2023 Volume 10 Pages 33-39
Blood blister aneurysms (BBAs) or pseudoaneurysms (PAs) in the internal carotid artery (ICA) have fragile necks; therefore, conventional neck clipping is difficult. The standard treatment for BBAs or PAs is trapping with high or low flow bypass. However, there is no consensus on whether or not anterior clinoidectomy should be performed together. Two patients with ruptured ICA PA (anterior protrusion) or BBA (posterior protrusion) were presented to our hospital. Complete trapping was safely performed for both types of aneurysms via extradural anterior clinoidectomy and the extradural approach with dural incision. The advantages of the procedure are 1) safe proximal clipping, 2) early identification of the ICA C3 portion, 3) minimized frontal lobe retraction, 4) optic canal opening to allow mobility of the optic nerve, and 5) dural ring incision to allow mobility of the ICA.
Blood blister aneurysms (BBAs) in the internal carotid artery (ICA) are relatively rare (0.5%-2.0% of all ICA aneurysms) and commonly located on the non-branching site (i.e., anterior wall of the ICA); however, recent reports showed that they also occurred in other arteries.1-5) BBAs are characterized by small size (<3 mm), lack of an identifiable neck, thin and fragile wall, and rapid growth, being prone to rebleeding.6-15) Although those larger than 3 mm are not technically called BBAs, previous reports indicated that some BBAs exhibited rapid morphological changes and progressed to saccular appearances with the formation of pseudoaneurysms (PAs).3,14) The authors also reported that depending on the site and direction of the projection, some BBAs appeared to be saccular aneurysms on preoperative vascular examinations due to the surrounding structures, such as the optic nerve, and that the surrounding anatomy of BBAs may play a role in their hemostasis.3) BBAs differ from saccular aneurysms in that the former are pathologically dissected and that neck clipping is mostly difficult.3-8,11,12) The standard treatment for BBAs is trapping with high or low flow bypass.4-9) However, there is no consensus on whether or not anterior clinoidectomy should be performed together. As most of ruptured ICA non-branching site aneurysms may be BBAs or PAs rather than saccular aneurysms, they should be approached with the same caution as BBAs.9,12,15) Here, we report two cases of ICA BBA or PA with different directions of the projection treated with extradural anterior clinoidectomy (EAC) and the extradural approach with dural incision. Furthermore, we discuss the advantages of the surgical approach for BBAs or PAs.
A 47-year-old man with a history of hypertension presented with sudden onset of severe headache, vomiting, and loss of consciousness. On admission, he was under semi-coma (Japan Coma Scale, II-20) and had left hemiparesis (manual muscle test [MMT], 3/5). Computed tomography (CT) of the head revealed diffuse subarachnoid hemorrhage (SAH) with intracerebral hemorrhage [Fig. 1A]. CT angiography (CTA) showed right ICA anterior wall aneurysm with no neck and branching [Fig. 1B], suggesting an ICA PA based on the shape and site of origin. Surgery was performed to prevent rebleeding. After performing an extracranial-intracranial (EC-IC) bypass using the great saphenous vein as a graft, EAC and the extradural approach with dural incision was performed to secure the ICA C3 portion [Fig. 1C]. The Sylvian fissure was opened from the skull base side using the epidural space. However, the aneurysm rebled when the frontal lobe was slightly retracted via a trans-Sylvian approach. It was considered that the blood clot that stopped the aneurysmal rupture point was peeled off by the retraction of its adhered frontal lobe, and when the frontal lobe retraction was immediately released, the bleeding stopped with the blood clot holding down the rupture point again. After the proximal ICA of the aneurysm was secured with minimized retraction of the frontal lobe and the temporary clip was applied [Fig. 1D], the ICA and a PA with clots were exposed [Fig. 1E]. When the blood clots were removed after trapping, no aneurysmal neck and wall were observed on the ICA, confirming that the aneurysm was a PA [Fig. 1F]. The direction of the ICA PA dissection in this case is presented in the schema [Fig. 1G]. Postoperative CTA revealed the occluded ICA PA [Fig. 1H]. The postoperative course was uneventful, but the patient was transferred to a convalescent hospital with modified Rankin Scale (mRS) 4.
