Staged coiling and flow diversion for a ruptured persistent primitive hypoglossal artery aneurysm: illustrative case

Abstract

BACKGROUND

A persistent primitive hypoglossal artery (PPHA) is a rare embryonic carotid-vertebrobasilar anastomosis that can serve as the dominant posterior circulation inflow and predispose to aneurysm formation; optimal management remains unsettled.

OBSERVATIONS

A 68-year-old woman presented with a World Federation of Neurosurgical Societies grade V subarachnoid hemorrhage resulting from a large, wide-necked aneurysm at the junction of the PPHA and vertebral artery. The contralateral vertebral artery was diminutive, and the anterior inferior cerebellar artery supplied the right posterior inferior cerebellar artery territory. To minimize acute-phase thromboembolic risk and prevent rebleeding, balloon-assisted coiling with hydrogel-coated coils was performed and Raymond-Roy class I occlusion (volume embolization ratio 20.2%) was achieved. The patient recovered to a modified Rankin Scale score of 1. Despite initial stability, recanalization occurred at 1 year. A FRED flow diverter was deployed by simple unsheathing without complications. Follow-up angiography showed complete occlusion at 6 months.

LESSONS

In the context of PPHA anatomy with high posterior circulation dependence, a staged strategy—acute stentless coiling followed by delayed flow diversion—can balance immediate protection with durable reconstruction. A detailed anatomical evaluation (including perforators, vertebral artery caliber, and vascular variants) and antiplatelet optimization are essential.

https://thejns.org/doi/10.3171/CASE2642

A persistent primitive hypoglossal artery (PPHA) is a rare embryonic remnant vessel, with a reported incidence of 0.027%–0.26%.¹ PPHA often serves as a major conduit to the posterior circulation and is therefore subject to increased hemodynamic stress, which predisposes it to aneurysm formation. However, the optimal treatment strategy for PPHA-associated aneurysms has not been established. Here, we report a case of a large PPHA-associated aneurysm presenting with subarachnoid hemorrhage that was treated using a flow diverter (FD).

Illustrative Case

A 68-year-old woman with no prior medical history, medications, or relevant family history was found collapsed in a prone position at home and brought to the emergency department by emergency medical services. She drank alcohol three times per week and had never smoked. Her premorbid modified Rankin Scale (mRS) score was 0. On arrival, she was comatose with a Japan Coma Scale score of III-200 and a Glasgow Coma Scale score of E1V1M2. Pupils were equal at 3 mm bilaterally. Vital signs showed a heart rate of 101 beats per minute, blood pressure of 114/89 mm Hg, respiratory rate of 20 per minute, oxygen saturation of 94% on 15 L/min oxygen, and body temperature of 35.8°C. Assessment of focal neurological deficits, including motor weakness, was limited by her impaired consciousness.

Noncontrast head CT revealed a subarachnoid hemorrhage predominantly in the basal cisterns (Fisher grade 3). A large aneurysmal lesion was noted anterior to the right side of the medulla oblongata, without intracerebral hemorrhage or acute hydrocephalus. CT angiography demonstrated a PPHA originating from the right cervical internal carotid artery, entering the posterior cranial fossa through the hypoglossal canal, and joining the basilar artery; a large aneurysm was located at this segment (Fig. 1A and B). Chest imaging demonstrated symmetrical ground-glass opacities in both lungs without cardiomegaly, consistent with neurogenic pulmonary edema.

FIG. 1.

A: CT angiogram revealing a PPHA passing through the hypoglossal canal into the posterior cranial fossa. B:Three-dimensional CT angiogram revealing the PPHA with a large aneurysm at the junction with the vertebral artery; the contralateral vertebral artery is hypoplastic. C and D:Anteroposterior (C) and lateral (D) right internal carotid artery angiograms demonstrating a PPHA arising from the cervical segment of the internal carotid artery, which makes an abrupt anterior turn with a curved course and serves as the almost sole arterial supply to the posterior circulation. E and F:Three-dimensional rotational angiograms showing a large, wide-necked, sidewall-type aneurysm; no apparent perforating arteries or involvement of the PICA was identified in the vicinity of the aneurysmal neck.

The patient was diagnosed with subarachnoid hemorrhage due to rupture of a large, wide-necked aneurysm associated with a PPHA, which was classified as World Federation of Neurosurgical Societies grade V and Hunt and Kosnik grade V. She developed severe hypoxemic respiratory failure attributed to neurogenic pulmonary edema, and endotracheal intubation was performed in the emergency department. Hemodynamic status remained otherwise stable, and prevention of rebleeding was prioritized. Endovascular coil embolization was undertaken under general anesthesia on hospital day 1.

