Supraclinoid Internal Carotid Artery Aneurysms


Supraclinoid Internal Carotid Artery Aneurysms

The majority of aneurysms involving the supraclinoid internal carotid artery (ICA) arise at the origins of the posterior communicating or anterior choroidal arteries. We will address aneurysms arising at these locations individually. In addition, over the past decade, increasing recognition has been given to a unique subset of aneurysms involving the ventral supraclinoid ICA not associated with a clear branch point or perforating vessel. These lesions are often dissecting aneurysms. They tend to have a highly malignant natural history and can be extremely unstable.

A pterional craniotomy is utilized for the treatment of aneurysms involving the supraclinoid portion of the ICA. For lesions arising at the origins of the posterior communicating or anterior choroidal arteries, the Sylvian fissure need be opened only to the level of the carotid bifurcation. In most cases, proximal control is readily achieved. We will discuss the management of ventral supraclinoid aneurysms as a separate entity.

Posterior Communicating Artery Aneurysms

Posterior communicating artery (PCommA) aneurysms have traditionally been thought of as “easy” aneurysms from a surgical perspective. In academic training programs, these lesions have often been considered reasonable fodder for mid-level residents yearning to clip their first aneurysms. In our experience, there is great variability in the difficulty associated with these lesions. Although most will be visible immediately upon opening the arachnoid lateral to the ICA just above the level of the optic nerve, these aneurysms can sometimes be obscured from view by a large anterior clinoid process, which can also compromise early establishment of proximal control ( Figs. 4.1, 4.2 ). In addition, when the supraclinoid ICA itself is short or lies in a very horizontal orientation, the aneurysm may point deeply away from the surgeon during a routine pterional exposure. Most often, however, these lesions are well exposed through a standard pterional approach.

Much has been written about proper patient positioning when treating a ruptured PCommA aneurysm based on whether or not the patient presents with a third-nerve palsy. In general, if the patient does not have a third-nerve palsy, then the aneurysm is suspected to be directed laterally, where its dome can adhere to the temporal lobe. In such cases, too much rotation of the head can encourage the surgeon to utilize aggressive temporal lobe retraction, which can cause the aneurysm to rebleed. In our experience, it is best to avoid deep temporal retraction in all PCommA aneurysms, and a standard pterional approach with the head turned no more than 45 degrees works best in such cases. By opening the proximal Sylvian fissure, the surgeon can identify the neck of the aneurysm first, and a small bit of subpial resection can be used to free the aneurysm dome if necessary prior to clip placement. This maneuver avoids any traction being placed on the deep temporal lobe, which can, in theory, result in tearing of the aneurysm.

(A) A small, very thin-walled PCommA aneurysm (arrowhead) on the right side is visualized through a pterional approach. Note the proximity to the third cranial nerve (star). (B) The aneurysm has been repaired with a clip. The optic nerve (star) and the proximal ICA (arrowhead) are seen. Note the normal PCommA origin (arrow), which is visible between the clip and the parent ICA.

For all PCommA aneurysms, the proximal Sylvian fissure should be opened sharply, exposing the supraclinoid ICA at the level of the optic nerve . This maneuver will establish proximal control in most cases. Depending on the size of the aneurysm, the surgeon will have to address both the PCommA itself as well as the neighboring anterior choroidal artery (AChA). The PCommA should be identified and its origin preserved ( Fig. 4.3 ). In some cases, the neck of the aneurysm may incorporate the origin of the artery, and a carefully placed clip will enable the reconstruction of the origin of the PCommA. In rare cases, when the PCommA origin is incorporated into the aneurysm neck and there is clear filling of the posterior cerebral artery (PCA) and the PCommA itself in retrograde fashion from the basilar artery, the PCommA origin can be occluded along with the aneurysm neck. In these very rare cases, we always check an intraoperative vertebral arteriogram to be sure the PCA as well as the PCommA both fill promptly. The PCommA typically gives rise to critical anterior thalamoperforating vessels, and these can be injured by overly long clip blades reaching past the aneurysm neck toward the perimesencephalic cistern.

(A) A right pterional craniotomy has been performed and the proximal supraclinoid ICA and the optic nerve (star) have been exposed. The PCommA aneurysm is not visible because of the large anterior clinoid process (arrowhead) and the horizontal orientation of the internal carotid artery. (B) A portion of the clinoid has been removed to allow for exposure of the aneurysm. (C) The aneurysm has been repaired with a fenestrated clip encircling the ICA.
(A) A pterional craniotomy has been performed to expose the neck (star) of a large PCommA aneurysm. The optic nerve (arrow) and supraclinoid ICA (arrowhead) are seen. (B) The true neck of the aneurysm (arrow) and the origin of the PCommA (white arrowhead) are now visible. Note how most of the aneurysm is hidden below the edge of the tentorium (white arrow). (C) The aneurysm has been clipped, and the large PCommA origin is visible (arrow) proximal to the clip.

Before operating on a PCommA aneurysm, it is important to understand the anatomy of the ipsilateral PCA based on preoperative angiography ( Fig. 4.4 ). If the PCommA represents a fetal PCA (i.e., the ipsilateral P1 is atretic), then occlusion or stenosis of the PCommA can result in a serious PCA infarction with complete hemianopsia. Ischemic injury due to loss of the anterior thalamoperforators can further complicate the situation. As a result, one should not sacrifice a fetal PCommA.

