1.Anatomy and Classification
Among the embryonic cervical-carotid anastomoses, the trigeminal artery (TA) is the most prominent and exhibits the longest duration of persistence. With embryonic development advancing to the stage of approximately 11.5 to 14 mm, the posterior communicating artery (PCoA) begins to form, thereby marking the start of the TA's regression process [1,8,9]. If the TA fails to regress completely during the transition to adulthood, it becomes a persistent primitive trigeminal artery (PPTA). Studies indicate that hemodynamic irregularities could be a primary factor influencing this developmental anomaly. Lasjaunias and Berenstein elucidated the persistence of the PPTA, highlighting its crucial function in preserving hemodynamic balance across anterior and posterior circulations. This mechanism compensates for the insufficient blood flow from the bilateral vertebral arteries (VA) [10].
Anatomically, the persistent primitive trigeminal artery (PPTA) emerges from the internal carotid artery (ICA) and courses posteriorly and laterally along the trigeminal nerve or superior to the sellar region, eventually establishing a juncture with the basilar artery (BA). The most common site of origin is often at the posterior curve or the lateral aspect of the cavernous segment of the ICA [11,12]. Salas proposed a classification scheme that categorizes PPTA into lateral and medial types according to its spatial relation to the abducens nerve [12]. Conversely, Iizuka et al. differentiated PPTA into embryonic and mature types by assessing the BA's blood supply regions via imaging [5]: the embryonic type principally supports the distal BA, and the mature type is characterized by a combined blood supply from both the vertebral artery (VA) and TA. Saltzman's categorization [13] further refines PPTA typology: Type 1 PPTA's distal extent reaches the distal portion of the anterior inferior cerebellar artery (AICA) and approaches the vertebrobasilar junction's proximal segment. This subtype may demonstrate potential developmental shortcomings in the proximal BA and a potential absence of the ipsilateral PCoA. In contrast, Type 2 PPTA is generally not associated with developmental deficits. The distal end of Type 2 PPTA lies at the proximal segment of the anterior superior cerebellar artery (ASCA), thus supplying it, and the posterior cerebral artery (PCA) chiefly obtains its blood supply from the PCoA. Clinically, Saltzman's classification assumes greater significance as it accommodates the diverse supply territories of PPTA.
2.Treatment of PPTA Aneurysms
Davis first reported the coexistence of a persistent primitive trigeminal artery (PPTA) and an intracranial aneurysm (IA) in 1956 [14]. Cerebral angiography studies indicate that unilateral PPTA aneurysms occur in approximately 0.1% to 0.6% of cases [2], and bilateral cases are exceedingly uncommon [15]. In an 18-year review of the literature, Cloft found that the prevalence of IA was around 3% among 34 PPTA cases, comparable to the 3.7% in the general population [7]. O’uchi E and colleagues analyzed 16,415 cases spanning three years, revealing a similar IA incidence of 3.9% [2], with 14-32% being PPTA-related [16]. Anomalies in the medial layer of the vascular wall predispose PPTA to IA formation and localized ruptures. Reports suggest a 50% rupture rate for PPTA aneurysms, with half leading to cavernous carotid fistulas (CCF), 45% to subarachnoid hemorrhage (SAH), and 5% to recurrent epistaxis [17]. Treatment strategies for PPTA aneurysms ought to be tailored according to their vascular territory, guided by Saltzman's classification. Preservation of Type 1 PPTA is critical; if infeasible, arterial bypass may be necessary to maintain posterior circulation. Vigilant monitoring of Type 2 PPTA is imperative due to its potential role in recurrence, with occlusion as an option if required. In the case under discussion, digital subtraction angiography (DSA) showed that the PPTA supplied the upper segment of the basilar artery (BA), classifying it as a Saltzman Type 1.
A PubMed search utilizing the keywords "persistent primitive trigeminal artery," "aneurysm," and "carotid cavernous fistula" retrieved 11 pertinent studies (see Table 1). Of the 11 patients profiled, 2 exhibited a documented trauma history (18.2%), with the remainder presenting spontaneous cases (81.8%). PPTA aneurysms or breaches at vulnerable sites within the PPTA vascular structure were identified as the primary etiologies [18]. Typical clinical presentations encompassed proptosis, conjunctival engorgement, cranial murmurs, and double vision. Therapeutic interventions for PPTA aneurysms comprise microsurgical clipping and endovascular coiling. Microsurgical clipping is optimally employed for IAs with narrow necks and diminutive sizes, featuring readily accessible anatomical structures. Nonetheless, the frequent positioning of PPTA aneurysm necks within the cavernous sinus renders surgical intervention complex and hazardous. While Enomoto and colleagues previously achieved success in treating several cases through ICA ligation [8], such an approach is heavily contingent upon the Circle of Willis' compensatory capabilities and may elevate the risk of flow-related IAs over time. Consequently, in light of considerable innovations in interventional methodologies since the 1990s, endovascular therapy has emerged as the favored modality for managing PPTA aneurysms [19]. This paradigm incorporates procedures like balloon occlusion, coiling, and the synergistic application of coils with Onyx embolization. Initially, detachable balloon occlusion was the treatment of choice [18]. However, the convoluted nature of vascular flow and pathways may at times impede balloon navigation through the fistula into the cavernous sinus [20,21], posing a risk of recurrence. Among the reviewed cases, a mere two instances of successful detachable balloon occlusion with positive prognoses are reported.Liu and associates were the pioneers in documenting the employment of detachable coils for the resolution of CCF secondary to ruptured PPTA aneurysms, with beneficial results [22]. While coils provide superior controllability compared to balloons, the typically larger size of PPTA aneurysms necessitates the use of an increased coil count for effective embolization.Moreover, the exclusive use of coils cannot assure the complete eradication of abnormal arteriovenous shunting, and the mass effect resulting from overfilling presents a significant resolution challenge.Fan et al. devised a surgical method that employs a hybrid of coils and Onyx glue, reducing the necessity for multiple coils and facilitating targeted treatment [23].However, Onyx glue's limited controllability poses a challenge, necessitating protective measures for the ICA and BA to prevent accidental embolization [24].
