Aneurysms of the Carotid Bifurcation


Aneurysms of the Carotid Bifurcation

Aneurysms arising at the bifurcation of the internal carotid artery (ICA) are common and can be challenging because of the frequent small perforating vessels that can be adherent to, or hidden by, these lesions. Both the recurrent artery of Heubner as well as A1 and M1 perforators will often cross these aneurysms and can be densely stuck to the aneurysm’s neck or dome.

Proper exposure of these lesions requires visualization of the proximal A1 and M1 segments, and the amount of opening of the Sylvian fissure should be guided by the size and orientation of the aneurysm in these cases. As a rule, the proximal aspect of the fissure is opened sharply to reach the ICA bifurcation. This will enable visualization of the aneurysm neck. We have found it important to open the fissure further in most cases, exposing at least some length of the M1 segment ( Fig. 5.1 ). In general, we prefer to dissect these aneurysms completely out of their beds, reflecting them forward to see all perforators, and then applying a permanent clip to the neck ( Fig. 5.2 ). This may require a small amount of subpial resection of the deep frontal lobe, which has not carried any clinical consequence in our experience. This technique is illustrated in several videos in this collection ( Fig. 5.3 ). Once mobilized, these aneurysms can usually be clipped in straightforward fashion ( Fig. 5.4 ).

ICA bifurcation aneurysms can point anteriorly, superiorly, or posteriorly. Those directed either anteriorly or superiorly are more straightforward from a surgical perspective, as they are more readily exposed through a standard pterional craniotomy ( Fig. 5.5 ). Posteriorly directed lesions point away from the surgeon and can be more difficult to expose. The surgeon must carefully identify, dissect, and separate the perforators running along the ICA bifurcation to expose the aneurysm neck ( Fig. 5.6 ). These lesions can then be treated either by applying a clip over the top of the bifurcation (most common) or by working along the lateral aspect of the distal ICA above the anterior choroidal artery (AChA). In the latter instance, the surgeon must be careful not to injure the AChA. When clipping a carotid bifurcation aneurysm, it is important to avoiding placing the clip too low on the parent artery, potentially stenosing the A1 or M1 segments.

In the setting of a subarachnoid hemorrhage (SAH), establishing proximal control for an ICA bifurcation aneurysm requires access to the proximal supraclinoid ICA as well as the A1 segment. Assuming the presence of a patent anterior communicating artery (ACommA) as well as normal bilateral A1 segments, placing a temporary clip on the supraclinoid ICA may only minimally decrease the bleeding from an ICA bifurcation aneurysm that ruptures in the operating room. It should also be noted that when a carotid bifurcation aneurysm bleeds, it can occasionally result in a large hematoma involving the overlying frontal lobe. This hematoma can rupture directly into the ventricle with only minimal associated SAH. In these cases, it is important to recognize the true source of the bleeding as a ruptured ICA bifurcation aneurysm ( Table 5.1 ).

(A) A small ventrally and superiorly directed aneurysm of the ICA bifurcation is exposed. Note its relationship to the supraclinoid ICA (arrowhead), the M1 segment (arrow), the A1 segment (circle), and the optic nerve (star). (B) The aneurysm has been clipped, and several perforators (arrow) are now visible behind the aneurysm. (C) The overall exposure and amount of opening of the Sylvian fissure are shown at the conclusion of the procedure.
A superiorly directed carotid bifurcation aneurysm has been reflected out of its bed (arrow), leaving a subfrontal vein undisturbed along the ventral aspect of the aneurysm.
(A) A complicated large and partially thrombosed carotid bifurcation aneurysm (arrow) is shown on a preoperative anteroposterior carotid arteriogram. (B) The aneurysm has been reconstructed with multiple clips on the intraoperative arteriogram. This case is shown in .
(A) Artist’s illustration demonstrates a wide-necked carotid bifurcation aneurysm that hides multiple perforating arteries. (B) The aneurysm has been fully mobilized and reflected forward out of its bed to enable dissection and visualization of the perforating vessels behind the aneurysm prior to safe clip application.
(A) Preoperative anteroposterior internal carotid arteriogram demonstrates a superiorly directed carotid bifurcation aneurysm. (B) Intraoperative angiography reveals that the lesion has been repaired satisfactorily with primary neck clipping.
(A) Two distinct posteriorly directed carotid bifurcation aneurysms are exposed along with the supraclinoid ICA (arrow), the M1 segment (arrowhead), and the A1 segment (star) overlying the optic nerve. The aneurysms are pointing away from the surgeon. (B) The lesions are clipped by working above the bifurcation, carefully preserving the associated perforators. Note the abnormal proximal A1 segment, which was subsequently wrapped with gauze.

ICA Bifurcation Aneurysm Pearls and Pitfalls

Use standard pterional craniotomy; open proximal Sylvian fissure to expose the aneurysm neck at the ICA bifurcation.

Consider fully freeing the aneurysm from its bed to properly visualize fine perforators that may be adherent to posterior aspect of dome.

Expose proximal aspect of M1 and A1 segments.

Preserve all perforating vessels.

Posteriorly directed lesions are most dangerous and difficult.

Watch the clip as it closes to avoid coming too low on the bifurcation, narrowing the A1 or less commonly the M1 segments.

Prepare distal supraclinoid ICA as well as ipsilateral A1 for temporary clipping in setting of recent rupture.

Occlusion of a deep perforator can result in contralateral hemiparesis.

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Jun 30, 2020 | Posted by in NEUROSURGERY | Comments Off on Aneurysms of the Carotid Bifurcation
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