Digital subtraction angiography (DSA) demonstrated a PPHA arising from the cervical segment of the internal carotid artery, which makes an abrupt anterior turn with a curved course and serves as the almost sole arterial supply to the posterior circulation (Fig. 1C and D). Three-dimensional rotational angiography demonstrated that the posterior inferior cerebellar artery (PICA) did not originate near the aneurysmal neck, and the right PICA territory was supplied by the ipsilateral anterior inferior cerebellar artery. No definite perforating arteries were identified in the vicinity of the aneurysmal neck. The contralateral left vertebral artery was present but measured less than half the diameter of the right vertebral artery (Fig. 1E and F). The aneurysm had dimensions of 13.2 × 13.8 × 11.2 mm and a neck width of 6.72 mm (Fig. 2A and B). Although stent-assisted coil embolization was considered, given the ruptured status and large size of the aneurysm, simple coiling without stent assistance was performed in the acute phase to minimize the risk of rebleeding, with a plan for delayed FD therapy. Via right femoral access, a 6-Fr, 25-cm sheath (Terumo) was placed. A 6-Fr BENCHMARK 071 guiding catheter (105 cm, Medicos Hirata) was advanced from the right cervical internal carotid artery to the proximal segment of the PPHA. A Scepter XC balloon catheter (150 cm, Terumo) was positioned over a Traxcess microguidewire (200 cm, Terumo) near the aneurysmal neck, and an Excelsior SL-10 microcatheter (150 cm, Stryker Japan) was navigated into the aneurysm sac over a Venture 14 microguidewire (200 cm, Mizuho). Framing was achieved with AXIUM PRIME FRAME coils (16 mm × 50 cm and 14 mm × 50 cm, Medtronic Japan), followed by deployment of 11 i-ED Coil ∞ coils (cumulative length 230 cm, Kaneka) and 9 HydroSoft 3D coils (cumulative length 110 cm, Terumo). In total, 440 cm of coils were inserted, yielding a volume embolization ratio of approximately 20.2%. Mild parent artery narrowing was suspected on the final angiogram, and gentle percutaneous transluminal angioplasty was performed with a balloon catheter. The final angiographic result demonstrated complete aneurysm occlusion (Fig. 2C–F).

FIG. 2.

A and B:Three-dimensional rotational angiogram demonstrating an aneurysm with a neck width of 6.72 mm and overall dimensions of 13.2 × 13.8 × 11.2 mm. C and D:Anteroposterior (C) and lateral (D) working-angle views obtained during the intervention. E and F: Final working-angle angiograms demonstrating complete aneurysm occlusion. G and H:Anteroposterior (G) and lateral (H) follow-up angiograms obtained 1 year after the initial treatment, revealing aneurysm recanalization.

Postoperatively, MRI performed on hospital day 5 showed no acute ischemic lesions, and MRA confirmed complete aneurysm occlusion without parent artery stenosis. Intravenous clazosentan was administered for vasospasm prophylaxis. The patient experienced no symptomatic cerebral vasospasm or hydrocephalus and was transferred to a rehabilitation hospital on hospital day 22 with an mRS score of 5, which subsequently improved to a score of 1 at discharge home on hospital day 74.

At approximately 1 year, follow-up DSA demonstrated recanalization of the aneurysm (Fig. 2G and H), and definitive treatment with an FD was planned. Antiplatelet function was assessed preoperatively using the VerifyNow system (I.L. Japan Co., Ltd.). Under general anesthesia, the right femoral artery was accessed, and a 6-Fr FUBUKI guiding sheath (Asahi Intecc) was advanced into the PPHA. Using a 5-Fr SOFIA SELECT intermediate catheter (Terumo) and a Headway Plus 27 microcatheter (Terumo), we navigated the microcatheter distal to the aneurysm. A FRED FD (3.5 mm × 22 mm, Terumo) was deployed predominantly by simple unsheathing (Fig. 3A–C). Postdeployment angiography showed contrast stagnation within the aneurysm (Fig. 3D). Cone-beam CT confirmed adequate device expansion and good wall apposition, and no adjunctive balloon angioplasty was required (Fig. 3E).

FIG. 3.

A–C:Intraoperative angiograms demonstrating easy deployment of the FRED (A) and adequate coverage of the aneurysmal neck (B and C). D:Post–FRED deployment cerebral angiogram demonstrating contrast stagnation within the aneurysm sac (arrow). E: Cone-beam CT image confirming good apposition of the device to the vessel wall.

The postoperative course was uneventful, and the patient was discharged home without complications. Follow-up MRI at 3 months demonstrated intra-aneurysmal thrombosis (Fig. 4), and DSA at 6 months confirmed complete aneurysm occlusion (Fig. 5).

FIG. 4.

