Though BBLAs involve other segments of the arteries irrigating the contents of the supratentorial or infratentorial cavities within the intracranium, the supraclinoid extent of the intracranial ICA constitutes the most classic location [6]. CTA and DSA are the best efforts of veteran investigators in selecting the most appropriate therapeutic modality for BBLA [4, 5]. Endovascular reconstruction of the segment of intracranial ICA containing the ostium of BBLA achieves the end of lesional obliteration in all patients.
Subintimal dissection extending from the supraclinoid extent of the intracranial ICA through variable extents into the middle cerebral artery likely underlies the development of BBLA. Guo and colleagues [7], Yanaka and colleagues [8], and Horie and colleagues [9] identified a transmural tear identified by visual inspection intraoperatively, and an intramural hematoma was identified by dedicated magnetic resonance imaging sequences preoperatively [8]. The presence of these sub-pathognomonic hallmarks typifying soi-disant pseudoaneurysms strongly corroborated the hypothesis that focal dissection underlies the development of BBLA, the precise elucidation of which will permit the optimization of treatment paradigms.
Hemodynamic shear stress impinges upon the curvilinearly contoured anterior wall of the ICA may reduce the threshold of a traumatic event between the fixed intracavernous and mobilize the supraclinoid segments of the ICA [10]. Spiral extension and weakening of the vessel wall of the supraclinoid extent of ICA facilitate focal enlargement of the vessel at zones of separation of the layers constituting the vessel wall. Laplace’s relationship states intraluminal pressure (P) exerted by a column of fluid within an expandable vessel exhibits direct and inverse proportionality with 2 times of the vessel wall tension (T) and vessel radius (r) (i.e., 2T=P×r). Relative flattening of the supraclinoid extent of the ICA from a contoured bulk of the cavernous segment reduces ICA radius to the end reducing ICA wall tension.
Cerebral ischemia constituted a presenting symptom in 73% of patients with dissections involving the middle and anterior cerebral arteries, anterior communicating artery, and bifurcation of the ICA. The prevalence of subarachnoid hemorrhage (SAH) successive to dissection of the ICA was reported to range between 12 and 20% among afflicted patients [11]. Contraverting SAH reportedly constitutes the major manifesting presentation in upwards of 99% of patients successively identified to harbor a BBLA. “String,” an extremely thin and meandering column of contrast interposed between two apposing segments of the vessel otherwise exhibiting normal caliber, or “pearl and string,” an extremely thin and meandering column of contrast interposed between two apposing segments of vessel otherwise exhibiting normal caliber adjacent to a small micro-puddle-like collection of contrast on DSA typifying stable chronic separation of the layers constituting the vessel wall, indicates the dissection commences within the micro-slab of extracellular matrix separating the internal elastic lamina from the irregularly stratified layer of vascular smooth muscle cells [12–14].
The separative cleavage plane immediately preceding instances of SAH typically propagates from the extracranial to the intracranial extents and expansion between the tunica media and tunica adventitia [15]. Dynamic systolic arterial blood pressure, site of vessel involvement, geometry of vessel curvature, and pattern of side branches dictate successive dynamic patterns of multivariate propagation of vessel wall separation and rates of hemorrhage. Dynamic separation of the layers of the vessel wall propagating dynamically and multivariately from a focal point indicates endovascular reconstruction may constitute an effective modality excluding the false aneurysmal fundus from the parent vessels. Iatrogenic intraoperative bleeding occurs among 20% of patients successive to trephination, and microsurgical treatment of these lesions frequently causes disfavorable patient neurological outcomes [16]. Successive sequential Sylvian dissection and distoproximal peri-arterial separation of arachnoid fibers are cumbersome to faithfully conduct in the presence of edematous lobar opercula in patients developing Hunt-Hess high-grade SAH [17, 18]. Endosaccular coil embolization of fundi aneurysm oft fails to prevent instances of re-bleeding from or regrowth of BBLA [19]. Endovascular preclusion of blood entry into a segment of the intracranial extent of the ICA is perverted by an aneurysmal ostium effectively excluding BBLA from traveling columns of blood under high pressure [17, 18]. Surgically or endovascularly, occlusion of the lumen of the ICA may render insufficient to provide blood supply supporting microcirculatory perfusion flow from the contralateral ICA to cause disfavorable neurological outcomes of patients.
