cervical ICA exposure or endovascular balloon placement in cervical ICA for large or giant aneurysms.

Identify and protect the ophthalmic artery itself.

The aneurysm neck must be fully exposed and freed prior to clip placement.

When using suction decompression, be sure to apply distal clip to supraclinoid ICA prior to suction.

Remember that the external carotid artery (ECA) may supply collaterals via the ophthalmic artery, preventing adequate decompression or resulting in ongoing bleeding if aneurysm ruptures intraoperatively.

Contralateral paraclinoid aneurysms can usually be treated at the same setting, particularly when small.

Large and giant aneurysms may be adherent to the optic apparatus and basal dura and may defy primary clipping attempts.

Visual impairment can result from:

  • Overly aggressive manipulation of optic apparatus without adequate opening of falciform ligament and optic canal

  • Ischemic injury to nerve or chiasm or occlusion of ophthalmic artery itself

  • Thermal injury from drilling near nerve

Carotid occlusion or stenosis may result in hemispheric ischemic insult, depending on adequacy of collateral circulation.

Unrecognized opening of pneumatized anterior clinoid process can predispose to delayed CSF fistula and/or infection.

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Jun 30, 2020 | Posted by in NEUROSURGERY | Comments Off on Paraclinoid Aneurysms
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