Neuroimaging and intraoperative findings in Case 1.
Computed tomography (CT) on admission reveals diffuse subarachnoid hemorrhage (SAH) and intracerebral hemorrhage in the right frontal lobe (A). CT angiography (CTA) shows an aneurysm at the non-branching site of the right intracranial internal carotid artery (ICA) anterior wall (bold arrow; B). After extradural anterior clinoidectomy, the extradural approach with dural incision reveals the ICA C3 portion (arrowhead; C). After securing the proximal ICA of the aneurysm with minimized frontal lobe retraction and applying the temporary clip (D), the ICA and aneurysm with clots are exposed (E). When the clots are removed after trapping of the aneurysm, there are no visible aneurysmal neck and wall on the ICA, suggesting a pseudoaneurysm (F; double thin arrow, the rupture point). The schema (G) presents securement of the ICA C3 portion (red arrowhead) and the direction of dissecting the aneurysm (blue arrow; from the ICA C3 portion to the distal C1 portion via space produced by anterior clinoidectomy). Postoperative CTA shows that the aneurysm is occluded (H). Double arrowhead, incised dura; thin arrow, distal dural ring. *Optic nerve.
A 57-year-old woman who had undergone removal of ruptured right frontal lobe arteriovenous malformation (AVM) about 30 years ago and was independent in daily life with mild left hemiparesis (MMT, 4/5) suddenly suffered from severe headache worsening for 4 days prior to her arrival on our hospital. On admission, the patient was alert, and CT of the head revealed diffuse SAH [Fig. 2A]. Digital subtraction angiography (DSA) on admission showed right ICA stenosis distal to the ophthalmic artery (OphA) and a very small aneurysmal dilatation dorsal to the stenosis, which was equivocal if it was a BBA [Fig. 2B]. Conservative therapy was started. On the 10th day, follow-up DSA revealed enlarged aneurysmal dilatation of the posterior wall of the right ICA [Fig. 2C], which was identified as the source of bleeding. As there was no obvious branching, it was considered a BBA. EC-IC bypass using a great saphenous vein and EAC and the extradural approach with dural incision were performed to secure the ICA C3 portion and OphA as in Case 1 [Fig. 2D], and the Sylvian fissure was opened via a trans-Sylvian approach. Although there was a tough adhesion around the ICA due to previous operation and the ICA was tortuous, the basal cistern was dissected with the ICA C3 portion and the optic nerve as the markers. Optic canal opening resulted in the securement of sufficient optico-carotid space by obtaining the optic nerve mobility, and by incising the dural ring and rotating the ICA both inward [Fig. 2E] and outward [Fig. 2F], the rupture point on the posterior wall of the ICA was exposed [Fig. 2F], leading to complete trapping [Fig. 2G]. The operative approach in this case is presented in the schema [Fig. 2H]. Because of bronchial asthma, only magnetic resonance angiography was performed postoperatively to show that there was no obvious BBA recurrence [Fig. 2I]. The patient was transferred to a convalescent hospital with mRS 3 without rebleeding.
Neuroimaging and intraoperative findings in Case 2.
Computed tomography on admission shows diffuse subarachnoid hemorrhage (A). Digital subtraction angiography (DSA) on admission shows a slight aneurysmal dilatation (bold arrow) in the right internal carotid artery (ICA; B), which is increased in size on follow-up DSA (C). Through extradural anterior clinoidectomy and the extradural approach with dural incision, the ICA C3 portion (arrowhead) is secured (D; thin arrow, distal dural ring; double arrowhead, incised dura). After the optic canal opening, the rupture point is being checked by rotating the ICA inward (E) or outward (F). The rupture point (double thin arrow) on the posterior wall of the ICA is exposed (F; triple arrowhead, ophthalmic artery), followed by complete trapping (G). The schema (H) presents securement of the ICA C3 portion (red arrowhead) and the ICA mobility to expose the BBA (two - way arrow). Postoperative magnetic resonance angiography shows that the BBA is occluded (I). *Optic nerve.
