Delayed transient optic neuritis after flow diverter placement with coil embolization for an asymptomatic paraclinoid internal carotid artery aneurysm: illustrative case

Abstract

BACKGROUND

Delayed optic neuropathy after flow diversion for paraclinoid internal carotid artery (ICA) aneurysms has mainly been reported in patients with preoperative mass effect; risk in asymptomatic, electively treated patients is unclear. The authors report transient, steroid-responsive optic neuritis after Pipeline Shield placement with coiling for an asymptomatic paraclinoid aneurysm.

OBSERVATIONS

A woman in her 50s underwent elective flow diversion for a growing, asymptomatic left paraclinoid ICA aneurysm (10.4 mm). A Pipeline Shield and two coils were deployed uneventfully; she was discharged on day 5. On day 10, she developed progressive vision loss. Fundoscopy was normal, but critical flicker frequency (CFF) was reduced and a paracentral scotoma was present, indicating retrobulbar optic neuropathy. MRI showed a doughnut sign without aneurysm enlargement, distinguishing inflammatory from compressive or ischemic mechanisms. Corticosteroid therapy produced complete recovery within 1 month, with CFF normalization.

LESSONS

Delayed optic neuritis can follow flow diversion in preoperatively asymptomatic patients; proximity of the optic nerve to the aneurysm, rather than mass effect, confers this risk. A normal fundus, reduced CFF, a scotoma, and a doughnut sign without sac enlargement identify inflammatory optic neuritis and warrant prompt corticosteroid treatment. Elective paraclinoid flow diversion merits counseling and early visual surveillance even when asymptomatic.

https://thejns.org/doi/10.3171/CASE26638

Paraclinoid internal carotid artery (ICA) aneurysms arise in close proximity to the optic nerve as it enters the optic canal, and their treatment, whether open surgical or endovascular, carries a ­well-recognized risk of visual injury from direct mechanical compression or inflammatory involvement of the nerve.^1,2 Flow diversion has become a mainstay of treatment for large or complex paraclinoid aneurysms and is effective in relieving compressive neuro-ophthalmological symptoms, with pooled rates of visual improvement of approximately 57% and complete visual recovery of approximately 31%.^2,3

Flow diversion is now also applied electively to asymptomatic paraclinoid aneurysms demonstrating interval growth, and emerging evidence suggests that visual risk is not confined to patients who are symptomatic at baseline. In a retrospective cohort of 32 aneurysms treated with flow diversion, 1 of 24 aneurysms without preoperative visual symptoms subsequently developed delayed postoperative visual dysfunction, and an additional 3 of 24 (12.5%) demonstrated poor ophthalmic artery visualization on completion angiography despite remaining clinically asymptomatic, indicating a broader spectrum of subclinical vulnerability than symptomatic status alone would suggest.⁴ Isolated case reports have similarly described severe, occasionally treatment-refractory optic neuropathy after endovascular treatment of paraclinoid aneurysms, underscoring that this complication, while uncommon, can be clinically significant when it occurs.⁵

Visual deterioration after endovascular treatment of a paraclinoid aneurysm may arise through at least three distinct mechanisms: retinal or ophthalmic arterial ischemia, which usually occurs within hours of the procedure;^6,7 compressive mass effect from a thrombosing, transiently enlarging sac, which typically evolves over days to weeks;^8,9 and inflammatory optic neuritis or perineuritis triggered by intra-aneurysmal thrombus, characterized by a doughnut sign on MRI.^4,5,10 These entities demand fundamentally different responses, namely antithrombotic therapy, retreatment or decompression, and corticosteroid therapy, respectively, yet they can be difficult to distinguish at the bedside.

Reported cases of posttreatment optic neuropathy have predominantly involved aneurysms that were symptomatic before treatment, producing mass effect on the visual apparatus,^2,3,8,9 and dedicated data on visual outcomes in preoperatively asymptomatic patients remain limited to a single cohort.⁴ Consequently, the visual risk faced by patients treated electively for asymptomatic aneurysm growth is not well characterized, and structured visual surveillance is not routinely applied in this population. The purpose of this report is to describe delayed, transient, steroid-responsive optic neuritis in such a patient and to outline a practical approach to distinguishing the mechanisms of vision loss after flow diversion.

Illustrative Case

History and Examination

A woman in her 50s with known bilateral ICA aneurysms had been followed conservatively. The left paraclinoid aneurysm demonstrated interval growth on serial imaging and was referred for elective endovascular treatment. She was entirely asymptomatic, with no visual complaints, headache, or cranial nerve deficit. Preoperative angiography demonstrated a left paraclinoid ICA aneurysm with a maximum diameter of 10.4 mm and a neck width of 4.6 mm (Fig. 1A and B). The ophthalmic artery was not opacified from this side. The right ICA aneurysm was stable and was managed conservatively.