Wild-type opacification of the middle and anterior cerebral arteries is through the anterior communicating artery successive to bolus injections of iodinated contrast within the contralateral ICA. But the anterior and posterior communicating artery calibers usually fail to exceed or recede greater than two standard deviations from the mean of Gaussian- or non-Gaussian-distributed vessel calibers. The proximally related large vessel vasospasm and high intracranial pressure putatively can also attenuate dynamic rates of flow through the cerebral collaterals [20]. Re-establishing flow bypassly to the vessels of the intracranium irrigates the neural substance from extracranial conduits, and endovascular occlusion of segments of aneurysmal ostium may effectively attenuate the risk of BBLA rupture [18]. The prevalence of neurologic sequelae of a thromboembolic and/or hemorrhagic etiology can not be irrivisable. Therapies preserving blood flow of the ICA yield a benign clinical course. The prevalence of morbidity and death ensuant from expeditions seeking to exclude BBLA from the intracranial vasculature microsurgically or endovascularly approximated 20% and 10.7% and 7.0 and 9.0%, respectively, in a survey retrospectively conducted upon a systematic review of 334 patients [21]. A specific type of endovascular technique and treatment instituted to exclude a BBLA from the intracranial circulation dictates the obliteration rates and neurological outcomes. Therapy of employing aneurysmal coiling, placement of flow-diverting stent across the ostium of BBLA, stent-assisted coiling, or stents across the ostium of BBLA actualizes good outcome in 52.9%, 82.2%, 85.2%, and 86.4% of patients, respectively. Immediate and delayed interval (mean 20.9 months) rates of obliteration of BBLA approximated 88.9% and 88.4% in the surgical group and 63.9% and 75.9% in the endovascular group in a systematic survey of 36 peer-reviewed articles, respectively, detailing the experiences of 256 patients during 2005 through 2015 [22]. The rates of intra- and post-procedural complications in patients undergoing microsurgical and endovascular treatment were 27.8% (95%CI, 19.6–37.8%) and 26.2% (95%CI, 18.4–35.8%), respectively.
The authors have attempted to place closed-cell stents across the ostium or overlapping stents with or without packing the aneurysm with coils to exclude BBLA. The placement of open-cell stents across the ostia of BBLA endovascularly reconstructing the lumen of involved parents vessels achieves acceptable rates of stable lesional obliteration according to the description of Fiorella and colleagues [23]. Placement of closed-cell stents across the ostia of BBLA was putatively culprit in the successive development of aneurysmal regrowth and lesional hemorrhagic re-rupture in 2 and 7 patients, respectively [24]. One of our patients developing re-bleeding from the BBLA underwent placement of a closed-cell stent across the ostium in our earliest experience [13]. Incomplete apposition between closed-cell stent and segments of the vessel of BBLA enhances the risk of sequential lesional re-rupture after the procedural intervention. Stenting across the ostia of BBLA and coiling of the aneurysm constituted typical endovascular treatment at our infirmary. Placement of novel LVIS and Pipeline flow-diverting stents with a braided-cell design exhibiting dense porosity (smaller holes in the wall of the stent compared with precedingly employed closed-cell stents) across the ostia of BBLA proved safe and effective in our experience [25, 26]. Feasibility of surgical or endovascular reconstruction of segments of the parent vessels of BBLA appears to constitute a method preferentially recapitulating physiological flow through the ICA.
In a recent review conducted by Szmuda and colleagues, 56 individuals amalgamated from 17 peer-reviewed manuscripts harboring BBLA involving the supraclinoid segment of the intracranial ICA excluded by the placement of flow-diverting stents across the ostia retrospectively evaluated from 2010 to 2016 [6]. Thirty-four patients were treated using a single flow-diverting stent, 17 underwent placement of 2 flow-diverting stents and placement of single flow-diverting stent, and occlusion of the lesion with coils in 3 patients to exclude BBLA. The immediate complete obliteration rates were 27.3%, 18.8%, and 100% by the 3 strategies, respectively. Patients unfortunately returning to secure lesion obliterate in 5, among whom 3 patients died. The Modified Rankin Scores of 0–2 were in 83.3% of these patients. Persistent flow to opacify aneurysmal pseudo-fundi after placement of stents across the ostia of BBLA leading to unfortunate instances of re-rupture and premature untimely expiration underscores deficiencies in currently extant therapies. The presumptive hastening of complete exclusion by the concomitant placement of coils to occupy aneurysmal fundi validates the demonstration by previous authors that the strategy may constitute putatively durable strategies to treat BBLA.
None of our patients experienced re-rupture after placement of flow-diverting stents across the ostia of BBLA. Requisiteness of dual antiplatelet therapy maximally diminishes the risk of hemorrhagic morbidity complicating the post-procedural course of endovascular reconstruction to exclude BBLA. Development of hydrostatic hydrocephalus secondary to SAH requiring diversion of the cerebrospinal fluid from the cavities of the ventricles yields bleeding between 3 and 10% of individuals receiving antiplatelet therapy precedingly undergoing stent-assisted coiling according to a study by Bodily and colleagues [5, 27].
Limitations of our study
Retrospective evaluation of the experience of a single institution, paucity of sampled patients, cohort heterogeneity, short span of follow-up, and/or possible selection bias and/or reporting bias constitutes the chief features of reducing the extendability of our results to refute a non-“a priori”-determined null hypothesis indicating parity between non-treatment, placebo, and treatment in acute dissection.