A and B: Time-of-flight MR angiograms obtained 1 month after the additional treatment, demonstrating residual intra-aneurysmal flow (arrows). C and D: Follow-up images obtained at 3 months, demonstrating satisfactory intra-aneurysmal thrombosis (arrowheads).

FIG. 5.

A and B:Follow-up 3D rotational angiograms obtained at 6 months confirming complete aneurysm occlusion.

At the 1-year follow-up, the patient remained neurologically intact without new deficits, with an mRS score of 0.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

A PPHA represents a persistent carotid-vertebrobasilar anastomosis from embryonic development. During the 4th to 5th weeks of gestation, transient segmental arteries connect the developing basilar artery to the internal carotid artery; these vessels normally regress with maturation of the vertebral arteries and posterior communicating arteries. Persistence of the hypoglossal artery results in a PPHA, an embryonic channel linking the anterior and posterior circulations.¹ Anatomically, a PPHA typically arises from the extracranial internal carotid artery at the level of the first to third cervical vertebrae, traverses the hypoglossal canal to enter the posterior cranial fossa, and anastomoses with the vertebral artery or the proximal basilar artery. In most cases, the vertebral artery is absent or hypoplastic.²

Several extremely rare variants of PPHA have been reported, including type 2 PPHA originating from the external carotid artery³ and variants in which the vessel passes through the hypoglossal canal anastomoses with the PICA. In type 2 variants, differentiation from a posterior meningeal artery arising from the hypoglossal branch of the ascending pharyngeal artery may be challenging; however, they can be distinguished by whether the distal territory supplies brain parenchyma (PPHA) or dura mater (posterior meningeal artery).⁴ Bilateral PPHA has also been reported, albeit extremely rarely.⁵

Epidemiologically, PPHA itself is a rare vascular anomaly, with a reported incidence of 0.027%–0.26%,^1–3 and cerebral aneurysms co-occur in approximately 20%–30% of patients with PPHA.^1,6 Among these aneurysms, 31.4% arise on the PPHA itself, whereas 53% occur in the posterior circulation.⁷ Regarding the pathogenesis of aneurysm formation in PPHA, it has been suggested that absence of the posterior communicating arteries and hypoplasia of the vertebral arteries result in posterior circulation flow highly dependent on the PPHA.^6–8 This hemodynamic configuration may increase shear stress at branching and anastomotic sites, particularly at the PPHA–basilar artery junction and the internal carotid artery–PPHA bifurcation, thereby promoting aneurysm formation, growth, and recurrence. In addition, intrinsic fragility of the PPHA vessel wall has been proposed as a contributing factor.^1,7,9,10

In the present case, the aneurysm arose at the segment where the PPHA traversed the hypoglossal canal, entered the posterior cranial fossa, and then sharply curved anteriorly to join the vertebrobasilar system. It is conceivable that marked hemodynamic stress was concentrated at this steep vascular curvature. Given this anticipated hemodynamic burden and the presence of a large, wide-necked aneurysm, the risks of recurrence and rebleeding were considered relatively high. To promote intra-aneurysmal thrombosis and reduce the likelihood of recanalization, coil embolization using hydrogel-coated coils was performed during the initial treatment.¹¹ Furthermore, anticipating the potential need for retreatment with an FD, stent-assisted techniques were avoided, and balloon-assisted coiling was selected. The distal access catheter could be advanced close to the aneurysmal neck, allowing stable embolization and achievement of a volume embolization ratio exceeding 20% without stent use. Complete occlusion corresponding to Raymond-Roy class I was achieved, reflecting dense coil packing. Although the proportion of hydrogel coils did not reach the reported 50%–75% threshold associated with a significant reduction in recanalization rates, embolization was performed with maximal feasible use of hydrogel coils to facilitate progressive thrombosis.^11–13

This strategy was considered sufficient to prevent rebleeding in the acute phase and was expected to provide a reasonably durable long-term occlusion. Nevertheless, aneurysm recanalization was detected relatively early, approximately 1 year after treatment.

Although careful radiographic surveillance was considered at that stage, observation alone was deemed insufficient. Residual filling after coil embolization in ruptured aneurysms cannot be regarded as entirely benign and may carry a potential risk of rerupture.¹⁴ Given that the aneurysm was ruptured, large, and located on a PPHA subjected to substantial hemodynamic stress, concerns regarding coil compaction, recurrence, and possible rerupture were significant. In this context, definitive retreatment was considered more appropriate than continued observation.

For retreatment, FD placement was selected over repeat coil embolization, with the expectation of achieving durable long-term healing. Given that pronounced hemodynamic stress and vessel wall fragility may contribute to PPHA-associated aneurysm formation,^1,7,9 FD-induced endothelialization was deemed a rational curative strategy.