FIG. 1.

Preoperative and postoperative images and visual field findings. A: Three-dimensional volume-rendered reconstruction of the left ICA showing the paraclinoid aneurysm (arrow; maximum diameter 10.4 mm, neck width 4.6 mm). B: Working-angle 2D digital subtraction angiogram of the same aneurysm (arrow); the ophthalmic artery is not opacified. C: Digital subtraction angiogram obtained after treatment showing partial obliteration of the aneurysm (arrow) following placement of the flow diverter and two coils. D: Cone-beam CT image showing the flow diverter (arrowheads) crossing the neck of the coil-filled aneurysm (arrow). E: Goldmann visual field examination of the left eye after treatment, demonstrating a paracentral scotoma. F: Gadolinium-enhanced coronal MR image obtained at the onset of visual symptoms showing a slightly enhancing rim around the left optic nerve, the doughnut sign (arrow). The contralateral right optic nerve shows no abnormal enhancement (arrowhead).

Operative Procedure

Under general anesthesia and dual antiplatelet therapy with aspirin and clopidogrel, a Pipeline Shield device (Medtronic) was deployed across the aneurysm neck. Two i-ED Infini coils (secondary diameter, length: 4–8 mm, 30 cm; 5–12 mm, 50 cm; Kaneka Medix Corporation) were then placed within the sac to promote thrombosis and reduce the risk of delayed rupture,¹¹ yielding a volume embolization ratio of 17%, a comparatively high packing volume for coiling adjunctive to flow diversion, rather than the sparser packing that would result from the shorter, smaller-diameter coils often selected in this setting (Fig. 1C and D). The procedure was completed without technical or neurological complications. Postoperative angiography confirmed satisfactory device apposition and partial aneurysm obliteration.

Postoperative Course

The patient was discharged on postoperative day 5 in good neurological condition and without visual symptoms. On postoperative day 10, she noted progressive blurring of vision in the left eye with left ocular pain, which worsened over several days. Ophthalmological evaluation revealed a normal fundus. Critical flicker frequency (CFF) was markedly reduced in the left eye, and visual field testing demonstrated a paracentral scotoma (Fig. 1E), findings consistent with retrobulbar optic neuropathy. MRI of the orbits and optic nerves demonstrated a doughnut-shaped area of high signal surrounding the left optic nerve, the doughnut sign (Fig. 1F), without interval enlargement of the aneurysm sac or displacement of the optic apparatus, indicating inflammatory optic neuritis adjacent to the thrombosing aneurysm rather than compressive or ischemic injury.⁵

Intravenous corticosteroid therapy was initiated promptly with methylprednisolone 1000 mg/day for 3 days, followed by an oral taper starting at betamethasone 4 mg/day and tapered by 1 mg weekly. Visual symptoms and ocular pain improved progressively, and complete clinical recovery was achieved within 1 month of symptom onset. Repeat CFF testing was normal, and there was no recurrence during subsequent follow-up.

Patient Perspective

The patient described considerable anxiety on first noticing the blurring of her vision, as this developed unexpectedly after she had been entirely asymptomatic before treatment. As her vision gradually improved with corticosteroid therapy, she reported that this anxiety diminished correspondingly, and she expressed relief once her vision had fully returned to normal.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

This case demonstrates that delayed inflammatory optic neuritis can follow flow diversion of a paraclinoid ICA aneurysm in a preoperatively asymptomatic patient, and that it may be fully reversible if recognized and treated promptly with corticosteroids.

This report is distinguished from previous literature by three key novel features. First, whereas prior studies by Moon et al.⁸ and Tanaka et al.⁴ attributed post–flow diversion visual deficits to a compressive mass effect from thrombus-related sac enlargement, our patient exhibited a purely inflammatory mechanism (doughnut sign) without sac expansion. Second, unlike previous cohorts in which patients had preexisting visual compromise or persistent deficits at final follow-up,^4,5,8 our patient achieved complete visual recovery. Third, we provide objective, quantitative documentation of retrobulbar function recovery via the normalization of CFF, a measure lacking in earlier reports. To our knowledge, this is the first reported case of fully reversible doughnut sign optic neuritis with objective CFF normalization following elective flow diversion for an asymptomatic, growing paraclinoid aneurysm.

Mechanisms of Posttreatment Vision Loss

Because the three principal mechanisms of postendovascular visual deterioration demand opposing therapeutic strategies, rapid clinical differentiation is essential (Table 1).

TABLE 1.