In the case under discussion, a cavernous carotid fistula (CCF) manifested subsequent to the rupture of a paraclinoid pseudoaneurysm of the internal carotid artery (PPTA) within the cavernous sinus. The fistula, situated at the proximal segment of the PPTA, demonstrated partial arteriovenous shunting. Given these characteristics, conventional treatment modalities, including microsurgical clipping and detachable balloon embolization, were deemed unsuitable. As a result, detachable coil embolization emerged as the treatment of choice. Preoperative computed tomography angiography (CTA), processed using Mimics 8 software (Materialise, USA), estimated the aneurysm volume at 675.56 mm³. The embolization procedure involved a dual microcatheter strategy, with a total of nine coils deployed for aneurysm occlusion. Post-embolization, the aneurysm volume was diminished to 275.75 mm³, yielding a packing density of 40.82%. Such a degree of embolization can be classified as considerable. Nonetheless, angiographic examination revealed substantial persistent arteriovenous shunting with elevated blood flow velocity. Although Onyx glue was contemplated as an adjunctive measure, achieving an efficacious seal at the aneurysm neck with the adhesive was particularly challenging in this anatomical context. Moreover, the inherent unpredictability of the embolization technique spurred apprehension regarding potential modifications in PPTA hemodynamics or inadvertent embolization. To circumvent these obstacles, adjunctive endovascular electrocoagulation was utilized along with coil embolization. This integrative method facilitated the comprehensive occlusion of the fistula, concurrently conserving the patency of the PPTA. This strategy effectively circumvented the mass effect linked to excessive coil deployment and attenuated the hazard of non-target embolization, a noted concern with Onyx glue application.
The novel technique of endovascular electrocoagulation was originated by Jiang Yuhua et al. at Beijing Tiantan Hospital, introduced to the medical field in 2016. Its initial application, in concert with bare metal microguidewires, addressed diminutive aneurysms nestled within the perforating arteries of the basilar artery. This approach was particularly advantageous in scenarios where access to these formidable loci was unattainable by the microcatheter tip [25]. An exhaustive exploration of databases such as PubMed and CNKI has yielded merely seven clinical case reports pertinent to this technique [26-29]. Commencing in 2018, our institution has broadened the utilization of this method, augmenting the instantaneous complete occlusion rates of cystic aneurysms still presenting with contrast filling post-coil embolization. The deployment of this expanded application has resulted in superlative treatment outcomes [27]. Jiang and his colleagues have conceptualized a theoretical framework for this technique, postulating that its microcosmic mechanism is underscored by two pivotal processes: thrombogenesis and thrombus organization [28]. Preliminary experiments at our institution have disclosed that electrification of the microguidewire tip, serving as an anode, draws in negatively charged blood constituents such as erythrocytes, thrombocytes, and leukocytes, thus catalyzing thrombogenesis. In tandem, plasma electrolysis at the microguidewire tip engenders bubble formation, furnishing a scaffolding for the accruing thrombus in the vicinity of the wire's tip. Additionally, the electrical current activity at the microguidewire tip generates an electrothermal effect, which causes denaturation and reorganization of the existing thrombus. Consequently, this process culminates in the creation of a more stable thrombotic structure. These findings robustly advocate for the feasibility and efficacy of this method for intravascular treatments designed to induce thrombosis [29]. Physics research has clarified that the intensity of current activity on metal surfaces is inversely correlated with the surface area of the metal submerged in a liquid medium. This crucial insight implies that enlarging the metal's contact surface area within a liquid can efficaciously disperse current activity, thus augmenting the safety of intravascular electrocoagulation procedures. Adopting a pioneering approach, our institution has implemented the use of mechanically detachable bare metal coils (specifically, Axium coils by ev3, USA) for intravascular electrocoagulation, boasting several significant advantages: (1) These coils provide an extensive contact surface area with the blood within the aneurysm sac, significantly enhancing thrombosis efficiency. The dispersion of current activity across the metal surface is broader compared to the confined tip of a microguidewire, leading to an improved safety profile. (2) The coils adopt a structure comparable to “reinforced concrete” within the aneurysm sac, bolstering the stability of the embolic material. (3) This innovative approach effectively mitigates the potential risk of reperfusion or distal embolization that may occur during the thrombus removal process post-electrocoagulation with microguidewires. Drawing from our institution's comprehensive experience, we have established that a voltage of 9V constitutes a relatively safe threshold for application. Extending the duration of electrical stimulation can achieve comparable thrombosis efficiency while ensuring an elevated level of safety. For this particular case, parameters of 9V/1mA were employed. After 7 minutes of continuous electrical stimulation, complete occlusion of the PPTA aneurysm sac was achieved. It is worth noting that the extended duration of electrical stimulation, relative to prior cases of saccular aneurysm occlusion, likely results from the PPTA aneurysm's larger size and the increased blood flow within the aneurysm sac, consequent to the associated CCF.