Ring-Like Aneurysms Show Alarming 37.5% Rupture Rate in Systematic Analysis

What Is the Significance of Ring-like Aneurysms?

Researchers have defined a distinct type of intracranial aneurysm with a circumferential lumen surrounding a central thrombus, reporting a significantly elevated rupture rate of 37.5% among 16 documented cases. The systematic review, published in the journal Diagnostics, distinguishes "ring-like aneurysms" from the radiological "donut sign" and proposes they represent an unstable, high-risk configuration requiring prompt intervention rather than a stable thrombotic state.

The study, which examined English-language reports from 1996 to 2024, consolidates the first comprehensive analysis of ring-like aneurysms as a distinct morphological entity. The researchers clarify that while the "donut sign" is merely an imaging descriptor that may appear in various aneurysm types, ring-like aneurysms represent a specific structural configuration with unique hemodynamic properties. This distinction has remained ambiguous in medical literature until now, despite the term's initial introduction by Ogawa et al. in 1996 and subsequent popularization by van Rooij et al. in 2014. The researchers propose that these aneurysms maintain their distinctive shape through a focused, tangential inflow jet that circulates along the aneurysm wall, creating a patent mural ring while preventing complete thrombosis. This dynamic flow architecture appears to contribute to the high rupture potential observed across the pooled dataset, where the 37.5% rupture prevalence substantially exceeds both annual population estimates (1.6-6.5%) and even lifetime rupture risk (~30%) for typical intracranial aneurysms. All documented cases involved large or giant aneurysms measuring at least 14mm in diameter, with a female predominance (69%) and frequent posterior circulation involvement (44%), particularly at the basilar tip. The overall mortality rate among evaluable patients was 20%, highlighting the clinical significance of proper identification and management of these lesions.

How Does the Aneurysm Morphology Evolve Under Hemodynamic Stress?

The research team further subdivides ring-like aneurysms into two patterns—bifurcation-type and trunk-type—based on their relationship to branching vessels, each associated with distinctive circulation dynamics. "The ring-like lumen is not a definitive anatomic subtype but a flow-dependent configuration sustained by shear-driven mural circulation," the authors explain, emphasizing the dynamic nature of this morphology. They document cases where the configuration emerged weeks after stent implantation in some patients, while in others, a clearly defined ring-like appearance disappeared during the interval between diagnostic imaging and planned treatment. This transformation indicates that the configuration fluctuates based on instantaneous hemodynamic conditions rather than stable structural features. The researchers propose that the "eaten apple-core" configuration of the central thrombus creates direct contact with the aneurysm wall, exposing these regions to inflammatory, proteolytic, and hypoxic injury mechanisms that, when combined with circumferential jet-inflow stress, may explain the elevated rupture risk. Histologic and 7T MRI studies have previously shown that partially thrombosed aneurysms harbor vasa vasorum proliferation, inflammation, and intramural hemorrhage adjacent to the thrombus—biological processes that can weaken the wall, particularly in regions exposed to shear stress.

Can Flow Diversion Tame the High-Risk Anatomy?

The study advocates for flow-diverter reconstruction as a physiologically plausible treatment approach. By suppressing tangential inflow and modifying wall-shear distribution, these devices promote gradual thrombosis and healing. However, the researchers caution that transient perianeurysmal edema may occur post-treatment, reflecting wall inflammation and thrombus reorganization. In some instances, delayed rupture has been documented either spontaneously or after incomplete hemodynamic exclusion, underscoring the importance of early and complete endovascular reconstruction of the inflow zone. "Radiologically, the ring-like configuration may be mistaken for stable thrombosis, but it should be interpreted as a hemodynamic warning," the authors emphasize, noting documented cases of ring-like aneurysms rupturing without warning in both adults and children. The team distinguishes these aneurysms from serpentine aneurysms, which feature separate inflow and outflow tracts and characteristically sluggish intra-aneurysmal flow, whereas ring-like aneurysms maintain a single neck with a focused, mural inflow jet that appears to confer reduced stability and higher rupture propensity.

What Future Insights Could Optimize Aneurysm Management?

Looking forward, the researchers recommend combining patient-specific computational fluid dynamics (CFD) with serial MRI and histologic correlation to better characterize shear-stress conditions associated with rupture risk. They suggest that dedicated CFD simulations of ring-like aneurysms are warranted to identify hemodynamic patterns that may precede or contribute to rupture, potentially bridging the current gap between morphologic observation and quantitative hemodynamic analysis. The establishment of a prospective registry of ring-like aneurysms could further clarify their natural history and treatment outcomes. "Early identification of this morphology and timely flow-modifying treatment may be important in preventing progression to rupture," the authors conclude, highlighting the clinical significance of their findings for neurointerventional practice and patient care. The study represents an important step forward in understanding a distinct and high-risk aneurysm subtype that requires specialized management strategies.

How Could These Findings Impact the Industry Landscape?

Industry Context: This research aligns with growing industry focus on precision neurovascular diagnostics and targeted interventional approaches. As device manufacturers continue developing next-generation flow diverters and advanced imaging technologies, the identification of specific high-risk aneurysm subtypes provides crucial guidance for both product development and clinical application. The findings may influence treatment algorithm development within healthcare systems and could drive increased adoption of flow-modifying devices specifically tailored to address the unique hemodynamics of ring-like aneurysms, representing a specialized but critically important segment of the neurovascular intervention market.

Summary

A systematic review published in Diagnostics has identified ring-like aneurysms as a distinct, high-risk subtype of intracranial aneurysm characterized by a circumferential lumen surrounding a central thrombus. Analysis of 16 documented cases revealed a rupture rate of 37.5%, substantially exceeding typical annual population estimates of 1.6-6.5% and even lifetime rupture risk of approximately 30% for conventional intracranial aneurysms. The researchers clarify that ring-like aneurysms represent a specific structural configuration maintained by a focused tangential inflow jet circulating along the aneurysm wall, distinguishing them from the radiological "donut sign" which merely describes an imaging appearance. All documented cases involved large or giant aneurysms measuring at least 14mm in diameter, with 69% occurring in females and 44% involving posterior circulation, particularly at the basilar tip. The overall mortality rate among evaluable patients reached 20%. The study demonstrates that this configuration is flow-dependent and can emerge or disappear based on hemodynamic conditions, sometimes developing weeks after stent implantation or vanishing between diagnostic imaging and planned treatment. The researchers propose that the central thrombus creates direct wall contact, exposing these regions to inflammatory, proteolytic, and hypoxic injury mechanisms that, combined with circumferential jet-inflow stress, explain the elevated rupture risk. Flow-diverter reconstruction is recommended as the physiologically appropriate treatment approach, though the researchers caution that the ring-like configuration may be mistakenly interpreted as stable thrombosis rather than a hemodynamic warning signal requiring prompt intervention. The study advocates for future research combining computational fluid dynamics with serial MRI and histologic correlation to better characterize shear-stress conditions and establish a prospective registry to clarify natural history and treatment outcomes.