Distinguishing the three mechanisms of visual deterioration after endovascular treatment of a paraclinoid ICA aneurysm

Type	Mechanism	Onset	Visual Pattern	Fundoscopy	Key Imaging	Treatment	Outcome
Arterial ischemia6,7	Ophthalmic or central retinal artery thromboembolism or hypoperfusion	Intraop to hrs	Sudden, often profound monocular loss; altitudinal or sectoral field loss	Retinal whitening, edema, cherry-red spot, visible embolus	Retinal fluorescein angiography; no optic nerve signal change	Antithrombotic therapy (e.g., glycoprotein IIb/IIIa inhibitor); steroids ineffective	Often permanent if not reversed w/in hrs
Compressive mass effect3,8,9,12	Transient sac expansion during intra-aneurysmal thrombosis	Days to wks	Progressive field loss; bitemporal or junctional pattern if chiasm involved	Normal	Interval enlargement of thrombosing sac; displacement of optic nerve or chiasm	Consider retreatment or surgical decompression; steroids of limited benefit	Frequently sustained, especially if symptom duration is prolonged
Inflammatory optic neuritis5	Perianeurysmal inflammation from rapid intra-aneurysmal thrombus, extending to optic nerve sheath	~1–2 wks (subacute)	Reduced CFF; central or paracentral scotoma (retrobulbar pattern)	Normal	Doughnut sign on coronal STIR/CISS around optic nerve; no sac enlargement	Prompt corticosteroid therapy	Often reversible if treated early; may be refractory & permanent if fulminant

CISS = constructive interference in steady state; STIR = short tau inversion recovery.

Ischemic events involving the ophthalmic or central retinal artery typically occur within hours of the procedure, present with fundoscopic abnormalities such as retinal whitening, and respond to antithrombotic therapy rather than corticosteroid treatment.^6,7 Rouchaud et al. underscored the necessity of early formal ophthalmological examination after noting new ophthalmic complications in 39.3% of patients whose ophthalmic artery origin was covered by a flow diverter, with retinal emboli occurring in 17.9%.⁶

Compressive neuropathy evolves more slowly over days to weeks and is characterized by radiographic enlargement of the thrombosing aneurysm sac or mechanical displacement of the optic apparatus.^4,8,9 Corticosteroids provide limited utility for this structural mass effect, which typically requires surgical decompression or endovascular retreatment.

Inflammatory optic neuritis, by contrast, presents subacutely with a normal fundus, an afferent pattern of dysfunction (comprising reduced CFF and central or paracentral field deficits), and a classic doughnut sign on coronal short tau inversion recovery or constructive interference in steady state sequences without concurrent sac enlargement.⁵ Unlike the ischemic or compressive etiologies, this inflammatory mechanism is uniquely responsive to prompt corticosteroid therapy.^5,10 The presentation in our patient corresponded precisely to this third, inflammatory pattern, justifying immediate corticosteroid administration.

Timing of Recognition and Treatment

Time to treatment is the dominant modifiable determinant of visual outcome, although the critical therapeutic windows differ by mechanism. For compressive neuropathy, multiple studies underscore the necessity of early intervention. In a meta-analysis of 594 patients treated with flow diversion for compressive ICA aneurysms, Kaiser et al. demonstrated that symptom improvement was greater than 10-fold more likely when intervention was initiated within 1 month of symptom onset.² Similarly, Akiyama et al. found that an onset-to-treatment time shorter than 6 months independently predicted improvement,¹² whereas Moon et al. reported that a symptom duration exceeding 2 months strongly predicted a failure of recovery.⁸

For the inflammatory mechanism, the therapeutic window is often even more urgent. When the postendovascular inflammatory response is fulminant or left untreated, it can quickly become steroid resistant, culminating in permanent vision loss and irreversible optic nerve degeneration.¹⁰ The complete visual recovery achieved in our patient highlights the favorable end of this spectrum. Our experience supports the immediate initiation of corticosteroid therapy as soon as an inflammatory pattern is recognized, rather than opting for a conservative period of clinical observation.

A Surveillance Gap in Asymptomatic Patients

Patients treated electively for an asymptomatic aneurysm, by definition, have no baseline visual deficits to track and are therefore highly unlikely to undergo structured postdischarge visual assessments. Our patient, for instance, was discharged on postoperative day 5 and only detected her deficit when it became symptomatic on day 10.

