Basilar Artery Perforator Aneurysms and their Contemporary Management
Keywords: Perforator aneurysm, flow diversion, overlapping stents, angiogram, subarachnoid hemorrhage
Basilar perforating aneurysms (BPA) are very rare vascular lesions that present with subarachnoid hemorrhage. They are mostly low flow, dissecting aneurysms. Their detection is complicated because multiple angiograms may be required for diagnosis. Direct microsurgical or endosaccular treatment is usually not feasible. The most intuitive treatment is endoluminal flow modification of the basilar artery with flow diversion (FD) or multiple overlapping stents (OS). We describe an interesting case of a ruptured BPA detected on the fourth angiogram and successfully treated with multiple OS. An updated literature review is provided, in the context of clinical presentation and management.
A comprehensive review of the literature was performed on PubMed using the search criteria “basilar aneurysm” AND “perforating aneurysm” AND “basilar perforator.” [Figure 1] depicts the search process. 21 papers describing 55 cases were found. 3 cases from 2 papers, were excluded due to unclear anatomic location and age. Three papers describing four patients were found from cross-references.,, Ultimately, 57 cases of basilar perforator aneurysms resulted, including ours [Figure 1].,,,,,,,,,,,,,,,,,,,,,, Patient demographics, imaging, treatment modality, ischemic complications, clinical and functional outcome and follow-up duration were collected. Good functional outcome was defined as modified Rankin Score (mRS) of 0–2. Where data was missing, the event rate was described such that the denominator represents the number accounted for in the papers.
A 62-year-old male presented with Hunt and Hess grade 2 subarachnoid hemorrhage (SAH). CT showed Fisher grade 4 SAH with prominent prepontine clot and intraventricular hemorrhage [Figure 2]a. An external ventricular drain (EVD) was placed. CTA and catheter angiogram were negative [Figure 2]b. Second angiogram at 7 days was negative. A third angiogram for vasospasm and clinical decline at day 12 did not reveal any culprit lesion. The spasm was treated. On day 27 he was noted to have fresh hemorrhage into the EVD. CTA revealed an enhancement off the basilar trunk [Figure 2]c and angiogram confirmed the presence of a left BPA [Figure 2]d. Three overlapping stents were placed in the basilar artery and no further aneurysm filling was noted [Figure 2]e. He eventually made a gradual recovery to being awake and alert and was discharged to rehabilitation on day 48 after shunt placement, with mRS of 4. At 3 months follow-up, he showed excellent improvement to outcome of mRS 2.
[Table 1] presents patient data. All presented with rupture. There were 34 males and 23 females. Age ranged from 27 to 82 years (mean 57.2, median). Vast majority of patients presented with Fisher grade 3/4 SAH (34/38). 7/49 patients presented in high grade SAH (Hunt and Hess grade 4 or 5). 34 aneurysms were detected on more than one angiogram (59.7%, 5 on third study).
[Figure 2] and [Table 1] show modality of treatment. Overall, 38/51 demonstrated complete occlusion of aneurysm at a follow-up range of 0.5–36 months. 1 death was noted. Residual or recurrence was described in 4 patients. Re-hemorrhage was documented in 2 patients. 11/44 (25%) had ischemic complications (both treated and conservative groups). Overall, 9/51 had poor outcome. 15 (26.3%) were treated conservatively. 2/13 (15.4%) in the conservative group had poor outcome. 6/9 showed spontaneous occlusion on short-term follow-up angiograms. 6 patients (10.5%) underwent up-front microsurgical clipping. 1/6 (16.7%) had poor outcome. 3 cases were documented as having complete exclusion.
The majority of patients (n = 37, 64.9%) underwent endovascular therapy. Failure was noted in 10 (27%, exact modality not described). 4 of these showed spontaneous occlusion, 2 underwent subsequent clipping with good outcome. 11 received overlapping stents in the basilar artery, with recurrence noted in 2 (treated with further stent placement and coiling respectively). 11 underwent flow diversion of basilar artery and all showed occlusion at 0.5–12 months follow-up and good outcomes in 10 patients. 8/11 (72.7%) ischemic complications (among the 43 cases that documented this) were from the endovascular group but only one each was from the flow diversion and stent group (9% each). 6/32 patients (18.75%) in the endovascular cohort had poor functional outcome.
This paper highlights several unique aspects of BPAs. This is a very rare entity, with only 56 cases described in literature. All documented BPAs presented with rupture. Most patients interestingly present in high Fisher grade (91% grade > = 3) with prominent blood in the prepontine cistern, but good clinical grade (only 15% high grade). Over 60% are detected after the first angiogram. Our case was detected after the fourth angiogram, following re-rupture during hospital course. The data provides impetus to the practice of a third and even fourth angiogram in cases of SAH with initial negative angiograms. While institutional preferences vary, it appears prudent to have a low threshold for performing 3D rotational vertebral artery angiography when the hemorrhage pattern on CT indicates prominent prepontine clot.
The management of BPAs in the literature has varied. Some advocate conservative management, on the premise that follow-up angiograms demonstrated occlusion of the aneurysm. However, there is sparse data on whether delayed angiograms were ever performed. Most authors agree that simple observation of a diagnosed culprit aneurysm in a patient with SAH is not standard of care. Microsurgical clipping has been described in a very small number of cases with inconclusive indications and results. Majority of posterior circulation aneurysms are currently treated with endovascular means.
Most BPAs are treated by endovascular means. Primary coiling is rarely feasible. Flow diversion or overlapping stents in the basilar artery appears to be treatment of choice in the literature. The overlapping configuration provides a degree of “flow diversion” while hopefully preserving perforator patency. Flow diversion in the basilar trunk has traditionally been met with a degree of hesitation because of fear of perforator occlusion. However it appears that flow diverting stents are highly effective and safe for BPAs. Although majority of ischemic complications were noted in the endovascular cohort, these were largely from cases with treatment attempts and failure. In conclusion, the data from literature suggests overlapping stents or flow diversion as the treatment of choice for BPAs.
Satti et al. proposed a classification for BPAs but did not provide validation with available cases in literature. Moreover, it is cumbersome and without clear relevance to treatment. We therefore attempted to describe BPAs as trunk (related to the basilar trunk circumference) and non-trunk (afferent and efferent channels being the perforator) types. Therefore Satti types I to IIb are “trunk” type and type III is “non-trunk” type. By reviewing angiographic images where available, we identified 28 non trunk type and 15 trunk type BPAs. No relation to presentation or treatment was evident even under this classification system but it proves to be far simpler in providing a uniform reporting template.
Our study suffers from all deficiencies of a retrospective review. Uniform reporting of parameters including follow up (clinical or angiographic) among papers were lacking. The proposed classification without review of source images or inter-rater assessment limits validity.
BPAs are very rare vascular lesions that present with rupture. Multiple angiograms are often necessary for their detection. Although resolution of BPAs has been described on conservative therapy, this does not represent a viable option at most centers. The treatment of choice appears to be endoluminal basilar artery flow modification with overlapping stents or flow diversion. Good outcomes can be achieved with endovascular therapy. Finally, a simpler BPA classification system like the one proposed here may assist in uniform documentation in the literature.
Financial support and sponsorship
No financial support was received.
Conflicts of interest
There are no conflicts of interest.
Drs. Spiotta and Lena are Consultants for Penumbra Inc., Alameda, California, USA.
[Figure 1], [Figure 2]