If the AChA is adherent to or running along the aneurysm dome, it must be thoroughly dissected away, at least from the aneurysm neck, prior to clip placement. AChA occlusion can result in contralateral hemiparesis, hemisensory loss, and hemianopsia, and such occlusion should be avoided in all situations ( Fig. 4.5 ) .

PCommA aneurysms are situated close to the third cranial nerve. An expanding PCommA aneurysm can result in partial or complete third-nerve palsy, a situation that should generally be treated with urgent repair of the aneurysm before a life-threatening subarachnoid hemorrhage (SAH) occurs ( Fig. 4.6 ). There is some controversy as to whether open surgery or endovascular coiling should be performed in this setting. In our experience, the third-nerve palsy tends to improve in the majority of cases treated in either fashion, although there may be a slight advantage to open surgery, which enables immediate deflation of the aneurysm and decompression of the nerve.

Artist’s overlay rendering illustrates the positioning of a PCommA aneurysm prior to opening of the proximal Sylvian fissure. Note the extent to which the fissure must be opened to expose the proximal and distal neck of the aneurysm.
(A) A lateral preoperative internal carotid arteriogram demonstrates a large aneurysm (arrow) of the PCommA as well as a distal ACA aneurysm (arrowhead). (B) Operative photomicrograph reveals the large posterior communicating region aneurysm (circle) as well as a smaller anterior choroidal aneurysm (star) with the AChA (arrowhead) sandwiched between the two aneurysms. The optic nerve is identified as well (arrow). (C) An intraoperative angiogram demonstrates good clip reconstruction of the aneurysms with preservation of the PCommA (arrow) and AChA (arrowhead). This surgical procedure is shown in . The incidentally noted distal ACA aneurysm was clipped in a subsequent surgery.

When PCommA aneurysms become large, they can become more difficult to treat using simple neck clipping. One important surgical strategy involves the use of fenestrated clips, often with right-angle blades, placed around the ICA to occlude the aneurysm neck ( Fig. 4.7 ). In these cases, one must be particularly careful to avoid compromising the origin of the AChA.

(A) A small posterior communicating artery aneurysm presenting with a partial third-nerve palsy is exposed. Note the thin blister-like area (arrowhead) at the aneurysm base, the origin of the PCommA (arrow), and the proximity to the third cranial nerve (star). (B) The aneurysm has been clipped, preserving the PCommA origin (arrow).
(A) A pterional craniotomy has been performed, revealing the frontal (arrowhead) and temporal (star) lobes. (B) The proximal Sylvian fissure has been opened to expose a giant, partially thrombosed aneurysm of the PCommA. A portion of the aneurysm is seen as a whitish gray structure underneath the suction tip and behind the supraclinoid ICA (star). (C) A more magnified view reveals the aneurysm (star), the optic nerve (arrowhead), and the third nerve (arrow). (D) The aneurysm has been reconstructed using a right-angled fenestrated clip applied around the internal carotid artery. Note how the aneurysm dome is beginning to turn blue. (E) An intraoperative angiogram demonstrates reconstruction of the supraclinoid ICA (arrow) without residual filling of the aneurysm.

Finally, PCommA aneurysms will occasionally present with a large temporal lobe hematoma or a subdural hematoma, resulting in a life-threatening herniation syndrome. A preoperative CT scan with contrast will often show the underlying aneurysm in such cases, and the patient is brought to the operating room on an emergency basis without a formal preoperative arteriogram. A generous craniotomy is performed to enable decompression, and then an intraoperative angiogram is performed to assess the neurovascular anatomy. In general, one can evacuate some of the hematoma to decompress the brain without rupturing the aneurysm. In these cases, we prefer to open the proximal Sylvian fissure, expose the aneurysm neck, and clip the aneurysm in standard fashion, rather than working through the hematoma cavity to reach the aneurysm. Once the aneurysm has been clipped, remaining hematoma is removed, and a decision can be made whether the bone flap can be replaced safely or whether the degree of brain swelling mandates that the flap be temporarily stored for later re-implantation ( Table 4.1 ).

Posterior Communicating Artery Aneurysm Pearls and Pitfalls

Use standard pterional craniotomy; avoid turning the head more than 45 degrees.

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

Open proximal Sylvian fissure sharply to expose the supraclinoid ICA at the level of the optic nerve for proximal control.

Not all PCommA aneurysms are simple; proximal control can be an issue in patients with very short and horizontal supraclinoid ICA segments.

The AChA and PCommA should be identified and preserved.

The PCommA gives rise to critical thalamoperforating arteries.

The PCommA should never be sacrificed unless one is absolutely sure there is a healthy P1 segment that fills the distal PCA and PCommA.

A fenestrated clip can be used to reconstruct the ICA in larger lesions, but watch the AChA origin.

Identify the origin of the AChA and free the AChA from the aneurysm neck as needed.

Subpial resection along aneurysm dome may be preferable to deep temporal lobe retraction if dome must be freed for proper clip placement.

Beware of following a hematoma cavity down to a ruptured aneurysm without first achieving proximal control and a good understanding of the critical anatomy at the neck of the aneurysm.

Occlusion of the PCommA can result in a PCA infarct with anterior thalmoperforating injury as well.

Occlusion of the AChA can result in contralateral hemiparesis, hemisensory loss, and hemianopsia.

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Jun 30, 2020 | Posted by in NEUROSURGERY | Comments Off on Supraclinoid Internal Carotid Artery Aneurysms
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