A review of the literature on initial management of PPHA-associated aneurysms suggests that, although microsurgical clipping was reported in earlier eras, advances in endovascular techniques have made endovascular therapy the predominant approach.^{6–10,15–19} While some aneurysms have been treated relatively straightforwardly with conventional coil embolization,^8,9,15 cases of recurrence and rebleeding have also been reported.^10,17 Particularly challenging cases involve complex vascular anatomy, such as associations with basilar artery fenestration or proximity to PICA branching.^7,16–19 In these settings, securing an optimal working angle and maintaining stable microcatheter positioning can be difficult. To improve catheter stability, proximal flow control using balloon occlusion has been described,^10,19 and stent-assisted embolization has been utilized even in the acute rupture phase when necessary.^16–18

In patients with a PPHA, both the ipsilateral and contralateral vertebral arteries are frequently hypoplastic or absent. Consequently, thromboembolic complications related to stent placement could result in ischemia affecting the entire posterior circulation.^6–8,18 If stent assistance is unavoidable, careful preprocedural assessment of the contralateral vertebral artery and institution of appropriate antiplatelet therapy are essential. Given reports of early recurrence or rebleeding after coil embolization,^10,17 consideration of FD therapy after the acute phase may be warranted when appropriate.

In the present case, although the contralateral vertebral artery was visualized on angiography, its small caliber raised concern that complete occlusion of the ipsilateral vertebral artery could critically compromise posterior circulation perfusion, necessitating particular caution. Marked vascular tortuosity at the PPHA origin and anastomotic segments required meticulous navigation of the distal access catheter. To minimize thrombotic complications, preoperative platelet reactivity was assessed using the VerifyNow system.²⁰ Deployment of the FD was facilitated by the characteristics of the FRED, allowing smooth deployment with an almost simple unsheathing maneuver.²¹ Even in the presence of severe vascular tortuosity, FRED deployment may be relatively straightforward provided that the intermediate catheter can be advanced sufficiently to ensure stable support.

In addition to ease of deployment, FRED is characterized by a dual-layer mesh design consisting of an outer low-density, high-porosity scaffold and an inner high-density mesh, intended to preserve perforator patency. The central portion covering the aneurysmal neck provides a strong flow-diverting effect, whereas the higher porosity of the outer mesh covering perforators and branch vessels facilitates maintenance of physiological blood flow.²² In the multicenter SAFE study,²³ the rate of adequate occlusion (complete occlusion plus neck remnant) was 69.5% at 6 months and 81.1% at 12 months, with favorable safety outcomes, including neurological deterioration with an mRS score > 2 in 2.9% and an overall mortality rate of 1.9% at 1 year. Furthermore, the newer FRED X incorporates surface modification aimed at reducing thrombogenicity.²⁴ These features are particularly advantageous for preserving perforators supplying the brainstem in settings where the posterior circulation is dependent on the PPHA.

In the present case, angiography demonstrated a so-called no-PICA type configuration, which has been reported to be associated with a higher number of perforating arteries compared with the typical configuration.²⁵ Although detailed evaluation of perforator anatomy is essential during treatment planning, the structural characteristics of FRED may confer advantages for perforator preservation. Despite the widespread adoption of FD therapy, peer-reviewed case reports specifically describing FD treatment of PPHA-associated aneurysms remain extremely limited. Most reported PPHA aneurysms have been treated with coil embolization, and clinical experience with FD devices such as FRED in this specific context remains limited.

For PPHA-associated aneurysms, comprehensive anatomical assessment is essential, including evaluation of posterior circulation dependence on PPHA, delineation of perforators, appraisal of the contralateral vertebral artery, and identification of vascular variants such as fenestrations. In light of aneurysm morphology and the anticipated risk of recurrence, incorporation of FD therapy into the treatment strategy appears reasonable.

Lessons

For PPHA-associated aneurysms, particularly when the posterior circulation is PPHA dependent and characterized by a high density of perforators, an approach that secures the rupture risk with stentless coiling in the acute phase, followed by implementation of delayed flow diversion for durable reconstruction, is feasible and may optimize outcomes. In order to refine patient selection, device choice, and antithrombotic protocols in this rare but high-stakes anatomy, larger series and longer-term data are required.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Hayashi, Goda, Nakayasu. Acquisition of data: Goda, Murai. Analysis and interpretation of data: Hayashi, Goda, Murai. Drafting the article: Hayashi, Goda. Critically revising the article: Hayashi, Goda, Nakayasu. Reviewed submitted version of manuscript: Hayashi, Goda, Imanishi, Murai. Approved the final version of the manuscript on behalf of all authors: Hayashi. Statistical analysis: Goda. Administrative/technical/material support: Goda, Maeda, Murai. Study supervision: Hayashi, Murai.

Correspondence

Hideki Hayashi: Uji Tokushukai Medical Center, Kyoto, Japan. nrsrgnhd@gmail.com.