The etiologies of BBAs are considered for vascular dissection due to hemodynamic stress, resulting in the formation of PAs: their walls are very fragile; thus, conventional neck clipping is difficult due to the high possibility of neck rupture.3-15) Trapping with high or low flow bypass, clipping on wrapping, coil embolization with or without stent, and flow diverter were previously reported as treatment strategies;14-19) however, trapping with high or low flow bypass seems to be the most standard treatment to prevent rebleeding of BBAs.4-9) Although there are some reports on the location of trapping in relation to the site of origin of BBAs and the ICA branches, such as OphA, posterior communicating artery (PcomA), and anterior choroidal artery,20-22) there are no studies examining the advantages of EAC and the extradural approach with dural incision.
The advantages of EAC and the extradural approach with dural incision in trapping with high or low flow bypass for BBAs or PAs are as follows: 1) safe proximal clipping, 2) early identification of the ICA C3 portion in the intracranial procedure, 3) minimized frontal lobe retraction, 4) optic canal opening to allow mobility of the optic nerve, and 5) dural ring incision to allow mobility of the ICA. In case the dissection extends around the OphA, EAC and the extradural approach with dural incision is necessary for proximal clipping.21) If BBA is located distal to the OphA and proximal to the PcomA, trapping with cervical ICA and intracranial ICA distal to the lesion may result in rerupture or aneurysm enlargement due to backflow from the OphA or visual impairment due to the OphA occlusion. Kikkawa et al demonstrated that in 16 patients with ruptured BBAs, clips were inserted distal to the OphA and proximal to BBAs in all cases, of which 4 (25%) required anterior clinoidectomy.21)
In cases of saccular aneurysms, such as aneurysms of the ICA-PcomA, the location of ICA is often confirmed through the anterior wall of the ICA. However, that is difficult in BBA cases due to the lesions existing in the same area. Therefore, EAC and the extradural approach with dural incision help confirm the location of the ICA C3 portion at the early stage of the intracranial procedure, which is used as a marker. Furthermore, even if the dissection extends the proximal intracranial ICA, it is possible to perform proximal control when BBAs rerupture and distally to dissect the hematoma attached to the anterior wall of the ICA [Fig. 3A-D; red arrowhead].
Illustrations that show the advantages of extradural anterior clinoidectomy (EAC) and the extradural approach with dural incision according to the direction of blood blister aneurysm (BBA) projection and classification of BBAs by the direction of the projection.
Illustrations show anterior (A), lateral (B), medial (C), and posterior (D) BBAs, respectively. EAC and the extradural approach with dural incision allow neurosurgeons to confirm the location of the ICA C3 portion at the early stage of intracranial procedure (A–D; red arrowhead), reduce the risk of rerupture by minimizing frontal lobe retraction (A–C; blue arrow, the directions of approach to BBAs with EAC and the extradural approach with dural incision, and dotted arrow, the directions of approach to BBAs without this approach), perform trapping more safely and less invasively on the optic nerve (C; green arrow, moving direction of the optic nerve), and perform complete trapping with the ICA mobility (D; purple two-way arrow). Schema of the coronal image of the right intracranial ICA (E).