This surveillance blind spot is widespread. Akiyama et al. reported that neuro-ophthalmological evaluations were performed preoperatively in only 71% of patients and at follow-up in only 44%.¹² Similarly, Tanaka et al. reported that postoperative visual symptoms were primarily self-reported because systematic ophthalmological testing was not routinely performed.⁴ Crucially, Rouchaud et al. demonstrated that post–flow diversion visual field defects can remain entirely asymptomatic, making them detectable only by formal examination.⁶

Rather than mandating neuro-ophthalmological evaluation in every patient, however, we suggest a risk-stratified approach. Preoperative assessment, including baseline CFF and perimetry, is most warranted when the size and morphology of a paraclinoid aneurysm place the sac in direct contact with or immediately adjacent to the optic nerve, since these are the patients in whom perianeurysmal inflammation is most likely to affect the nerve. For all patients undergoing paraclinoid flow diversion, including those who are asymptomatic, we nonetheless recommend preoperative counseling about the risk of delayed visual deterioration and explicit instruction to report any visual change immediately, so that corticosteroid therapy can be initiated without delay. In our case, CFF proved a simple and reproducible bedside tool: it detected clinical retrobulbar dysfunction when the fundus appeared entirely normal, providing objective, quantitative documentation of both the deficit and its recovery.

The Role of Adjunctive Coils

Adjunctive coils are frequently added to flow diversion to reduce the risk of delayed aneurysm rupture, a catastrophic complication attributed to residual inflow-zone jetting and thrombus-induced degeneration of the aneurysm wall.^11,13 However, it is notable that documented cases of postendovascular inflammatory optic neuritis, including those reported by Tanaka et al. and our own, have frequently involved these intrasaccular coils.^4,5 Furthermore, severe, steroid-refractory optic neuropathy has been described after coil embolization alone, without a flow diverter.¹⁰

A unifying hypothesis is that the accelerated rate and volume of intra-aneurysmal thrombus formation, rather than the specific endovascular device used, drives the local perianeurysmal inflammatory response.^4,10,13 While this observation is currently hypothesis generating, adjunctive coiling has been shown to accelerate complete aneurysm occlusion.³ In our case, the two coils had relatively large secondary diameters and long lengths and produced a comparatively high packing volume (volume embolization ratio 17%), so that a substantial thrombus mass was established rapidly within a sac lying in direct contact with the optic nerve, whereas sparser packing with shorter coils would plausibly have generated a smaller and more slowly organizing thrombus burden. If the rate and volume of thrombosis are indeed the operative variables, coil selection, and not merely the decision to add coils, may modulate this risk, which argues for routine reporting of coil dimensions and packing metrics in future series of visual complications after flow diversion. Ultimately, the clinical trade-off between delayed rupture prophylaxis and the risk of perianeurysmal inflammation in paraclinoid aneurysms merits systematic, prospective study.

Lessons

Delayed optic neuritis can follow flow diversion of a paraclinoid ICA aneurysm even in patients who are entirely asymptomatic before treatment. Proximity of the optic nerve to the aneurysm—rather than preexisting mass effect—appears to confer this risk, so visual complications should be anticipated and discussed even in elective, asymptomatic cases.

A normal fundus, reduced CFF, a central or paracentral scotoma, and a doughnut sign on MRI without sac enlargement together identify inflammatory optic neuritis and distinguish it from ischemic and compressive causes (Table 1). This distinction guides treatment, since corticosteroid therapy is effective for the inflammatory mechanism but not for the other two; therapy should begin as soon as the pattern is recognized, as delay is the principal modifiable risk factor for permanent deficit.

This report is limited by its single-case design, which precludes any inference about causation or incidence. The inflammatory mechanism is supported by imaging findings and corticosteroid response but was not confirmed histologically, and the contribution of adjunctive coiling cannot be established. Follow-up extended to only 1 month after symptom resolution, so late recurrence cannot be excluded. Despite these limitations, the case illustrates a recognizable and treatable syndrome and supports counseling all patients undergoing paraclinoid flow diversion about delayed visual deterioration, with monitoring for visual change after discharge, since no baseline deficit exists to prompt routine follow-up otherwise.

Acknowledgments

We acknowledge Hiroki Toda, MD, PhD, and Jun Hashimoto, MD, for their contributions to the preparation and editing of the manuscript.

We used Claude (Opus 4.8, Anthropic) to assist with language editing and manuscript formatting. We reviewed and verified all content for accuracy and assume full responsibility for the final manuscript.

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: both authors. Acquisition of data: Agawa. Analysis and interpretation of data: both authors. Drafting the article: Agawa. Critically revising the article: Agawa. Reviewed submitted version of manuscript: Agawa. Approved the final version of the manuscript on behalf of both authors: Agawa. Statistical analysis: Agawa. Administrative/technical/material support: both authors. Study supervision: both authors.

Correspondence

Yuji Agawa: Kokura Memorial Hospital, Kitakyushu, Fukuoka, Japan. y-agawa@kitano-hp.or.jp.