The authors previously classified BBAs according to the direction of the projection [Fig. 3E] and reported that the surrounding anatomy plays a role in hemostasis, with the medial type being hemostatic by optic nerve and some cases appearing as saccular aneurysms on preoperative vascular examinations.3) Although the anterior type is the most common in all BBAs, the role of 3) -5) described above may be very effective depending on the direction of the projection (Table 1). If BBAs protrude anteriorly, laterally, or medially, the bleeding is often stopped by the frontal lobe, and they can easily rerupture via frontal lobe retraction. EAC and the extradural approach with dural incision can provide space and minimize frontal lobe retraction, reducing risks of rerupture. Therefore, even in cases where anterior clinoidectomy is unnecessary due to the long distance from the dural ring to proximal BBAs, EAC and the extradural approach with dural incision can reduce the risk of rerupture by minimizing frontal lobe retraction [Fig. 3A-C]. When BBAs protrude medially, the optic nerve is also often involved in hemostasis as aforementioned,1) and trapping can be performed more safely and less invasively through the optic canal opening, providing mobility to the optic nerve [Fig. 3C]. Although BBAs protruding posteriorly are rare, they can be adequately observed and completely trapped by opening the dural ring to provide mobility to the ICA [Fig. 3D]. However, when the anterior clinoid process is close to the ICA or an aneurysm, EAC carries a risk of the ICA injury or aneurysmal rerupture in addition to visual impairments; therefore, in such cases, intradural anterior clinoidectomy may be considered. Intradural anterior clinoidecomy has an advantage that clinoidectomy can be performed while confirming an aneurysm, although retraction of the frontal and temporal lobes is required, potentially resulting in rerupture. Thus, although EAC and the extradural approach have various advantages (Table 1), especially in the anterior and lateral BBA or PA of the ICA, the application should be judged on a case-by-case basis.
| Projection | Hemostatic tissue | Advantages |
|---|---|---|
| BBA, blood blister aneurysm; C3, internal carotid artery (ICA) C3 portion; DR, dural ring; PA, pseudoaneurysm | ||
| Anterior | Frontal lobe | Early securement of C3, minimized frontal lobe retraction |
| Medial | Frontal lobe Optic nerve Carotid cave |
Early securement of C3, minimized frontal lobe retraction, Safe exposure of BBA or PA with the optic nerve mobility by optic canal opening |
| Lateral | Frontal lobe Temporal lobe |
Early securement of C3, minimized frontal lobe retraction |
| Posterior | Dura | Early securement of C3, complete trapping with the ICA mobility by DR incision |
Case 1 was a case of an ICA PA with anterior projection. When the frontal lobe was slightly retracted to confirm the ICA, rebleeding occurred and was stopped by returning the retraction. The space created by EAC and the extradural approach with dural incision allowed minimized retraction of the frontal lobe, and trapping was performed thereafter without rebleeding.
Case 2 was a rare case of a posterior BBA. Although there were severe adhesions due to postoperative cerebral hemorrhage from the ruptured AVM, EAC and the extradural approach with dural incision allowed early identification of the optic nerve and the ICA C3 portion and were effective in the operative field development. In addition, by incising the dural ring and providing ICA mobility, the BBA, which was otherwise difficult to observe, was directly observed, and complete trapping was performed.
Oono et al. reported a case with intraoperative rerupture during anterior clinoidectomy resulting in poor outcome, even though the site of ruptured BBA was far from the anterior clinoid process.9) Thus, securement of the cervical ICA and high or low flow bypass should be performed before anterior clinoidectomy. It is also important to familiarize the technique due to a risk of visual impairment. Although there are reports of BBAs that neck clipping was performed in the same way as saccular aneurysms,23,24) there is no established method for adequate preoperative evaluation of BBAs or PAs. BBAs and PAs are generally difficult to clip due to the lack of firm necks even if they appear to be saccular aneurysms on preoperative examinations,3) and EAC and the extradural approach with dural incision may reduce a risk of rebleeding.
The standard treatment for BBAs is trapping with high or low flow bypass, and EAC and the extradural approach with dural incision is considered to have some advantages in performing trapping more safely and surely.
The authors certify that they have obtained all appropriate consent.
All authors have no conflicts of interests.
